Forest Biomass for Energy - ACS Publications - American Chemical

2 Forest Biomass for Energy A Perspective R. L. SAJDAK, Y. Z. LAI, G. D. MROZ, and M . F. JURGENSEN

Downloaded by UNIV LAVAL on November 22, 2015 | http://pubs.acs.org Publication Date: January 29, 1981 | doi: 10.1021/bk-1981-0144.ch002

Department of Forestry, Michigan Technological University, Houghton,MI49931

A primary challenge of the near future is the development of alternative energy sources to make this nation less dependent on imported oil. Increasing the use of wood for energy production has been suggested as one method of meeting this goal (1,2). There are a number of advantages for developing a wood-related energy base in this country. Most importantly, wood is a renewable resource and its production normally has a relatively low environmental impact. Wood can be burned and thus converted directly into energy. Used in this way, it is a relatively clean fuel and the residual ash is useful as a fertilizer. The technology also exists for converting wood into other energy forms such as oil, gas, alcohol, charcoal, and electricity. The forest resource of the United States can make a significant contribution toward meeting national energy needs. Forests occupy about one third of our land area and the wood inventory of this resource is enormous. Of the total annual biomass produced in these forests, only about thirty percent is presently used (3). Better utilization of our annual forest production could make significant quantities of wood material available for energy purposes. However, annual forest growth is well below what is currently possible. More intensive management systems could double the productivity of our forest lands within fifty years (4). Wood now supplies about two percent of total U.S. energy needs, primarily through the use of manufacturing wastes and mill residues for boiler fuel.

0097-6156/81/0144-0021$07.00/0 © 1981 American Chemical Society

In Biomass as a Nonfossil Fuel Source; Klass, D.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

22

BIOMASS AS A NONFOSSIL FUEL SOURCE


V a r i o u s studies s u g g e s t w o o d c o u l d s u p p l y up t o 10 p e r c e n t of t h e Nation's c u r r e n t energy needs w i t h i n t h e next decade. D e p e n d i n g u p o n t h e strategies used, e v e n t u a l l y it m a y be possible t o s u p p l y 2 0 p e r c e n t of o u r t o t a l e n e r g y b u d g e t (5). H o w e v e r , t h e use of w o o d for e n e r g y p r o d u c t i o n m u s t be kept in p r o p e r perspective. W o o d is n o t t h e o n l y p r o d u c t of o u r forests. These lands play a v i t a l role in p r o v i d i n g various social a n d c u l t u r a l benefits s u c h as w i l d e r n e s s , o u t d o o r r e c r e a t i o n , w i l d l i f e , f i s h , a n d clean w a t e r . Therefore, no single resource or forest use can be e x a m i n e d in isolation f r o m t h e others. Energy uses w i l l have, t o be b a l a n c e d a g a i n s t t h e g r o w i n g d e m a n d on our forests for l u m b e r , fiber p r o d u c t s , a n d recreational o p p o r t u n i t i e s . This paper w i l l analyze t h e feasibility a n d i m p l i c a t i o n s of increased utilization of o u r forests as a source of energy. C o n s i d e r a t i o n w i l l also be g i v e n t o t h e p r o d u c t i o n of b i o m a s s f r o m intensively c u l t u r e d p l a n t a t i o n s as w e l l as t h e q u a l i t y of t h e b i o m a s s p r o d u c e d by d i f f e r e n t m a n a g e m e n t t e c h n i q u e s . T H E U. S. F O R E S T R E S O U R C E A b o u t 7 4 0 m i l l i o n acres or 3 3 p e r c e n t of t h e land area of t h e U n i t e d States is classified as forest land. In order t o be classified as forest, at least 10 p e r c e n t of t h e land m u s t be s t o c k e d w i t h trees of a n y size. A l s o in this c a t e g o r y are lands t h a t f o r m e r l y had tree c o v e r b u t have n o t been d e v e l o p e d for o t h e r purposes, as w e l l as lands w h o s e p r i m a r y use is not t i m b e r p r o d u c t i o n . Nearly t w o - t h i r d s of t h i s area, or 4 8 8 m i l l i o n acres, is classified as c o m m e r c i a l forest land. C o m m e r c i a l forests are d e f i n e d as f o r e s t e d land c a p a b l e of p r o d u c i n g at least 2 0 c u b i c feet of industrial w o o d per acre per year, a n d is not reserved for uses w h i c h are i n c o m p a t i b l e w i t h t i m b e r p r o d u c t i o n (6). T h u s , National Parks, w i l d e r n e s s areas, a n d o t h e r special use areas are n o t i n c l u d e d in this category. T o help deal w i t h t h e d i v e r s i t y a n d c o m p l e x i t y of v e g e t a t i o n a l a n d e n v i r o n m e n t a l differences in various parts of t h e c o u n t r y , t h e forest resource is discussed by f o u r major g e o g r a p h i c regions: N o r t h e r n , S o u t h e r n Rocky M o u n t a i n s — Great Plains, a n d t h e Pacific Coast. T h e N o r t h e r n Region i n c l u d e s M a r y l a n d , W e s t V i r g i n i a , K e n t u c k y . M i s s o u r i , a n d all states n o r t h a n d w e s t t o t h e Great Plains. T h e S o u t h e r n Region e n c o m p a s s e s V i r g i n i a . Tennessee, Arkansas, O k l a h o m a , and states t o t h e s o u t h . T h e Rocky M o u n t a i n s — Great Plains Region includes W e s t e r n S o u t h Dakota a n d all states w e s t of t h e Great Plains e x c e p t t h o s e b o r d e r i n g on t h e Pacific Ocean. T h e Pacific Coast Region has t h e f o u r states a l o n g t h e Pacific Ocean, including Hawaii.


2.

SAJDAK ET A L .

23

Forest Biomass for Energy

The Northern Forest Region This r e g i o n , w h i c h c o n t a i n s over o n e - h a l f of t h e Nation's p o p u l a t i o n (53 percent), is t h e s e c o n d m o s t densely forested area w i t h 3 5 p e r c e n t o f t h e t o t a l land in c o m m e r c i a l forests (Table I). It is also t h e o n l y region t o register an increase in c o m m e r c i a l forest acreage d u r i n g t h e period 1 9 5 2 - 1 9 7 7 . Private, n o n - i n d u s t r i a l land o w n e r s h i p in t h e states of N e w York, Pennsylv a n i a , a n d W e s t V i r g i n i a c o n t r i b u t e d t o m o s t of t h i s increase. This o w n e r s h i p makes u p 7 1 p e r c e n t of t h e forest h o l d i n g s in t h e N o r t h e r n Region.


T a b l e I. D I S T R I B U T I O N O F C O M M E R C I A L F O R E S T L A N D I N T H E U N I T E D S T A T E S B Y R E G I O N A N D B Y O W N E R S H I P C L A S S (6)

Ownership Region

Area

Public

Industry

Private

(%)

(%)

(%)

170,769

35

19

10

71

188.433 South Rocky M o u n t a i n s — Great Plains 57.765

39

9

19

72

12

75

4

21

Pacific Coast

14

63

17

20

North

TOTAL

Distribution

6

(%)

8

70.758

6

487,725

a

T h o u s a n d acres.

b

Percentages o f t h e t o t a l U.S. c o m m e r c i a l forest land.

c

Percentages of t h e region.

T h e N o r t h e r n Region's forests vary c o n s i d e r a b l y as d o their uses. S e v e n t y - f i v e p e r c e n t of t h e t i m b e r v o l u m e is in h a r d w o o d s , w h i c h are utilized for f u r n i t u r e , veneer, p u l p , pallets, a n d railroad ties (Table II). S o f t w o o d v o l u m e is t h e smallest of any region (25 percent). The s t o c k i n g levels are t h e l o w e s t in t h e c o u n t r y a n d t h e average a n n u a l g r o w t h per acre is q u i t e l o w (Table III). It s h o u l d be n o t e d t h a t these v o l u m e figures are based o n c o m m e r c i a l - s i z e d t i m b e r a n d d o n o t i n c l u d e w o o d present in small, n o n - m e r c h a n t a b l e trees a n d in t h e t o p s a n d limbs o f m e r c h a n t a b l e trees.


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Table II. T I M B E R PRODUCTION O N UNITED STATES C O M M E R C I A L F O R E S T L A N D I N 1 9 7 7 (6)

Total Volume Region

(million c u . ft.)

(cubic feet)

(%)

(%)

200.337 230.037

1173

25

1221

43

75 57

112.405

1946

94

6

258.024

3646 1997

92

8

62

38

North South


Rocky tains-

Average Volume Timber Type Per A c r e Softwood Hardwood

Moun-

Great Plains Pacific Coast TOTAL

800.803

Table III. NET A N N U A L G R O W T H A N D H A R V E S T O N C O M M E R C I A L T I M B E R L A N D S I N T H E U N I T E D S T A T E S (6) Average Growth Growth Harvest ( 1 0 0 0 c u . ft.) ( 1 0 0 0 c u . ft.)

Region

Per A c r e (cubic feet)

North South Rocky M o u n t a i n s — Great Plains

5.927.587 10.826.042 1.689.553

2.739.535 6.571,223 845.786

34.7 57.4 29.2

Pacific Coast TOTAL

3.431.151 21.874.333

4.278.868 14.425.230

48.5 44.8

The Southern Region T h i s r e g i o n is t h e m o s t densely forested in t h e N a t i o n w i t h 3 9 p e r c e n t of t h e land area in c o m m e r c i a l forests. It is also t h e s e c o n d m o s t d e n s e l y p o p u l a t e d . C o m m e r c i a l forest acreage d e c l i n e d d u r i n g t h e 2 5 year p e r i o d . 1 9 5 2 t o 1 9 7 7 . p r i m a r i l y d u e t o c o n v e r s i o n of forest lands t o a g r i c u l t u r a l uses. Forest o w n e r s h i p , as in t h e N o r t h , is p r i m a r i l y in private n o n - i n d u s t r i a l h o l d i n g s (72 percent). I n d u s t r y o w n e r s h i p is t h e largest of any region (19 percent) a n d p u b l i c o w n e r s h i p is t h e smallest (9 percent). S o u t h e r n forests are q u i t e e q u a l l y d i v i d e d b e t w e e n h a r d w o o d a n d s o f t w o o d tree species. Forty-three p e r c e n t of t h e t i m b e r v o l u m e is in s o f t w o o d s . A v e r a g e a n n u a l g r o w t h per acre of forest land is t h e h i g h e s t of any region. T h e S o u t h is p r o j e c t e d t o s u p p l y over o n e - h a l f of t h e Nation's s o f t w o o d r e q u i r e m e n t s by t h e year 2 0 3 0 . nearly d o u b l i n g its 1 9 7 6 o u t p u t .


2.

SAJDAK ET AL.

25


The Rocky M o u n t a i n s - G r e a t Plains Region This region c o n t a i n s t h e smallest p e r c e n t a g e (12 percent) of this c o u n t r y ' s c o m m e r c i a l forests a n d is t h e least p o p u l a t e d . M o s t o f t h e forest land is in p u b l i c o w n e r s h i p (75 percent). D u r i n g t h e period 1 9 5 2 t o 1 9 7 7 , this region lost over 10 p e r c e n t o f its forest land, m o s t of w h i c h w a s e n t e r e d into t h e


w i l d e r n e s s and National Park s y s t e m . These forests are p r e d o m i n a n t l y s o f t w o o d s w h i c h c o m p r i s e 9 4 p e r c e n t of t h e t i m b e r v o l u m e . A b o u t o n e - t h i r d o f t h i s v o l u m e is in t h e p i n y o n p i n e / j u n i p e r t i m b e r t y p e w h i c h is relatively u n i m p o r t a n t f o r w o o d p r o d u c t i o n . A n n u a l g r o w t h averages 2 9 c u b i c feet per acre per year, t h e l o w e s t o f all regions. These forests are very i m p o r t a n t f o r w a t e r s h e d , recreation, a n d livestock grazing. The Pacific Coast Region There is a t r e m e n d o u s a m o u n t o f d i v e r s i t y o f t h e forests in t h i s region. T h e c l i m a t e ranges f r o m arctic t o t r o p i c a l a n d s o m e of t h e m o s t

productive

forests in t h e w o r l d are f o u n d a l o n g t h e coast f r o m N o r t h e r n California t o W a s h i n g t o n . O n l y 1 4 p e r c e n t o f t h e t o t a l land area is in c o m m e r c i a l forests a n d like t h e Rocky M o u n t a i n Region, m o s t is in p u b l i c o w n e r s h i p . This region also recorded a d e c l i n e in c o m m e r c i a l forest land d u e t o transfers

into

w i l d e r n e s s areas a n d parks. M o s t of t h e t i m b e r v o l u m e is in s o f t w o o d s (92 percent) a n d t h e average a n n u a l g r o w t h is s e c o n d h i g h e s t in t h e N a t i o n . A v e r a g e g r o w i n g stock per acre is t h e h i g h e s t in a n y r e g i o n , a n d a n n u a l t i m b e r c u t is m o r e t h a n n e t i n g r o w t h . O v e r c u t t i n g is d u e t o t h e accelerated removal o f o l d g r o w t h , o v e r m a t u r e stands. This region n o w supplies over one-half o f o u r s o f t w o o d t i m b e r needs. T h e p r o j e c t i o n s are for t h i s region's s o f t w o o d o u t p u t t o d e c l i n e after 1 9 9 0 . FOREST P R O D U C T I V I T Y

ASSESSMENT

In e v a l u a t i n g t h e forest resource t o d e t e r m i n e h o w m u c h w o o d is available for e n e r g y p r o d u c t i o n , a m u l t i t u d e o f factors needs t o be c o n s i d e r e d . M o s t o f t h e c o m m e r c i a l forest land in t h e N o r t h e r n a n d S o u t h e r n Regions is in private, n o n - i n d u s t r i a l o w n e r s h i p . It is d i f f i c u l t t o assess t h e c o n t r i b u t i o n these lands w i l l m a k e t o w a r d s u p p l y i n g o u r e n e r g y needs. O b j e c t i v e s o f forest o w n e r s h i p vary c o n s i d e r a b l y a n d t i m b e r p r o d u c t i o n is o f t e n s e c o n d t o n o n - t a n g i b l e goals. Private forest lands are o f t e n m a n a g e d o n a n o p p o r t u n i s t i c basis w i t h little regard t o a r e g u l a t e d a n d s u s t a i n e d t i m b e r y i e l d .


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Therefore, it m a y be d i f f i c u l t t o o b t a i n a d e p e n d a b l e s u p p l y of w o o d f r o m a p a r t i c u l a r g e o g r a p h i c area. A l s o , m o s t private forest h o l d i n g s are small a n d t h e m o s t e f f i c i e n t t o t a l tree h a r v e s t - s y s t e m s c a n n o t o p e r a t e e c o n o m i c a l l y in s u c h situations. W h e n c o n d u c t i n g c o n v e n t i o n a l r o u n d w o o d harvests, t h e r e m o v a l of l o g g i n g residue f r o m s m a l l , w i d e l y scattered o p e r a t i o n s poses a difficult problem. T h e private forest resource c a n be very p r o d u c t i v e . A recent s t u d y i n d i c a t e d t h a t w o o d p r o d u c t i o n o n t h e s e lands w a s 6 1 p e r c e n t of c a p a c i t y u n d e r c u r r e n t m a n a g e m e n t p r a c t i c e . In c o n t r a s t , t h e N a t i o n a l Forests g r e w w o o d at 4 9 p e r c e n t of c a p a c i t y (7). I m p r o v e d m a n a g e m e n t of small forests for increased b i o m a s s p r o d u c t i o n m a y be t h e m o s t d i f f i c u l t p r o b l e m of all. Usually l a c k i n g is t h e w i l l i n g n e s s a n d c a p a c i t y of t h e small l a n d - o w n e r t o m a k e i n v e s t m e n t s for a r e t u r n w h i c h w i l l be 2 0 - 3 0 years a w a y (8). S u b s t a n t i a l increases in t h e s u p p l y of w o o d f r o m t h e s e o w n e r s h i p s can be a c h i e v e d o n l y t h r o u g h g o v e r n m e n t a l assistance, s u c h as c o s t - s h a r i n g a n d t e c h n i c a l assistance p r o g r a m s (9). C o n c e i v a b l y , m u c h of t h e w o o d f r o m p r i v a t e forests m a y be used for h o m e h e a t i n g purposes, p a r t i c u l a r l y in t h e m o r e p o p u l a t e d forested areas. A s t h e cost of h e a t i n g oil increases, h e a t i n g w i t h w o o d b e c o m e s m o r e a t t r a c t i v e a n d m o r e p r i v a t e forests w i l l be d e d i c a t e d for f u e l w o o d p r o d u c t i o n . In M a i n e , for e x a m p l e , over 5 0 p e r c e n t of t h e h o m e s are c u r r e n t l y b e i n g h e a t e d w i t h w o o d . T h e i m p a c t of t h i s t y p e of m a n a g e m e n t o n f u t u r e s u p p l i e s of h i g h v a l u e s a w l o g s in a p a r t i c u l a r region c o u l d be s i g n i f i c a n t . Increasing Timber Output W i t h b e t t e r m a n a g e m e n t . U.S. t i m b e r s u p p l i e s c o u l d be d r a m a t i c a l l y increased in t h e f u t u r e . A v e r a g e a n n u a l g r o w t h o n c o m m e r c i a l forest land in 1 9 7 6 w a s 4 5 c u b i c feet per acre. If t h e forests w e r e f u l l y s t o c k e d , average g r o w t h w o u l d average 7 5 c u b i c feet per acre per year. This increase in a n n u a l g r o w t h w o u l d r o u g h l y equal t h e t o t a l v o l u m e harvested f r o m all forests in 1 9 7 6 (6). T h e possibilities f o r i n t e n s i f y i n g m a n a g e m e n t exist for all o w n e r s h i p s a n d in all regions of t h e c o u n t r y e x c e p t for t h e Rocky M o u n t a i n s - G r e a t Plains. Preliminary results of t h e U.S. Forest Service a n d Forest Industries C o u n c i l s t u d i e s i n d i c a t e t h e r e are e c o n o m i c o p p o r t u n i t i e s for i n t e n s i f i e d m a n a g e m e n t o n 1 6 0 m i l l i o n acres of c o m m e r c i a l t i m b e r l a n d or a b o u t 3 4 p e r c e n t of t h e N a t i o n ' s t o t a l . T h e o p p o r t u n i t i e s are m o s t c o n c e n t r a t e d in t h e 1 1 3 m i l l i o n acres of t h e S o u t h e r n Region. A b o u t t h r e e - f o u r t h s of t h e t r e a t m e n t strategies involve regeneration of n o n - s t o c k e d areas, h a r v e s t i n g m a t u r e forests,


2.

SAJDAK ET AL.

27


r e g e n e r a t i n g higher y i e l d i n g y o u n g stands, a n d c o n v e r t i n g e x i s t i n g stands t o m o r e p r o d u c t i v e species. T h e e s t i m a t e d t o t a l cost o f t r e a t i n g t h e S o u t h e r n acreage is $8.8 billion. This i n v e s t m e n t w o u l d increase a n n u a l g r o w t h in this region by m o r e t h a n 8.5 billion c u b i c feet. The National Forests, p a r t i c u l a r l y those in t h e W e s t , also have t h e c a p a b i l i t y o f s u p p o r t i n g larger harvests. Additional

investments

would

be needed

f o r road

construction,

stand

i m p r o v e m e n t , reforestation, a n d salvage (9). Increased forest yields c a n be o b t a i n e d b y using k n o w n a n d p r o v e n intensive c u l t u r e t e c h n i q u e s . Use of g e n e t i c a l l y i m p r o v e d p l a n t i n g stock can increase


yields b y 10 t o 2 0 percent. Fertilization a n d t h i n n i n g p r o g r a m s , better tree s p a c i n g , a n d increased fire, insect, a n d disease p r o t e c t i o n c a n all i m p r o v e yields s i g n i f i c a n t l y . T h e limits t o increasing w o o d yields b y intensive c u l t u r a l t e c h n i q u e s are n o t k n o w n . A reasonable e s t i m a t e is t h a t t h e g r o w t h c o u l d d o u b l e o n half o f t h e c o m m e r c i a l forest land in 5 0 years (3). Availability o f W o o d f o r Energy Production W e c a n o n l y s p e c u l a t e o n t h e t r u e size o f t h e t o t a l t i m b e r resource of t h e U n i t e d States. T o d a t e , all of t h e inventories a n d surveys o n a national scale have been based o n v o l u m e m e a s u r e m e n t s of t h e m e r c h a n t a b l e parts of trees. Tables I. II, a n d III reflect this. M e r c h a n t a b l e v o l u m e is a v a g u e t e r m , p a r t i c u l a r l y since m e r c h a n t a b i l i t y limits are rapidly c h a n g i n g . The c o n c e p t of w h o l e - t r e e utilization has reinforced t h i s c o n f u s i o n . W i t h t h e d e v e l o p m e n t o f w h o l e - t r e e h a r v e s t i n g m e t h o d s , previously n o n - m e r c h a n t a b l e parts o f t h e tree are c h i p p e d a n d used f o r p u l p a n d paper, c o m p o s i t e p r o d u c t s , a n d fuel. These n e w c o n c e p t s of utilization m a k e t h e w h o l e tree t h e basic u n i t of m e a s u r e m e n t . Since a c c u r a t e v o l u m e d e t e r m i n a t i o n is d i f f i c u l t o n irregular s h a p e d o b j e c t s , w e i g h t o f biomass is t h e n e w s t a n d a r d of measure for all tree components. There have been n u m e r o u s e s t i m a t e s m a d e o n t h e t o t a l biomass a n d biomass p o t e n t i a l o f o u r forests (3.1Ω). T h e i n v e n t o r y p r o c e d u r e used is based o n e s t i m a t e s a n d averages, a n d is fully d e s c r i b e d by W a h l g r e n a n d Ellis ( U ) . Forest surveys based o n biomass m e a s u r e m e n t t e c h n i q u e s are needed t o a c c u r a t e l y d e t e r m i n e t h e q u a n t i t i e s a n d l o c a t i o n of our w o o d resource. M a n y studies o n m e a s u r i n g t h e w e i g h t o f i n d i v i d u a l trees, a n d t o a lesser e x t e n t forest stands, have been made. T h i s w o r k has been s u m m a r i z e d b y Keays (12). a n d H i t c h c o c k a n d M c D o n n e l l (12). A s w o r k in forest b i o m a s s m e a s u r e m e n t is r e f i n e d , regional w e i g h t tables c a n be d e v e l o p e d a n d a c c u r a t e biomass inventories c o m p i l e d .


28


W o r k has already b e g u n in this d i r e c t i o n . Pioneering w o r k i n i t i a t e d by Y o u n g a n d others in M a i n e has resulted in t h e c o m p l e t i o n of a forest biomass i n v e n t o r y o n nearly t w o m i l l i o n acres in t h a t state (14)· T h e next forest survey of M a i n e , t o be s t a r t e d in 1 9 8 0 . by t h e U.S. Forest Service w i l l be in t e r m s of b o t h m e r c h a n t a b l e v o l u m e a n d t o t a l w o o d biomass. I n f o r m a t i o n s u c h as t h i s , as w e l l as m e a s u r e m e n t of a n n u a l d r y m a t t e r p r o d u c t i o n , w i l l d e t e r m i n e t h e


availability of w o o d supplies o n a regional basis for industrial a n d energy purposes. Biomass inventories m u s t also u n d e r g o e c o n o m i c assessments since in m a n y s i t u a t i o n s , t h e c o s t of c o l l e c t i n g , p r o c e s s i n g , a n d t r a n s p o r t i n g b i o m a s s materials w o u l d e x c e e d a n y reasonable v a l u e a n t i c i p a t e d for fuel or other products. Forest Residue Forest residue is d e f i n e d as t h e b i o m a s s left in t h e w o o d s after harvest a n d i n c l u d e s tree t o p s , l i m b s , c u l l m a t e r i a l , a n d all present a n d f u t u r e n o n m e r c h a n t a b l e trees. This differs f r o m m i l l residue s u c h as bark, e d g i n g s , a n d s a w d u s t , w h i c h is o f t e n f u l l y utilized as boiler f u e l . T h e a m o u n t of residue r e m a i n i n g after harvest w i l l v a r y a c c o r d i n g t o m e r c h a n t a b i l i t y s t a n d a r d s , m e t h o d of harvest, a n d forest s t a n d c o m p o s i t i o n a n d q u a l i t y . In a t y p i c a l h a r d w o o d s a w l o g harvest as m u c h as 5 0 p e r c e n t of t h e p o t e n t i a l usable b i o m a s s m a y be left as residue. If t h e s a w l o g s t a n d is o v e r m a t u r e or of poor q u a l i t y , a d d i t i o n a l residue m a y be left. In c o n t r a s t , if t h e s t a n d is w h o l e - t r e e c h i p p e d for p u l p m a t e r i a l , very little residue w i l l r e m a i n . T h r o u g h o u t t h e U n i t e d States t h e r e are a n u m b e r of o n g o i n g studies w h o s e o b j e c t i v e s are t o d e t e r m i n e , o n a regional basis, t h e real p o t e n t i a l a n d e c o n o m i c a v a i l a b i l i t y of w o o d y b i o m a s s for energy. T h e D e p a r t m e n t of Energy in c o o p e r a t i o n w i t h t h e U.S. Forest Service is in t h e process of d e v e l o p i n g a N a t i o n a l W o o d Energy Data S y s t e m . This s y s t e m w i l l i d e n t i f y a m o u n t s a n d locations of w o o d fuels in excess of c o m m e r c i a l needs. The i n f o r m a t i o n w i l l be d e l i n e a t e d by state a n d in s o m e cases d o w n t o t h e c o u n t y level. In a d d i t i o n , t h e l o c a t i o n of c u r r e n t a n d p o t e n t i a l large w o o d b u r n i n g s y s t e m s w i t h i n each u n i t w i l l be i d e n t i f i e d (14). T h e M a r y l a n d D e p a r t m e n t of N a t u r a l Resources r e c e n t l y c o m p l e t e d an assessment of t h e availability, cost, a n d reliability of w o o d fuels o n t h e D e l m a r v a Peninsula (14). T h e s t u d y c o n c l u d e d t h a t c u l l trees a n d t i m b e r harvest residue c o u l d p r o v i d e o v e r 1.9 m i l l i o n t o n s o f w o o d fuel a n n u a l l y at a cost t o users of $ 1 2 . 5 0 per green t o n . O t h e r studies in M i n n e s o t a , N e w York, O r e g o n , a n d W a s h i n g t o n are i n v o l v e d in similar utilization a n d biomass assessments t o d e t e r m i n e t h e availability of w o o d fuels for energy.



2.

SAJDAK ET AL.

29


Recently, t h e N o r t h e r n W i s c o n s i n a n d U p p e r M i c h i g a n region w a s intensively s t u d i e d b y t h e U.S. Forest Service t o d e t e r m i n e t h e a m o u n t of residue available in t h e region U s i n g available forest s u r v e y i n f o r m a t i o n a n d c o m p u t e r s i m u l a t i o n , t h e harvest a m o u n t s a n d delivered cost of biomass w e r e d e t e r m i n e d . A " M a n a g e d H a r v e s t " p r o c e d u r e w a s used t o d e t e r m i n e t h e a m o u n t of w o o d p r o d u c t a n d residue t h a t s h o u l d be r e m o v e d each year for a 10-year period. O n l y t w o p r o d u c t s w e r e c o n s i d e r e d : s a w l o g s a n d w o o d chips. T h e a s s u m p t i o n w a s m a d e t h a t excess c h i p s n o t n e e d e d f o r paper p r o d u c t s w o u l d be available f o r e n e r g y purposes or m o r e s u c c i n c t l y , " p u l p t h e best a n d b u r n t h e rest." T h e overall o b j e c t i v e of t h e " M a n a g e d H a r v e s t " p r o c e d u r e w a s t o m o v e t h e forests t o a f u l l y - r e g u l a t e d a n d m o r e p r o d u c t i v e condition. Several h a r v e s t i n g strategies w e r e e x a m i n e d a n d s i g n i f i c a n t differences w e r e f o u n d t o exist in t h e deliverable cost a n d a m o u n t of recovered b i o m a s s a m o n g t h e h a r v e s t i n g s y s t e m s used. O n e h a r v e s t i n g strategy i n v o l v e d t h e m e c h a n i z e d t h i n n i n g o f o v e r s t o c k e d , small d i a m e t e r forest stands. Over three m i l l i o n d r y t o n s of b i o m a s s w a s p r o j e c t e d t o be deliverable f r o m t h e entire s t u d y area in 1 9 8 0 at a cost of $ 1 5 . 9 1 per t o n . This v o l u m e w o u l d also be available in each s u c c e e d i n g year. A s e c o n d s t r a t e g y i n v o l v e d t h e c l e a r c u t t i n g o f m a t u r e a n d o v e r m a t u r e stands a n d stands t o o poorly s t o c k e d t o be carried t o a n o r m a l c u t t i n g age. S a w l o g s w e r e r e m o v e d before t h e residual s t a n d w a s c h i p - h a r v e s t e d . This s t r a t e g y is used w h e r e e v e n - a g e d forest m a n a g e m e n t

is p r a c t i c e d a n d also

where

stands w o u l d be c o n v e r t e d t o a f u l l y - s t o c k e d s i t u a t i o n . Ten m i l l i o n t o n s c o u l d be p r o d u c e d a n n u a l l y , e x c l u s i v e o f s a w l o g s . at a n average cost o f $ 1 2 . 3 5 per t o n delivered. The costs per delivered t o n are averages f o r t h e entire t o n n a g e available. S u b s t a n t i a l v o l u m e s o f forest biomass are available at l o w e r costs, b u t as an a t t e m p t is m a d e t o recover increasing a m o u n t s of t h e biomass, t h e costs increase. The s t u d y c o n c l u d e d t h a t s i g n i f i c a n t forest biomass q u a n t i t i e s are available in t h i s r e g i o n . For b o t h N o r t h e r n W i s c o n s i n a n d Upper M i c h i g a n , 30.5 m i l l i o n dry t o n s a n n u a l l y w o u l d be deliverable at a 1 9 8 0 p r o j e c t e d cost of $ 1 6 . 0 7 per t o n . These biomass q u a n t i t i e s w o u l d be available each year f o r t h e next 1 0 years. A t t h e e n d of t h e 10-year p e r i o d , a n e w assessment w i l l have t o be made. The

costs

for w o o d y

residue

materials

will

change

as m o r e

efficient

h a r v e s t i n g e q u i p m e n t is d e v e l o p e d . Koch a n d N i c h o l s o n (1Q) d e s c r i b e d a


30


m o b i l e c h i p p e r d e s i g n e d t o effectively harvest b i o m a s s o n relatively flat t e r r a i n . Their s t u d i e s s h o w t h a t if a m i n i m u m of 2 5 t o n s (green w e i g h t ) of b i o m a s s is available per acre, a b o u t 8 5 p e r c e n t of s u c h b i o m a s s c o u l d be recovered a n d d e l i v e r e d t o t h e forest roadside for a b o u t $ 1 1 . 8 2 per green t o n . This m a c h i n e w a s d e s i g n e d t o recover forest residue t h a t is o r d i n a r i l y b u l l d o z e d a n d b u r n e d d u r i n g t h e p r e p a r a t i o n of a site for p l a n t i n g .


INTENSIVE PLANTATION CULTURE T r a d i t i o n a l p l a n t a t i o n c u l t u r e in t h i s c o u n t r y has a p p r o x i m a t e d w h a t o c c u r s in nature. In t h i s s i t u a t i o n trees are p l a n t e d at fairly w i d e s p a c i n g (6 feet or more) o f t e n w i t h little or no site p r e p a r a t i o n . Occasionally, t h e trees are released f r o m c o m p e t i n g v e g e t a t i o n a n d t h e p l a n t a t i o n m a y be t h i n n e d o n c e or t w i c e . T h e r o t a t i o n l e n g t h of these p l a n t a t i o n s m a y be 3 0 years or more, d e p e n d i n g o n t h e g r o w t h rate a n d e n d p r o d u c t desired. Coniferous trees, p a r t i c u l a r l y t h e pines, have been p l a n t e d far m o r e o f t e n t h a n h a r d w o o d s . Recently, interest has d e v e l o p e d in t h e i n t e n s i v e c u l t u r e o f p l a n t a t i o n s o n a short r o t a t i o n . H o w e v e r , t h i s c o n c e p t is n o w n e w . T h e Europeans have been m a n a g i n g p l a n t a t i o n s in t h i s m a n n e r for d e c a d e s a n d in t h e 1960's. M c A l p i n e a n d his c o w o r k e r s f u r t h e r d e v e l o p e d t h e c o n c e p t in t h e U n i t e d States w i t h s y c a m o r e (P/atanus occidentalis L ) (1Ζ)· Since t h a t t i m e , studies have been i n i t i a t e d w i t h o t h e r tree species t h r o u g h o u t t h e U n i t e d States a n d Canada. In c o n c e p t , t h e intensive c u l t u r e of p l a n t a t i o n s o n a short r o t a t i o n is essentially an a g r o n o m i c s y s t e m . Trees are p l a n t e d on prepared sites at close s p a c i n g (4 feet or less), c u l t i v a t e d , fertilized, a n d irrigated d u r i n g t h e r o t a t i o n . A g r i c u l t u r a l - t y p e forage e q u i p m e n t w o u l d t h e n harvest t h e c r o p at ages of less t h a n 10 years. T h e e n t i r e a b o v e g r o u n d p o r t i o n of t h e tree is utilized. Regeneration of t h e p l a n t a t i o n w o u l d be by c o p p i c e g r o w t h , t h e r e b y l i m i t i n g t h e p l a n t a t i o n s m a i n l y t o h a r d w o o d s w h i c h s t u m p or root s p r o u t after cutting. A n u m b e r of a d v a n t a g e s are e v i d e n t in t h e intensive c u l t u r e of p l a n t a t i o n s o n a short rotation w h e n contrasted to conventional plantation

(1S,12). These 1.

management

are:

Higher yields per u n i t of land area, therefore less land w o u l d be needed t o p r o d u c e a g i v e n a m o u n t of biomass.

2.

Early a m o r t i z a t i o n of p l a n t a t i o n e s t a b l i s h m e n t costs.


2. 3.

SAJDAK ET AL.


31

Increased e f f i c i e n c y o f m o s t c u l t u r a l a n d h a r v e s t i n g o p e r a t i o n s because of c o m p l e t e m e c h a n i z a t i o n .

4.

Reduced p l a n t a t i o n regeneration costs after t h e first r o t a t i o n .

5.

Genetically i m p r o v e d trees c a n be utilized q u i c k l y .

6.

T h e biomass p r o d u c e d w i l l be o f m o r e u n i f o r m q u a l i t y .


There are s o m e s i g n i f i c a n t d i s a d v a n t a g e s , h o w e v e r : 1.

Initial p l a n t a t i o n e s t a b l i s h m e n t a n d m a n a g e m e n t costs per acre are very h i g h , t h e r e b y increasing t h e f i n a n c i a l risk i n v o l v e d .

2.

Site l i m i t a t i o n s are i m p o r t a n t f o r t h i s t y p e of forest practice. T h e land m u s t be relatively flat a n d soil t e x t u r e , s t r u c t u r e , d r a i n a g e a n d stoniness w i l l be i m p o r t a n t c o n s i d e r a t i o n s .

3.

T h e relatively u n i f o r m g e n e t i c m a k e u p of t h e trees increase e p i d e m i c disease a n d insect hazards.

H a r d w o o d s have been preferred f o r intensive p l a n t a t i o n m a n a g e m e n t because o f their s p r o u t i n g c a p a b i l i t y a n d t h e fast g r o w t h of these s p r o u t s f o r t h e first 1 0 - 2 0 years, as c o m p a r e d t o conifers.There are e x c e p t i o n s , h o w e v e r , w h e r e conifers m a y be m o r e desirable. W i l l i f o r d et al. (20) reported loblolly pine {Pinus taeda L.) t o be superior in b i o m a s s p r o d u c t i o n o n m a n y sites in t h e s o u t h . Studies b y t h e U.S. Forest Service at Rhinelander, W i s c o n s i n , i n d i c a t e conifers m a y have a d v a n t a g e s u n d e r certain site c o n d i t i o n s (21.). For e x a m p l e , jack pine (Pinus banks/ana Lamb.) is w e l l a d a p t e d t o t h e N o r t h , has f e w serious insect a n d disease p r o b l e m s , a n d is less d e m a n d i n g of n u t r i e n t s and moisture than many hardwoods. N u m e r o u s species trials are u n d e r w a y in various parts of t h e c o u n t r y t o i d e n t i f y t h e best species f o r localized b i o m a s s p r o d u c t i o n (14). Several of t h e m o r e intensively s t u d i e d c a n d i d a t e species are discussed in m o r e detail as follows: American Sycamore This w a s t h e first species a d v o c a t e d f o r short r o t a t i o n intensive c u l t u r e . S y c a m o r e p l a n t a t i o n s are established u s i n g seedlings or f r o m c u t t i n g s . If c u t t i n g s are used, a clonal p l a n t a t i o n is established w h i c h results in a h i g h degree of tree u n i f o r m i t y . S y c a m o r e w o o d is m o d e r a t e l y dense w i t h a specific


32


g r a v i t y of a b o u t 0.46 a n d a s a p w o o d m o i s t u r e c o n t e n t of 1 3 0 p e r c e n t o n an


o v e n d r y basis (4Q). This species is m o s t p r o d u c t i v e o n rich alluvial land in t h e s o u t h . Plantations o n u p l a n d sites have y i e l d e d p o o r survival a n d u n a c c e p t a b l e levels of g r o w t h (22). H o w l e t t a n d G a m a c h e (18) r e v i e w e d n u m e r o u s studies on t h e biomass p r o d u c t i v i t y of s y c a m o r e in t h e s o u t h a n d f o u n d g r o w t h rates as h i g h as 9 d r y t o n s per acre per year. T h e average yield w a s a b o u t 4.5 d r y t o n s per acre per year a n d in s o m e studies yields w e r e as l o w as 2 t o n s per acre per year. Usually, higher initial s t a n d densities p r o d u c e d h i g h e r yields for r o t a t i o n ages of up t o f o u r years. H o w e v e r , d i r e c t c o m p a r i s o n s a m o n g sites are d i f f i c u l t because of t h e d i f f e r e n t c u l t u r a l t r e a t m e n t s a p p l i e d in t h e various studies. Poplars and C o t t o n w o o d V a r i o u s species a n d h y b r i d s of t h e g e n u s Populus are s o m e of t h e m o r e p r o m i s i n g c a n d i d a t e s for i n t e n s i v e b i o m a s s p r o d u c t i o n . This g r o u p has long been c u l t i v a t e d in Europe a n d m o r e r e c e n t l y in t h e Eastern U n i t e d States a n d Canada. Poplar h y b r i d s are easily d e v e l o p e d a n d t h e r e s u l t i n g p r o g e n y are p r o p a g a t e d v e g e t a t i v e l y using s t e m c u t t i n g s . C o n s e q u e n t l y , t h e r e are literally h u n d r e d s of n u m b e r e d or n a m e d clones e s t a b l i s h e d t h r o u g h o u t t h e Eastern U n i t e d States. T h e w o o d is m o d e r a t e l y l i g h t as i n d i c a t e d by specific g r a v i t y values of 0.32 t o 0.37 a n d t h e m o i s t u r e c o n t e n t of t h e s a p w o o d is a b o u t 146 p e r c e n t (4Q). Certain h y b r i d poplar c l o n e s s h o w e x c e l l e n t response t o i n t e n s i v e c u l t u r e t e c h n i q u e s . D a w s o n (21J r e p o r t e d a m e a n a n n u a l biomass yield of nearly 7 t o n s per acre on a 12 i n c h s p a c i n g d u r i n g t h e first r o t a t i o n . A n d e r s o n a n d Zsuffa (23) r e p o r t e d c o p p i c e d s t a n d s y i e l d i n g 8.5 t o n s per acre per year o n a t w o year r o t a t i o n . Eucalypts Species of Eucalyptus appear t o have p r o m i s e as c a n d i d a t e s for biomass p r o d u c t i o n in intensively c u l t u r e d p l a n t a t i o n s . H o w e v e r , a lack of c o l d hardiness w o u l d restrict t h e i r usage t o t h e s o u t h e a s t e r n states, California a n d H a w a i i . This e v e r g r e e n h a r d w o o d g e n u s c o n t a i n s over 5 0 0 species, m o s t of w h i c h are n a t i v e t o A u s t r a l i a . T h e e u c a l y p t s have been p l a n t e d t h r o u g h o u t t h e w o r l d a n d display a w i d e a d a p t a b i l i t y t o a variety of sites. Especially n o t e w o r t h l y is t h e i r c a p a b i l i t y t o t h r i v e o n d r o u g h t y a n d n u t r i e n t - d e f i c i e n t sites. A l t h o u g h p r i m a r i l y s u i t e d for frost-free areas, studies by industrial c o o p e r a t o r s in t h e s o u t h e a s t e r n states i n d i c a t e d t h a t c o n s i d e r a b l e v a r i a t i o n exists in resistance t o freezing t e m p e r a t u r e s . (24). T h e g e n e t i c v a r i a t i o n


2.

SAJDAK ET AL.

33


i n d i c a t e d w a s s u c h t h a t selection f o r freeze-tolerant e u c a l y p t u s species a n d races m a y be possible. L i m i t e d g r o w t h d a t a is available b u t it has s h o w n a m e a n a n n u a l biomass p r o d u c t i o n of over 4 t o n s per acre per year. Greater productivity from eucalyptus

plantations should

be possible w i t h

more

i n t e n s i v e c u l t u r e a n d g e n e t i c a l l y i m p r o v e d stock.


Nitrogen-Fixing Species N i t r o g e n is t h e m o s t l i m i t i n g m a c r o n u t r i e n t needed for tree g r o w t h o n m o s t forest sites. Concern over t h e h i g h cost o f n i t r o g e n fertilizers for intensive p l a n t a t i o n c u l t u r e has p r o m p t e d c o n s i d e r a b l e interest in plants c a p a b l e of using a t m o s p h e r i c n i t r o g e n . Zavitkovski et al. (25) r e v i e w e d t h e studies w h i c h p e r t a i n t o t h e use o f n i t r o g e n - f i x i n g w o o d y a n d herbaceous species f o r forestry purposes. A s s e s s m e n t s w e r e m a d e o n t h e possibility of using red alder (A/nus rubra Bong.) f o r b i o m a s s p r o d u c t i o n , t h e use of n i t r o g e n - f i x i n g trees in m i x t u r e s w i t h n o n - n i t r o g e n f i x i n g trees a n d t h e use of herbaceous l e g u m e s as nurse crops in intensively m a n a g e d p l a n t a t i o n s . This r e v i e w i n d i c a t e s s i g n i f i c a n t m a n a g e m e n t benefits are possible t h r o u g h t h e use o f n i t r o g e n - f i x i n g trees. Red alder biomass yields are c o m p a r a b l e t o o t h e r fast g r o w i n g species. T h e use o f n i t r o g e n - f i x i n g trees a n d herbaceous material has g i v e n s i g n i f i c a n t increases in biomass yields. Cost-benefit ratios have n o t been d e t e r m i n e d because of t h e variety o f s t u d y c o n d i t i o n s e n c o u n t e r e d . M u c h a d d i t i o n a l i n f o r m a t i o n is needed t o f u l l y assess t h e feasibility of using n i t r o g e n - f i x i n g species in s h o r t - r o t a t i o n i n t e n s i v e p l a n t a t i o n c u l t u r e . Economics of Intensive Plantation Culture T h e yields f r o m intensively c u l t u r e d p l a n t a t i o n s are c o n s i d e r a b l y greater t h a n t h o s e f r o m natural s t a n d s o f similar tree species. It m u s t be e m p h a s i z e d , h o w e v e r , t h a t m a n y o f t h e r e p o r t e d p l a n t a t i o n yields are f r o m small s t u d y plots a n d i n d i c a t e w h a t is b i o l o g i c a l y possible. T o project s u c h yields over a larger area m a y be i n a p p r o p r i a t e . Several studies in W i s c o n s i n , S o u t h Carolina a n d Georgia (26,27,28) are c u r r e n t l y u n d e r w a y t o d e t e r m i n e t h e feasibility of intensive p l a n t a t i o n c u l t u r e o n a large scale. Rose a n d DeBell (29) assessed t h e e c o n o m i c s o f intensive p l a n t a t i o n c u l t u r e for w o o d fiber p r o d u c t i o n . S p a c i n g o f trees a n d l e n g t h o f r o t a t i o n a p p e a r e d t o be particularly cost sensitive in d e t e r m i n i n g e c o n o m i c feasibility. W i d e s p a c i n g ( 4 X 4 feet a n d 1 2 X 2 feet) a n d longer c o p p i c e rotations (4 year a n d 10 year, respectively) appeared feasible w h i l e t w o year c o p p i c e rotations d i d not.



34

BIOMASS AS A NONF OSSIL FUEL SOURCE

Using a d i f f e r e n t p e r s p e c t i v e . Eimers (30) e v a l u a t e d t h e e c o n o m i c s of i n t e n s i v e p l a n t a t i o n c u l t u r e as an e n e r g y source f r o m t h e s t a n d p o i n t of a c o m p a n y h a v i n g e x t e n s i v e e x p e r i e n c e in g r o w i n g a n d h a n d l i n g forest p r o d u c t s . His c o n c l u s i o n s w e r e t h a t fuel p l a n t a t i o n s are c u r r e n t l y u n e c o n o m i c a l . H o w e v e r , i n d i c a t i o n s are t h a t t h i s c o u l d c h a n g e if c e r t a i n costs w e r e r e d u c e d . T h e e c o n o m i c o u t l o o k for intensive m a n a g e m e n t s y s t e m s w o u l d i m p r o v e if h a r v e s t i n g costs c o u l d be r e d u c e d a n d e n e r g y c o n v e r s i o n costs l o w e r e d . The overall cost p i c t u r e m a y also be m o r e favorable if a dual p u r p o s e c r o p c o u l d be p r o d u c e d . For e x a m p l e , t h e biomass material p r o d u c e d f r o m p l a n t a t i o n s w o u l d be s o r t e d i n t o h i g h q u a l i t y c h i p s for fiber p r o d u c t s a n d l o w q u a l i t y c h i p s c o n v e r t e d i n t o energy. A d i r e c t parallel already exists in m a n y forest i n d u s t r i e s w h i c h c u r r e n t l y use residues f r o m t h e m a n u f a c t u r e of forest p r o d u c t s t o fire boilers. Eimers (30) also p o i n t s o u t t h a t p l a n t i n g at close s p a c i n g offers s o m e m a n a g e m e n t f l e x i b i l i t y w h e n t h i n n i n g is c o n s i d e r e d . T h a t is, t h i n n i n g f r o m i n t e n s i v e l y m a n a g e d p l a n t a t i o n s c a n be used for e n e r g y , w h i l e t h e r e m a i n i n g trees c a n be g r o w n for c o n v e n t i o n a l forest p r o d u c t s . T h e a d v a n t a g e t o this m a n a g e m e n t s t r a t e g y is t h a t d e c i s i o n s c o n c e r n i n g w o o d use can be deferred t o a f u t u r e date w h e n t h e e c o n o m i c s of e n e r g y s u p p l y m a y be less t u r b u l e n t t h a n at present. C H A R A C T E R I Z A T I O N OF B I O M A S S T h e p h y s i c a l a n d c h e m i c a l n a t u r e of b i o m a s s materials has a p r o f o u n d i n f l u e n c e o n t h e i r end-uses. For e x a m p l e , m o i s t u r e c o n t e n t a n d specific g r a v i t y are i m p o r t a n t properties for t h e p r o d u c t i o n of solid w o o d a n d paper p r o d u c t s , as w e l l as for c o n v e r s i o n into energy. O t h e r p h y s i c a l a n d m e c h a n i c a l properties of w o o d , s u c h as fiber l e n g t h , fibril a n g l e a n d s t r e n g t h of i n d i v i d u a l fibers, are n o t i m p o r t a n t for e n e r g y a p p l i c a t i o n s . T h e c u r r e n t t r e n d s t o w a r d w h o l e tree utilization a n d e n e r g y p l a n t a t i o n s t h r o u g h intensive m a n a g e m e n t can result in s u b s t a n t i a l c h a n g e s in t h e nature of w o o d resources available for i n d u s t r i a l a n d c o m m e r c i a l use. T h e effects of v a r i o u s intensive m a n a g e m e n t s y s t e m s o n w o o d properties have been reported in n u m e r o u s p u b l i c a t i o n s a n d w e r e r e c e n t l y s u m m a r i z e d in t h r e e articles (31.32,33). It w a s clearly i n d i c a t e d t h a t t h e m a j o r c h a n g e s in w o o d properties are associated w i t h shorter r o t a t i o n s , w h i c h result in a h i g h e r p r o p o r t i o n of j u v e n i l e w o o d . This y o u n g w o o d , as c o m p a r e d t o m a t u r e w o o d , c o n t a i n s a h i g h e r m o i s t u r e c o n t e n t , l o w e r specific g r a v i t y a n d a h i g h p r o p o r t i o n of r e a c t i o n w o o d . T h e effects of c h a n g i n g t h e s e w o o d properties on t h e solid w o o d p r o d u c t a n d paper i n d u s t r y have been e x t e n s i v e l y r e v i e w e d by Bendtsen (31.) a n d Einspaphr (32.33), respectively. In t h e


2.

SAJDAK ET AL.

following

35


s e c t i o n , those

wood

properties

which

are i m p o r t a n t

to the

c o n v e r s i o n of w o o d y biomass into e n e r g y uses are discussed.


Distribution of Tree Components Total a b o v e - g r o u n d tree biomass is generally d i v i d e d into foliage, b r a n c h , a n d s t e m c o m p o n e n t s . The b r a n c h e s a n d s t e m s can be separated f u r t h e r into bark a n d w o o d portions. The i m p o r t a n c e of branches a n d foliage t o total tree w e i g h t is d e p e n d e n t u p o n t h e age a n d / o r size o f t h e tree (34). It is e s t i m a t e d t h a t t h e a b o v e - g r o u n d biomass c u r r e n t l y p r o d u c e d o n c o m m e r c i a l forest land in t h e U n i t e d States is a p p r o x i m a t e l y d i s t r i b u t e d as w o o d (80 percent), bark (12 percent), a n d foliage (8 percent) (11). Table IV s h o w s s o m e representative d i s t r i b u t i o n s o f tree c o m p o n e n t s by species a n d age. T h e d a t a clearly s h o w t h a t y o u n g trees have a s u b s t a n t i a l l y h i g h e r c o n t e n t of foliage a n d bark b i o m a s s t h a n older, larger trees. These t w o c o m p o n e n t s are not desirable f o r t h e p r o d u c t i o n o f fiber related p r o d u c t s , s u c h as paper, b u t are desirable f o r e n e r g y p r o d u c t i o n d u e t o t h e i r h i g h e n e r g y c o n t e n t , part i c u l a r l y bark. T h e t r e n d t o w a r d s h o r t e r s t a n d r o t a t i o n or t h e e s t a b l i s h m e n t of e n e r g y p l a n t a t i o n s w o u l d increase t h e availability of y o u n g tree biomass f o r e n e r g y use. Moisture Content M o i s t u r e c o n t e n t is a p a r t i c u l a r l y i m p o r t a n t characteristic w h e n usine w o o d y biomass as f u e l , a n d is generally expressed as p e r c e n t of t h e d r y w e i g h t . W a t e r c o n t a i n e d in biomass a d d s t o t h e cost o f t r a n s p o r t a t i o n , a n d l o w e r s t h e e f f i c i e n c y o f e n e r g y c o n v e r s i o n b y a d i r e c t c o m b u s t i o n process, because of t h e e n e r g y required f o r e v a p o r a t i o n o f t h e w a t e r . It is e s t i m a t e d t h a t a b o u t 15 p e r c e n t o f t h e t o t a l available heat in a w o o d or bark fuel is required f o r m o i s t u r e e v a p o r a t i o n , a s s u m i n g a 1 0 0 p e r c e n t m o i s t u r e c o n t e n t (38). H o w e v e r , c o n v e r s i o n b y anaerobic d i g e s t i o n or f e r m e n t a t i o n m e t h o d s are m o r e efficient w h e n u s i n g h i g h - m o i s t u r e biomass materials. T h e p r o c e d u r e for e s t i m a t i n g e f f e c t i v e heat values f o r b o t h w o o d a n d bark fuels u n d e r v a r y ing m o i s t u r e c o n t e n t a n d f u r n a c e e n v i r o m e n t s has been s u m m a r i z e d b y Ince (39). The m o i s t u r e c o n t e n t of various forest biomass varies w i d e l y w i t h species, g e o g r a p h i c locations, g e n e t i c differences, tree c o m p o n e n t s used, a n d tree age. Published d a t a indicate t h a t m o i s t u r e c o n t e n t o f m a t u r e w o o d m a y range f r o m a b o u t 3 0 p e r c e n t t o m o r e t h a n 2 0 0 p e r c e n t (40). A l s o , m o i s t u r e c o n t e n t o f t h e s t e m s a p w o o d p o r t i o n is usually h i g h e r t h a n t h a t of t h e associated h e a r t w o o d . For y o u n g h a r d w o o d s p r o u t s (6 t o 15 years old), a n average



L.

Marsh.

Lamb.

—

— —

— — —

(29)

(27) (22)

(19)

67

64 68

68 b

10

22 16

—

—

(38)

— — —

—

— — — —

%

%

88

52 80

— — —

—

%

N u m b e r s in t h e parentheses are bark p e r c e n t a g e s of t h e tree c o m p o n e n t .

S u m of s t e m s a n d b r a n c h e s

40

6 40

2

3

2

2

%

(19)

(20) (10)

— — —

—

%

2

24 4

33

36 32

32

%

The d a t a clearly s h o w t h a t y o u n g trees have a s u b s t a n t i a l l y h i g h e r c o n t e n t of foliage a n d bark b i o m a s s t h a n older, larger trees. These t w o c o m p o n e n t s are n o t desirable for t h e p r o d u c t i o n of f i b e r - r e l a t e d p r o d u c t s , s u c h as paper, b u t are desirable for e n e r g y p r o d u c t i o n due t o t h e i r h i g h energy c o n t e n t , p a r t i c u l a r l y bark. T h e t r e n d t o w a r d s h o r t e r s t a n d r o t a t i o n or t h e e s t a b l i s h m e n t of e n e r g y p l a n t a t i o n s w o u l d increase t h e a v a i l a b i l i t y of y o u n g - t r e e biomass for e n e r g y uses.

b

a

Populus tremuloides M i c h x . (aspen)

(jack pine)

Pinus banksiana

Robinia pseudoaccacia L. (black locust)

(red maple)

Acer rubrum

(sugar maple)

%

Stems Total Bark Foliage

yr

Age,

W o o d y Biomass" Branches Bark Bark Total Total

Acer saccharum

Species

BIOMASS

T a b l e IV. TREE C O M P O N E N T S A S PERCENT OF A B O V E - G R O U N D


2.

SAJDAK ET AL.


37

m o i s t u r e c o n t e n t o f 8 0 p e r c e n t w a s reported f o r nine species c o l l e c t e d in m i d s u m m e r , r a n g i n g f r o m 5 9 p e r c e n t f o r green ash (Frax/nus pennsylvanica Marsh.) t o 9 9 p e r c e n t f o r y e l l o w poplar (Liriodendron tuplipifera L.) (41).


It has been s h o w n t h a t w o o d m o i s t u r e c o n t e n t has an inverse c o r r e l a t i o n w i t h tree age (35,42). In general, w o o d f r o m a y o u n g tree c o n t a i n s m o r e w a t e r t h a n w o o d f r o m a n older o n e o f t h e s a m e species (42). This is p r o b a b l y associated w i t h t h e v i g o r o u s g r o w t h a n d t h e h i g h p r o p o r t i o n of s a p w o o d in t h e y o u n g e r tree. There is n o general c o n s e n s u s c o n c e r n i n g a seasonal t r e n d of m o i s t u r e c o n t e n t in trees (43). S o m e researchers have reported larger seasonal variations w h i l e others have f o u n d very little. H o w e v e r , it appears t h a t t h e y o u n g trees or s p r o u t s , in c o n t r a s t t o m a t u r e trees, display a s i g n i f i c a n t seasonal v a r i a t i o n in m o i s t u r e c o n t e n t , p a r t i c u l a r l y for t h o s e g r o w i n g in n o r t h e r n c l i m a t e s . Figure I s h o w s seasonal variations in m o i s t u r e c o n t e n t f o r 3-year o l d s u g a r m a p l e (Acer saccharum Marsh) s p r o u t s (35) a n d 50-year old y e l l o w poplar (43). The m a p l e , g r o w n in t h e Upper Peninsula of M i c h i g a n , displays a m a r k e d seasonal v a r i a t i o n in m o i s t u r e c o n t e n t w h i c h reaches a m a x i m u m in J u n e . This w o o d m o i s t u r e p a t t e r n is essentially parallel t o s p r o u t g r o w t h a c t i v i t y . In c o n t r a s t , t h e m o i s t u r e c o n t e n t of m a t u r e y e l l o w poplar g r o w n in t h e S o u t h e r n A p p a l a c h a i n M o u n t a i n s of N o r t h Carolina does n o t vary s i g n i f i c a n t l y f r o m season t o season.

Specific Gravity Specific g r a v i t y indicates t h e a m o u n t of solid material in a g i v e n v o l u m e , a n d is usually c o n s i d e r e d t h e best single index of intrinsic w o o d q u a l i t y f o r fiber, w o o d p r o d u c t s , a n d e n e r g y p r o d u c t i o n . Specific g r a v i t y is inversely correlated w i t h w o o d m o i s t u r e c o n t e n t (44). T h u s , it also varies w i t h species, tree c o m p o n e n t s , a n d t h e age of t h e tree. In general, j u v e n i l e w o o d has a relatively l o w e r specific g r a v i t y t h a n m a t u r e w o o d . In s o m e species, t h e j u v e n i l e g r o w h t period m a y last f o r at least 10 years, d u r i n g w h i c h there is a steady increase in specific g r a v i t y (45). Therefore, y o u n g trees w i l l n o t p r o v i d e t h e s a m e yield o f solid material or fiber per u n i t v o l u m e of w o o d as c o m p a r e d t o older trees. Chemical Composition The c h e m i c a l c o m p o s i t i o n o f biomass materials is generally discussed in t e r m s o f cell w a l l p o l y s a c c h a r i d e s (cellulose a n d hemicelluloses), p h e n o l i c s (lignin a n d p o l y p h e n o l s ) , extractives, a n d ash c o n t e n t . W o o d n o r m a l l y c o n tains small a m o u n t s of ash (1 percent) a n d various q u a n t i t i e s of e x t r a c t i v e s


38



FEB.

APRIL

JUNE

AUG.

OCT.

DEC.

MONTH

Figure 1. Season variation of moisture content of (O bark, · wood) 3-year-old sugar maple and (A bark, A wood) 50-year-old yellow poplar (43)


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d e p e n d i n g o n tree species (46). Extractive-free h a r d w o o d s have a lignin c o n t e n t b e t w e e n 18 p e r c e n t a n d 2 5 p e r c e n t ; it varies b e t w e e n 2 5 percent and 3 5 percent f o r t h e s o f t w o o d s . T h e r e m a i n i n g materials in t h e w o o d are t h e polysaccharides (46).


There are d e f i n i t e c h a n g e s in t h e c h e m i c a l c o m p o s i t i o n of reaction w o o d . Compression w o o d has a s i g n i f i c a n t increase in lignin a n d a c o r r e s p o n d i n g decrease in polysaccharides as c o m p a r e d t o n o r m a l s o f t w o o d . Tension w o o d has j u s t t h e o p p o s i t e relationship. Since j u v e n i l e w o o d t e n d s t o c o n t a i n a h i g h level o f reaction w o o d , its c h e m i c a l c o m p o s i t i o n s h o u l d differ f r o m t h a t of m a t u r e w o o d . Other tree c o m p o n e n t s , s u c h as foliage a n d bark, c o n t a i n a s u b s t a n t i a l l y higher c o n t e n t of e x t r a c t i v e s , a n d a s l i g h t l y higher ash c o n t e n t t h a n w o o d . A l s o , bark has a h i g h e r c o n t e n t of p h e n o l i c s other t h a n l i g n i n , i n c l u d i n g p h e n o l i c acid a n d t a n n i n s as c o m p a r e d t o w o o d . C h e m i c a l c o m p o s i t i o n , as discussed in t h e next s e c t i o n , is closely related t o t h e caloric values of biomass, a n d also affects t h e efficiency of c o n v e r s i o n , particularly w h e n using a biological a p p r o a c h . For e x a m p l e , t h e presence of p h e n o l i c s , p a r t i c u l a r l y l i g n i n , presents a major roadblock f o r e n z y m a t i c c o n version o f p o l y s a c c h a r i d e s t o a l c o h o l . The c o n v e r s i o n of j u v e n i l e biomass has been s h o w n t o have a higher m o i s t u r e c o n t e n t a n d l o w e r specific g r a v i t y t h a n m a t u r e w o o d (47), a n d m a y respond m o r e f a v o r a b l y t o s u c h a t r e a t m e n t process. The energy c o n v e r s i o n o f j u v e n i l e biomass materials b y a t h e r m a l or biological m e t h o d s needs t o be e x p l o r e d . Caloric Values* The caloric value, or heat of c o m b u s t i o n , of a natural fuel o n w e i g h t basis is a f u n c t i o n o f t h e c h e m c i a l c o m p o s i t i o n . It has been s h o w n t h a t a linear relat i o n s h i p exists b e t w e e n t h e heat of c o m b u s t i o n a n d t h e c a r b o n c o n t e n t of t h e substrate (48). L i g n i n has a higher heat of c o m b u s t i o n t h a n t h a t of a p o l y s a c c h a r i d e ( 5 8 8 4 vs. 3 8 5 3 c a l / g ) , because of its l o w e r o x y g e n c o n t e n t . The extractives (terpenoid h y d r o c a r b o n s or resin) w i t h even l o w e r o x y g e n c o n t e n t s have still h i g h e r heat c o n t e n t s ( 8 1 2 4 and 9 0 2 7 cal/g) (49). In c o n trast h i g h e r ash c o n t e n t w i l l have a negative effect o n t h e calorific value. The caloric values of natural fuels reported in t h e literature have been s u m marized b y various a u t h o r s (38,29,41,48,50,51,52). The average values taken f r o m these reviews are listed in Table V. A n average heat c o n t e n t of 4 7 8 1 a n d

• A l l heating values discussed in this section are high heating values.



a

5177

— —

— —

5010

5197(13)

—

5 2 4 1 (3) 5 2 6 6 (9) 5 0 3 3 (24)

5149 (15)

Softwood Bark

5133(16)

— —

4886(16)

— —

Wood 8

5081

—

5016(1)

—

5145(1)

— — —

Needles

Figures in parentheses are t h e n u m b e r o f species e x a m i n e d .

Average

Ince Koch Neenam and Steinbeck

S u s o t t et al.

Harder a n d Einspahr Corder Corder

Harder a n d Einspahr

Author

4781

4 7 7 7 (9)

—

4 9 7 1 (13)

— —

4 5 9 6 (7)

—

Wood

4 6 3 1 (9) 4664

—

—

4 6 7 2 (9)

4 6 8 8 (21)

—

4613(15)

4715(9)

Hardwood Bark

T a b l e V. A V E R A G E C A L O R I C V A L U E S OF N A T U R A L FUELS (cal/g)


4759

5 0 4 7 (9)

— —

4 4 7 0 (4)

— —

Needles

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5 0 1 0 c a l / g w a s f o u n d f o r h a r d w o o d a n d s o f t w o o d , respectively. It appears t h a t little v a r i a t i o n in caloric values exists a m o n g various h a r d w o o d species. Larger variations have been o b s e r v e d a m o n g s o f t w o o d species because o f t h e m a r k e d differences in e x t r a c t i v e c o n t e n t . H o w e v e r , it c a n generally be c o n c l u d e d t h a t t h e caloric value for a g i v e n v o l u m e of biomass material is p r i marily d e t e r m i n e d b y its m o i s t u r e c o n t e n t a n d specific gravity. PERSPECTIVE The near t e r m a n d e x t e n d e d o u t l o o k of increasing use of w o o d f o r energy


purposes is favorable. C o m m e r c i a l forests c o n t a i n a n a b u n d a n c e of biomass for fuel a n d intensively c u l t u r e d p l a n t a t i o n s c o u l d a d d a d d i t i o n a l a m o u n t s . The q u e s t i o n is h o w m u c h a n d at w h a t cost? The use o f w o o d f o r e n e r g y w i l l c o m p e t e w i t h w o o d f o r material use. W o o d as a c o n s t r u c t i o n material is m u c h m o r e i m p o r t a n t in t h e Nation's energy b u d g e t t h a n as a fuel. T h e m a n u f a c t u r e of l u m b e r a n d p l y w o o d f r o m w o o d is much

less e n e r g y - i n t e n s i v e t h a n t h e m a n u f a c t u r e of m e t a l a n d plastic

p r o d u c t s . Also, t h e e n e r g y savings d u e t o t h e h i g h i n s u l a t i n g value of w o o d b u i l d i n g c o m p o n e n t s s h o u l d be n o t e d . Forest survey statistics i n d i c a t e w e harvest a n d use u p w a r d s o f 3 0 p e r c e n t o f c u r r e n t forest p r o d u c t i o n f o r c o n v e n t i o n a l forest p r o d u c t s . The r e m a i n i n g 7 0 p e r c e n t has been s h o w n t o be p o t e n t i a l l y available f o r various energy uses (3.10). H o w e v e r , before s u c h increased w o o d use o c c u r s , a n u m b e r of factors need t o be e x a m i n e d a n d h o p e f u l l y resolved. Conventional W o o d Needs It is a p p a r e n t t h a t increasing d e m a n d s f o r t r a d i t i o n a l forest p r o d u c t s w i l l require s o m e of t h e c u r r e n t b i o m a s s surplus. It is also a p p a r e n t t h a t s o m e of t h e s u r p l u s biomass m a y be unavailable f o r e c o n o m i c reasons o r u n h a r v e s t a ble d u e t o c o n s t r a i n t s i m p o s e d b y o t h e r forest users or e n v i r o n m e n t a l factors. C o n s e q u e n t l y , w h a t is t h e n left o f t h e surplus w o u l d be p o t e n t i a l l y available for e n e r g y use. A recent s t u d y f o r t h e A m e r i c a n P u l p w o o d A s s o c i a t i o n evaluated t h e w o r l d w o o d s u p p l y a n d d e m a n d s i t u a t i o n t o t h e year 2 0 0 0 (7). T h e U n i t e d States w a s i d e n t i f i e d as one o f t h e c o u n t r i e s w h i c h w i l l need m o r e w o o d t h a n it can s u p p l y . H o w e v e r , t h e s t u d y c o n c l u d e d t h a t w e have t h e p o t e n t i a l t o n o t o n l y e l i m i n a t e t h e e x p e c t e d d e f i c i t b u t also t o b e c o m e a n e t e x p o r t e r o f forest p r o d u c t s . T o a c c o m p l i s h this g o a l , w e w i l l need t o increase utilization o f c u r r e n t g r o w t h as w e l l as increase p r o d u c t i v i t y o n all available lands.


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Increasing Utilization


W o o d c u r r e n t l y u n u s e d because of p o o r m a r k e t s a n d h i g h utilization s t a n d a r d s w i l l help alleviate t h e p r o j e c t e d U.S. w o o d deficit. Smaller logs m u s t be harvested a n d t h e r e m a i n i n g p o r t i o n s of t h e trees c h i p p e d . High q u a l i t y c h i p s w o u l d likely be utilized for fiber p r o d u c t s w h i l e l o w q u a l i t y m a t e r i a l c a n be b u r n e d . I m p r o v e d b i o m a s s inventories are also n e e d e d t o i d e n t i f y t h e a m o u n t s , q u a l i t y , locations, a n d deliverable costs of t h e excess forest biomass. Increasing t h e utilization of forest b i o m a s s is p a r t i c u l a r l y cost-sensitive. A s greater a m o u n t s of forest residue are r e m o v e d f r o m a g i v e n area, t h e costs w i l l increase. In m a n y cases, it m a y not be e c o n o m i c a l l y feasible t o recover t h e residue g e n e r a t e d by small l a n d o w n e r harvest o p e r a t i o n s a n d t r a n s p o r t t h i s t o a large e n e r g y user. M o r e likely, t h i s residue a n d possibly h i g h e r value t i m b e r w i l l be i n c r e a s i n g l y used for h o m e h e a t i n g in a d i r e c t response t o rising c o n v e n t i o n a l h e a t i n g costs. Utilization w i l l p r o b a b l y be m o s t intense in t h e N o r t h e r n a n d S o u t h e r n Regions w h e r e m o s t of o u r p o p u l a t i o n exists a n d t h e forests are also m o s t diverse. Impact on Other Forest Uses Increasing t h e utilization of o u r forests w i l l have a d e f i n i t e i m p a c t o n o t h e r forest uses s u c h as w i l d l i f e , r e c r e a t i o n , a n d w a t e r . I n d e e d , s o m e s e g m e n t s of o u r s o c i e t y place t i m b e r p r o d u c t i o n s e c o n d a r y as is e v i d e n c e d by recent c o u r t d e c i s i o n s w h i c h l i m i t m a n a g e m e n t p r e r o g a t i v e s o n c e r t a i n National a n d State Forests. T h e m o s t efficient h a r v e s t i n g s y s t e m s , i.e.. c l e a r c u t t i n g w i t h w h o l e - t r e e c h i p p i n g , are especially in disfavor. H o w e v e r , it m u s t be n o t e d t h a t t h e i n h e r e n t n a t u r e of species like aspen (Populus) a n d j a c k pine requires t h a t c l e a r c u t t i n g be used for r e g e n e r a t i o n . T h e removal of t o p s , l i m b s , a n d cull trees in a selective log harvest, w h i l e i m p r o v i n g t h e visual i m p a c t , w i l l d e s t r o y t h e c o v e r n e e d e d for s m a l l a n i m a l s a n d birds. A m u l t i p l e use m a n a g e m e n t a p p r o a c h is necessary w h e n i m p l e m e n t i n g increased forest u t i l i z a t i o n , b u t at s o m e sacrifice in y i e l d . Not every acre can be utilized t o its fullest p o t e n t i a l for b i o m a s s p r o d u c t i o n . Impact on Site Quality M o r e i n f o r m a t i o n is n e e d e d t o d e t e r m i n e t h e i m p a c t t h a t increased utilization w i l l have o n site q u a l i t y s u c h as soil o r g a n i c m a t t e r c o n t e n t , w a t e r h o l d i n g c a p a c i t y a n d f e r t i l i t y levels. (53) It appears t h a t t h e m o r e intensive t h e harvest, t h e greater t h e o p p o r t u n i t y for soil d e t e r i o r a t i o n . The increased


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r e m o v a l o f leaves a n d small b r a n c h e s represents a s i g n i f i c a n t drain o f n u t r i e n t capital o n s o m e sites a n d m a y cause s o m e l o n g - t e r m r e d u c t i o n in site p r o d u c t i v i t y .


Increasing Forest Productivity A s stated earlier, m a n y forests are u n d e r s t o c k e d . S o m e of t h e biomass surplus w i l l need t o be left o n site t o increase t h e a m o u n t of g r o w i n g stock a n d therefore increase f u t u r e yields. T h e increasing d e m a n d f o r w o o d p r o d u c t s a n d f u e l w o o d presents a n o p p o r t u n i t y for forest i m p r o v e m e n t practices as never before. P r e - c o m m e r c i a l t h i n n i n g s a n d i m p r o v e m e n t c u t t i n g s m a y n o w be p r o f i t a b l e in s u p p l y i n g w o o d for e n e r g y uses w h i l e increasing t h e p r o d u c t i o n of q u a l i t y t i m b e r in t h e f u t u r e . It is e x p e c t e d t h a t t h e forest p r o d u c t s industries w i l l lead t h e w a y t o w a r d increasing forest p r o d u c t i v i t y . Industry lands are already t h e m o s t p r o d u c t i v e as c o m p a r e d t o private a n d p u b l i c lands. A t present, w i t h a b o u t 14 p e r c e n t of t h e c o m m e r c i a l forest land area, t h e forest industries p r o d u c e 3 3 p e r c e n t o f t h e w o o d in t h e U n i t e d States. Less certain is t h e e x t e n t t o w h i c h small private forests w i l l increase p r o d u c t i v i t y . The w o o d markets are assured b u t t h e i n v e s t m e n t required f o r forest i m p r o v e m e n t is u n a t t r a c t i v e f o r i n d i viduals, especially in t h e face o f rising land costs, interest rates a n d taxes, a n d increasing regulations. Public lands are least p r o d u c t i v e because o f l o c a t i o n , terrain a n d land use history a n d because o f t h e pressures f r o m o t h e r users. Large increases in g o v e r n m e n t a l f u n d i n g w i l l be needed a n d policy c h a n g e s i n i t i a t e d before s i g n i f i c a n t increases in p r o d u c t i v i t y can be realized. Biomass Energy Plantations Intensively c u l t u r e d s h o r t - r o t a t i o n p l a n t a t i o n s have been a d v o c a t e d as p r o v i d i n g a d d i t i o n a l sources o f b i o m a s s for e n e r g y use. The land base needed for t h e i m p l e m e n t a t i o n o f t h i s proposal o n a n extensive scale w o u l d seem t o present a nearly i n s u r m o u n t a b l e p r o b l e m . For e x a m p l e , Evans (54) c a l c u l a t e d t h a t a 1 0 0 m e g a w a t t electric f a c i l i t y w o u l d require a forest biomass p l a n t a t i o n nearly 2 0 0 square miles in size if o v e n d r y yields of five t o n s per acre per year c o u l d be a t t a i n e d . It m u s t be n o t e d t h a t t h e h i g h yields o b t a i n e d f r o m small plot studies m a y be d i f f i c u l t t o o b t a i n o n s u c h a large scale. Biomass e n e r g y p l a n t a t i o n s w o u l d m o s t likely be relegated t o s u b - m a r g i n a l a g r i c u l t u r a l lands or areas w h e r e forests are n o t n o r m a l l y f o u n d . T h e i n p u t s needed o n these lands t o achieve h i g h yields o f biomass m a y n o t be feasible or e c o n o m i c a l . A s i n d i c a t e d earlier, t h e l o w e r specific g r a v i t y a n d higher m o i s t u r e c o n t e n t o f s h o r t - r o t a t i o n b i o m a s s m a y affect t h e e n e r g y c o n v e r s i o n process.


44



Natural n o r t h e r n h a r d w o o d s t a n d s in N o r t h e r n M i c h i g a n w e r e f o u n d t o p r o d u c e nearly t w o d r y t o n s of b i o m a s s per acre per year over a 5 0 - y e a r period. These yields w e r e o b t a i n e d w i t h no m a n a g e m e n t i n p u t s w h a t s o e v e r (35). Frederick a n d C o f f m a n (55) r e p o r t e d m e a n a n n u a l d r y w e i g h t p r o d u c t i o n of nearly 2.5 t o n s per acre in a 2 5 year o l d u n m a n a g e d red p i n e (Pinus resinosa Ait.) p l a n t a t i o n . Even greater yields are possible in t h e S o u t h a n d t h e Pacific N o r t h w e s t . A m o r e realistic a p p r o a c h m i g h t be t o use t h e k n o w l e d g e gained from the intensive culture studies and supply this to improved m a n a g e m e n t of c o n v e n t i o n a l forest p l a n t a t i o n s . In c o n c l u s i o n , w o o d w i l l play an increasingly i m p o r t a n t role in s u p p l y i n g a part of o u r Nation's e n e r g y needs. T o w h a t e x t e n t t h i s w i l l o c c u r is u n k n o w n a n d w i l l d e p e n d in part o n t h e costs of m o r e c o n v e n t i o n a l fuels. Using w o o d for e n e r g y is t h e least p r o f i t a b l e use of t h i s resource a n d t h e d i f f e r e n t i a l s h o u l d c o n t i n u e . T h e forest p r o d u c t s i n d u s t r y w i l l likely lead t h e w a y in increasing t h e use of w o o d for energy. This i n d u s t r y has had t h e expertise in g r o w i n g , h a n d l i n g , a n d utilizing w o o d b o t h for m a n u f a c t u r i n g p r o d u c t s a n d for energy. T h e use of w o o d in g e n e r a t i n g e l e c t r i c i t y w i l l increase b u t on a smaller scale as utilities take a d v a n t a g e of s u r p l u s w o o d in t h e heavily f o r e s t e d regions. It is a p p a r e n t t h a t t h e use of w o o d as a h o m e h e a t i n g fuel w i l l c o n t i n u e t o e x p a n d d r a m a t i c a l l y . T h e effects of t h e s e v a r i o u s w o o d e n e r g y uses o n t h e e n v i r o n m e n t are largely u n k n o w n . ACKNOWLEDGEMENT T h e a u t h o r s w i s h t o t h a n k t h e U.S. D e p a r t m e n t of Energy for t h e i r partial s u p p o r t of t h i s endeavor. A l s o a p p r e c i a t e d is t h e e n c o u r a g e m e n t received f r o m t h e E n v i r o n m e n t a l Sciences Division. Oak Ridge N a t i o n a l Laboratory.


2.

SAJDAK ET AL.


45


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Forest Biomass for Energy - ACS Publications - American Chemical

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