（圖片來源：(inset) Christian Ziegler; (forest) Marcos Guerra/STRI）
氣候變化對熱帶森林到底會造成什么樣的影響,？這一直是個懸而未決的難題,。近日，一個國際科學(xué)家小組通過研究世界多個熱帶森林后認(rèn)為,，氣候變化對熱帶森林生物多樣性造成的影響可能并沒有先前想象得那么嚴(yán)重,。不過，二氧化碳的增加是否起到“肥化”熱帶森林的作用仍不清楚,。相關(guān)論文3月4日發(fā)表在《公共科學(xué)圖書館·生物學(xué)》（PLoS Biology）上,。
全球氣候變化對人類來說可能是個壞消息，而在對熱帶森林的影響方面,，之前有研究認(rèn)為,，高水平的二氧化碳和溫暖的氣候?qū)τ?ldquo;速生”（fast-growing）樹種有利。結(jié)果這些樹種最終有可能將“慢生”（slower-growing）樹種排擠開去,，從而導(dǎo)致熱帶森林整體多樣性的損失,。不過也有科學(xué)家認(rèn)為氣候變化有可能幫助熱帶森林的所有樹種更快生長，表現(xiàn)為森林總體量的增加,，即所謂的“肥化作用”（fertilization effect）,。
為了弄清這個問題，一個由30多位森林學(xué)家組成的國際科學(xué)家小組收集了對12個熱帶森林20多年的測量數(shù)據(jù),，這些森林分布在巴拿馬,、印度以及馬來西亞。研究人員采用了超過200萬個對于樹木寬度的測量數(shù)據(jù),，建成了比之前任何研究都要大的數(shù)據(jù)庫,。研究結(jié)果顯示，不論是速生還是慢生樹種,，在研究進行的年份里單位面積增長量大致相等,。
論文合作者、巴拿馬史密森尼熱帶研究所（Smithsonian Tropical Research Institute）的Helene Muller-Landau表示,，這一結(jié)果與速生樹種排擠慢生樹種的理論背道而馳,。不過這一研究并沒有弄清氣候變化是否促進了熱帶森林的增長。雖然整體森林量增加了（大約每公頃增長半噸）,，但這很可能是森林自身從伐木和厄爾尼諾現(xiàn)象恢復(fù)的后果,。“這可能與大氣中的二氧化碳毫無關(guān)系。”Muller-Landau說,。
美國亞利桑那大學(xué)的生態(tài)學(xué)家Scott Saleska對此次迄今為止最大規(guī)模的研究表示贊賞,。為了解決有關(guān)“肥化”的問題，Saleska已計劃前往亞馬遜森林展開研究,。屆時將應(yīng)用激光成像設(shè)備來計算樹木的高度,，以得到更多樹木生長的數(shù)據(jù),。這將使研究的范圍擴大許多，并且包括了此次研究沒有調(diào)查到的亞馬遜森林,。（科學(xué)網(wǎng) 梅進/編譯）
生物谷推薦原始出處：
（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.
