Publications

Patterns of nitrogen-fixing tree abundance in forests across Asia and America

Menge, Duncan N.L.; Chisholm, Ryan A.; Davies, Stuart J.; Abu Salim, Kamariah; Allen, David; Alvarez, Mauricio; Bourg, Norm; Brockelman, Warren Y.; Bunyavejchewin, Sarayudh; Butt, Nathalie; Cao, Min; Chanthorn, Wirong; Chao, Wei Chun; Clay, Keith; Condit, Richard; Cordell, Susan; Silva, João Batista da; Dattaraja, H.S.; Andrade, Ana Cristina Segalin de; Oliveira, Alexandre A. de; Ouden, Jan den; Drescher, Michael; Fletcher, Christine; Giardina, Christian P.; Savitri Gunatilleke, C.V.; Gunatilleke, I.A.U.N.; Hau, Billy C.H.; He, Fangliang; Howe, Robert; Hsieh, Chang Fu; Hubbell, Stephen P.; Inman-Narahari, Faith M.; Jansen, Patrick A.; Johnson, Daniel J.; Kong, Lee Sing; Král, Kamil; Ku, Chen Chia; Lai, Jiangshan; Larson, Andrew J.; Li, Xiankun; Li, Yide; Lin, Luxiang; Lin, Yi Ching; Liu, Shirong; Lum, Shawn K.Y.; Lutz, James A.; Ma, Keping; Malhi, Yadvinder; McMahon, Sean; McShea, William; Mi, Xiangcheng; Morecroft, Michael; Myers, Jonathan A.; Nathalang, Anuttara; Novotny, Vojtech; Ong, Perry; Orwig, David A.; Ostertag, Rebecca; Parker, Geoffrey; Phillips, Richard P.; Abd. Rahman, Kassim; Sack, Lawren; Sang, Weiguo; Shen, Guochun; Shringi, Ankur; Shue, Jessica; Su, Sheng Hsin; Sukumar, Raman; Fang Sun, I.; Suresh, H.S.; Tan, Sylvester; Thomas, Sean C.; Toko, Pagi S.; Valencia, Renato; Vallejo, Martha I.; Vicentini, Alberto; Vrška, Tomáš; Wang, Bin; Wang, Xihua; Weiblen, George D.; Wolf, Amy; Xu, Han; Yap, Sandra; Zhu, Li; Fung, Tak

Summary

Symbiotic nitrogen (N)-fixing trees can provide large quantities of new N to ecosystems, but only if they are sufficiently abundant. The overall abundance and latitudinal abundance distributions of N-fixing trees are well characterised in the Americas, but less well outside the Americas. Here, we characterised the abundance of N-fixing trees in a network of forest plots spanning five continents, ~5,000 tree species and ~4 million trees. The majority of the plots (86%) were in America or Asia. In addition, we examined whether the observed pattern of abundance of N-fixing trees was correlated with mean annual temperature and precipitation. Outside the tropics, N-fixing trees were consistently rare in the forest plots we examined. Within the tropics, N-fixing trees were abundant in American but not Asian forest plots (~7% versus ~1% of basal area and stems). This disparity was not explained by mean annual temperature or precipitation. Our finding of low N-fixing tree abundance in the Asian tropics casts some doubt on recent high estimates of N fixation rates in this region, which do not account for disparities in N-fixing tree abundance between the Asian and American tropics. Synthesis. Inputs of nitrogen to forests depend on symbiotic nitrogen fixation, which is constrained by the abundance of N-fixing trees. By analysing a large dataset of ~4 million trees, we found that N-fixing trees were consistently rare in the Asian tropics as well as across higher latitudes in Asia, America and Europe. The rarity of N-fixing trees in the Asian tropics compared with the American tropics might stem from lower intrinsic N limitation in Asian tropical forests, although direct support for any mechanism is lacking. The paucity of N-fixing trees throughout Asian forests suggests that N inputs to the Asian tropics might be lower than previously thought.