Correspondence Comment on “Why Large-Scale Afforestation Efforts in China Have Failed To Solve the Desertification Problem” A Viewpoint entitled “Why Large-Scale Afforestation Efforts in China Have Failed to Solve the Desertification Problem” (1) concluded that large-scale afforestation in China is actually increasing land degradation in arid and semiarid areas (i.e., causing desertification). Unfortunately, many confusing concepts and faulty conclusions based on incorrect evidence have led to the author’s untenable viewpoint. To avoid misleading readers who may be unfamiliar with the area or concepts, we identify and carefully explore the three main shortcomings of this paper. First, two basic concepts are confused. (i) Afforestation is not equivalent to forestry; all the projects listed by the author are forest ecology projects and not afforestation projects. Here, we assume the author wants to describe afforestation effects as components of forestry projects. Also, the term “planting trees” is improperly defined and nearly becomes a substitute for afforestation throughout the paper. However, planting shrubs for protection is included in the afforestation activities by the Forest Law of China (2). Shrubs have actually been planted in all afforestation-related projects in recent years. In the fourth stage of the Three Norths Shelter Forest System Project (2001-2010), 40% of 9.5 million ha of planned afforestation area will be covered with shrubs (3). (ii) The author replaced “sandy desertification” with “desert” in describing the desertification dynamics and listed expansion areas or time frames that cannot be found in the references cited (refs 4, 15, and 17). Second, the author seems unfamiliar with Chinese forestry, desertification, and large-scale forest ecology projects, and the relationships among them; hence, much of the evidence that he uses to make his point is unclear and even incorrect. Here, we highlight several key errors. (i) There are mistakes in Figures 1 and 2. For example, the author gives the wrong unit in Figure 1. The maximum total afforestation is shown to be about 2000 million ha in 2003, which is more than twice China’s territory (960 million ha); even if the author had used the correct units, these data are not identical to those in the citation (ref 8). The same mistake occurs twice in the text: “29.1% of China’s land area (2.2 billion ha) was converted into forest by afforestation” (1) (p 1827), which would mean that China’s territory would actually be 7.56 billion ha (1) (p 1827), and “400 million ha of P. tremula monoculture is affected...by two wood-boring beetles” (1) (p 1828). This means that at least 40% of Chinese territory had been planted with poplar, and that all poplar were affected by beetles. The sandstorm frequency shown in Figure 2 is problematic, regardless of its conflicting trend with most scientific literature sources (e.g., ref 4), we could not find these data used in Figure 2, especially the data for 2000-2006 in seven cited references published in or before 2005. (ii) The author is unfamiliar with desertification theories and dryland characteristics in China. One example is that he hypothesizes a mechanism responsible for increased desertification in Figure 3; only ref 27 appears to be used as evidence, as well as a photo of severe wind erosion under an artificial poplar shelterbelt at Yijinhole Banner, Ordos Plateau. However, this kind of forest, planted mostly before the 1980s 7722
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 20, 2008
in gentle and loose sandy soil, does not represent the main forest condition in the Ordos Plateau. Even if this hypothesized mechanism is based on the above forest type, three unreasonable points makes the hypothesis untenable: (a) Individual tree-based mechanism used to extrapolate forestland degradation seems to be too simplistic; (b) The interaction surface for one single tree between the wind and the tree trunk is not a plane but a convex shape, and the up-flow and down-flow in the wind flow field is less than the around-flow which is totally neglected in Figure 3; (c) For a forest patch or belt, understory gaps create “wind tunnels” that result in a funnel effect with accelerated wind speed (5). Near-surface wind speed will, of course, increase, and soil erosion will be much higher for land with low surface cover or bare ground. Another obvious problem is that the author points out that wind erosion aggravated by planting trees in arid areas offsets the advantage of water erosion control by afforestation (photo, ref 1, p 1826), i.e., “large-scale afforestation in arid and semiarid China appears to have been unable to control desertification and may actually be exacerbating the problem” (1) (p 1829). Actually, in the dryland of China, water erosion occurs mainly on the Loess Plateau, and wind erosion occurs in and around deserts, steppes, and sandlands; the two types of erosion do not overlap in most regions. It can be deduced from the photo (1) (p 1826) and the cited references that the author’s evidence comes from the Loess Plateau. The Loess Plateau, which originated from aeolian loess deposits (6), is famous for its severe water erosion, whereas wind erosion is relatively weak (7). Hence, it would be impossible for the water erosion effect to be offset by wind erosion. (iii) The author knows little about afforestation-related projects and their effects. In his paper, three afforestation and desertification related projects are listed. (a) For the Three Norths Shelter Forest System Project, the author cites ref 7, which is from a local popular science magazine; we could not find this particular reference, and some of the questionable data could not be searched from other documents and articles. (b) For the Desertification Combating Project in the Blown-sand Source Area around Beijing and Tianjin, the author incorrectly describes this as the Taihang Mountain Afforestation Project. However, the main part of Taihang Mountain is located southwest of Beijing, and sandstorms enter Beijing from the north or northwest, so his description makes no sense. For the Grain for Green Project, all data and the descriptions that he uses could not be found in either of the two references cited (refs 9 and 10). Grain for Green is an intensive phase of a project that is transforming farmland into forestland or grassland using food as a subsidy and incentive. It should be clarified that no grassland was destroyed by these afforestation activities. However, to reinforce his own viewpoint that afforestation activities converting grassland into forestland result in environmental degradation, the author subjectively listed grassland areas converted into forest twice in this project and once in the Three Norths Shelter Forest System Project. Third, and most egregiously, many of the references that are used as evidence are misinterpreted or falsified. Some have been pointed out above, and the others are as follows: (i) many data could not be found in his cited references. For example, “the overall survival rate of trees...only 15%...in China since 1949” is emphasized twice and used to strengthen his argument. However, in the cited source about steppe 10.1021/es8011194 CCC: $40.75
2008 American Chemical Society
Published on Web 09/19/2008
degradation in the Xilin River Basin (ref 9), we could not find this value, and furthermore, trees and forests were not even discussed. Two other pieces of data also have no source; i.e., “10-15% of newly planted trees were killed by windblown sand (ref 27)” and “ >70% of the trees had died and vegetation cover fell to even lower levels...” (ref 37). Originally, we thought that these data were correct and that the author had simply cited the wrong references. However, the following examples changed our minds about the cause of the mistakes. In another article by the same author about the impact of soil types on afforestation (ref 25), we could not find the following description: “Net decrease of 30.5% occurred by the seventh year after trees were planted in grassland areas...,” and “in contrast with natural grassland...soil moisture content...in afforestation areas...decreased by 32-37%”. The author even misspelled hs own name in this reference! (ii) Some irrelevant references are cited to support the author’s views, i.e., refs. 21 and 23. In summary, the author uses incorrect concepts, groundless hypothesis mechanisms, and an unserious attitude toward cited sources to finally draw an incorrect conclusion that “afforestation projects are actually increasing environmental degradation in arid and semiarid areas with ecosystem deteriorating and wind erosion increasing.” In fact, desertification is a complex combination of geobiophysical processes, geobiochemical cycles, and geobiosocial relationships (8), and it must be controlled with integrated dryland development paradigms (9). Due to the weak resilience of dryland ecosystems, afforestation is not unique but one effective measure that facilitates ecosystem restoration (10). We do not deny that some of the forest planted in the past has had suboptimal results caused by using unsuitable tree species and initial densities, as well as by some of the afforestation methods (11), but forest ecology projects have undoubtedly contributed greatly to combating desertification and have, therefore, become the emphasis of the sustainable development of dryland (12).
Literature Cited (1) Cao, S. Why large-scale afforestation efforts in China have failed to solve the desertification problem. Environ. Sci. Technol. 2008, 42, 1826–1831. (2) China Government. Forestry Law of China; China Law Press: Beijing, 2001. (3) The General Plan for the Fourth Stage of the Three Norths Shelter Forest System Project; State Forestry Administration: Beijing, 2000. (4) Qian, W.; Quan, L.; Shi, S. Variations of the dust storm in China and its climatic control. J. Climate 2002, 15, 1216– 1229. (5) Cornelis, W. M. W.; Gabriels, M. D. Optimal windbreak design for wind-erosion control. J. Arid Environ. 2005, 61, 315–332. (6) Guo, Z. T.; Ruddiman, W. F.; Hao, Q. Z.; Wu, H. B.; Qiao, Y. S.; Zhu, R. X.; Peng, S. Z.; Wei, J. J.; Yuan, B. Y.; Liu, T. S. Onset of Asian desertification by 22 Myr ago inferred from loess deposits in China. Nature 2002, 416, 159–163. (7) Shi, H.; Shao, M. Soil and water loss from the Loess Plateau in China. J. Arid Environ. 2000, 45, 9–20. (8) Schlesinger, W. H.; Reynolds, J. F.; Cunningham, G. L.; Huenneke, L. F.; Jarrell, W. M.; Virginia, R. A.; Whitford, W. G. Biological feedbacks in global desertification. Science 1990, 247, 1043–1048. (9) Reynolds, J. F.; Smith, D. M. S.; Lambin, E. F.; Turner, B. L., II; Mortimore, M.; Batterbury, S. P. J.; Downing, T. E.; Dowlatabadi, H.; Ferna´ndez, R. J.; Herrick, J. E.; HuberSannwald, E.; Jiang, H.; Leemans, R.; Lynam, T.; Maestre, F. T.; Ayarza, M.; Walker, B. Global desertification: building a science for dryland development. Science 2007, 316, 847– 851. (10) Li, W. Degradation and restoration of forest ecosystems in China. Forest Ecol. Manag. 2004, 201, 33–41. (11) Zhang, P.; Shao, G.; Zhao, G.; Le Master, D. C.; Parker, G. R.; Dunning, J. B., Jr.; Li, Q. China’s Forest Policy for the 21st Century. Science 2000, 288, 2135–2136. (12) Yang, X.; Ci, L.; Zhang, X. Dryland characteristics and its optimized eco-productive paradigms for sustainable development in China. Nat. Resour. Forum 2008, 32, 215–226.
Xiaohui Yang and Longjun Ci* Research Institute of Forestry, Chinese Academy of Forestry, Yiheyuanhou, Haidian District, Beijing, 100091 China ES8011194
VOL. 42, NO. 20, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
7723
