Dale G. Brockway

Long-term effects of dormant-season prescribed fire on plant community diversity, structure and productivity in a longleaf pine wiregrass ecosystem

Abstract A flatwoods longleaf pine wiregrass ecosystem, which regenerated naturally following wildfire in 1942, on the Coastal Plain of southern Georgia was treated over a period of four decades with prescribed fire at annual, biennial and triennial intervals during the winter dormant season. Burning caused substantial changes in the understory plant community, with significant reductions in the foliar cover of Ilex glabra in the shrub layer resulting in corresponding increases in the cover of Vaccinium myrsinites, Sporobolus curtissii, Aristida stricta and Andropogon spp. Understory plant species richness, diversity and evenness also increased as a result of periodic fire. Dormant-season burning decreased the cover of litter on the forest floor and significantly increased the standing biomass of A. stricta, S. curtissii, Andropogon spp., all other grasses and all forbs. Recurrent fire also prevented the development of a vigorous midstory, that impedes understory growth and poses a serious fire hazard to the stand. Overstory trees were largely unaffected by burning. Historical light grazing on the site produced no measurable effects on the plant community. Findings suggest that the biennial burning interval results in declines of I. glabra in the shrub layer and litter cover on the forest floor, leading to the largest increases in understory plant species richness and diversity and the biomass productivity of grasses and forbs. Although flatwoods plant communities evolved in environments characterized by growing-season fires of variable frequency, long-term application of dormant-season fire is also recommended as a useful option for sustaining resource values in this and similar longleaf pine wiregrass ecosystems.

Gap-phase regeneration in longleaf pine wiregrass ecosystems

Abstract Naturally regenerated seedlings of longleaf pine are typically observed to cluster in the center of tree fall canopy gaps and be encircled by a wide zone from which they are generally excluded. Twelve representative canopy gaps distributed across 600 ha of a naturally regenerated uneven-aged longleaf pine forest in the sandhills of north central Florida were examined to determine which aboveground and belowground factors are responsible for development of this seedling exclusionary zone. Within 12 m of adult trees growing along the gap edge, significantly fewer longleaf pine seedlings were present. The canopy of overstory trees, however, extended only 4–5 m into the gap. The relatively open structure of the longleaf pine canopy (57% cover) allowed photosynthetically active radiation (PAR) to be evenly distributed upon the forest floor across each canopy gap. Thus, light availability was not related to pine seedling clustering near gap centers. Significantly greater forest litter mass beneath adult trees (5 Mg ha −1 ) could result in fires more intense than would be supported by the litter mass near gap centers (2.5 Mg ha −1 ). However, litter mass was significantly elevated only within 4 m of the gap edge. The fine root biomass within 12 m of the gap edge (3–4.5 Mg ha −1 ) was two to six times that measured near the gap center and most closely coincided with the width of the seedling exclusionary zone along the margin of each gap. Thus, while the canopy of adjacent adult trees may indirectly influence seedling mortality through deposition of needle litter and greater fire intensity within 4 m of the gap edge, the root systems of these adults also appear to directly compete with seedlings within 12–16 m of the gap edge for limited site resources. To effectively regenerate and sustain longleaf pine wiregrass ecosystems, caution should be used in prescribing single-tree selection harvest methods so as not to create gap openings so small (

Restoring longleaf pine wiregrass ecosystems: hexazinone application enhances effects of prescribed fire.

A longleaf pine wiregrass ecosystem in the sandhills of north central Florida, upon which turkey oak gained dominance following a wildfire, was treated with applications of hexazinone (1.1 or 2.2 kg/ha) in May 1991. All applications successfully reduced competition from oaks in the overstory and understory (mortality >80%), resulting in progressive increases in the foliar cover of wiregrass, all graminoids and forbs through time. Broadcast application caused a decline in forb cover and species richness during the initial growing season, which recovered by the following year. The 2.2 kg/ha spot application resulted in an increase in species richness, while evenness declined with the continuing expansion of wiregrass. The entire site was then burned in June 1995 by prescribed fire, which caused a widespread decrease in the cover of oaks, shrubs, wiregrass, all graminoids and forbs and plant species richness. In the following year, forb cover increased and oak cover remained significantly lower on plots treated with the combination of hexazinone plus fire than on fire-only plots. The overall cover of forbs, graminoids, shrubs and longleaf pines continued to increase through time. Broadcast application initially exposed a greater number of understory plants to direct contact with herbicide, posing a higher mortality risk than may be acceptable in restoration efforts. Although recovery occurred in subsequent years, the lower selectivity of broadcast application makes it a less suitable restoration technique. Spot application of hexazinone was more selective in its effects upon the plant community. The 2.2 kg/ha spot application produced increases in the cover of wiregrass, all graminoids and forbs and the highest levels of species richness and diversity. The 2.2 kg/ha application rate was also most effective in controlling woody plant competition and is therefore recommended for restoring longleaf pine wiregrass ecosystems in sandhills and similar environments. Hexazinone application followed by prescribed fire accelerates the rate of ecosystem restoration over that achievable by using fire alone. The ecological benefits of controlling competition and rebalancing floristic composition rapidly achieved through this combination of treatments would likely require many cycles of prescribed fire, if used as an individual treatment, over a period of several decades.

Longleaf pine regeneration ecology and methods

Regenerating longleaf pine (Pinus palustris) is key to its long-term sustainable production of forest resources and its perpetuation as the dominant tree species in a variety of important ecosystems ranging from xeric to mesic to hydric site conditions. Early regeneration to problems and the subsequent efforts to overcome these are significant features of the continuing longleaf pine saga. This chapter discusses recent restoration relevant to longleaf pine regeneration, disturbance dynamics including fire as an ecological process and describes the uniqueness of longleaf pines regeneration environment.

Restoring longleaf pine wiregrass ecosystems: plant cover, diversity and biomass following low-rate hexazinone application on Florida sandhills

A longleaf pine wiregrass ecosystem in the sandhills of north central Florida, upon which turkey oak gained dominance following a wildfire, was treated with low-rate (1.1 or 2.2 kg/ha) applications of the herbicide hexazinone during the 1991 growing season. All applications successfully reduced oak in the overstory and understory, mortality ranging from 83 to 93%. The declining competition from oaks was associated with progressive increases in foliar cover of wiregrass, all graminoids and forbs over time. Plant species diversity declined in the initial year, but recovered by the second growing season. Species richness increased overall, while evenness declined with the continuing expansion of wiregrass. Initial increases in the standing biomass of wiregrass did not persist beyond the second growing season. The broadcast application method exposed a greater number of understory plants to contact with hexazinone, resulting in initial declines in forb cover, species richness and diversity. Although recovery was noted in subsequent years, because of lower selectivity this broadcast application method is not recommended as a restoration technique. Spot application of liquid hexazinone was generally more selective in its effect upon the plant community. The 1.1 and 2.2 kg/ha application rates, while producing an initial year reduction in diversity and evenness, resulted in increases in the cover of all graminoids and forbs and the highest species richness. While both application rates are useful, the 2.2 kg/ha application is most effective in controlling woody plant competition and stimulating increases in wiregrass and is therefore recommended for restoring xeric sandhills and similar longleaf pine wiregrass ecosystems.

Forest plant diversity at local and landscape scales in the Cascade Mountains of southwestern Washington

Old-growth forests in the Pacific Northwest are known to support high levels of diversity across the varied landscapes they occupy. On 1200 plots distributed over the Cascade Mountains in southwestern Washington, climatic, physiographic, edaphic and floristic data were collected to evaluate the ecological characteristics of these coniferous forests and develop a classification framework useful in land management. The resulting abundance of data provided a unique opportunity to analyze plant diversity relationships at multiple levels and identify the environmental and biotic factors which influence diversity at local and landscape scales. Plant species richness and diversity were generally lower in communities characterized by environmental extremes (i.e., excessive or scarce moisture and severely cold high elevation) than in mesic environments at low-to-middle elevations. Evenness among plant species was greatest at higher elevations, where severe climate limited the ability of any single or group of species to dominate. Species turnover rates were also higher near the environmental extremes. High turnover rates among mountain hemlock associations were attributed to highly variable topography and local microclimates which resulted in substantial geographical isolation and species specialization among site types. Moisture appeared to have the most influence on species richness (alpha diversity) and sequential turnover rates (beta diversity) at high elevations, where available water is seasonally limited by low temperatures. Temperature had the greatest influence on overall species turnover (gamma diversity) throughout the landscape. Species richness of the landscape (epsilon diversity) was quite accurately predicted (within 7% for temperature and moisture gradients) by a computational method which uses independent measures of alpha, beta and gamma diversity. Patterns of forest plant diversity appear to be the result of environmental conditions at larger scales and the complex interactions among biological and physical variables at smaller scales, within an historical context of stochastic disturbance events. Managers wishing to restore and sustain the high diversity characteristic of these old-growth coniferous forests will need to consider the respective roles of various biophysical factors and the disturbance dynamics in these unique ecosystems.

Analyzing the complexity of cone production in longleaf pine by multiscale entropy

Abstract The longleaf pine (Pinus palustris Mill.) forests are important ecosystems in the southeastern USA because of their ecological and economic value. Since European settlement, longleaf pine ecosystems have dramatically declined in extent, to the degree that they are now listed as endangered ecosystems. Its sporadic seed production, which limits the frequency of natural regeneration, is identified as a significant factor in this decline. Previous studies did not characterize the complexity in cone production. Here a method of multiscale entropy is used to analyze long-term data for cone production in longleaf pine forests at six sites across its native range. Our results indicate that there exists a regime shift for cone production at each site. The corresponding time scales of the regime shift are generally 1–9, 10–12, 13–16, and 17–24 yr. Overall patterns for the complexity of cone production with the change of time scale are similar among sites, with exception of the Red Hills (FL). There are high correlations between entropy of cone production and entropy of annual mean air temperature and annual total precipitation at all sites. These results provide new insight into the complexity of cone production of longleaf pine forests with significant management implications.

Restoring a legacy: longleaf pine research at the Forest Service Escambia Experimental Forest

Longleaf pine ecosystems are a distinct part of the forest landscape in the southeastern USA. These biologically diverse ecosystems, the native habitat of numerous federally listed species, once dominated more than 36.4 million ha but now occupy only 1.4 million ha of forested land in the region. The Escambia Experimental Forest was established in 1947 through a 99-year lease with the T.R. Miller Mill Company of Brewton, AL, to explore all aspects of longleaf pine management. The 1,214-ha tract in southwest Alabama constitutes a unique example of longleaf pine ecosystems in all stages of development. Long-term studies and demonstrations include stand management alternatives, growth and yield of even-aged natural stands, cone production, and fire ecology.

Temperature-related sex allocation shifts in a recovering keystone species, Pinus palustris

Background: The possible effects of climate change on sex allocation of a species have recently emerged as a topic of interest, relative to population sustainability via natural regeneration. Also, the universality of pollen limitation for reproduction and how climate may influence it in different taxonomic groups remain to be explored. Aims: The aim of this study was to examine how climate fluctuation may affect sex allocation in Pinus palustris. Methods: We used a long-term observational data on P. palustris (1957–2014), including pollen, female conelets and cone production. Results: We found that, unlike cone production with its ca. 3-year cycle, (1) pollen (male) and unfertilised conelet (female) production did not exhibit any temporal cycles, (2) pollen and unfertilised conelet production showed lower variation than cone production, (3) pollen and unfertilised conelet production were positively correlated to one another and to final cone production, (4) an optimal male-to-female sex allocation ratio exists for promoting cone production and (5) sex allocation ratio was positively correlated with temperature. Conclusions: Our findings shed new light on both the reproductive ecology and management of P. palustris ecosystems under changing climates (e.g., through alteration of pollen density and thus the resulting sex allocation).