Species In Eastern Forests Research Articles

Landscape variables influence Phytophthora cinnamomi distribution within a forested Kentucky watershed

Invasive pests and pathogens have contributed to widescale forest change around the world, but especially in the eastern US. Phytophthora cinnamomi, one such introduced pathogen, causes root rot in American chestnut (Castanea dentata) and shortleaf pine (Pinus echinata), among other eastern forest species of interest, and has inhibited chestnut restoration efforts in some cases. Traditionally, P. cinnamomi has been associated with low landscape positions and moister soils; however, its distribution patterns in the eastern US are poorly understood. Improved understanding of P. cinnamomi distribution may enable forest managers to prioritize sites with low risk of P. cinnamomi presence for chestnut restoration. To elucidate landscape factors associated with P. cinnamomi distribution, two sets of soil samples from an eastern Kentucky forest (representing two levels of sampling intensity) were screened for P. cinnamomi incidence, and data were analyzed for spatial distribution patterns. In general, sites in which P. cinnamomi was detected tended to be warmer (higher annual solar radiation) and drier (lower moisture indices), than sites in which P. cinnamomi were not detected. P. cinnamomi incidence was also found to be associated with oak (Quercus spp.) abundance and (weakly) negatively associated with soil microbial activity under certain conditions. Overall, P. cinnamomi was found to be distributed across a wide range of landscape variables, including both drier ridge-top sites and moister streamside sites, contrary to traditional associations. In addition, the association with oak abundance suggests that the drier upland sites preferred by oak species in eastern Kentucky are not “safe” from P. cinnamomi. Given that P. cinnamomi was found distributed across a range of environmental conditions, forest managers cannot assume that any landscape position is phytophthora-free, and soil screening should be used for site selection to inform restoration of chestnut and other susceptible species.

Disassociating tree species associations in the eastern United States

Ecologists have a long history of describing species associations including oak-hickory, one of the predominant associations in the eastern United States. But historically, oak composition did not appear particularly related to hickory composition. I assessed the relevance of the oak-hickory association and other associations using older and recent (c. 1981 and 2007) USDA Forest Service surveys. For common hickory and oak species, I determined percent composition (i.e., percent of total stems ≥12.7 cm in diameter, relative density or abundance) in ecological subsections, changes in composition throughout ranges, and compared composition of oaks and hickories and other potential associations using correlation and ordination. Oaks were among the most abundant species while hickories were minor species. Hickory composition was stable while the trajectory of oak continued to decrease during the survey intervals from presettlement dominance. Rank-order correlation between oaks and hickories throughout their ranges was about the maximum as for other species (0.55 and 0.42 during the two survey periods) and in the Oak-Hickory forest region, correlation between oaks and hickories was 0.04 (older surveys) and 0.16 (recent surveys). Oaks were not associated with hickory in the “oak-hickory” forests of Missouri during the mid-1800s, nor were oaks associated with hickory more recently beyond correlations that occur between other eastern forest species. Oak-hickory association in particular is not an informative term for either historical open oak ecosystems or current eastern broadleaf forests. Mixed mesophytic associations, perhaps not best termed as an association, are eastern broadleaf forests where many tree species dominate forested ecosystems in the absence of filtering disturbance. Associations, even if species share similar traits, generally are not strong, stable in time, or extensive in space; differences between species result in different and changing distributions in response to the environment, land use, disease, and other influential factors.

Ready or Not, Garlic Mustard Is Moving In: Alliaria petiolata as a Member of Eastern North American Forests

Garlic mustard (Alliaria petiolata) is a nonnative, shade-tolerant forb that was introduced into North America in the mid-1800s. Currently, garlic mustard is spreading across the landscape at a rate of 6400 square kilometers per year. In this article, we synthesize the current state of knowledge on the mechanisms underlying garlic mustard's widespread success and the ecological impacts of its invasion. Although no single mechanism appears to explain the success of garlic mustard, a combination of plant traits—all slightly different from those of native plants—seems to confer garlic mustard with tremendous success in the new habitats it invades. The domination of this new species in eastern forests is clearly changing the ecology of these systems. The consequences of garlic mustard invasion include the loss of biological diversity, ripple effects through higher trophic levels, and changes in the function of soil microbial communities.

Susceptibility of Some Eastern Forest Species to Phytophthora ramorum.

We tested some common Eastern forest species for their reaction to stem and leaf inoculation with Phytophthora ramorum, the pathogen that causes sudden oak death. Stem lesions were produced on inoculated seedlings of 12 Eastern forest species following 72 to 76 days of incubation in a containment greenhouse cubicle at 20°C. Chestnut oak (Quercus prinus) and white oak (Q. alba) were followed by northern red oak (Q. rubra) in susceptibility to stem inoculation. Sugar maple (Acer saccharum) and black walnut (Juglans nigra) were more resistant to stem inoculation than most of the oak species tested. P. ramorum was isolated on selective medium at distances of up to 8 mm from stem lesion margins. Foliar lesions were observed within 7 days when seedlings were inoculated with 5,000 sporangia/ml followed by incubation at 20°C in a dew chamber. Chestnut oak was followed by tanoak (Lithocarpus densiflorus) and coast live oak (Q. agrifolia) in susceptibility to P. ramorum by foliar inoculation. Chestnut oak, an ecologically important species in parts of the Eastern United States, emerged as the most susceptible host tested in both stem and foliar inoculations. The results indicate that, under controlled conditions, P. ramorum is able to infect some important Eastern forest species and cause lesions on stems and foliage. It remains to be determined whether infection of these species by P. ramorum would occur under natural conditions.