Wiregrass (Aristida beyrichiana) may limit woody plant encroachment in longleaf pine (Pinus palustris) ecosystems

Wiregrass (Aristida beyrichiana) is a dominant groundcover species that facilitates fire in southeastern U.S.A. pine savannas, thereby limiting woody plant cover and maintaining a herbaceous dominated understory. In December 1993 two of us planted a plot of wiregrass (Aristida beyrichiana) in the midst of fire-maintained little bluestem (Schizachyrium scoparium) longleaf pine (Pinus palustris) savanna in the outer Coastal Plain of South Carolina. The plot and the surrounding area burned three times in the following 20 y. Vegetation sampling carried out in late summer 2013 indicated wiregrass dominated the plot and the majority of little bluestem had disappeared. The wiregrass plot was comparatively open and grass dominated, whereas the surrounding formerly bluestem dominated stand had filled in with loblolly pine (Pinus taeda) saplings as well as hardwood trees and shrubs. In addition wiregrass had reproduced and established away from the original planted area, most noticeably within a soil-disturbed plow line. A subsequent prescribed fire in spring 2014 burned with higher intensity within the wiregrass plot than in the surrounding area. Our observations suggest suppression of woody plant encroachment by dense wiregrass in pine savannas even during long fire free periods, which should reduce the likelihood of transition to hardwood dominated ecosystems

Large-scale synchrony of gap dynamics and the distribution of understory tree species in maple-beech forests

Large-scale synchronous variations in community dynamics are well documented for a vast array of organisms, but are considerably less understood for forest trees. Because of temporal variations in canopy gap dynamics, forest communities—even old-growth ones—are never at equilibrium at the stand scale. This paucity of equilibrium may also be true at the regional scale. Our objectives were to determine (1) if nonequilibrium dynamics caused by temporal variations in the formation of canopy gaps are regionally synchronized, and (2) if spatiotemporal variations in canopy gap formation aVect the relative abundance of tree species in the understory. We examined these questions by analyzing variations in the suppression and release history of Acer saccharum Marsh. and Fagus grandifolia Ehrh. from 481 growth series of understory saplings taken from 34 mature stands. We observed that (1) the proportion of stems in release as a function of time exhibited a U-shaped pattern over the last 35 years, with the lowest levels occurring during 1975–1985, and that (2) the response to this in terms of species composition was that A. saccharum became more abundant at sites that had the highest proportion of stems in release during 1975–1985. We concluded that the understory dynamics, typically thought of as a stand-scale process, may be regionally synchronized

Temporal, spatial, and structural patterns of adult trembling aspen and white spruce mortality in Quebec's boreal forest

Temporal, spatial, and structural patterns of adult trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) mortality were studied in intact 150-year-old stands in the southwestern boreal forest of Quebec. For both species, mortality decreases (number of dead trees/total number of trees) with distance from the lake edge until 100-150 m, from which point it slightly increases. Strong peaks in mortality were found for 40- to 60-year-old aspen mainly between 1974 and 1992. Such mortality in relatively young aspen is likely related to competition for light from the dominant canopy trees. Also, the recruitment of this young aspen cohort is presumably the result of a stand breakup that occurred when the initial aspen-dominated stand was between 90 and 110 years old. For spruce, strong peaks in mortality were found in 110- to 150-year-old trees and they occurred mainly after 1980. No clear explanation could be found for these peaks, but we suggest that they may be related to senescence or weakening of the trees following the last spruce budworm outbreak. Suppressed and codominant aspen had a much higher mortality ratio than spruce in the same height class, while more surprisingly, no difference in mortality rate was found between dominant trees of the two species. Most spruce trees were found as standing dead, which leads us to reject the hypothesis that windthrow is an important cause of mortality for spruce in our forests

Longleaf Pine Ground-Layer Vegetation in Francis Marion National Forest: Reintroduction, Restoration, and Vegetation Assembly

Study represents significant progress in understanding of compositional gradients in longleaf pine plant communities of Central South Carolina. Study shows the importance of water table depths as a controlling variable with vegetation patterns in the field and similar effects in a garden experiment. Grass planting study suggests that observed field distributions of dormant pine savannah grasses derive from complex interactive effects of fire history, hydrology and light environments. Use of regional longleaf data set to identify candidate species for introduction also appears to be a pioneering effort

Data from: Ontogenetic responses of four plant species to additive and interactive effects of land-use history, canopy structure and herbivory

The strength of interactions among species is often highly variable in space and time, and a major challenge in understanding context-dependent effects of herbivores lies in disentangling habitat-mediated from herbivore-mediated effects on plant performance. We conducted a landscape-scale experiment that manipulated light availability in woodlands with either a history of agricultural use or no history of agricultural use and coupled this with performance measurements of three life stages on four perennial herbaceous species exposed to varying levels of herbivory. We found that the context-dependent effects of herbivory on plant performance changed as plants grew: juvenile plant survival was reduced by herbivores in low-light habitats whereas biomass of adult plants was reduced by a more diverse insect fauna in high-light environments. A history of agricultural land use also had negative effects on seedling establishment and adult performance, independent of herbivory. Synthesis. This work experimentally separates the habitat-mediated effects on plant performance from the herbivore-mediated effects on plant performance and highlights how context-dependent interactions depend on plant ontogenetic stages