No abstract

Summary 1We identified species with low re-colonization potential, which could be used as indicators of recovery of species-rich pine savannas, by comparing the ground-cover flora of a 64-year-old slash pine plantation (recovery site) with that of a nearby natural longleaf pine savanna (reference site). We also determined life-history traits that were useful predictors of recolonization potential. 2 The high floristic overlap in species between reference and recovery sites and similar species richness at scales ≥ 10 m 2 suggests that substantial vegetation recovery occurred over the 65-year period. However, for areas < 10 m 2 the lower species packing in the recovery sites indicates that coexistence of a high number of species at small scales is dependent on local dispersal and establishment, and may take much longer to achieve. 3 The absence, or near absence, of some species from the recovery site, even after 65 years, suggests that some species may be particularly vulnerable to disturbance and may re-establish infrequently, if ever. Several dispersal distance-restricted species were identified that require active reintroduction. While no particular guild of species was a strong indicator of recovery in this study, we identified a group of species that assess the absence of or the degree of recovery from, prior soil disturbance. 4 Local dispersal appears to be an important factor structuring species richness patterns in pine savannas. Limitations of dispersal distance in some species, particularly those with gravity and ant-dispersal mechanisms, represent an obstacle to passive restoration that can only be overcome either by introduction of propagules in the restoration process or by allowing for longer periods of recruitment. 5 This study demonstrates a method for identifying a suite of species that may be unsuccessful at recolonization. The method would be applicable to numerous degraded ecosystems, particularly similar species-rich savannas, grasslands and forests.

Woody plants in fire‐frequented ecosystems commonly resprout from underground organs after fires. Responses to variation in characteristics of fire regimes may be a function of plant physiological status or fire intensity. Although these hypotheses have been explored for trees in southeastern longleaf pine (Pinus palustris) savannas, responses of other life forms and stages have not been studied. We examined effects of fire season and frequency, geography, habitat, and underground organ morphology on resprouting of shrubs. In 1994, we located replicated sites, each containing two habitats, upslope savannas and downslope seepages, in Louisiana and Florida. Each site, which contained quadrats located along transects within a 30 × 60 m plot, was burned either during the dormant or growing season and then reburned similarly two years later. Maximum fire temperatures were measured, and densities of shrub stems were censused in quadrats before and after fires. Shrubs collectively resprouted more following dormant than growing‐season fires, regardless of habitat or geographic region. After repeated dormant‐season fires, collective densities in seepages of both regions and densities of root‐crown‐bearing shrubs in Florida seepages were greater than those initially and after repeated growing‐season fires. Shrub responses were generally unrelated to fire temperatures, supporting the hypothesis that resprouting of shrubs may be more dependent on their physiological status at the time of fires. There was, nonetheless, an inverse relationship between collective and root‐crown‐bearing shrub densities following repeated fires and maximum fire temperatures in Florida seepages. Anthropogenic dormant‐season fires over many decades may have resulted in increases in shrub densities in longleaf pine savannas, especially seepages. Repeated growing‐season fires, however, neither increased nor reduced densities of established shrubs. Long‐term shifts in characteristics of fire regimes, even in fire‐frequented habitats, may produce effects that are not reversible in the short term (<10 yr) by simply reintroducing prescribed fires that resemble those that occurred naturally during the growing season.

Resource availability and planted longleaf pine (Pinus palustris Mill.) seedling and understory vegetation response within and among three sizes of experimentally created canopy gaps (0.11, 0.41, 1.63 ha) in a mature longleaf pine savanna were investigated for 2 years. Longleaf pine seedlings and understory vegetation showed increased growth in gaps created by tree removal. Longleaf pine seedling growth within gaps was maximized approximately 18 m from the uncut savanna. Increased longleaf pine seedling survival under the uncut savanna canopy observed after the first year suggests that the overstory may facilitate establishment of longleaf pine seedlings rather than reduce survival through competition. Despite the relative openness of the uncut longleaf pine forest, light quantity was increased by tree removal. Light was also the resource most strongly correlated with seedling and understory vegetation growth. Although net N mineralization was correlated to seedling response, the amount of variation explained was low relative to light. Belowground (root) gaps were not strong, in part because of non-pine understory roots increasing in biomass following tree removal. These results suggest that regeneration of longleaf pine may be maximized within gap sizes as small as approximately 0.10 ha, due largely to increases in light availability.