Results of the randomized complete block design ANCOVA for ground-cover evenness at the treatment scale by year.

This study examines the complex feedback mechanisms that regulate a positive relationship between species richness and productivity in a longleaf pine-wiregrass woodland. Across a natural soil moisture gradient spanning wet-mesic to xeric conditions, two large scale manipulations over a 10-yr period were used to determine how limiting resources and fire regulate plant species diversity and productivity at multiple scales. A fully factorial experiment was used to examine productivity and species richness responses to N and water additions. A separate experiment examined standing crop and richness responses to N addition in the presence and absence of fire. Specifically, these manipulations addressed the following questions: (1) How do N and water addition influence annual aboveground net primary productivity of the midstory/overstory and ground cover? (2) How do species richness responses to resource manipulations vary with scale and among functional groups of ground cover species? (3) How does standing crop (including overstory, understory/midstory, and ground cover components) differ between frequently burned and fire excluded plots after a decade without fire? (4) What is the role of fire in regulating species richness responses to N addition? This long-term study across a soil moisture gradient provides empirical evidence that species richness and productivity in longleaf pine woodlands are strongly regulated by soil moisture. After a decade of treatment, there was an overall species richness decline with N addition, an increase in richness of some functional groups with irrigation, and a substantial decline in species richness with fire exclusion. Changes in species richness in response to treatments were scale-dependent, occurring primarily at small scales (≤10 m2 ). Further, with fire exclusion, standing crop of ground cover decreased with N addition and non-pine understory/midstory increased in wet-mesic sites. Non-pine understory/midstory standing crop increased in xeric sites with fire exclusion, but there was no influence of N addition. This study highlights the complexity of interactions among multiple limiting resources, frequent fire, and characteristics of dominant functional groups that link species richness and productivity.

Frequency and intensity of fire determines the structure and regulates the function of savanna ecosystems worldwide, yet our understanding of prescribed fire impacts on carbon in these systems is rudimentary. We combined eddy covariance (EC) techniques and fuel consumption plots to examine the short-term response of longleaf pine forest carbon dynamics to one prescribed fire at the ends of an edaphic gradient (mesic and xeric sites). We also introduce novel (to the EC research community) statistical time-series approaches to quantify the drivers of carbon dynamics in these systems. We determined that our mesic site was a moderate sink of carbon (−157.7 ± 25.1 g C m−2 year−1), while the xeric site was carbon neutral (5.9 ± 32.8 g C m−2 year−1) during the study. The fire released 408 and 153 g C m−2 year−1 for the mesic and xeric sites, respectively. When loss associated with fire was combined with net ecosystem exchange rates, both sites became moderate carbon sources for the year. Analyses of assimilation and respiration parameters (e.g., maximum photosynthesis, quantum efficiency, and daytime ecosystem respiration) showed a positive trend over time pre-fire and a negative trend over time post-fire for maximum ecosystem CO2 uptake rates, and the opposite relationship for daytime ecosystem respiration rates. Within 30 days following fire, ecosystem physiological activity was statistically similar to pre-fire and appeared to be driven by the pine canopy. Our results suggest that prescribed fire (low intensity, high frequency) maintains the existing structure and function (in this case, carbon flux rates) because longleaf pine ecosystems have evolved with fire. This study, 1 year in length, provides a foundational understanding of the complex interaction between fire and carbon dynamics for longleaf pine ecosystems. Moreover, it provides a case study for applying time series analysis methods to EC data where there are complex relationships between ecosystem physiological activity and environmental drivers. However, to elicit a broader understanding of the complex interaction occurring between fire and carbon dynamics long- term studies are needed.

The recent focus on restoration of longleaf pine (Pinus palustris Mill.) forests has frequently led to planting longleaf pine on old-field and cutover sites. While many perceptions regarding response of longleaf pine to management are based upon measurements in naturally regenerated stands, it is generally observed that crown development in planted longleaf stands is dissimilar to that observed in natural stands; that is, planted longleaf pine trees tend to have more branches and wider, more “full” crowns at young ages in comparison to naturally regenerated trees. Many planted longleaf stands are reaching the size and age for thinning and with these observed differences in crown characteristics, it is important to explore further whether the response of tree crowns in plantations differs from that of naturally regenerated trees. Few (if any) published studies other than Minor (1951), however, have examined crown dimensions of individual longleaf pine trees as influenced by stand characteristics.

We completed an investigation of the long term legacies of fuels treatments in longleaf pine sandhills at Eglin Air Force Base in the panhandle of Florida. From 1994-1999, The Nature Conservancy conducted a large-scale, long-term study at Eglin Air Force Base to compare the effectiveness of midstory reduction treatments, including herbicide, growing season fire, and mechanical clearing on the restoration of longleaf sandhill pine forests. The study plots have been monitored continuously since the completion of the original study and information still exists for all experimental sites, which have been burned as part of the prescribed fire program at Eglin AFB since the study concluded. We examined the legacy of these treatments on fire behavior 15+ years later in these plots. We measured multiple aspects of fuels and fire behavior in a subset of the original plots using a combination spatially explicit fuel sampling, high resolution visual and thermal imagery, wide and narrow field of view radiometers, thermocouples and thermopiles to collect data on fuel type, fuel loading, radiant and convective heat fluxes. We collected data in nine large operational prescribed fires that included the treatment plots in 2011. Preliminary data analyses showed that the impact of the treatments was not detectable in our measurements. The occurrence of frequent low intensity fires in the treatments appeared to have driven a convergence of fuel characteristics in plots with and without management interventions in as little as 16 years. Within stand variation in overstory derived fuels appeared to be more important in explaining fire behavior than the original treatments. We also completed an investigation of heat transfer in midstory oak stems. While these results are still being analyzed we found that in species with rough bark, heat transfer is much more complex and necessitates the consideration of three-dimensional information on bark topography and surface heating to develop accurate tissue damage models. The data we have collected will allow us to make those improvements. We also have developed a promising means (photogrammetry coupled with IR imagery) to rapidly capture the fine scale surface topography and heating of stems useful for improving such models.

The Climate Action Reserve's Forest Project Protocol Version 3.2 is the current basis for the participation of US-based forest carbon projects in California's cap-and-trade system, yet is largely untested in forests beyond California, particularly those of the southeastern US Coastal Plain. Applying the Protocol to a hypothetical project on a longleaf pine site managed primarily for ecological restoration produced on-site gains of 0.3 mt CO2/ac/yr, but net emissions of 0.8 mt CO2/ac/yr over the project lifetime. These results are based on site-specific conditions (e.g., low stand density) and certain elements of the Protocol (e.g., heavy influence of off-site stocks), highlighting the potential conflict between managing for both climate benefits and ecological restoration on some lands. We recommend that forest owners conduct preliminary analyses to determine whether implementing a carbon project on their forestlands would likely produce their desired results. We further recommend modifications to the Protocol to improve its utility.

John K. Hiers, Robert J. Mitchell, Analie Barnett, Jeffrey R. Walters, Michelle Mack, Brett Williams and Rob Sutter

Longleaf pine (Pinus palustris) savannas of the southeastern U.S. represent an archetype of a fire dependent ecosystem. They are known to have very short fire return intervals (∼1–3 years) that perpetuate understory plant diversity (up to 50 species m−2), support pine recruitment, and suppress fire sensitive hardwoods. Understanding the relationships that regulate longleaf and southern hardwoods is especially critical. With decreased fire frequency, insufficient intensity, or lack of underground competition, a woody mid-story rapidly develops, dominated by fire sensitive trees and shrubs that in-turn suppress more fire dependent species (including pine seedlings). This may occur in forest gaps, where pine-needle abundance is diminished, reducing fire spread potential. The interactions between longleaf pine, hardwoods, forest fuels, and fire frequency are complex and difficult to understand spatially. The objective of this study was to develop a spatially explicit longleaf pine–hardwood stochastic simulation model (LLM), incorporating tree demography, plant competition, and fuel and fire characteristics. Data from two longleaf pine study sites were used to develop and evaluate the model with the goal to incorporate simple site-specific calibration parameters for model versatility. Specific model components included pine seed masting, hardwood clonal sprouting, response to fire (re-sprouting, mortality), and tree density driven competition effects. LLM spatial outputs were consistent with observed forest gap dynamics associated with pine seedling establishment and hardwood encroachment. Changes in fire frequency (i.e., fire probability = 0.35–0.05) illustrated a shift in community structure from longleaf pine dominated to a hardwood dominated community. This approach to assessing model response may be useful in characterizing longleaf ecosystem resilience, especially at intermediate fire frequencies (e.g., 0.15) where the community may be sensitive to small changes in the fire regime. Height distributions and population densities were similar to in situ findings (field and LIDAR data) for both study sites. Height distributions output by the LLM illustrated fluctuations in population structure. The LLM was especially useful in determining knowledge gaps associated with fuel and fire heterogeneity, plant–plant interactions, population structure and its temporal fluctuations, and hardwood demography. This is the first known modeling work to simulate interactions between longleaf pine and hardwoods and provides a foundation for further studies on fire and forest management, especially in relation to ecological forestry practices, restoration, and site-specific applications.

Over the last 10 years, multiple-value, ecosystem-based approaches to management on public forestlands have become more prevalent. However, less attention has been paid to this concept in the private sector. Although it is recognized that nonindustrial private forest (NIPF) landowners own forestland for a diversity of reasons, information on management approaches that seek to more fully meet multiple objectives is needed, particularly for southern US pine forests. Alternatives to plantation management are available, but little information exists on the economic implications so that NIPF landowners can make informed decisions regarding implementation. This study develops a simple economic model as a heuristic tool to compare financial performance of extensive, multiple-value management approaches. The 50-year projection illustrates that, although not equal to more intensive management systems by some economic performance metrics, multiaged, selection-based alternatives can provide substantial net cash flow, maintain significant timber volume, and have comparable total value.

ABSTRACT: Southern old-growth forests are small and rare, but critical in their support of biodiversity. While the remnant old-growth forests contain diversity that is significant regionally and globally, they most likely represent only a portion of the variety that old forests once sustained. High within-habitat diversity and rarity in the landscape magnify the conservation value of these systems. Old-growth stands of two particular communities—longleaf pine (Pinus palustris) forests and floodplain (bottomland/swamp) forests—have emblematic links to two notable bird species of concern, the Red-cockaded (Picoides borealis) and Ivory-billed (Campephilus principalis) Woodpeckers. In addition to conservation importance, southern old forests have social and economic values that are in danger of further impoverishment if these systems are lost to future generations. Summarizing the findings from a recenatus and values, identify current threats, and describe potential strategies to promote greater long-term conservation of old forests across the South.

Fire is a dominant disturbance within many forested ecosystems worldwide. Understanding the complex feedbacks among vegetation as a fuel for fire, the effects of fuels on fire behavior, and the impact of fire behavior on future vegetation are critical for sustaining biodiversity in fire-dependent forests. Nonetheless, understanding in fire ecology has been limited in part by the difficulties in establishing the connections between fire behavior and vegetation response. To address this issue, we present the concept of the ecology of fuels, which emphasizes the critical role that fuels play in conceptually linking feedbacks between fire and vegetation. This article explores the ecology of the fuels concept for longleaf pine woodlands and illustrates its utility by evaluating the principles of ecological forestry (incorporating legacies of disturbances, understanding intermediate stand development processes, and allowing for recovery periods) in this chronically disturbed ecosystem. We review the research behind our understanding of these feedbacks in longleaf pine ecosystems of the southeastern United States and review the applications of these principles through the Stoddard-Neel method of ecological forestry. Understanding these feedbacks is critical for integrating fire ecology and ecological forestry in the Southeast and in other fire-dependent forest types.

In ecosystems with frequent surface fire regimes, fire and fuel heterogeneity has been largely overlooked owing to the lack of unburned patches and the difficulty in measuring fire behavior at fine scales (0.1-10 m). The diverse vegetation in these ecosystems varies at these fine scales. This diversity could be driven by the influences of local interactions among patches of understorey vegetation and canopy-supplied fine fuels on fire behavior, yet no method we know of can capture fine-scale fuel and fire measurements such that these relationships could be rigorously tested. We present here an original method for inventorying of fine-scale fuels and in situ measures of fire intensity within longleaf pine forests of the south-eastern USA. Using ground-based LIDAR (Light Detection and Ranging) with traditional fuel inventory approaches, we characterized within-fuel bed variation into discrete patches, termed wildland fuel cells, which had distinct fuel composition, characteristics, and architecture that became spatially independent beyond 0.5 m(2). Spatially explicit fire behavior was measured in situ through digital infrared thermography. We found that fire temperatures and residence times varied at similar scales to those observed for wildland fuel cells. The wildland fuels cell concept could seamlessly connect empirical studies with numerical models or cellular automata models of fire behavior, representing a promising means to better predict within-burn heterogeneity and fire effects.

Research into the effects of rising atmospheric carbon dioxide (CO2) on plant diseases remains limited despite the economic importance of this subject. Loblolly pine (Pinus taeda) seedlings were exposed to ambient and twice ambient levels of atmospheric CO2 prior to inoculation with the fusiform rust fungus (the obligate pathogen Cronartium quercuum f.sp. fusiforme, CQF) or the pitch canker fungus (the facultative pathogen Fusarium circinatum, FC). Additionally, northern red oak seedlings (Quercus rubra; an alternate host of CQF) were exposed to ambient or elevated levels of atmospheric CO2 prior to inoculation with CQF. In all cases, disease incidence (percent of plants infected) and disease severity (proportion of each plant affected) were determined; with the oak seedlings, the latent period (time to sporulation) was also monitored. In general, disease incidence was decreased by exposure to elevated CO2. This exposure also increased the latent period for CQF on oak seedlings. In no instance did exposure to elevated CO2 affect disease severity. This research demonstrated that plants may benefit from exposure to the increasing concentration of CO2 in the atmosphere through decreases in fungal disease incidence.