Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, USA.
Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland.
Glob Chang Biol. 2024 Aug;30(8):e17432. doi: 10.1111/gcb.17432.
How terrestrial ecosystems will accumulate carbon as the climate continues to change is a major source of uncertainty in projections of future climate. Under growth-stimulating environmental change, time lags inherent in population and community dynamic processes have been posed to dampen, or alternatively amplify, short-term carbon gain in terrestrial vegetation, but these outcomes can be difficult to predict. To theoretically frame this problem, we developed a simple model of vegetation dynamics that identifies the stage-structured demographic and competitive processes that could govern the timescales of carbon storage and loss. We show that demographic lags associated with growth-stimulating environmental change can allow a rapid increase in population-level carbon storage that is lost back to the atmosphere in later years. However, this transient carbon storage only emerges when environmental change increases the transition of adult individuals into a larger size class that suffers markedly higher mortality. Otherwise, demographic lags simply slow carbon accumulation. Counterintuitively, an analogous tradeoff between maximum adult size and survivorship in two-species models, coupled with environmental change-driven replacement, does not generate the transient carbon gain seen in the single-species models. Instead lags in competitive replacement slow the approach to the eventual carbon trajectory. Together, our results suggest that time lags inherent in demographic and compositional turnover tend to slow carbon accumulation in systems responding to growth-stimulating environmental change. Only under specific conditions will lagged demographic processes in such systems drive transient carbon accumulation, conditions that investigators can examine in nature to help project future carbon trajectories.
随着气候持续变化，陆地生态系统将如何积累碳是未来气候预测中不确定性的主要来源。在促进生长的环境变化下，种群和群落动态过程中的时滞会抑制或放大陆地植被的短期碳增益，但这些结果可能难以预测。为了从理论上阐述这个问题，我们开发了一个简单的植被动态模型，该模型确定了可能控制碳储存和损失时间尺度的阶段结构人口统计和竞争过程。我们表明，与促进生长的环境变化相关的人口统计滞后可以使种群水平的碳储存迅速增加，但这些碳在以后的年份中又会回到大气中。然而，只有当环境变化增加了成年个体向更大体型类别的转变，而这些更大体型类别的死亡率明显更高时，才会出现这种短暂的碳储存。否则，人口统计滞后只会减缓碳的积累。与直觉相反，在两种物种模型中，最大成年体型和存活率之间的类似权衡，加上环境变化驱动的替代，不会产生在单物种模型中看到的短暂碳增益。相反，竞争替代的滞后会减缓最终碳轨迹的接近速度。总之，我们的研究结果表明，在响应促进生长的环境变化的系统中，人口统计和组成变化中的固有滞后往往会减缓碳的积累。只有在特定条件下，此类系统中的滞后人口统计过程才会推动短暂的碳积累，研究人员可以在自然界中检验这些条件，以帮助预测未来的碳轨迹。
