MULTI-MODEL ANALYSIS OF TREE COMPETITION ALONG ENVIRONMENTAL GRADIENTS IN SOUTHERN NEW ENGLAND FORESTS (original) (raw)
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Ecological Applications, 2006
We use permanent-plot data from the USDA Forest Service's Forest Inventory and Analysis (FIA) program for an analysis of the effects of competition on tree growth along environmental gradients for the 14 most abundant tree species in forests of northern New England, USA. Our analysis estimates actual growth for each individual tree of a given species as a function of average potential diameter growth modified by three sets of scalars that quantify the effects on growth of (1) initial target tree size (dbh), (2) local environmental conditions, and (3) crowding by neighboring trees. Potential growth of seven of the 14 species varied along at least one of the two environmental axes identified by an ordination of relative abundance of species in plots. The relative abundances of a number of species were significantly displaced from sites where they showed maximum potential growth. In all of these cases, abundance was displaced to the more resource-poor end of the environmental gradient (either low fertility or low moisture). The pattern was most pronounced among early successional species, whereas late-successional species reached their greatest abundance on sites where they also showed the highest growth in the absence of competition. The analysis also provides empirical estimates of the strength of intraspecific and interspecific competitive effects of neighbors. For all but one of the species, our results led us to reject the hypothesis that all species of competitors have equivalent effects on a target species. Most of the individual pairwise interactions were strongly asymmetric. There was a clear competitive hierarchy among the four most shade-tolerant species, and a separate competitive hierarchy among the shade-intolerant species. Our results suggest that timber yield following selective logging will vary dramatically depending on the configuration of the residual canopy, because of interspecific variation in the magnitude of both the competitive effects of different species of neighbors and the competitive responses of different species of target trees to neighbors. The matrix of competition coefficients suggests that there may be clear benefits in managing for specific mixtures of species within local neighborhoods within stands.
Journal of Ecology, 2011
1. Plant interactions play a central role in regulating plant communities and this role can be altered by abiotic stress. With increasing stress, ecological theory predicts that the role of competition decreases whilst that of facilitation increases. Such predictions have been tested with short-term plant removal experiments using two distinct indices evaluating the role of plant interactions: the intensity (absolute impact) and the importance (impact relative to that of other abiotic constraints) of plant interactions. 2. Using data on individual tree radial growth from more than 17 000 forest plots covering the habitat conditions of 16 species in the Alps and the Jura mountains of France, we show that nonmanipulative estimates of plant interactions provide an alternative to this experimental approach. We developed a Bayesian neighbourhood growth competition model to test theoretical predictions about plant-plant interactions with a much larger spatio-temporal scope and set of study species than classically used in experimental studies of plant-plant interactions. 3. Our analyses revealed that competition -measured as neighbours effects on adult tree growthvaries in importance but not in intensity along two major bioclimatic gradients (degree-day sum and water availability). Observed patterns of competition importance differed between shade-tolerant and shade-intolerant tree species. First, the mean importance of competition was found to be much higher for shade-intolerant species. Second, for shade-intolerant species the importance of competition remained high even at low crowding indices (i.e. at a low competitor density), whereas for shade-tolerant species competition only became important at high crowding indices. 4. Synthesis. Our non-manipulative approach to the study of plant-plant interactions allows analysing interactions among many species over large climatic gradients. Our results clearly demonstrate that a quantitative estimation of density dependence effects is key to understanding how plantplant interactions vary along abiotic gradients. Growth predictions derived from our model can easily be integrated with other results on tree regeneration and mortality in individual-based models to investigate how plant-plant interactions drive tree population and community dynamics under varying climatic conditions.
PLoS ONE, 2013
We examined the effect of competition on stem growth of Picea glauca and Populus tremuloides in boreal mixedwood stands during the stem exclusion stage. We combined traditional approaches of collecting competition data with dendrochronology to provide retrospective measurements of stem diameter growth. Several competition indices including stand basal area (BA), the sum of stem diameter at breast height (SDBH), and density (N) for the broadleaf and coniferous species, as well as similar indices considering only trees with diameters greater than each subject (BAGR, SDBHGR, and NGR), were evaluated. We used a nonlinear mixed model to characterize the basal area increment over the past 5, 10, 15, 20, 25, 30, and 35 years as a function of growth of nearby dominant trees, the size of the subject trees, deciduous and coniferous competition indices, and ecoregions. SDBHGR and BAGR were better predictors for spruce, and SDBHGR and NGR were better for aspen, respectively, than other indices. Results showed strongest correlations with long-term stem growth, as the best models integrated growth for 10-25 years for aspen and $25 for spruce. Our model demonstrated a remarkable capability (adjusted R 2 .0.67) to represent this complex variation in growth as a function of site, size and competition.
European Journal of Forest Research, 2013
One of the pivotal objectives in forestry research is to estimate the response of silvicultural target variables to climate change scenarios at high temporal resolution in order to consider within-year feedbacks between growth and environmental conditions. To meet this challenge, models are needed which support and complement the widely used observation-based decision systems in forest management and consulting. Physiological models in particular provide the fundamental prerequisites to reflect the impact of various simultaneously changing environmental conditions. However, a physiological representation at the individual tree level is computationally very expensive and sensitive to uncertain initializations. We thus propose an approach that combines a modern representative of the physiological cohort model type, MoBiLE-PSIM, with the individual tree competition concept of a distance-dependent empirical growth simulator (SILVA). The resulting hybrid provides a key feature for the consideration of forest management in long-term simulations at high computational efficiency. The extended model was evaluated with growth-diameter distributions obtained from core-boring at two beech (Fagus sylvatica L.) forest sites in south-west Germany that differ in exposure and soil conditions. The mean bias of annual standscale growth from 2001 to 2007 decreased from -0.59 to -0.41 mm at one evaluation plot and from -0.55 to -0.24 mm at the other when the competition module was coupled in. Inclusion of the SILVA-based individual tree module into MoBiLE-PSIM improved the size-dependent representation of competition and growth on five-year and even annual timescale. This was particularly the case where the spatial distribution of dominant trees was clustered.
Environmental Reviews, 2013
Competition in forest stands has long been of interest to researchers. However, much of the knowledge originates from empirical studies that examined the effects of competition. For instance, many studies were focused on the effects of the presence of herbaceous species on the development of tree seedlings or the decrease in individual tree growth with increases in stand density. Several models that incorporate competitive effects have been developed to predict tree and stand growth, but with simplified representations of competitive interactions. While these studies provided guidance useful for forest management, they contributed only partially to furthering our understanding of competitive mechanisms. Also, most competition studies were conducted in single-species stands. As competitive interactions occurring in mixed stands are characterized by a higher degree of complexity than those in single-species stands, a better understanding of these mechanisms can contribute to developin...
Forest landscape models (FLMs) are important tools for testing basic ecological theory and for exploring forest changes at landscape and regional scales. However, the ability of these models to accurately predict changes in tree species' distributions and their spatial pattern may be significantly affected by the formulation of site-scale processes that simulate gap-level succession including seedling establishment, tree growth, competition, and mortality. Thus, the objective of this study is to evaluate the effects of site-scale processes on landscape-scale predictions of tree species' distributions and spatial patterns.
A neighborhood analysis of canopy tree competition: effects of shading versus crowding
Canadian Journal of Forest Research-revue Canadienne De Recherche Forestiere, 2004
We have developed extensions of traditional distance-dependent, spatial competition analyses that estimate the magnitude of the competitive effects of neighboring trees on target tree growth as a function of the species, size, and distance to neighboring trees. Our analyses also estimate inter- and intra-specific competition coefficients and ex- plicitly partition the competitive effects of neighbors into the effects of shading
A research gap in the interactive effects of climate and competition on trees growth
Tree growth depends on an intrinsic component (age, size, genetic structure) and external factors. The radial growth linear aggregate model [Graybill, 1982; Cook, 1990] outlines five classes of variables influencing tree-ring growth: (1) age-size-related trend, (2) climatic influence, (3) autogenic disturbances (plant to plant interactions), (4) allogenic disturbances, and (5) unexplained variations not related to the other components. Even if these variables are often studied separately, they are interconnected. The individual climate-growth relationships can be influenced by competitive processes. Moreover plant-plant interactions can be altered by environmental (climatic) conditions. In 1996 Schweingruber highlighted dendrochronological research needs to investigate the effects of relationship between stand hierarchy and climate on tree ring width. However in last years the majority of dendrochronological studies have focused on climate factor, excluding other variables and possible correlations. Few studies addressing climate-competition interactions have shown often variation in climate responses among different crown classes. However results are not consistent and it is not possible to generalize yet on certain processes. Advance in knowledge of interactive effects of climate and competition should improve dendroecology and dendroclimatology, and should be useful for individual-tree and stand growth models development.
Competitive interactions between aspen and white spruce vary with stand age in boreal mixedwoods
Forest Ecology and Management, 2007
Effects of aspen (Populus tremuloides Michx.) competition on growth of white spruce (Picea glauca (Moench) Voss) were examined using a neighbourhood approach across an age sequence of nine boreal mixedwood stands in Alberta, Canada. Three similar natural stands were selected for each of the three age classes considered (10-20, 20-40 and 40-60 years). Several competition indices based on density (number of trees, basal area and spacing factor), distance-dependent and independent size-ratio (Hegyi's and Lorimer's) and crown characteristics (crown volume, surface area and cross-sectional area) were examined for their effectiveness at predicting light transmittance and spruce growth. Transmittance was poorly predicted by competition indices, except for some indices based on density, with relationships generally explaining less than 40% of variation. Models of spruce growth (diameter and height increment) indicated variable performance among stands and indices tested. Competition accounted for up to 70% of growth variation, with some of the best results provided by Lorimer's, Hegyi's and crown volume indices. The addition of initial size as a second explanatory variable increased the predictive ability of growth models. Best models of spruce growth were selected and tested for differences between stands and age classes using indicator variable tests. Results indicated that data from stands within the 20-40 and 40-60 year age classes could be pooled across sites and across the two age classes into a single model. Data from the youngest age class (10-20 years) could not be pooled with those from the two older age classes. Results from this study indicate that relationships between growth and levels of competition may differ between young and older stands and suggest it may be necessary to parameterize growth models separately for different age classes when growth is predicted as a function of competition. #
Forest Science
Crown-based competition measures were used to assess the relationships between growth and competition for trees in young mixed-hardwood stands on two ecosystems with contrasting site conditions. The two southwestern Wisconsin ecosystems compared were gently sloping summits with deep loessal soils and steeply sloping southwesterly backslopes with loam soils. Individual trees were sampled from variable-radius plots located in 15 stands of 4 to 42 years old. The two best predictors of height growth are the height of a tree relative to the average height of dominants and codominants, and the cross-sectional area of the exposed portion of the crown at its widest point. The data confirmed theoretical relationships between growth and light intensity for species of differing shade tolerance. However, growth rates as a function of relative height did not approach an asymptote for any species, while growth response to increasing exposed crown area was asymptotic for the tolerant species. Spec...