Allelopathic Interference with Regeneration of the Allegheny

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Allelopathic Interference with Regeneration of the Allegheny Hardwood Forest Stephen B. Horsley

Downloaded by UNIV OF MISSOURI COLUMBIA on April 16, 2018 | https://pubs.acs.org Publication Date: January 8, 1987 | doi: 10.1021/bk-1987-0330.ch019

Northeastern Forest Experiment Station, U.S. Department of Agriculture Forest Service, Warren, PA 16365

Herbaceous weeds were a major cause of regeneration failure in some stands following turn-of-the-century logging. Forest openings became dominated by species of fern, grass, goldenrod, and aster, which are present today, 60 or more years after logging. Studies of the reasons for regeneration failure showed strong evidence of allelopathic interference between the weed species and black cherry. Today, in second-growth stands, other species of ferns and grass are a critical barrier to regeneration. A study to separate the independent effects of weeds and herbivory by deer showed that ferns and grass are the primary reason for regeneration failure. Deer had no direct effect on desirable species because the weeds prevented them from growing enough to emerge from the herbaceous cover where these species could be seen and browsed. Blackberries, raspberries, yellow and black birches, and pin cherry that did emerge from the herbaceous cover were browsed by deer. Interference between weeds and forest tree seedlings is a significant cause of regeneration failure in the cherry-maple (Prunus-Acer) Allegheny hardwood forest found along the northern tier counties of Pennsylvania and the southern tier counties of New York. Difficulties in regenerating black cherry (Prunus serotina) were encountered on some areas at the turn of the century when the original forest was cut (1). Weeds are a critical barrier to regeneration of many stands today as the second-growth forest is cut (_2, 3) . This paper summarizes work conducted to determine the reasons for regeneration failure after cutting both the original forest and second-growth Allegheny hardwood stands. Interference with Regeneration after Cutting of the Original Forest Most of the Allegheny Plateau was cut over between 1890 and 1930. On most areas, new fast-growing stands of black cherry, red maple This chapter not subject to U.S. copyright. Published 1987 American Chemical Society

Waller; Allelochemicals: Role in Agriculture and Forestry ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


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ALLELOCHEMICALS: ROLE IN AGRICULTURE AND FORESTRY

(Acer rubrum), sugar maple (Acer saccharum), white ash (Fraxinus americana), and beech (Fagus grandifolia) developed and are present today; but on some areas, new forests did not develop. T y p i c a l l y , these areas that f a i l e d to regenerate are found on extremely acid, imperfectly drained s o i l i n stream bottoms or on high f l a t s that were cut after 1920 when deer browsing had become a serious obstacle to forest regeneration. A l l of these s i t e s had been burned by slash f i r e s that were common at the time (4, 5). Locally, these areas are called orchard stands i f they contain a few scattered black cherry and red maple trees, or savannahs i f they are treeless. Deer and f i r e apparently prevented i n i t i a l regeneration of orchard stands and savannahs, and allowed development of a dense herbaceous ground cover dominated by bracken fern (Pteridium aquilinum), wild oat grass (Danthonia compressa), rough-stemmed goldenrod (Solidago rugosa), and flat-topped aster (Aster umbellatus). These species are present today, more than 60 years after harvest cutting, and there i s l i t t l e evidence of succession to longer l i v e d species. Young black cherry seedlings are present beneath the crowns of the widely spaced overstory trees, but they l i v e only a few years and grow an average of only 3 or 4 cm per year. In a series of f i e l d and greenhouse experiments, a number of possible sources of interference with black cherry growth were eliminated or shown to have minimal e f f e c t . White-tailed deer (Odocoileus virginianus) undoubtedly played a role i n the e s t a b l i s h ment of orchard stands, but they are not responsible for their maintenance. About 30% of the seedlings we marked were clipped, whether or not they were protected with wire cages. The c l i p p i n g c h a r a c t e r i s t i c s were those of small mammals, not deer. Microclimate at the study s i t e was moderate during the 2 years of measurement. S o i l temperatures ranged from 18 to 20°C, whether or not weeds were present, and within this range would not cause slow seedling growth. Surface s o i l moisture was high, ranging from 30 to 38% by volume on weeded plots and 26 to 35% by volume on unweeded plots during both years. S o i l samples showed a fragipanl i k e layer underlying the study s i t e that caused s o i l s to be imperf e c t l y drained, despite the fact that the sandy loam texture would otherwise have allowed better drainage. Herbaceous canopies reduced the quantity of sunlight by 70 to 80% at the seedling l e v e l . In a f i e l d experiment, 4 combinations of presence or absence of shade and weeds were evaluated: 1) shade and weeds present, 2) shade present, weeds absent, 3) shade absent, weeds present, and 4) shade and weeds absent. In treatment 2, weeds were removed and shade of similar intensity to that produced by the weeds was reimposed with Saran shade c l o t h . In treatment 3, shade was removed by restraining the herbaceous vegetation behind a b a r r i er made of wood stakes and s t r i n g that allowed seedlings to receive a 45° cone of l i g h t from above. Results of this experiment showed that during the 2 years that measurements were made, shading or competition for l i g h t did not cause a s i g n i f i c a n t reduction i n either shoot height increment or annual stem diameter increment. However, the physical presence of weeds resulted i n s i g n i f i c a n t l y less increment i n both of these measures i n the second year of the experiment. Thus, weeds had an effect on the growth of black cherry seedlings that was independent of shading. Further work indicated that the action of the weeds was exerted through the s o i l .



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I t was not n e c e s s a r y f o r weeds to be c o n t i n u o u s l y p r e s e n t t o have t h i s i n h i b i t i n g e f f e c t . S e e d l i n g s removed from an o r c h a r d s t a n d and grown i n a greenhouse i n the sandy loam s o i l from an o r c h a r d s t a n d , w i t h o u t weed c o m p e t i t i o n , grew the same amount as s e e d l i n g s growing i n t h e f i e l d . However, t h e s e s e e d l i n g s were c a p a b l e o f a l a r g e r growth r e s p o n s e . A n o t h e r group o f s e e d l i n g s removed from the f i e l d and grown w i t h o u t c o m p e t i t i o n i n an a g r i c u l t u r a l sandy loam s o i l t h a t d i d not have a h i s t o r y o f weeds produced 10 times as much growth. I f the weeds had d e p l e t e d the s o i l o f some e s s e n t i a l n u t r i e n t , i t s h o u l d be p o s s i b l e t o r e p l a c e t h a t n u t r i e n t by f e r t i l i z a t i o n . Whether o r not weeds were p r e s e n t , f e r t i l i z a t i o n of p l a n t e d b l a c k c h e r r y s e e d l i n g s w i t h ammonium n i t r a t e and t r i p l e s u p e r p h o s p h a t e , an Ν, P, Ca t r e a t m e n t , i n amounts c a p a b l e o f s t i m u l a t i n g s i g n i f i c a n t growth o f b l a c k c h e r r y s e e d l i n g s on s i t e s w i t h o u t a h i s t o r y o f herbaceous p l a n t s , had no e f f e c t on t h e growth o f b l a c k cherry seedlings (6). I t was p o s s i b l e t o o b t a i n a r e s p o n s e t o added n u t r i e n t s i f they were a p p l i e d r e p e a t e d l y . A d d i t i o n o f a complete m i n e r a l n u t r i e n t s o l u t i o n t o s e e d l i n g s growing i n a greenhouse i n the sandy loam s o i l from an o r c h a r d s t a n d r e s u l t e d i n a s i g n i f i c a n t i n c r e a s e i n s e e d l i n g growth. I n a second e x p e r i m e n t , we attempted t o d e t e r m i n e which n u t r i e n t elements gave the same q u a n t i t a t i v e r e s p o n s e as the com plete mineral nutrient s o l u t i o n . R e s u l t s o f t h i s experiment demon s t r a t e d t h a t n i t r o g e n ( N O 3 ) , p h o s p h o r u s , and c a l c i u m , the elements a p p l i e d i n the f i e l d s t u d y , were t h e ones needed t o produce a growth r e s p o n s e q u a n t i t a t i v e l y the same as the complete m i n e r a l n u t r i e n t solution. The need f o r r e p e t i t i v e a p p l i c a t i o n o f t h e s e elements s u g g e s t s t h a t one o r more may have a d u a l r o l e , f i r s t as a n u t r i e n t and second as a s o i l c o n d i t i o n e r t h a t might exchange o r complex w i t h an i n h i b i t o r y m o l e c u l e d e p o s i t e d i n the s o i l by t h e herbaceous weeds. A d d i t i o n a l s t u d i e s gave s t r o n g e v i d e n c e o f a l l e l o p a t h i c interference. The p o s s i b i l i t y o f an a l l e l o p a t h i c i n t e r a c t i o n was i n v e s t i g a t e d at 3 p h y s i o l o g i c a l s t a g e s i n the development of b l a c k cherry seedlings: d u r i n g seed g e r m i n a t i o n , growth on c o t y l e d o n a r y r e s e r v e s , and growth once c o t y l e d o n a r y r e s e r v e s were e x h a u s t e d . F o l i a g e e x t r a c t s were produced by s o a k i n g 50 g f r e s h weight o f whole leaves of f e r n , g r a s s , goldenrod, or a s t e r i n 1 l i t e r of d i s t i l l e d water a t room t e m p e r a t u r e f o r 16 h . These e x t r a c t s were d i l u t e d w i t h d i s t i l l e d water o r complete m i n e r a l n u t r i e n t s o l u t i o n t o form a c o n c e n t r a t i o n s e r i e s o f s o l u t i o n s c o n t a i n i n g 0 , 5, 2 5 , 5 0 , o r 100% f o l i a g e e x t r a c t , and used t o m o i s t e n peat i n which b l a c k c h e r r y seeds were s t r a t i f i e d , t o water newly germinated s e e d l i n g s growing on c o t y l e d o n a r y r e s e r v e s , o r t o water 3 0 - d a y - o l d s e e d l i n g s t h a t had exhausted c o t y l e d o n a r y r e s e r v e s . R e s u l t s o f t h e s e e x p e r i m e n t s showed t h a t most c o n c e n t r a t i o n s o f f e r n , g o l d e n r o d , and a s t e r f o l i a g e e x t r a c t caused s i g n i f i c a n t r e d u c t i o n s i n the g e r m i n a t i o n o f b l a c k c h e r r y s e e d . Grass e x t r a c t i n h i b i t e d g e r m i n a t i o n a t the l o w e s t c o n c e n t r a t i o n , but n o t a h i g h e r concentrations. D u r i n g the c o t y l e d o n a r y r e s e r v e p e r i o d , o n l y a s t e r f o l i a g e e x t r a c t i n h i b i t e d growth o f b l a c k c h e r r y s e e d l i n g s . When 100% e x t r a c t was a p p l i e d i n d i s t i l l e d water t o s e e d l i n g s growing i n s a n d , t h e r e was 35% l e s s shoot h e i g h t growth and 58% fewer f i r s t - o r d e r



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l a t e r a l roots on treated seedlings than on plants receiving only d i s t i l l e d water. Roots of aster-treated plants had brown, necrotic epidermal patches and dead terminal meristems. Similar reductions i n shoot growth were obtained when 100% aster foliage extract (50 g of leaves soaked i n 1 l i t e r of d i s t i l l e d water) was applied to seedlings growing i n the sandy loam s o i l from an orchard stand or an adjacent f u l l y stocked forest stand that did not have a h i s t o r y of herbaceous plants. When the experiment was repeated i n the same a g r i c u l t u r a l s o i l used e a r l i e r , i n h i b i t i o n was not evident. This s o i l had a higher organic matter content, higher pH, and evidence of a c t i v i t y of s o i l organisms. Thus, i t i s possible that the i n h i b i tory constituents of the extract were bound by the s o i l or used as carbon sources by s o i l microorganisms. Foliage extracts of a l l 4 species of plants inhibited the growth of plants that had exhausted cotyledonary reserves, whether the seedlings were grown i n sand or i n the sandy loam s o i l from an orchard stand. Foliage extracts were applied at 0, 5, 25, and 50% concentrations i n the same complete mineral nutrient solution used e a r l i e r . Results for the effects of aster on height growth were t y p i c a l . Both rate and duration of shoot growth were reduced as the concentration of foliage extract increased. Reductions i n shoot growth were attributable to both production of fewer nodes and shorter internode length. Trends i n shoot dry weight paralleled those of shoot growth. Root dry weight was reduced, but to a lesser extent than shoot dry weight. Effects of root washings of the 4 herbaceous plants on black cherry seedling growth were investigated by the " s t a i r s t e p " technique Ç7). Root washings of aster and goldenrod, but not fern and grass, caused s i g n i f i c a n t interference with black cherry growth. Shoot growth was reduced 50% by either species. Root washings of a single aster plant reduced shoot and root dry weight by 75%. Allelopathy appears to be the primary source of interference i n orchard stands, though i t i s possible that other factors contribute to the problem. It i s probable that allelochemicals accumulate i n the s o i l over a period of years so that even when the herbaceous plants were removed, growth responses of seedlings continued to be poor. In well-aerated s o i l s , organic chemical residues are normally metabol i z e d by indigenous s o i l microorganisms. This probably occurs only slowly i n orchard stand s o i l s and i s abetted by the inherent s o i l c h a r a c t e r i s t i c s , such as imperfect s o i l drainage, high s o i l a c i d i t y , and low organic matter content. Isolation and i d e n t i f i c a t i o n of allelochemicals from plants and s o i l and demonstration of their p a r t i c i p a t i o n i n growth i n h i b i t i o n of black cherry would confirm the presence of an a l l e l o p a t h i c r e l a t i o n s h i p . Interference with Regeneration i n Second-Growth Allegheny Hardwood Stands Herbaceous plants are also playing a major role i n the regeneration of many second-growth stands. Unlike other eastern hardwood forest types, natural regeneration frequently f a i l s a f t e r c l e a r c u t t i n g of the Allegheny hardwood forest; these areas are often dominated by ferns and grass. Studies of factors associated with successful regeneration after c l e a r c u t t i n g have shown that the presence of



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l a r g e numbers o f hardwood s e e d l i n g s b e f o r e c l e a r c u t t i n g was h i g h l y c o r r e l a t e d with s u c c e s s f u l r e g e n e r a t i o n a f t e r c l e a r c u t t i n g (8). There i s overwhelming e v i d e n c e from a v a r i e t y of s t u d i e s t h a t b r o w s i n g by w h i t e - t a i l e d deer i s r e s p o n s i b l e f o r many o f t h e s e f a i l ures (9). Where deer have been e x c l u d e d by f e n c i n g , r e g e n e r a t i o n i s o f t e n s u c c e s s f u l ; but where t h e y a r e not e x c l u d e d , r e g e n e r a t i o n often f a i l s . Many uncut A l l e g h e n y hardwood s t a n d s a l s o c o n t a i n dense ground c o v e r s o f f e r n s and g r a s s , p a r t i c u l a r l y h a y s c e n t e d f e r n ( D e n n s t a e d t i a p u n c t i l o b u l a ) , New York f e r n ( T h e l y p t e r i s n o v e b o r a c e n s i s ) , and s h o r t husk g r a s s ( B r a c h y e l y t r u m e r e c t u m ) . When t h e s e p l a n t s a r e p r e s e n t i n dense s t a n d s , t h e y too have a s u b s t a n t i a l i n h i b i t i n g e f f e c t on r e g e n e r a t i o n . In a s u r v e y of t h i n n e d s t a n d s , I found 50 to 80% fewer b l a c k c h e r r y and o t h e r d e s i r a b l e hardwood s e e d l i n g s where dense herbaceous p l a n t s were p r e s e n t t h a n where they were a b s e n t , and 40 t o 65% s h o r t e r s e e d l i n g h e i g h t (_2) . R e c e n t l y , s h e l t e r w o o d c u t t i n g has been proposed t o r e g e n e r a t e A l l e g h e n y hardwood s t a n d s t h a t do not have enough advance r e g e n e r a t i o n to q u a l i f y f o r c l e a r c u t t i n g ( 1 0 ) . In t h e s h e l t e r w o o d method, the f i r s t o r seed c u t removes a p o r t i o n o f the o v e r s t o r y . The moderate environment c r e a t e d i s f a v o r a b l e f o r g e r m i n a t i o n and e a r l y growth o f b l a c k c h e r r y , r e d and sugar maple, w h i t e a s h , and o t h e r d e s i r a b l e hardwood s p e c i e s . The s t r a t e g y i s t o b u i l d up the numbers of hardwood s e e d l i n g s and t h e n , when t h e r e i s enough, to remove the o v e r s t o r y w i t h a second or removal c u t and a l l o w t h e s e s e e d l i n g s to grow r a p i d l y out of r e a c h o f d e e r . A n y t h i n g t h a t p r e v e n t s the e a r l y b u i l d u p i n numbers of s e e d l i n g s o r t h e i r subsequent growth a f t e r the removal c u t p r e c l u d e s the use o f the s h e l t e r w o o d method. Many A l l e g h e n y hardwood s t a n d s a r e exposed t o heavy deer b r o w s i n g and a l s o c o n t a i n dense f e r n or g r a s s ground c o v e r s . R e c e n t l y , we e v a l u a t e d the r e l a t i v e i m p o r t a n c e of deer and weeds at the 2 c r i t i c a l s t a g e s i n the r e g e n e r a t i o n p r o c e s s o f s h e l t e r w o o d c u t s t a n d s — a f t e r t h e seed cut and a f t e r t h e removal c u t ( 3 ) . I d e n t i c a l e x p e r i m e n t s were performed i n 2 s t a n d s which had b o t h a dense herbaceous ground c o v e r and a h i g h deer p o p u l a t i o n . One s t a n d r e c e i v e d a s h e l t e r w o o d seed c u t ; the o t h e r , which had r e c e i v e d a seed c u t 6 y e a r s e a r l i e r , r e c e i v e d t h e s h e l t e r w o o d removal c u t . The e f f e c t s o f weeds and deer were s e p a r a t e d u s i n g 3 f e n c i n g and weeding t r e a t m e n t s a p p l i e d to c l u s t e r s o f t h r e e 1.83-m r a d i u s p l o t s : 1) f e n c i n g to e x c l u d e d e e r , but not weeds ( f e n c e d ) , 2) f e n c i n g p l u s r e p e a t e d hand weeding to e x c l u d e deer and weeds (fenced/weeded), and 3) no f e n c i n g or weeding, a l l o w i n g a c c e s s by b o t h deer and weeds to the p l o t s ( c o n t r o l ) . The e f f e c t s o f deer were e s t i m a t e d as the d i f f e r e n c e between fenced and c o n t r o l p l o t s . The e f f e c t s of weeds were e s t i m a t e d as the d i f f e r e n c e between fenced/weeded and f e n c e d plots. Both e x p e r i m e n t s r a n f o r 5 y e a r s . The s t a n d r e c e i v i n g the s h e l t e r w o o d seed c u t had a dense u n d e r s t o r y o f h a y s c e n t e d f e r n c o v e r i n g n e a r l y 80% o f the g r o u n d . The o v e r s t o r y i n t h i s s t a n d was p r i m a r i l y b l a c k c h e r r y and r e d maple and t h e s e were the major s p e c i e s r e p r e s e n t e d i n the r e g e n e r a t i o n . A l a r g e b l a c k c h e r r y seed c r o p d u r i n g the s t u d y r e s u l t e d i n i n c r e a s e d numbers o f b l a c k c h e r r y s e e d l i n g s on a l l p l o t s t h e f o l l o w i n g y e a r . The amount of i n c r e a s e i n numbers was 60% g r e a t e r on fenced/weeded p l o t s t h a n on f e n c e d or c o n t r o l p l o t s . S e e d l i n g s on fenced/weeded



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plots also survived better. There were o n l y 2% fewer b l a c k c h e r r y s e e d l i n g s i n t h e second y e a r a f t e r s e e d f a l l . B o t h fenced and c o n t r o l p l o t s had 48% fewer s e e d l i n g s . P a t t e r n s i n g e r m i n a t i o n and s u r v i v a l were s i m i l a r f o r r e d maple. A l a r g e r e d maple seed c r o p d u r i n g t h e s t u d y r e s u l t e d i n a 244% i n c r e a s e i n numbers o f r e d maple s e e d l i n g s on fenced/weeded p l o t s v e r s u s a 34% i n c r e a s e on fenced o r control plots. S u r v i v a l o f t h e s e s e e d l i n g s was 90% on fenced/weeded p l o t s compared w i t h o n l y 36% on fenced o r c o n t r o l p l o t s . The n e t e f f e c t was t h a t 4 y e a r s a f t e r t r e a t m e n t t h e r e were 43,000 d e s i r a b l e s e e d l i n g s p e r h e c t a r e on fenced/weeded p l o t s , b u t o n l y 8,000 p e r h e c t a r e on f e n c e d o r c o n t r o l p l o t s . We c o n c l u d e d t h a t t h e f e r n c o v e r , b u t n o t d e e r , i n t e r f e r e d w i t h g e r m i n a t i o n and s u r v i v a l o f these small s e e d l i n g s . In a d d i t i o n t o t h e r e p r o d u c t i o n o f d e s i r a b l e s p e c i e s , dormant seed o f p i n c h e r r y (Prunus p e n s y l v a n i c a ) a r e t y p i c a l l y s t o r e d i n t h e l i t t e r o f N o r t h e r n hardwood s t a n d s and germinate a f t e r c u t t i n g o r disturbance. S t o r a g e o f p i n c h e r r y seed i n t h e l i t t e r f o r p e r i o d s i n e x c e s s o f 50 y e a r s i s w e l l known ( 1 1 , 12) . Many o f t h e s e s t o r e d p i n c h e r r y seeds germinated on fenced/weeded p l o t s . A t t h e peak, 2 y e a r s a f t e r t h e s t u d y began, t h e r e were 64,000 s e e d l i n g s / h a . These i n t o l e r a n t s e e d l i n g s d i d not s u r v i v e l o n g ; most d i e d w i t h i n a y e a r o r two. T h i s experiment does n o t t e l l us how f e r n removal a f f e c t s germination of p i n cherry seed. However, Auchmoody (13) r e p o r t e d that a p p l i c a t i o n of n i t r a t e i o n to the f o r e s t f l o o r of Allegheny hardwood s t a n d s w i t h o u t p h y s i c a l d i s t u r b a n c e r e s u l t e d i n t h e g e r m i n a t i o n o f many p i n c h e r r y s e e d s . Thus, i t i s p o s s i b l e that the f e r n s have a r o l e i n r e g u l a t i n g s o i l n i t r i f i c a t i o n , t h e b i o l o g i c a l p r o c e s s t h a t c o n v e r t s ammonium-N t o n i t r a t e - N , and t h a t t h e i r removal r e s u l t s i n an i n c r e a s e i n t h i s p r o c e s s t h a t may a f f e c t g e r m i n a t i o n and growth o f t r e e s e e d l i n g s . Black cherry seedlings, f o r example, grow w e l l when s u p p l i e d n u t r i e n t s o l u t i o n s c o n t a i n i n g a n i t r a t e - N s o u r c e , b u t grow p o o r l y when t h e Ν s o u r c e i s ammonium. A t t h e b e g i n n i n g o f t h e experiment i n t h e s t a n d t h a t r e c e i v e d the s h e l t e r w o o d removal c u t , o n e - h a l f o f t h e s t a n d had a dense c o v e r of g r a s s , and t h e o t h e r h a l f a dense c o v e r o f f e r n . A f t e r the removal c u t , t h e r e were s u b s t a n t i a l changes i n t h e herbaceous c o v e r . B l a c k b e r r y (Rubus a l l e g h e n i e n s i s ) and r a s p b e r r y (Rubus o c c i d e n t a l i s ) , which made up l e s s than 5% o f t h e ground c o v e r a t t h e b e g i n n i n g o f the e x p e r i m e n t , i n c r e a s e d t o 70 t o 75% coverage on f e r n - c o v e r e d p l o t s and 80 t o 95% on g r a s s - c o v e r e d p l o t s . As Rubus i n c r e a s e d i n ground c o v e r a g e , f e r n c o v e r d e c r e a s e d by 25 t o 45% and g r a s s c o v e r d e c r e a s e d by 30 t o 40%. Even though Rubus i s a f a v o r i t e deer f o o d , deer had l i t t l e l a s t i n g e f f e c t on Rubus c o v e r i n t h i s s t a n d , though i n s t a n d s where Rubus i s l e s s p l e n t i f u l , deer a r e a b l e t o remove much o f i t ( 1 4 ) . Hardwood s e e d l i n g r e p r o d u c t i o n was a f f e c t e d by b o t h t h e t y p e o f ground c o v e r p r e s e n t b e f o r e t h e s t u d y began and t h e t r e a t m e n t . About 90% o f t h e s e s e e d l i n g s were b l a c k c h e r r y ; t h e next most abundant s p e c i e s were b l a c k b i r c h ( B e t u l a l e n t a ) and y e l l o w b i r c h (Betula a l l e g h a n i e n s i s ) . B e f o r e t r e a t m e n t , g r a s s - c o v e r e d p l o t s had more t h a n 3 t i m e s as many d e s i r a b l e s e e d l i n g s as f e r n - c o v e r e d p l o t s , s u g g e s t i n g t h a t f e r n i n t e r f e r e n c e was g r e a t e r t h a n g r a s s i n t e r f e r ence. A f t e r t h e removal c u t , t h e numbers o f a l l s p e c i e s p r e s e n t a t



19.

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Allelopathic

Interference with Hardwood

Forest Regeneration

211

the beginning of the experiment declined continuously over the next 4 years. Fencing had l i t t l e effect on seedling numbers, but fencing and weeding resulted in significantly more seedlings 4 years after cutting. Thus, the presence of fern or grass, but not deer, affected numbers of seedlings. Treatment effects on seedling height growth differed with species. Deer had no effect on height of black cherry seedlings. There was l i t t l e difference between fenced and control plots with either fern or grass cover; the herbaceous cover prevented the seedlings from growing through i t where they could be seen and browsed by deer. Fenced/weeded black cherry seedlings were signifi cantly taller than seedlings on either fenced or control plots. Ferns were the more inhibitory of the 2 herbaceous species. The birches were affected differently. Birch typically grew rapidly through fern or grass cover and was not affected by i t . Height of birches was similar on fenced/weeded and fenced plots. Once the birches grew above the herbaceous cover where they could be seen by deer, they were invariably browsed. Deer had a direct effect on birch, but ferns and grass had no effect. This study suggests that in Allegheny hardwood stands where both high deer populations and dense fern or grass cover are present, interference from ferns and grass is the primary factor that hinders the establishment of desirable species of regeneration, such as black cherry; deer browsing had l i t t l e or no direct effect under these conditions because these seedlings were unable to grow above the herbaceous cover where they could be browsed. Where we have been able to compare the relative inhibition by ferns and grass, the ferns interfered more strongly than grass. How do these ground cover plants, particularly the ferns, cause such strong interference with the establishment of black cherry seedlings? Previous research at our laboratory has shown that black cherry seedling growth can be modulated by supplies of nutrients, particularly nitrogen and phosphorus (15), water (16), light (16, 10), and allelochemicals (_1, 2) within the range that these factors occur in the natural environment. Thus, ferns could interfere with the establishment of black cherry seedlings by interfering with the production, availability, or use of site or environmental resources. We are conducting experiments to determine how hayscented fern interferes with the growth of black cherry seedlings in shelterwood seed cut Allegheny hardwood stands. These experiments measure the changes in site or environmental resources that occur in the presence and absence of hayscented fern cover, and the response of black cherry seedlings to these changes. We are investigating changes in light quantity and quality, plant water status, nitrogen production, and phosphorus and mycorrhizal status. Potential allelochemical effects of foliage leachings, root and rhizome wash ings, and foliage volatiles are being studied. The results of these studies should give us a clearer view of how hayscented fern inter feres with the establishment of black cherry seedlings. Literature Cited 1. Horsley, S. B. Can. J. For. Res. 1977, 7, 205-216. 2. Horsley, S. Β. Can. J. For. Res. 1977, 7, 515-519.



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3. Horsley, S. B.; Marquis, D. A. Can. J. For. Res. 1983, 13, 61-69. 4. Hough, A. F. Ecology 1945, 26, 235-250. 5. Hough, A. F. Pennsylvania For. 1955, 35, 36. 6. Horsley, S. B. North. J. Appl. For. 1985, 2, 22-26. 7. Bell, D. T.; Koeppe, D. E. Agron. J. 1972, 64, 321-325. 8. Grisez, T. J.; Peace, M. USDA For. Serv. 1973, Res. Note NE-180. 9. Marquis, D. Α.; Brenneman, R. USDA For. Serv. 1981, Gen. Tech. Rep. NE-65. 10. Marquis, D. A. J. For. 1979, 77, 140-144. 11. Marks, P. L. Ecol. Monogr. 1974, 44, 73-88. 12. Marquis, D. A. Can. J. For. Res. 1975, 5, 478-484. 13. Auchmoody, L. R. Can. J. For. Res. 1979, 9, 514-516. 14. Marquis, D. Α.; Grisez, T. J. USDA For. Serv. 1978, Res. Note NE-270. 15. Auchmoody, L. R. Can. J. For. Res. 1982, 12, 319-325. 16. Marquis, D. A. Ph.D. Dissertation, Yale University, New Haven, Connecticut, 1973. RECEIVED December 17, 1985


Allelopathic Interference with Regeneration of the Allegheny

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