Competitive hierarchies of temperate tree species: Interactions between resource availability and white-tailed deer (original) (raw)
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Journal of Ecology, 2007
Interspecific relationships between fundamental demographic rates, often called demographic trade-offs, emerge from constraints within individuals related to morphology, physiology and resource allocation. Plant species that grow fast in high light usually have high mortality in shade, and this well-established relationship in part defines a species' successional niche. More generally, this relationship represents a trade-off between a species' ability to grow quickly to exploit abundant resources vs. avoiding mortality when resources are less plentiful, but few studies have described this demographic trade-off with respect to environmental factors other than light. 2. Using demographic data from 960 tree species in Bornean rain forest, we examined the evidence for an interspecific demographic trade-off between fast growth and low mortality and its variation among habitats defined by variation in soil fertility and moisture. Such a trade-off could contribute to sorting of tree species among habitats and partly explain the striking patterns of species' edaphic associations in this and other forests. 3. We found strong evidence for this demographic trade-off, both within the same habitat and when growth on edaphically rich habitats was compared with mortality on a habitat with lower below-ground resource availability. 4. The slope of the growth-mortality relationship varied among habitats, being steepest on the habitat lowest in below-ground resources. For species with the fastest potential growth rates, mortality was higher on this habitat than at comparable growth rates on the three more edaphically rich habitats, providing a possible mechanism by which fast-growing species may be eliminated from the poorest habitat. Adaptations for fast growth may entail a greater mortality risk, if inherently fast-growing species fail to maintain a positive C-balance when below-ground resources are scarce. 5. Conversely, for species with the slowest potential growth rates, the highest species' mortality rates occurred on the habitats with greatest below-ground resource availability, implying that slow-growing species may have a competitive disadvantage in resource-rich environments. 6. Synthesis. Differences among habitats in the steepness of this trade-off may sort species into different habitats along this edaphic gradient, whereas on the same soil, this demographic trade-off could facilitate coexistence of at least some species in this forest. Thus, by generating emergent demographic trade-offs that vary along resource gradients, plant life-history strategies can influence species diversity and distribution.
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, 2009
A central concept in forest ecology is that differences in the growth rates and shade tolerances of tree species determine patterns of secondary succession. The most shade-tolerant tree species are the competitive dominants in late-successional forests, while species with fast growth rates persist through rapid establishment after disturbance. There is ample support for niche differentiation along the shade-tolerance axis, at least for temperate forests, but less thought has been given to the range of shade tolerances and growth rates encountered within a community and to how it might vary along environmental gradients. 2. We hypothesized that a wider range of growth rates and shade tolerances are found on nutrientrich soils, because such soils not only support fast-growing species with high metabolic rates, but also species capable of tolerating the very deep shade cast by forest canopies growing where nutrients are plentiful. We test our hypothesis by quantifying light transmission through two neighbouring forests in southern New Zealand, one on phosphorus-rich alluvial soil and one on phosphorus-depleted marine-terrace soil, and comparing the growth rates of saplings on these contrasting sites. 3. Less light was transmitted to the forest floor on alluvial sites than on marine terraces (2.5% vs. 7.5% daylight, on average) and neighbourhood analyses within mapped stands indicated that large-leaved subcanopy species were responsible for intercepting that extra light. Sapling growth was strongly inhibited by shade in the understorey of the alluvial forests, but was less inhibited under the terrace forests. 4. Fast-growing subcanopy species were common on the alluvial sites and these species had characteristically soft leaves and high foliar-nutrient concentrations. Slow-growing shade-tolerant species were also abundant on these sites. Therefore, the interspecific variance in growth rates was greater on nutrient-rich sites, supporting our hypothesis of a greater range of shade tolerance niches on better soils. Of the five species found on both forest sites, all five had greater high-light growth rate on the alluvial sites. 5. Synthesis : A wider range of growth rates was observed in the nutrient-rich forests. This wider range may translate into a greater number of shade tolerance niches and thereby provides an explanation for the greater numbers of species commonly found on nutrient-rich soils when compared with neighbouring nutrient-poor sites.
Plant Ecology, 2009
This paper compares vegetation composition, light availability, carbon and nutrient pools and Ellenberg indicator values among four old-field successional permanent plots that have received an initial treatment (ploughing, herbicide or sterilisation) prior to being left undisturbed in 1969, a second set of six plots received additional treatments (continued ploughing or mulching until 1982). On all plots species rich pioneer forests developed. Vegetation still varies among plots with different initial treatments: Sterilised plots can be distinguished from the others by dominance of Betula pendula, ploughed plots by Fraxinus excelsior, whereas herbicide-treated plots are intermediate with proportions of both species. By affecting light availability at the ground, tree species in turn influences ground vegetation and soil properties. Light availability turned out to be the dominant factor determining the composition of the vegetation in old-field succession.
Forests , Competition and Succession
2011
Competition, the struggle for limited resources, and succession, the sequence of change in dominant organisms following colonization, have long been key concepts employed by ecologists to understand and organize the patterns of nature. Although competition and succession are distinct processes, they are closely related for at least two reasons. First, successional trajectories are largely driven by interactions among organisms, including (but not restricted to) competition. Second, both are intimately related to the degree of equilibrium or disequilibrium in ecosystems and landscapes. Ecologists once believed that succession led inexorably to a stable equilibrium within a given community of organisms, the composition of which was determined in large part by who won the struggle for limited resources. Although that view has not been totally discarded, most ecologists now recognize that change is the rule rather than the exception in nature, with few if any ecological communities achi...
Landscape Ecology, 2012
In landscapes dominated by late-successional plant communities, early-successional species may lead a tenuous existence, persisting only as fugitives or relying on refuges in marginal habitats to provide a persistent seed source. The objective of this study was to relate fine-scale distributions of earlysuccessional tree species in hemlock-hardwood forests of northern Wisconsin, USA to potential landscape persistence strategies. A special emphasis was placed on eastern white pine (Pinus strobus), a restoration priority in the region. Witness tree data from nineteenth century US Public Land Survey records (encompassing 40,610 km 2 and 106,790 trees) were used with modern environmental data to relate species distributions to habitat characteristics. Early-successional tree species had strong positive associations with marginal habitats such as inclusions of sandy soil and margins of lakes, wetlands, and rivers. Marginal habitats occupied *44 % of the landscape, which may help account for the abundance of early-successional species in our study area relative to other hemlock-hardwood forests. Populations of early-successional species in marginal habitats could also have provided important seed sources for the upland mesic landscape matrix, as [70 % of the landscape was within 200 m of these habitats. The degree to which early-successional species were limited to marginal habitats largely followed predictions based on species lifehistory characteristics, except that white pine was more common than expected in upland mesic habitats. These findings illustrate the potential importance of landscape heterogeneity for persistence of earlysuccessional species in late-successional forest landscapes and provide baseline information on habitat associations and landscape dynamics that will be useful in restoration efforts.
Coexistence of Acer saccharum and Fagus grandifolia in an old-growth forest
Mechanisms of coexistence were studied through an old-growth forest co-dominated by sugar maple (Acer saccharum) and American beech (Fagus grandifolia). The goal of the field study was to evaluate three hypotheses involving competition in trees, and the maintenance and regeneration of beech and sugar maple within Warren Woods, Michigan, USA. First, evidence of trade-off's of beech and sugar maple as they make their way to the canopy was evaluated. Second, competition within the various size classes was reviewed with the goal of highlighting any commonality in response or unique environmental condition (e.g., distribution correlated to light gaps afforded by a certain canopy tree species). Third, the relationship between beech and sugar maple was evaluated to assess if a highly despotic form of lottery competition was evident, in that though many trees attempt to reach the canopy, few ever do. Of the plots surveyed, the density and frequency of occurrence of understory stems revealed that sugar maple was more abundant and occurred in larger proportions among the three sub-canopy class sizes. Though the frequency of beech canopy trees was smaller than that of sugar maple, it achieved higher density in the forest. The mechanism of reciprocal replacement could not be confirmed, noting sugar maple and beech frequencies remained consistent across sub-canopy and canopy size classes. Furthermore, there was indication that canopy trees were responding to habitat or resource preferences, since neighboring canopy trees tended to be the same species. A mechanism of coexistence was evident when the understory light environment of each species was evaluated. Sugar maple appears to prefer the light levels offered by a beech canopy, while beech seedlings and saplings were found in higher frequencies and density under sugar maple canopies. However, no plausible correlation could be made between the size of the trunk and the area of canopy reach, as beech appeared to double the investment in structural support while only achieving similar canopy areas to the sugar maple. These two species appear to respond to canopy disturbances with equal veracity and equal success, though they may do so under variable conditions. Each are adapted to persist in low light conditions, each exploit canopy gaps quickly and efficiently and at different points in their growth cycle, and each appear to coexist comfortably with the other while preventing other tree species from establishing any presence in this pristine beech-maple forest.
Ecological Applications, 2006
Robust predictions of competitive interactions among canopy trees and variation in tree growth along environmental gradients represent key challenges for the management of mixed-species, uneven-aged forests. We analyzed the effects of competition on tree growth along environmental gradients for eight of the most common tree species in southern New England and southeastern New York using forest inventory and analysis (FIA) data, information theoretic decision criteria, and multi-model inference to evaluate models. The suite of models estimated growth of individual trees as a species-specific function of average potential diameter growth, tree diameter at breast height, local environmental conditions, and crowding by neighboring trees. We used ordination based on the relative basal area of species to generate a measure of site conditions in each plot. Two ordination axes were consistent with variation in species abundance along moisture and fertility gradients. Estimated potential growth varied along at least one of these axes for six of the eight species; peak relative abundance of less shade-tolerant species was in all cases displaced away from sites where they showed maximum potential growth. Our crowding functions estimate the strength of competitive effects of neighbors; only one species showed support for the hypothesis that all species of competitors have equivalent effects on growth. The relative weight of evidence (Akaike weights) for the best models varied from a low of 0.207 for Fraxinus americana to 0.747 for Quercus rubra. In such cases, model averaging provides a more robust platform for prediction than that based solely on the best model. We show that predictions based on the selected best models dramatically overestimated differences between species relative to predictions based on the averaged set of models.