Crown plasticity and canopy dynamics in northern hardwood forests

林冠在森林的种群、群落和生态系统动态中起着核心作用。然而，森林冠层仍然知之甚少，因为难以接近高大的树木，限制了直接在森林冠层进行研究的数量和范围。这种信息的缺乏反过来又限制了可用于模拟和阐明森林冠层动态的模型的发展。我提出了一个综合方案的经验和建模研究，进行在中部安大略的森林，这将阐明如何冠层可塑性和冠层结构的影响动态的北方硬木林。一个移动的空中升降机将被用来进行树冠可塑性的原位研究，通过树冠的横向生长和退缩来测量。实证研究将被设计用于两个目的：1）研究树冠可塑性如何使不同大小，年龄和物种的树木竞争冠层空间，以及2）校准模型，逼真地模拟树冠可塑性和冠层空间的竞争。模型的关键状态变量将是暴露的树冠面积（暴露在阳光直射下的树冠投影面积），这是一个反映竞争结果的指标，可用于预测树木随后的生长和死亡率。一旦校准，该模型将用于解决以下问题。冠的可塑性如何影响大小结构的发展和自疏率？冠层可塑性是否随年龄而降低，从而增加冠层周转？通过优化林冠空间在树木之间的分配，可以提高生产力和木材产量吗？虽然冠层可塑性被广泛认为是森林冠层动态的重要驱动力，但尚未得到深入研究，也很少被纳入森林模拟模型。拟议的实地研究将提供新的见解冠可塑性的原因和后果，拟议的建模研究将提供一个工具，探索冠和冠层动态之间的相互作用，并预测替代管理制度的结果。

The canopy plays a central role in the population, community and ecosystem dynamics of forests. Yet, forest canopies remain poorly understood because the difficulty of accessing tall trees has limited the number and scope of studies conducted directly in forest canopies. This dearth of information has in turn limited the development of models that can be used to simulate and elucidate the dynamics of forest canopies. I propose an integrated program of empirical and modeling studies, to be conducted in the forests of central Ontario, that will elucidate how crown plasticity and canopy structure influence the dynamics of northern hardwood forests. A mobile aerial lift will be used to conduct in-situ studies of crown plasticity, as measured by the lateral growth and recession of tree crowns. The empirical studies will be designed for two purposes: 1) to examine how crown plasticity enables trees of different sizes, ages, and species to compete for canopy space, and 2) to calibrate a model that realistically simulates crown plasticity and competition for canopy space. The key state variable of the model will be exposed crown area (the projected area of crown exposed to direct sunlight), a metric that reflects the outcome of competition and can be used to predict the subsequent growth and mortality of trees. Once calibrated, the model will be used to address the following questions. How does crown plasticity influence the development of size structure and the rate of self-thinning? Does crown plasticity decrease with age and thereby increase canopy turnover? Can productivity and timber yield be enhanced by management practices that optimize the allocation of canopy space among trees? While crown plasticity is widely acknowledged to be an important driver of forest canopy dynamics, it has not been thoroughly studied and has rarely been included in forest simulation models. The proposed field studies will provide new insights into the causes and consequences of crown plasticity, and the proposed modeling studies will provide a tool for exploring the interplay between crown and canopy dynamics and predicting the outcome of alternative management regimes.