Bioclimatic envelope models predict a decrease in tropical forest carbon stocks with climate change in Madagascar

Abstract

1. Recent studies have underlined the importance of climatic variables in determining tree height and biomass in tropical forests. Nonetheless, the effects of climate on tropical forest carbon stocks remain uncertain. In particular, the application of process-based dynamic global vegetation models has led to contrasting conclusions regarding the potential impact of climate change on tropical forest carbon storage. 2. Using a correlative approach based on a bioclimatic envelope model and data from 1771 forest plots inventoried during the period 1996-2013 in Madagascar over a large climatic gradient, we show that temperature seasonality, annual precipitation and mean annual temperature are key variables in determining forest above-ground carbon density. 3. Taking into account the explicative climate variables, we obtained an accurate (R 2 = 70% and RMSE = 40 Mg ha À1 ) forest carbon map for Madagascar at 250 m resolution for the year 2010. This national map was more accurate than previously published global carbon maps (R 2 ≤ 26% and RMSE ≥ 63 Mg ha À1 ). 4. Combining our model with the climatic projections for Madagascar from 7 IPCC CMIP5 global climate models following the RCP 8.5, we forecast an average forest carbon stock loss of 17% (range: 7-24%) by the year 2080. For comparison, a spatially homogeneous deforestation of 0.5% per year on the same period would lead to a loss of 30% of the forest carbon stock. 5. Synthesis. Our study shows that climate change is likely to induce a decrease in tropical forest carbon stocks. This loss could be due to a decrease in the average tree size and to shifts in tree species distribution, with the selection of small-statured species. In Madagascar, climate-induced carbon emissions might be, at least, of the same order of magnitude as emissions associated with anthropogenic deforestation.

Human migration to the forest frontier: Implications for land use change and conservation management

“…In many parts of the tropics, large‐scale agri‐business expansion and international land‐grabbing has become the most significant driver of deforestation (Lambin and Meyfroidt ), just as urbanisation trends reduce rates of clearance by smallholder farmers (Meyfroidt et al., ). Such large‐scale land appropriations are increasing in Madagascar (Burnod, Gingembre, & Andrianirina Ratsialonana, ), but given the geography of the remaining forest zones (most remaining forest is found at relatively high altitude in inaccessible areas; Vieilledent et al., ), the activities of small‐scale farmers at the forest frontier remain likely to be the primary driver of deforestation in the foreseeable future. An important question is therefore the extent to which rural depopulation will result in a forest transition.…”

New formula and conversion factor to compute tree species basic wood density from a global wood technology database

“…It helps understand the functionning of forest ecosystems both in terms of carbon sequestration (Chave et al , 2005; Vieilledent et al , 2012) and community dynamics (Diaz et al , 2016; Kunstler et al , 2016; Westoby & Wright, 2006). In carbon cycle research, tree wood density is used to compute forest carbon stock and assess the role of forests in mitigating climate change (Pan et al , 2011; Vieilledent et al , 2016) or evaluate the impact of deforestation on climate (Achard et al , 2014). In community ecology, wood density is a proxy for species performance (Lachenbruch & McCulloh, 2014), reflecting a trade-off between growth potential and mortality risk from biomechanical or hydraulic failure (Diaz et al , 2016).…”

“…This database combines measured (40% of the data) and inferred (60% of the data) basic wood densities. It has been extensively used to compute forest biomass and carbon stock with the aim of studying the role of forest in the global carbon cycle (Avitabile et al , 2016; Baccini et al , 2012, 2017; Saatchi et al , 2011; Vieilledent et al , 2016) or addressing questions in functional ecology (Baraloto et al , 2010; Chave et al , 2009; Kunstler et al , 2016).…”

Anthropogenic threats can have cascading homogenizing effects on the phylogenetic and functional diversity of tropical ecosystems

“…Madagascar's bioclimatic zones comprise humid, subhumid, montane, dry, and subarid environments with distinct geographic features and vegetation patterns (Humbert 1955, Cornet 1974, Schatz 2000. These five broad climatic zones have been widely adopted and incorporated in numerous insightful taxonomic, evolutionary, ecological, conservation and biogeographic studies (Megson et al 2009, Buerki et al 2010, Irwin et al 2010, Brown et al 2014, Blair et al 2015, Vieilledent et al 2016, Crowley et al 2017, Wahlert et al 2017. Although the montane bioclimate is fairly limited in area ( Fig.…”