Disturbance-mediated plant competition - Much of my current research is focused on testing the disturbance-mediated competition hypothesis, which predicts that moderate disturbances have the potential to increase rather than decrease competition by increasing the ability of disturbance-resistant or disturbance-resilient species to interfere with the recovery of less resistant or resilient species from disturbance. I'm currently testing the hypothesis in three "settings." First, I've applied for funding from NSF to test the hypothesis that fire maintains plant species diversity in wet pine savannas, not just by decreasing interspecific competition, but also by INCREASING intraspecific competition relative to interspecific competition. The idea here is that resource demand increases relative to supply after low intensity fires. Hence, species coexistence may require niche partitioning among species and/or density-dependent negative feedbacks within species. Second, I currently have a paper in press (Ecosphere) demonstrating increased competitive effects of oaks on their neighbors following fires, due to differential resistance to topkill between oaks and their neighbors. Hence, fires increase the competitive effects of non-topkilled oaks on their topkilled neighbors. Finally, I am examining restoration treatments (canopy reduction and fire) can increase resource availability and the competitive effect of rapidly-growing, resilient invasive grass, Microstegium vimineum, on native groundcover species.
Restoration synchrony of fuels and community composition in fire-excluded oak-hickory woodlands in north Mississippi – I am a co-PI on a Joint Fire Sciences Program award to Morgan Varner at Mississippi State University ($138,408 to University of Mississippi; Total Award - $321,011). We have the opportunity with the proposed research to take advantage of an established long-term field experiment to answer complementary restoration and fuels treatment questions. To restore biodiversity and ecosystem processes in mature oak-hickory forests that had experienced prolonged fire exclusion, a restoration experiment was established at Strawberry Plains Audubon Center in the loess plains of north-central Mississippi in 2003. Results to date reveal increases in groundcover plant diversity and abundance of open-woodland indicator plants (Brewer and Menzel 2009), increases in arthropod diversity (Ryndock et al. 2012), and improved conditions for some flammable, warm-season grasses (Maynard and Brewer 2013). In addition, ongoing research is currently examining restoration treatment effects on invasive plant species, amphibian populations, arbuscular mycorrhizae, and nutrient and carbon cycling. Much of this research is being by conducted via a USDA NIFA National Needs Fellowship grant targeted at training graduate students for careers in forest management. The National Audubon Society has provided funding for and the staff at the Strawberry Plains Audubon Center has assisted with treatment implementation.
The anticipated products will include individual publications related to long-term changes in plant community composition and fuels, with a novel, synthetic analysis of the degree of coincidence in recovery of vegetation and fuels across temporal and spatial scales relevant to the region’s managers. We will use our connections with managers via our research experience and involvement in the Mississippi Prescribed Fire Council and the JFSP-supported Southern Fire Exchange (SFE) to mount a vigorous technology transfer program. We will extend our results via field tours at our study sites, via web connections with the SFE consortium, in manager-focused presentations at annual Mississippi Prescribed Fire Council meetings, in peer-reviewed outlets, and at regional and national conferences.
Effects of Natural Disturbances and Salvage Logging on Plant Communities: Implications for Ecological Restoration - I was previously funded through a joint venture agreement with the USDA National Forest Service ($381,711; 2008-2013) to initiate a long-term experiment examining the effects of tornado damage and salvage logging on plant communities in mature oak-shortleaf forests in north Mississippi (specifically, the Tallahatchie Experimental Forest). In February 2008, a tornado struck and damaged about half of the long-term vegetation plots I had previously established in the early 2000s. This natural disturbance provided a rare and unique opportunity to examine both the impact of a natural disturbance on plant communities and the impact of post-storm salvage-logging operations. My previous research in the Tallahatchie Experimental Forest has shown that current composition and stand structure is an artifact of prolonged fire suppression in the past (Surrette, Aquilani, and Brewer 2008). The tornado, however, has created conditions comparable to thinning treatments. Hence, this research determined whether natural disturbances provided an opportunity to move forward with true restoration. This research examined the degree to which such restoration is compromised or negated altogether by salvage logging, with the concern being that the expected positive response of groundcover vegetation and oak regeneration to canopy openings will be eliminated by intense disturbance of the groundcover associated with salvage logging operations. Results so far show that salvage logging in severely damaged stands has a negative effect on open woodland and forest indicative groundcover vegetation and on oak regeneration. We also found that repeated fires in unlogged but damaged stands can be an effective tool for restoring fire-dependent groundcover vegetation and for giving oak saplings a competitive advantage over other species. We are continuing to monitor groundcover vegetation responses to salvage logging and prescribed burning.
Effects of Invasive Plants - I am interested in how environmental conditions (in particular disturbance regimes) influence competitive interactions between invasive species and native species. I recently published a study that showed that invasive plants have the greatest competitive impact on natives in those communities that lack severe disturbance. Hence, severe disturbance may be an inverse indicator of displacement of natives by non-natives. However, I would argue that less severe disturbances (low intensity fires, canopy gaps) that increase resource availability without causing substantial mortality may increase competitive interactions between invasive and native species. I am currently quantifying competitive interactions between the invasive grass, Microstegium vimineum, and groundcover vegetation in oak forests that are currently in the process of restoration to open oak woodlands. My graduate student, Sean Moyer, is currently conducting an experiment to determine if the number and/or degree of habitat specialization of native species groundcover species has an effect on the growth and survival of Microstegium.
I am also currently callaborating with Drs. Giselda Durigan, Flaviana Maluf de Sousa, and Ray Callaway on a trans-continental competition experiment examing the effect of Pinus elliottii (slash pine) on savanna vegetation in its home range in Mississippi and its introduced range of the cerrado of southern Brazil.
Ecological Restoration of Open Oak Woodlands in the Loess Plains of North Central Mississippi - I am continuing a long-term experiment I designed at the Strawberry Plains Audubon Center, which was begun in 2003. I am examining how plant communities respond to the combination of selective thinning of off-site trees (i.e., those that invaded during fire suppression) and biennial prescribed burning during the lightning season. This experiment is the focal restoration project associated with two, consecutive USDA National Needs Fellowship Grants (2008, 2011)for which I am a Co-PI. The ultimate goal of the restoration experiment (which includes replicated sites and controls) is determine the impact of the restoration treatments on biodiversity (plants, fungi, arthropods) and ecosystem processes. Preliminary results reveal positive results in terms of increased plant species richness, increased abundance of open woodland indicators, increased spider diversity, and no increase in weedy disturbance indicators as a group. To date, six students have been supported on Fellowships, with three publications so far.