（图片来源：(inset) Christian Ziegler; (forest) Marcos Guerra/STRI）
气候变化对热带森林到底会造成什么样的影响？这一直是个悬而未决的难题。近日，一个国际科学家小组通过研究世界多个热带森林后认为，气候变化对热带森林生物多样性造成的影响可能并没有先前想象得那么严重。不过，二氧化碳的增加是否起到“肥化”热带森林的作用仍不清楚。相关论文3月4日发表在《公共科学图书馆·生物学》（PLoS Biology）上。
全球气候变化对人类来说可能是个坏消息，而在对热带森林的影响方面，之前有研究认为，高水平的二氧化碳和温暖的气候对于“速生”（fast-growing）树种有利。结果这些树种最终有可能将“慢生”（slower-growing）树种排挤开去，从而导致热带森林整体多样性的损失。不过也有科学家认为气候变化有可能帮助热带森林的所有树种更快生长，表现为森林总体量的增加，即所谓的“肥化作用”（fertilization effect）。
为了弄清这个问题，一个由30多位森林学家组成的国际科学家小组收集了对12个热带森林20多年的测量数据，这些森林分布在巴拿马、印度以及马来西亚。研究人员采用了超过200万个对于树木宽度的测量数据，建成了比之前任何研究都要大的数据库。研究结果显示，不论是速生还是慢生树种，在研究进行的年份里单位面积增长量大致相等。
论文合作者、巴拿马史密森尼热带研究所（Smithsonian Tropical Research Institute）的Helene Muller-Landau表示，这一结果与速生树种排挤慢生树种的理论背道而驰。不过这一研究并没有弄清气候变化是否促进了热带森林的增长。虽然整体森林量增加了（大约每公顷增长半吨），但这很可能是森林自身从伐木和厄尔尼诺现象恢复的后果。“这可能与大气中的二氧化碳毫无关系。”Muller-Landau说。
美国亚利桑那大学的生态学家Scott Saleska对此次迄今为止最大规模的研究表示赞赏。为了解决有关“肥化”的问题，Saleska已计划前往亚马逊森林展开研究。届时将应用激光成像设备来计算树木的高度，以得到更多树木生长的数据。这将使研究的范围扩大许多，并且包括了此次研究没有调查到的亚马逊森林。（科学网 梅进/编译）
生物谷推荐原始出处：
（PLoS Biology），doi:10.1371/journal.pbio.0060045，Jér?me Chave，Elizabeth C. Losos
Assessing Evidence for a Pervasive Alteration in Tropical Tree Communities
Jérome Chave, Richard Condit, Helene C. Muller-Landau, Sean C. Thomas, Peter S. Ashton, Sarayudh Bunyavejchewin, Leonardo L. Co, Handanakere S. Dattaraja, Stuart J. Davies, Shameema Esufali, Corneille E. N. Ewango, Kenneth J. Feeley, Robin B. Foster11, Nimal Gunatilleke, Savitri Gunatilleke, Pamela Hall, Terese B. Hart, Consuelo Hernández, Stephen P. Hubbell, Akira Itoh, Somboon Kiratiprayoon, James V. LaFrankie, Suzanne Loo de Lao, Jean-Rémy Makana, Md. Nur Supardi Noor, Abdul Rahman Kassim, Cristián Samper, Raman Sukumar, Hebbalalu S. Suresh, Sylvester Tan, Jill Thompson, Ma. Dolores C. Tongco, Renato Valencia, Martha Vallejo, Gorky Villa, Takuo Yamakura, Jess K. Zimmerman, Elizabeth C. Losos
In Amazonian tropical forests, recent studies have reported increases in aboveground biomass and in primary productivity, as well as shifts in plant species composition favouring fast-growing species over slow-growing ones. This pervasive alteration of mature tropical forests was attributed to global environmental change, such as an increase in atmospheric CO2 concentration, nutrient deposition, temperature, drought frequency, and/or irradiance. We used standardized, repeated measurements of over 2 million trees in ten large (16–52 ha each) forest plots on three continents to evaluate the generality of these findings across tropical forests. Aboveground biomass increased at seven of our ten plots, significantly so at four plots, and showed a large decrease at a single plot. Carbon accumulation pooled across sites was significant (+0.24 MgC ha?1 y?1, 95% confidence intervals [0.07, 0.39] MgC ha?1 y?1), but lower than reported previously for Amazonia. At three sites for which we had data for multiple census intervals, we found no concerted increase in biomass gain, in conflict with the increased productivity hypothesis. Over all ten plots, the fastest-growing quartile of species gained biomass (+0.33 [0.09, 0.55] % y?1) compared with the tree community as a whole (+0.15 % y?1); however, this significant trend was due to a single plot. Biomass of slow-growing species increased significantly when calculated over all plots (+0.21 [0.02, 0.37] % y?1), and in half of our plots when calculated individually. Our results do not support the hypothesis that fast-growing species are consistently increasing in dominance in tropical tree communities. Instead, they suggest that our plots may be simultaneously recovering from past disturbances and affected by changes in resource availability. More long-term studies are necessary to clarify the contribution of global change to the functioning of tropical forests.
