Department of Ecology and Evolutionary Biology, Princeton University, 106A Guyot Hall, 08544, Princeton, NJ, USA.
Department of Botany, Universidade de Brasília, 70910-900 Brasília, DF, Brazil.
Glob Chang Biol. 2016 Mar;22(3):1235-43. doi: 10.1111/gcb.13110. Epub 2016 Jan 4.
Numerous predictions indicate rising CO2 will accelerate the expansion of forests into savannas. Although encroaching forests can sequester carbon over the short term, increased fires and drought-fire interactions could offset carbon gains, which may be amplified by the shift toward forest plant communities more susceptible to fire-driven dieback. We quantify how bark thickness determines the ability of individual tree species to tolerate fire and subsequently determine the fire sensitivity of ecosystem carbon across 180 plots in savannas and forests throughout the 2.2-million km(2) Cerrado region in Brazil. We find that not accounting for variation in bark thickness across tree species underestimated carbon losses in forests by ~50%, totaling 0.22 PgC across the Cerrado region. The lower bark thicknesses of plant species in forests decreased fire tolerance to such an extent that a third of carbon gains during forest encroachment may be at risk of dieback if burned. These results illustrate that consideration of trait-based differences in fire tolerance is critical for determining the climate-carbon-fire feedback in tropical savanna and forest biomes.
大量预测表明，二氧化碳（CO2）浓度升高将加速森林向热带稀树草原扩张。尽管不断扩张的森林在短期内可以固碳，但增加的火灾和干旱与火灾相互作用可能会抵消碳汇的增加，而这种增加可能会因更易受到火灾导致衰退影响的森林植物群落向这一方向转变而加剧。我们量化了树皮厚度如何决定树种个体耐受火灾的能力，随后确定了巴西塞拉多地区（Cerrado region） 220 万平方千米范围内 180 个热带稀树草原和森林样地中生态系统碳的火灾敏感性。我们发现，不考虑树种间树皮厚度的变化会使森林中的碳损失低估约 50%，整个塞拉多地区的碳损失总计为 0.22 PgC。森林中植物物种的较低树皮厚度使火灾耐受性降低到如此程度，如果森林受到火灾，森林扩张期间获得的三分之一碳汇可能有面临衰退的风险。这些结果表明，考虑火灾耐受性方面的特征差异对于确定热带稀树草原和森林生态系统的气候-碳-火灾反馈至关重要。
