Temperature influences carbon accumulation in moist tropical forests.
ABSTRACT Evergreen broad-leaved tropical forests can have high rates of productivity and large accumulations of carbon in plant biomass and soils. They can therefore play an important role in the global carbon cycle, influencing atmospheric CO2 concentrations if climate warms. We applied meta-analyses to published data to evaluate the apparent effects of temperature on carbon fluxes and storages in mature, moist tropical evergreen forest ecosystems. Among forests, litter production, tree growth, and belowground carbon allocation all increased significantly with site mean annual temperature (MAT); total net primary productivity (NPP) increased by an estimated 0.2-0.7 Mg C x ha(-1) x yr(-1) x degrees C(-1). Temperature had no discernible effect on the turnover rate of aboveground forest biomass, which averaged 0.014 yr(-1) among sites. Consistent with these findings, forest biomass increased with site MAT at a rate of 5-13 Mg C x ha(-1) x degrees C(-1). Despite greater productivity in warmer forests, soil organic matter accumulations decreased with site MAT, with a slope of -8 Mg C x ha(-1) x degrees C(-1), indicating that decomposition rates of soil organic matter increased with MAT faster than did rates of NPP. Turnover rates of surface litter also increased with temperature among forests. We found no detectable effect of temperature on total carbon storage among moist-tropical evergreen forests, but rather a shift in ecosystem structure, from low-biomass forests with relatively large accumulations of detritus in cooler sites, to large-biomass forests with relatively smaller detrital stocks in warmer locations. These results imply that, in a warmer climate, conservation of forest biomass will be critical to the maintenance of carbon stocks in moist tropical forests.
- SourceAvailable from: Sandra M Durán[Show abstract] [Hide abstract]
ABSTRACT: AimTo develop an integrative framework to evaluate variation in aboveground carbon storage (AGC). A model that can be applied to understand and predict how global-change drivers influence tropical carbon sinks.LocationOld-growth tropical forests world-wide.Methods Using structural equation modelling (SEM), we propose an a priori model to evaluate the direct and indirect effects of climate, stand variables (basal area, tree diameter and wood density at plot level) and liana abundance on AGC. Our model indicated that stand variables increased AGC while liana abundance decreased AGC indirectly via negative effects on stand variables. We used a multigroup SEM to test the generality of our framework using a standardized dataset of 145 plots (0.1 ha) in dry, moist and wet tropical forests.ResultsOur model explained over 85% variation in AGC and showed a positive and consistent relationship between stand variables and AGC across forests types. The effects of climate on AGC were indirect rather than direct, with negative effects of temperature in all forests. Liana abundance reduced tree diameter and basal area in moist forests, but did not affect AGC in wet or dry forests.Main conclusionsOur results suggest that climate affects AGC indirectly, via its direct influence on stand variables and liana abundance. The effects of lianas on AGC result from reductions in stand variables and are as important as climate for moist forests, which harbour the greatest tropical carbon pools. Our model was consistent across forest types. This highlights the usefulness of an integrative framework to improve predictions of the effects of drivers of global change on tropical carbon sinks.Global Ecology and Biogeography 04/2015; DOI:10.1111/geb.12304 · 7.24 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: The priming effect (PE) is one of the most important interactions between C input and output in soils. Here we aim to quantify patterns of PE in response to six addition rates of (13)C-labeled water-soluble C (WSC) and determine if these patterns are different between soil organic and mineral layers in a temperate forest. Isotope mass balance was used to distinguish WSC derived from SOC-derived CO2 respiration. The relative PE was 1.1-3.3 times stronger in the mineral layer than in the organic layer, indicating higher sensitivity of the mineral layer to WSC addition. However, the magnitude of cumulative PE was significantly higher in the organic layer than in the mineral layer due to higher SOC in the organic layer. With an increasing WSC addition rate, cumulative PE increased for both layers, but tended to level off when the addition rate was higher than 400 mg C kg(-1) soil. This saturation effect indicates that stimulation of soil C loss by exogenous substrate would not be as drastic as the increase of C input. In fact, we found that the mineral layer with an WSC addition rate of 160-800 mg C kg(-1) soil had net C storage although positive PE was observed. The addition of WSC basically caused net C loss in the organic layer due to the high magnitude of PE, pointing to the importance of the organic layer in C cycling of forest ecosystems. Our findings provide a fundamental understanding of PE on SOC mineralization of forest soils and warrant further in situ studies of PE in order to better understand C cycling under global climate change.Oecologia 03/2015; DOI:10.1007/s00442-015-3290-x · 3.25 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Loss of biodiversity within relatively pristine protected areas presents a major challenge for conservation. At La Selva Biological Station in the lowlands of Costa Rica, amphibians, reptiles, and understory birds have all declined over the past four decades, yet the factors contributing to these declines remain unclear. Here, we conduct two tests of the hypothesis that faunal declines are linked to shifting dynamics of leaf litter, a critical microhabitat for amphibians and reptiles and a major component of forest carbon cycles. First, we conduct a 16-month manipulation of leaf litter and measure response by terrestrial amphibians and reptiles. Second, we synthesize three year-long datasets collected over four decades to evaluate potential multi-decade change in standing litter depth. We show that litter depth regulates density of amphibians and reptiles, and that the strongest response to manipulations is in species that decline most rapidly based on long-term data. Our synthesis of litter depth data suggests considerable interannual variability in standing stocks of leaf litter with lowest quantity of leaf litter in the most recent sampling period. These tests are consistent with the hypothesis that these faunal declines may be in part driven by changes in forest litter dynamics, and ultimately to climate-sensitive carbon cycles. A MPHIBIAN assemblages across the world have suffered rapid, unexpected population declines and widespread extinctions (Alford and Richards, 1999; Young et al., 2001; Stuart et al., 2004). Conventional threats such as habitat loss and modification are directly responsible for many of these declines, yet much research attention has been focused on so-called ''enigmatic declines'' (Lips et al., 2006, 2008; Pounds et al., 2006)—those declines occurring in protected habitats that cannot be attributed to obvious local anthropogenic disturbances (Stuart et al., 2004). One of the best-documented examples of such declines is at La Selva Biological Station—a protected lowland (,150 m asl) reserve in Costa Rica where populations of terrestrial amphibians declined by ,75% between 1970 and 2005 (Whitfield et al., 2007). These declines cannot be attributed to direct anthropogenic effects (i.e., habitat loss, overex-ploitation) because La Selva is protected and has experi-enced minimal recent human disturbance. La Selva's declines are largely inconsistent with other published accounts of amphibian declines because these declines occurred over decades rather than a few months, and because virtually all other sites in the Neotropics where widespread amphibian declines have been reported are from montane regions with cooler climates (generally .400 m asl; Whitfield et al., in press). A comprehensive understand-ing of causative agents of declines is critical for effective conservation management of amphibian biodiversity. Declines at La Selva may be a part of broader ecosystem-wide shifts ultimately tied to climatic change (Clark et al., 2003, 2011; Sigel et al., 2006). Long-term meteorological data from La Selva indicates an average 0.25uC increase in air temperature per decade since the 1960s, primarily driven by increases in daily minimum temperatures (Clark and Clark, 2011). These temperature increases drive reductions in tree growth (Clark et al., 2003) and increases in tree mortality (Clark et al., 2011). Long-term vertebrate populations trends show major declines in density of not only terrestrial amphibians, but also terrestrial reptiles (Whitfield et al., 2007) and understory insectivorous birds (Sigel et al., 2006). Leaf litter depth has been correlated with density of both terrestrial amphibians and terrestrial reptiles across seasons, elevations, and biogeographic regions (Fauth et al., 1989; Scott, 1976; Lieberman, 1986; Heinen, 1992; Whitfield and Pierce, 2005), and is the base of brown food webs upon which understory insectivorous birds rely (Sigel et al., 2006). Most biomass produced by trees eventually falls to the forest floor as leaf litter, thus climate-induced reductions in tree growth may be associated with reductions in litter production. Further, decomposition rates are climate-sensitive and in-crease with temperature (Raich et al., 2006). Thus, long-term shifts in vertebrate population densities may be the result of broader ecosystem-level shifts in quantity of standing leaf litter, and ultimately, carbon balance in tropical forests. Here, we present two tests of the hypothesis that long-term reductions in standing litter is a component of faunal declines at La Selva. First, we conduct a replicated field experiment to demonstrate that leaf litter amphibian and reptile populations are limited by quantity of standing leaf litter. Second, we use two year-long historic datasets of standing litter quantity with a two-year modern dataset using the same methodology to show potential long-term change in standing litter stocks.Copeia 10/2014; 14(4):454-461. DOI:10.1643/CE-13-061 · 0.21 Impact Factor