Ramage Benjamin S, Johnson Daniel J, Chan David M
Biology Department Randolph-Macon College Ashland Virginia USA.
School of Forest, Fisheries, & Geomatics sciences University of Florida Gainesville Florida USA.
Ecol Evol. 2023 Aug 15;13(8):e10413. doi: 10.1002/ece3.10413. eCollection 2023 Aug.
Forest biodiversity is likely maintained by a complex suite of interacting drivers that vary in importance across both space and time. Contributing factors include disturbance, interannual variation in abiotic variables, and biotic neighborhood effects. To probe ongoing uncertainties and potential interactions, we investigated tree seedling performance in a temperate mid-Atlantic forest ecosystem. We planted seedlings of five native tree species in mapped study plots, half of which were subjected to disturbance, and then monitored seedling survival, height growth, and foliar condition. The final year of data collection encompassed a drought, enabling comparison between intervals varying in water availability. Seedling performance was analyzed as a function of canopy cover and biotic neighborhood (conspecific and heterospecific abundance), including interactions, with separate generalized linear mixed models fit for each interval. All species exhibited: (a) pronounced declines in height growth during the drought year, (b) detrimental effects of adult conspecifics, and (c) beneficial effects of canopy openness. However, despite these consistencies, there was considerable variation across species in terms of the relevant predictors for each response variable in each interval. Our results suggest that drought may strengthen or reveal conspecific inhibition in some instances while weakening it or obscuring it in others, and that some forms of conspecific inhibition may manifest only under particular canopy conditions (although given the inconsistency of our findings, we are not convinced that conspecific inhibition is critical for diversity maintenance in our study system). Overall, our work reveals a complex forest ecosystem that appears simultaneously and interactively governed by biotic neighborhood structure (e.g., conspecific and/or heterospecific abundance), local habitat conditions (e.g., canopy cover), and interannual variability (e.g., drought).
森林生物多样性可能由一系列复杂的相互作用驱动因素维持，这些驱动因素在空间和时间上的重要性各不相同。促成因素包括干扰、非生物变量的年际变化以及生物邻域效应。为了探究当前的不确定性和潜在的相互作用，我们在大西洋中部温带森林生态系统中研究了树木幼苗的表现。我们在划定的研究地块中种植了五种本地树种的幼苗，其中一半受到干扰，然后监测幼苗的存活情况、高度生长和叶片状况。数据收集的最后一年包括一场干旱，从而能够比较不同水分可利用区间的情况。将幼苗表现作为树冠覆盖度和生物邻域（同种和异种丰度）的函数进行分析，包括相互作用，针对每个区间拟合单独的广义线性混合模型。所有物种都表现出：（a）干旱年份高度生长显著下降，（b）成年同种个体的有害影响，以及（c）树冠开阔度的有益影响。然而，尽管存在这些一致性，但在每个区间内，每个响应变量的相关预测因子在物种间存在相当大的差异。我们的结果表明，干旱在某些情况下可能会加强或揭示同种抑制，而在其他情况下则会削弱或掩盖它，并且某些形式的同种抑制可能仅在特定的树冠条件下才会显现（尽管鉴于我们研究结果的不一致性，我们并不确信同种抑制对我们研究系统中的多样性维持至关重要）。总体而言，我们的工作揭示了一个复杂的森林生态系统，它似乎同时受到生物邻域结构（例如同种和/或异种丰度）、当地栖息地条件（例如树冠覆盖度）和年际变异性（例如干旱）的共同和交互作用的支配。
