Effects of tree size and spatial distribution on growth of ponderosa pine forests under alternative management scenarios

Abstract

Forest ecosystems may be actively managed toward heterogeneous stand structures to provide both economic (e.g., wood production and carbon credits) and environmental benefits (e.g., invasive pest resistance). In order to facilitate wider adoption of possibly more sustainable forest stand structures, defining growth expectations among alternative management scenarios is crucial. To estimate the effect of tree size and spatial distributions on growth for forest structures commonly considered in uneven-aged forest stand management, large (0.2 ha?) plots were established in 14 uneven-aged ponderosa pine stands in eastern Montana. All study trees were stem-mapped and measured for diameter and 10-year sapwood and basal area increment. A generalized growth model was developed to predict both total and merchantable 10-year basal area increment for nine hypothetical stand structures [three diameter distributions (reverse-J, irregular, flat) 9 three spatial distributions (clumpy, partial clumpy, uniform)]. Results indicate that the size and spatial distributions of individual trees have a considerable effect on overall stand growth. The greatest total stand growth was in stands with reverse ''J'' shaped tree size distributions, while the greatest merchantable stand growth was in stands with ''flat'' diameter distributions and uniform spatial distributions. Through better comprehension of generalized uneven-aged stand growth dynamics, forest managers may better assess the effects of alternative stand structures on stand growth while providing forest stand structures that may be more resilient in a changing climate.

Effects of thinning-induced changes in structural heterogeneity on growth, ingrowth, and mortality in secondary coastal Douglas-fir forests

“…For example, tree species diversity metrics were likely not influential in our analysis because of the limited number of species present. Consequently, different age or cohort structures of the studied forest ecosystems, as well as different modeling approaches, might explain the varying findings (O'Hara 1996;Woodall et al 2009). In addition, when both tree species and tree size diversity, as well as their potential interaction, were included in the same model, the tree size diversity metric was the only influential factor.…”

“…Spatially nonexplicit measures of stand structure have also been used to evaluate the effects of varying forest structural heterogeneity on stand growth and mortality (Sterba and Monserud 1995;Edgar and Burk 2001;Liang et al 2005Liang et al , 2007. These studies add to the knowledge derived from semi-empirical modelling to investigate the influence of diameter distribution (or cohort structure) or spatial tree arrangement on stand volume increment (Pukkala 1988;Miina 1994;O'Hara 1996;Shao and Shugart 1997;Woodall et al 2009; see also Hardiman et al 2011). However, findings from these studies are often inconsistent and contradictory.…”