Understanding forest dynamics and plantation transformation using a simple size-structured model

1. Concerns about biodiversity and the long-term sustainability of forest ecosystems have led to changing attitudes with respect to plantations. These artificial communities are ubiquitous, yet provide reduced habitat value in comparison with their naturally established counterparts, key factors being high density, homogeneous spatial structure, and their even-sized/aged nature. However, transformation management (manipulation of plantations to produce stands with a structure more reminiscent of natural ones) produces a much more complicated (and less well understood) inhomogeneous structure, and as such represents a major challenge for forest managers. 2. We use a stochastic model which simulates birth, growth and death processes for spatially distributed trees. Each tree’s growth and mortality is determined by a competition measure which captures the effects of neighbours. The model is designed to be generic, but for experimental comparison here we parameterise it using data from Caledonian Scots Pine stands, before moving on to simulate silvicultural (forest management) strategies aimed at speeding transformation. 3. The dynamics of simulated populations, starting from a plantation lattice configuration, mirror those of the well-established qualitative description of natural stand behaviour conceived by Oliver and Larson (1996), an analogy which assists understanding the transition from artificial to old-growth structure. 4. Data analysis and model comparison demonstrates the existence of local scale heterogeneity of growth characteristics between the trees composing the considered forest stands. 5. The model is applied in order to understand how management strategies can be adjusted to speed the process of transformation. These results are robust to observed growth heterogeneity. 6. We take a novel approach in applying a simple and generic simulation of a spatial birth-death-growth process to understanding the long run dynamics of a forest community as it moves from a plantation to a naturally regenerating steady 1 ar X iv :0 91 0. 03 87 v1 [ qbi o. PE ] 2 O ct 2 00 9 state. We then consider specific silviculture targeting acceleration of this transition to “old-growth”. However, the model also provides a simple and robust framework for the comparison of more general sivicultural procedures and goals.