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Spatial structure is a fundamental attribute of complex stands that is relevant both to the growth of trees in these stands and the value of the stands as wildlife habitat. Stand structure can be complex, both vertically and horizontally, in many natural forests and such complexity may be an important goal of management when considering biodiversity issues or trying to emulate natural forest processes. To effectively manage stands for structural features it is necessary to understand how tree growth contributes to stand structural development. Interactions among individual trees are pivotal to the structural development of stands. Tree crowns are a key component of stand structure, and the ways in which neighbours (of the same species and of other species) modify the crown of an individual is fundamental to understanding stand structural development. Crowding can reduce crown length by causing the mortality of lower branches. However, the effects on crown length can depend on the size and species identity of neighbours. Smaller individuals can be strongly affected by larger individuals because of asymmetric competition for light among trees.
Understanding how trees respond to neighbours is fundamental to evaluating possible effects of silvicultural systems employing partial cuts of various sorts. Stands dominated by mixtures of Engelmann spruce (Picea engelmannii) and subalpine fir (Abies lasiocarpa) are common in the ESSF Biogeoclimatic zone in the interior of British Columbia. During a series of studies of the dynamics of spruce-fir forests in the southern interior we obtained precise information on tree size, location, growth rings, and crown length for completely stem-mapped plots at two sites, Adams Lake and Damfino Creek. At each site all trees over 10 cm in diameter were mapped in 4 plots totalling 1 ha in area. We have previously completed and published the results based on tree rings and spatial patterns (Antos and Parish 2002a, b; Parish and Antos 2002). Thus we have presented the disturbance history and age structure of these stands, but we have not examined the crown structure. Building on this previous work, we can efficiently utilize the data from these sites to address crown structure. All field data has been collected, but the data on crown lengths has never been analyzed. We plan to analyze these data by building crown length models based on amounts of crowding by neighbours. We have locations, sizes, and species of neighbouring trees. We will explore various model forms and independent variables when developing the models. We anticipate that final models will allow us to effectively predict crown length, which is a key component of stand structure. Preliminary results from similar efforts to predict crown length in high elevation coastal forests appear very promising, which gives us confidence that such a modelling effort will be fruitful in these Interior spruce-fir stands. Results of this work will provide detailed information about crown development and stand structural diversity. Such information is necessary to evaluate how partial cuts or natural disturbances causing tree mortality may affect subsequent stand structural development. Given that management for structural features of stands is an important concern both for tree growth and wildlife habitat, we anticipate that the results will prove useful when considering silvicultural approaches that try to maintain complex stand structures.
Parish, Roberta. 2008. Effects of competition among trees on crown structure in spruce-fir forests. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2008MR033
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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