Temporal Change Within and Among Forest Communities of Great Smoky Mountains National Park: The Influence of Historic Disturbance and Environmental Gradients

Understanding how ecological communities change over time is critical for biodiversity conservation. However, few long-term studies directly address decadal-scale changes in the ecological communities of protected areas. In this study, we take advantage of a network of permanent forest plots, established in Great Smoky Mountains National Park in 1978, to investigate temporal changes in plant communities. In particular, we examine the factors that influence temporal change in species richness and composition within communities and temporal change in compositional similarity among communities. In 2007, we revisited 15 permanent plots that were logged in the late 1920s and 15 permanent plots that have no documented history of intensive human disturbance. In addition to differences in disturbance history, these plots varied in elevation and a variety of edaphic parameters. We found that understory species richness decreased by an average of 4.3 species over the 30-year study period in the logged plots, while understory richness remained relatively unchanged in the unlogged plots. In addition, tree density decreased by an average of 145 stems/ha in the logged plots but was relatively stable in the unlogged plots. Historic logging had no effect on within-site understory or tree compositional turnover. However, sites with higher soil pH had higher understory turnover and higher tree turnover than did sites with lower soil pH. In addition, sites at lower elevations and sites with lower understory productivity in 1978 had higher understory turnover than did sites at higher elevations and sites with higher understory productivity in 1978. Among-community similarity was unchanged from 1978 to 2007 in the understory communities and in the tree communities of both the logged and unlogged plots. Taken together, our results indicate that human disturbance can affect plant communities for decades following the disturbance event but that the extent of temporal change in community composition may depend more on environmental gradients than on the legacy of large-scale but short-lived historic disturbances, such as logging. In addition, our results suggest that variation in temporal turnover within communities may not necessarily translate into changes in compositional similarity among communities over time

Non-Additive Effects of Genotypic Diversity Increase Floral Abundance and Abundance of Floral Visitors

Background: In the emerging field of community and ecosystem genetics, genetic variation and diversity in dominant plant species have been shown to play fundamental roles in maintaining biodiversity and ecosystem function. However, the importance of intraspecific genetic variation and diversity to floral abundance and pollinator visitation has received little attention. Methodology/Principal Findings: Using an experimental common garden that manipulated genotypic diversity (the number of distinct genotypes per plot) of Solidago altissima, we document that genotypic diversity of a dominant plant can indirectly influence flower visitor abundance. Across two years, we found that 1) plant genotype explained 45 % and 92 % of the variation in flower visitor abundance in 2007 and 2008, respectively; and 2) plant genotypic diversity had a positive and non-additive effect on floral abundance and the abundance of flower visitors, as plots established with multiple genotypes produced 25 % more flowers and received 45 % more flower visits than would be expected under an additive model. Conclusions/Significance: These results provide evidence that declines in genotypic diversity may be an important but little considered factor for understanding plant-pollinator dynamics, with implications for the global decline in pollinators due t

communities of Great Smoky Mountains National

To the Graduate Council: I am submitting herewith a dissertation written by Windy A. Bunn entitled “Temporal change within and among forest communities of Great Smoky Mountains National Park: The influence of historic disturbance and environmental gradients. ”

Historical high-severity fire patches in mixed-conifer forests

Two ends of the fire regime spectrum are a frequent low-intensity fire regime and an infrequent high-intensity fire regime, but intermediate fire regimes combine high- and low-severity fire over space and time. We used fire-scar and tree-age data to reconstruct fire regime attributes of mixed-conifer and aspen forests in the North Rim area of Grand Canyon National Park, with a goal of estimating patch sizes of historical high-severity fire and comparing them with modern patch sizes. We used three methods based on (i) aspen groves, (ii) even-aged stands, and (iii) inverse distance weighting, to estimate occurrence and patch sizes of historical high-severity fire. Evidence of high-severity fire was common in the 1800s, and high-severity fire years were associated with drought. High-severity fire patch sizes likely ranged from 10−1 to 102 ha. However, the forest is quite young, and we cannot rule out a historical large high-severity fire that could have reinitiated much of the 1400 ha study area. Fire scars, which are indicative of low-severity fire, were also common. Historical fire was likely heterogeneous across the landscape. Maintaining heterogeneity of fire severity, size, and frequency would promote heterogeneity of forest structure and composition and resilience to future disturbances

USA National Phenology Network, National Coordinating Office

Abstract Research in community invasibiliy has focused on biotic and abiotic factors that influence the establishment of invasive species and whether such factors vary with spatial scale. Here, we investigate the role of both biotic and abiotic factors associated with the initial establishment of Lespedeza cuneata (L. cuneata) and its abundance at three spatial scales: neighborhoods (9-m 2 plots), communities (50-m 2 transect) and old fields (5,000-70,000 m 2 ). We asked: (1) Do resource availability and community structure affect the establishment of L. cuneata?, and (2) Are resource availability and community structure associated with patterns of L. cuneata abundance from neighborhood scales to old-field scales? To investigate the first question, we manipulated soil nitrogen (N) availability at three levels in an existing old-field community and tracked emergence and persistence of L. cuneata seedlings, as well as total plant biomass of the community, availability of light, and soil moisture content. To address the second question, we performed surveys in which we estimated L. cuneata foliar cover at community scales (50-m 2 belt transects) and old-field scales (total area of 28 ha), and assessed the same biotic and abiotic variables as in the field experiment. The experiment revealed that establishment and persistence by L. cuneata seedlings were 159 and 59 lower in N-added plots than in N-reduced plots. Total plant community biomass was 30% greater in N-added plots than in N-reduced plots. Conversely, light and soil moisture were 60 and 20% lower in N-added plots than in N-reduced plots. Surveys of old fields indicated that community biomass was positively associated with L. cuneata cover at old-field scales likely resulting from greater soil N input from nitrogen fixation in fields with greater L. cuneata cover. In sum, these results indicate that biotic factors associated with establishment of a Rank 1 invasive plant species at the community scale are also related to its distribution at the old-field scale, but the direction of such associations changed across scales

Appendix A. List of journals included in Web of Science literature searches.

List of journals included in Web of Science literature searches