Potential trajectories of old-growth Neotropical forest functional composition under climate change

Quantifying relationships between plant functional traits and abiotic gradients is valuable for evaluating potential responses of forest communities to climate change. However, the trajectories of change expected to occur in tropical forest functional characteristics as a function of future climate variation are largely unknown. We modeled community level trait values of Costa Rican rain forests as a function of current and future climate, and quantified potential changes in functional composition. We calculated per-plot community weighted mean (CWM) trait values for leaf area (LA), specific leaf area (SLA), leaf dry matter content (LDMC), leaf nitrogen (N) and phosphorus (P) content, and wood basic specific gravity (WSG), for tree and palm species in 127 0.25 ha plots. We modeled the response of CWM traits to current temperature and precipitation gradients using generalized additive modeling. We then predicted and mapped CWM traits values under current and future climate, and quantified potential changes under a global warming scenario (RCP8.5, year 2050). We calculated the area within the multi trait functional space occupied by forest plots under both current and future climate, and determined potential changes in functional space occupied by forest plots. Overall, precipitation predicted CWM traits better than temperature. Models indicated increases in CWM SLA, N and P, and a decrease in CWM LDMC under climate change. Lowland forest communities converged on a single direction of change towards more acquisitive CWM trait values, indicating a change in forest functional composition resulting from a changed climate. Functional space occupied by forest plots was reduced by 50% under the future climate. Functional composition changes may have further effects on forests ecosystem services. Assessing functional trait spatial-gradients can help bridge the gap between species-based biogeography and biogeochemical approaches to strengthen biodiversity and ecosystem services conservation efforts.量化植物功能性状与非生物梯度间的关联，可为评估森林群落对气候变化的潜在响应提供关键支撑。然而，热带森林功能特征随未来气候变化的预期变化轨迹，目前仍尚未明确。本研究以当前及未来气候为自变量，构建了哥斯达黎加雨林的群落水平性状值模型，并量化了功能组成的潜在变化。我们针对127块0.25公顷样地中的树木与棕榈物种，计算了样地水平的群落加权平均值（community weighted mean, CWM）性状值，涵盖叶面积（leaf area, LA）、比叶面积（specific leaf area, SLA）、叶片干物质含量（leaf dry matter content, LDMC）、叶片氮（N）与磷（P）含量，以及木材基本密度（wood basic specific gravity, WSG）。我们采用广义加性模型，探究了群落加权平均值性状对当前温度与降水梯度的响应。随后，我们预测并绘制了当前及未来气候下的群落加权平均值性状空间分布，并量化了全球变暖情景（典型浓度路径8.5，RCP8.5，2050年）下的潜在变化。我们计算了当前与未来气候下森林样地所占据的多性状功能空间面积，并明确了森林样地功能空间的潜在变化。总体而言，降水对群落加权平均值性状的预测效果优于温度。模型结果显示，气候变化下群落加权平均值的比叶面积、氮含量与磷含量均有所上升，而叶片干物质含量则呈下降趋势。低地森林群落朝着单一的变化方向收敛，即朝向更具获取策略的群落加权平均值性状，这表明气候改变引发了森林功能组成的转变。未来气候情景下，森林样地所占据的功能空间缩减了50%。功能组成的变化可能会进一步对森林生态系统服务产生影响。评估功能性状的空间梯度，有助于弥合基于物种的生物地理学与生物地球化学方法之间的鸿沟，从而强化生物多样性与生态系统服务保护工作。