Patterns of biodiversity and the mechanisms driving them must be thoroughly understood to guide an effective monitoring and resource management program. In addition, other dimensions of biodiversity along with new diversity metrics, such as interaction diversity, can act as more sensitive indicators of how ecological communities respond to management activities, disturbances, or global change parameters. These detailed measures of diversity, combined with knowledge of theoretical and mechanistic underpinnings of diversity, then must be made relevant for managers of natural resources. This combination of diversity pattern, process, and management has been the overarching theme of the SERDP RC-2243 project. The strategy outlined below shows how the research team divided their activities into three sub-themes: 1) cross-scale spatial and temporal patterns of diversity; 2) fine-scale examination of the role of fire in driving patterns of diversity; and 3) coarser-scale linkages useful for expanding mechanistic understanding to landscape and management relevant scales.
These themes both framed the research and were tactical; the project was large and complex and it was an efficient and effective strategy for guiding the research activities. The research team adopted this framework for the final report not because they executed three independent projects, but rather because each topic area was crucial for understanding the mechanisms linking fire, biological diversity and forest structure. Understanding these links mechanistically is critical for both guiding management now and in the future under the novel conditions expected with global change. The research team have completed all the planned activities and broadened the project in three important areas: fuel and fire behavior spatial dynamics and fuelbed modeling without adding any additional costs. While the research team has completed all promised analyses and syntheses, the work reported here will form the foundation for several new avenues of research being actively pursued. The research team was also mindful that the focus of the research was to produce management applications. They saw the challenge as generating applied knowledge and tools that have a solid mechanistic and theoretical foundation.
This table shows examples of how the project has generated both basic and applied knowledge for science and management.
One major focus of RC-2243 was aimed at identifying the mechanisms driving the relationship between fire and fine-scale patterns of diversity. The research team has hypothesized and has empirical evidence to support that at one end of the fire frequency spectrum, the high plant diversity found at very fine scales is driven by stochastic community assembly processes. This was not because researchers were joining the more than 5000 studies that have cited Hubbell’s influential 2001 book on the unified theory of biodiversity and biogeography (or the 20,000+ publications on neutral theory), but because researchers hypothesized that the mechanisms that ecologists have identified as neutral processes (e.g., random mortality and recruitment limitation) are the actual drivers of the patterns of biodiversity that have been observed. These processes affect more than just a simple number count of species, they affect multiple dimensions of diversity, including genetic, taxonomic, functional, and interaction biodiversity. Understanding these mechanisms will allow researchers to make realistic predictions on the impacts of management on biodiversity. Because the research team has developed new ways to measure spatial and temporal patterns of fire energy release, they believe they have identified the mechanistic key to understanding how so many species coexist in such proximity in a nearly uniform substrate. Fuels such as grasses and pine needles dominate fire spread in frequently burned longleaf ecosystems and most plant species survive exposure to the burning of these fuels; the longleaf flora is dominated by perennial species and species composition post fire on the whole generally mirrors what was present prior to fire. However, fuels that burn for longer periods such as pine cones and tree branches release considerably more energy concentrated in a small area. This energy release represents the agent of random mortality key to neutral community dynamics. Researchers also know that when fire is excluded, diversity declines and this process is not random, but predictable as certain species are released (e.g. woody plants) and competitively exclude other species. This represents a clear deviation from neutrality. Reconciling these processes has been described as the “Continuum Hypothesis” (Gravel et al. 2006), which posits that different disturbance regimes or scales, allow for both neutral processes and significant deviations from neutrality to affect diversity.
There are aspects of this work that if continued will contribute substantively to both basic ecological theory and very practical guidance for management of Department of Defense (DoD) forests. The unified neutral theory of biodiversity has never been tested as effectively and thoroughly as this research team has done for diversity of all plants and as they are doing for total ecosystem plant-insect diversity. Additionally, the chemical ecology of fire has never been fully explored by collaborations between chemists and ecologists. This project yielded data to examine the null models that comprise neutral theory and to demonstrate how deviations from neutrality are structured by moving away in space and time from fire. This work also provides unprecedented insight into the spatial and temporal scales needed to assess the impact of fire management on maintaining sustainable levels of biodiversity. This project also laid the ground work for future chemical ecology research to examine how variation in longleaf pine chemistry and variation in plant chemistry across longleaf pine understory plants can contribute to fire intensity and maintenance of plant-insect biodiversity. These are exciting areas of research for fire ecology and for understanding effective management of diverse and interesting ecosystems managed by the DoD.
This project focused on understanding mechanisms driving diversity and community dynamics in pristine habitats. This was crucial for understanding how a fully functioning, intact ecosystem operated. This approach was successful in clarifying how these systems function but also identified topics that could be of interest to DoD land managers. For example, the approach could be used to model the impact of military training on changes in fire behavior and fuels, but would need further work to incorporate the impact of soil disturbance and vegetation disturbance that occur at multiple scales.