On the influence of stand spatial structure and species diversity on growth and recruitment of structurally complex forests: evaluating the role of distance-dependent and species-sensitive competition indices within the Acadian region of northeastern North America
Final Report Abstract
Forest management in many parts of the Northern hemisphere is moving away from conventional singlespecies, even-aged management toward selection harvesting systems. The widespread adoption of such practices has outpaced fundamental research addressing the ability of selection systems to meet the intended objectives of creating more complex and diverse forest structures and ensuring the continuous provision of ecosystem goods and services. By simulating and predicting long-term future developments forest growth models are a potential means to overcome these deficiencies. However, the majority of existing models were developed from and hence for even-aged, single species stands. This project analyzed how variation in forest structure such as species diversity and spatial distribution of trees influences stand dynamics including recruitment and mortality as well as individual tree growth. Using data from replicated thinning experiments located in the Pacific Northwest and Northeastern regions of North America, i) intercorrelations between management, forest structure, and stand dynamics and ii) prediction ability of spatially explicit and spatially implicit structural diversity measures and competition indices were evaluated. Stand- and tree neighborhood-level structural diversity measures included standard deviation of tree diameters, Gini coefficient, Shannon–Weaver diversity index and the spatially explicit mean DBH differentiation index, mean directional index, structural complexity index, and mingling index. In addition, second order summary statistics such as pair and mark correlation functions and mark variogram were also derived. Distance independent tree-level competitions measures comprised stand basal area and basal area in larger trees while distance dependent metrics included weighted area potentially available, crown surface area facing sky, and distance to harvester trial. Structural diversity measures, spatially explicit ones in particular, were able to differentiate between the various treatments evaluated in the thinning studies. Thinning-induced changes in tree size diversity and spatial distribution of trees also helped explain observed trends in individual-tree growth rate. Furthermore, temporal dynamics in growth dominance patterns revealed that forest structural changes imposed by commercial thinning influenced tree growth patterns, which further modified stand structure. Incorporating structural diversity measures in stand-level growth, ingrowth, and mortality prediction models improved predictive ability and model performance only marginally. Moreover, spatially explicit structural diversity measures and competition indices rarely outperformed their spatially implicit counterparts in stand- and tree-level growth models, respectively. Overstory species diversity, however, proved to be a significant predictor in forest regeneration composition models. It was concluded that the inclusion of sophisticated structural diversity measures and competition indices in growth, recruitment, and mortality models can be beneficial, but further work is needed to clarify the underlying relationships, particularly at the individual-tree level.
Publications
- 2015. Effects of thinning-induced changes in structural heterogeneity on growth, ingrowth, and mortality in secondary coastal Douglas-fir forests. Canadian Journal of Forest Research 45: 1448-1461
Kuehne C., Weiskittel A.R., Fraver S., Puettmann K.J.
(See online at https://doi.org/10.1139/cjfr-2015-0113) - Assessing the factors influencing natural regeneration patterns in the diverse, multi-cohort, and managed forests of Maine, USA. Journal of Vegetation Science, Vol 27 Issue 6, Nov 2016, Pages 1140-1150
Bose A., Weiskittel A.R., Wagner R.G., Kuehne C.
(See online at https://doi.org/10.1111/jvs.12433)
