Global Change Biology (2016) 22, 2216–2227, doi: 10.1111/gcb.13164
Convergent elevation trends in canopy chemical traits of tropical forests G R E G O R Y P . A S N E R and R O B E R T A E . M A R T I N Department of Global Ecology, Carnegie Institution for Science, 260 Panama Street, Stanford, CA 94305, USA
Abstract The functional biogeography of tropical forests is expressed in foliar chemicals that are key physiologically based predictors of plant adaptation to changing environmental conditions including climate. However, understanding the degree to which environmental filters sort the canopy chemical characteristics of forest canopies remains a challenge. Here, we report on the elevation and soil-type dependence of forest canopy chemistry among 75 compositionally and environmentally distinct forests in nine regions, with a total of 7819 individual trees representing 3246 species collected, identified and assayed for foliar traits. We assessed whether there are consistent relationships between canopy chemical traits and both elevation and soil type, and evaluated the general role of phylogeny in mediating patterns of canopy traits within and across communities. Chemical trait variation and partitioning suggested a general model based on four interconnected findings. First, geographic variation at the soil-Order level, expressing broad changes in fertility, underpins major shifts in foliar phosphorus (P) and calcium (Ca). Second, elevation-dependent shifts in average community leaf dry mass per area (LMA), chlorophyll, and carbon allocation (including nonstructural carbohydrates) are most strongly correlated with changes in foliar Ca. Third, chemical diversity within communities is driven by differences between species rather than by plasticity within species. Finally, elevation- and soil-dependent changes in N, LMA and leaf carbon allocation are mediated by canopy compositional turnover, whereas foliar P and Ca are driven more by changes in site conditions than by phylogeny. Our findings have broad implications for understanding the global ecology of humid tropical forests, and their functional responses to changing climate. Keywords: chemical phylogeny, functional biogeography, functional traits, leaf traits, plant traits Received 9 September 2015 and accepted 20 October 2015
Introduction Humid tropical forests occupy about 20 million km2 of land area, and occur across a wide range of elevations stretching from sea level to equatorial treeline at more than 3500 m. Many tropical elevation gradients are also accompanied by changes in soil type and fertility. Montane forests (>1500 m) are often found on geochemically young substrates, on slopes undergoing enhanced erosion, and on soils of relatively high fertility (Porder et al., 2007). By contrast, lowland forests (
Convergent elevation trends in canopy chemical traits of tropical forests G R E G O R Y P . A S N E R and R O B E R T A E . M A R T I N Department of Global Ecology, Carnegie Institution for Science, 260 Panama Street, Stanford, CA 94305, USA
Abstract The functional biogeography of tropical forests is expressed in foliar chemicals that are key physiologically based predictors of plant adaptation to changing environmental conditions including climate. However, understanding the degree to which environmental filters sort the canopy chemical characteristics of forest canopies remains a challenge. Here, we report on the elevation and soil-type dependence of forest canopy chemistry among 75 compositionally and environmentally distinct forests in nine regions, with a total of 7819 individual trees representing 3246 species collected, identified and assayed for foliar traits. We assessed whether there are consistent relationships between canopy chemical traits and both elevation and soil type, and evaluated the general role of phylogeny in mediating patterns of canopy traits within and across communities. Chemical trait variation and partitioning suggested a general model based on four interconnected findings. First, geographic variation at the soil-Order level, expressing broad changes in fertility, underpins major shifts in foliar phosphorus (P) and calcium (Ca). Second, elevation-dependent shifts in average community leaf dry mass per area (LMA), chlorophyll, and carbon allocation (including nonstructural carbohydrates) are most strongly correlated with changes in foliar Ca. Third, chemical diversity within communities is driven by differences between species rather than by plasticity within species. Finally, elevation- and soil-dependent changes in N, LMA and leaf carbon allocation are mediated by canopy compositional turnover, whereas foliar P and Ca are driven more by changes in site conditions than by phylogeny. Our findings have broad implications for understanding the global ecology of humid tropical forests, and their functional responses to changing climate. Keywords: chemical phylogeny, functional biogeography, functional traits, leaf traits, plant traits Received 9 September 2015 and accepted 20 October 2015
Introduction Humid tropical forests occupy about 20 million km2 of land area, and occur across a wide range of elevations stretching from sea level to equatorial treeline at more than 3500 m. Many tropical elevation gradients are also accompanied by changes in soil type and fertility. Montane forests (>1500 m) are often found on geochemically young substrates, on slopes undergoing enhanced erosion, and on soils of relatively high fertility (Porder et al., 2007). By contrast, lowland forests (
