Competition Among Secondary-Successional Pine Communities: A Field Study of Effects and Responses

Abstract

Three common associates on secondary-successional pine sites (Andropogon virginicus, Liquidambar styraciflua, and Pinus taeda) were established in a field study in which a wide array of plant densities and species proportions were established using an additive series design. To mimic a specific competitive scenario (i.e., a managed earlysuccessional Pinus stand), Andropogon and Liquidambar were established a year prior to the establishment of Pinus. Competitive effect (the attenuation of resources) and competitive response (the growth of each species as a function of resource availability) were determined.Effect on soil water varied among species, depth of soil, and time. In the surface soil, soil water was largely influenced through non-uptake effects, while uptake effects were predominant in deeper portions of the solum. When competitor abundance was expressed on an aboveground biomass basis, rather than a density basis, species differences in effects on soil water were eliminated. Differences among the species in effects on soil water per unit leaf area or leaf biomass appear to be largely explained by differences in stomatal conductance. Predawn leaf-water potential was integrated over the season using a waterstress integral. Analysis of the water-stress integral suggested that Liquidambar and Andropogon both affected water available to Pinus; however, only Liquidambar affected Andropogon, and only Andropogon affected seasonal water available to Liquidambar. Light was most strongly influenced by Liquidambar density; however, as Andropogon density increased, the effects of Liquidambar were reduced.Andropogon response was correlated with light but not with water stress or leaf nitrogen. This reflects high light requirements and high water use efficiency of C 4 plants. Liquidambar response was related to water stress and leaf nitrogen, perhaps reflecting the greater nitrogen requirements of hardwoods. Pinus response was significantly related to all three resources individually, i.e., water stress, light, and leaf nitrogen. Pinus response was better explained by a regression model that included light and water stress than by water stress or light alone. Pinus growth as a function of water stress and light indicated that communities dominated by Liquidambar largely reduced Pinus growth through reduction in light, while communities dominated by Andropogon reduced Pinus growth primarily by increasing water stress. In mixed communities of Liquidambar and Andropogon, pine growth was constrained more equally by light and water stress.

Photosynthesis, nitrogen-use efficiency, and water-use efficiency of jack pine seedlings in competition with four boreal forest plant species

“…The lack of a correspondence between the influence of competitor density on jack pine E or WUE, and the low and often insignificant correlations between jack pine P n and water availability suggested that competition for water was not as important as that for N or light (Shropshire 1999) in our study. Competition for light and water were more apparent in a similar study (Mitchell et al 1999), as seen in growth and physiological response of loblolly pine to light attenuation and water availability in the Upper Coastal Plain of Alabama. Mitchell et al (1999) observed a significant decrease in available soil water throughout the growing season, a phenomenon not observed in our study.…”

“…Competition for light and water were more apparent in a similar study (Mitchell et al 1999), as seen in growth and physiological response of loblolly pine to light attenuation and water availability in the Upper Coastal Plain of Alabama. Mitchell et al (1999) observed a significant decrease in available soil water throughout the growing season, a phenomenon not observed in our study. We concur with Mitchell et al (1999) that competitive effect and response are important to understand mechanisms regulating competitive interactions when spatiotemporal resource heterogeneity is considered.…”

“…Mitchell et al (1999) observed a significant decrease in available soil water throughout the growing season, a phenomenon not observed in our study. We concur with Mitchell et al (1999) that competitive effect and response are important to understand mechanisms regulating competitive interactions when spatiotemporal resource heterogeneity is considered. Our data suggest that N availability, not available water, may have a greater effect on early succession in jack pine stands where low net N mineralization rates and reduced N availability limit growth of jack pine and associated plant species.…”

“…Nitrogen and (or) water uptake of pine has been correlated with growth when competing vegetation re-duced N and moisture availability (Larson and Schubert 1969;Sands and Nambiar 1984;Elliott and White 1987;Morris et al 1993;Nambiar and Sands 1993). Mitchell et al (1999) concluded that response of Pinus spp. to competition was associated with the physiological response of species to available light and water, as well as the ability to acquire resources.…”

Performance of Oak Seedlings Grown under Different Oust® XP Regimes

“…Both herbaceous and woody competition threaten survival of planted oak seedlings, with herbaceous competition posing the greatest risk during the first years of establishment [10,11]. Greater impact of herbaceous competition is likely the result of increased exploitation of soil moisture and nutrients due to the more extensive nature of herbaceous species root systems [12].…”