Kellner Kenneth F, Swihart Robert K
Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN, United States of America.
PLoS One. 2017 Jun 20;12(6):e0179643. doi: 10.1371/journal.pone.0179643. eCollection 2017.
Early tree life history and demography are driven by interactions with the environment such as seed predation, herbivory, light availability, and drought. For oak (Quercus) in the eastern United States, these interactions may contribute to oak regeneration failure. Numerous studies have examined the impact of individual factors (like seed predation) on the oak regeneration process, but less information is available on the relative and combined impacts of multiple intrinsic and extrinsic factors on early oak life history. We developed an individual-based, spatially explicit model to Simulate Oak Early Life history (SOEL). The model connects acorn survival, acorn dispersal, germination, seedling growth, and seedling survival submodels based on empirical data with an existing gap model (JABOWA). Using SOEL, we assessed the sensitivity of several metrics of oak regeneration to different parameters associated with early oak life history. We also applied the model in three individual case studies to assess: (1) how variable acorn production interacts with timing of timber harvest; (2) the effect of shelterwood harvest-induced differences on seed predation; and (3) the consequences of interactions between drought, seedling growth and survival, and timber harvest. We found that oak regeneration metrics including percent emergence, seedling density, and sapling density were most sensitive to the amount of acorn production, acorn caching probability by scatterhoarders, and seedling growth rates. In the case studies, we found that timing harvest to follow large acorn crops can increase the density of oak regeneration in the short term following harvest, at least under some conditions. Following midstory removal, lower weevil infestation probability and lower post-dispersal acorn survival resulted in a modest decline in seedling density, but the decline did not persist to the sapling life stage class. Drought frequency had a powerful negative impact on both growth and survival for individual seedlings, which resulted in large reductions in both seedling and sapling density. The case studies presented here represent only a few examples of what could be accomplished within the SOEL modeling framework. Further studies could focus on different early life history parameters, or connect the parameter values to different predictor variables based on field data.
树木早期的生活史和种群统计学受到与环境相互作用的驱动，如种子捕食、食草作用、光照可利用性和干旱。对于美国东部的橡树（栎属）而言，这些相互作用可能导致橡树更新失败。众多研究探讨了单个因素（如种子捕食）对橡树更新过程的影响，但关于多种内在和外在因素对橡树早期生活史的相对和综合影响的信息较少。我们开发了一个基于个体的、空间明确的模型来模拟橡树早期生活史（SOEL）。该模型将基于经验数据的橡子存活、橡子传播、萌发、幼苗生长和幼苗存活子模型与现有的林隙模型（JABOWA）相连接。使用SOEL，我们评估了橡树更新的几个指标对与橡树早期生活史相关的不同参数的敏感性。我们还将该模型应用于三个单独的案例研究中，以评估：（1）橡子产量的变化如何与木材采伐时间相互作用；（2）渐伐诱导的差异对种子捕食的影响；（3）干旱、幼苗生长和存活以及木材采伐之间相互作用的后果。我们发现，包括出苗率、幼苗密度和幼树密度在内的橡树更新指标对橡子产量、散贮者贮藏橡子的概率以及幼苗生长速率最为敏感。在案例研究中，我们发现至少在某些条件下，在大量橡子收获后进行采伐能够在短期内提高采伐后橡树更新的密度。中层林木移除后，象鼻虫侵染概率降低以及散布后橡子存活率降低导致幼苗密度适度下降，但这种下降并未持续到幼树生活阶段。干旱频率对单个幼苗的生长和存活都有强大的负面影响，这导致幼苗和幼树密度大幅降低。这里展示的案例研究仅代表在SOEL建模框架内可以实现的少数几个例子。进一步的研究可以关注不同的早期生活史参数，或者根据实地数据将参数值与不同的预测变量联系起来。
