Past agricultural land use and present-day fire regimes can interact to determine the nature of seed predation

Arthropods and Fire Within the Biologically Diverse Longleaf Pine Ecosystem

The longleaf pine Pinus palustris Miller (Pinales: Pinaceae) ecosystem once covered as many as 37 million hectares across the southeastern United States. Through fire suppression, development, and conversion to other plantation pines, this coverage has dwindled to fewer than 2 million hectares. A recent focus on the restoration of this ecosystem has revealed its complex and biologically diverse nature. Arthropods of the longleaf pine ecosystem are incredibly numerous and diverse-functionally and taxonomically. To provide clarity on what is known about the species and their functional roles in longleaf pine forests, we thoroughly searched the literature and found nearly 500 references. In the end, we tabulated 51 orders 477 families, 1,949 genera, and 3,032 arthropod species as having been stated in the scientific literature to occur in longleaf pine ecosystems. The body of research we drew from is rich and varied but far from comprehensive. Most work deals with land management objective associated taxa such as pests of pine, pests of-and food for-wildlife (red-cockaded woodpecker, northern bobwhite quail, gopher tortoise, pocket gopher, etc.), and pollinators of the diverse plant understory associated with longleaf pine. We explored the complex role frequent fire (critical in longleaf pine management) plays in determining the arthropod community in longleaf pine, including its importance to rare and threatened species. We examined known patterns of abundance and occurrence of key functional groups of longleaf pine-associated arthropods. Finally, we identified some critical gaps in knowledge and provide suggestions for future research into this incredibly diverse ecosystem.

Fire Occurrence Mediates Small-Mammal Seed Removal of Native Tree Species in a Neotropical Savanna

Seed dispersal and predation are critical processes for plant recruitment which can be affected by fire events. We investigated community composition of small mammals in gallery forests with distinct burning histories (burned or not burned ∼3 years before) in the Cerrado (neotropical savanna). We evaluated the role of these animals as seed removers of six native tree species, potentially mediated by the occurrence of fire. We sampled four previously burned sites and four unburned ones. Seed removal was assessed using two exclusion treatments: exclusive access of small rodents and access of all seed-removing vertebrates. The previous burning changed the structural characteristics of the forests, increasing the density of the understory vegetation and herbaceous cover, which determined differences in species composition, richness, and abundance of small rodents (abundance in the burned forests was 1/6 of the abundance in the unburnt ones). Seed removal rates across the six species were reduced in burnt forests in both treatments and were higher for the “all vertebrates” treatment. Other vertebrates, larger than small rodents, played a significant role as seed removers for five of the six species. The effects of fire were consistent across species, but for the two species with the largest seeds (Hymenaea courbaril and Mauritia flexuosa) removal rates for both treatments were extremely low in the burned forests (≦5%). The observed decline in small rodent seed predation in the burned forests may have medium to long-term consequences on plant communities in gallery forests, potentially affecting community composition and species coexistence in these forests. Moreover, fire caused a sharp decline in seed removal by large mammals, indicating that the maintenance of dispersal services provided by these mammals (mainly the agouti Dasyprota azarae) for the large-seeded species may be jeopardized by the burning of gallery forests. This burning would also affect several small mammal species that occur in the surrounding typical savanna habitats but also use these forests. Fire events have been increasing in frequency and intensity because of human activities and climate changing. This current scenario poses a serious threat considering that these forests are fire-sensitive ecosystems within the Cerrado.

Past agricultural land use affects multiple facets of ungulate antipredator behavior

Antipredator behavior affects prey fitness, prey demography, and the strength of ecological interactions. Although predator-prey interactions increasingly occur in habitats that experience multiple forms of human-generated disturbance, it is unclear how different forms of disturbance might affect antipredator behavior. Fire is a contemporary disturbance that has dramatic effects on terrestrial habitats. Such habitats may have also experienced past disturbances, like agricultural land use, that leave lasting legacies on habitat structure (e.g., overstory and understory composition). It is unclear how these past and present disturbances affect the use of different antipredator behaviors, like temporal avoidance and vigilance. We examined whether variation in disturbance regimes generates differences in ungulate antipredator behavior by using cameras to measure white-tailed deer vigilance and activity time across 24 longleaf pine woodlands that vary in past land use and contemporary fire regime. Regardless of land-use history, woodlands with high fire frequencies had 4 times less vegetation cover than low-fire woodlands, generating riskier habitats for deer; however, deer responded to fire with different antipredator strategies depending on land-use history. In nonagricultural woodlands, fire affected deer activity time such that activity was nocturnal in low-fire woodlands and crepuscular in high-fire woodlands. In post-agricultural woodlands, fire affected vigilance and not activity time such that deer were more vigilant in high-fire woodlands than in low-fire woodlands. These results suggest that ungulate antipredator behavior may vary spatially depending on past land use and contemporary fire regime, and such disturbances may generate “landscapes of fear” that persist for decades after agricultural use.

Agricultural land-use history does not reduce woodland understory herb establishment

Agricultural land use is a leading cause of habitat degradation, leaving a legacy of ecological impacts long after agriculture has ceased. Yet the mechanisms for legacy effects, such as altered plant community composition, are not well understood. In particular, whether plant community recovery is limited by an inability of populations to establish within post-agricultural areas, owing to altered environmental conditions within these areas, remains poorly known. We evaluated this hypothesis of post-agricultural establishment limitation through a field experiment within longleaf pine woodlands in South Carolina (USA) and a greenhouse experiment using field-collected soils from these sites. In the field, we sowed seeds of 12 understory plant species associated with remnants (no known history of agriculture) into 27 paired remnant and post-agricultural woodlands. We found that post-agricultural woodlands supported higher establishment, resulting in greater species richness of sown species. These results were context dependent, however, with higher establishment in post-agricultural woodlands only when sites were frequently burned, had less leaf litter, or had less sandy soils. In the greenhouse, we found that agricultural history had no impact on plant growth or survival, suggesting that establishment limitation is unlikely driven by differences in soils associated with agricultural history when environmental conditions are not stressful. Rather, the potential for establishment in post-agricultural habitats can be higher than in remnant habitats, with the strength of this effect determined by fire frequency and soil characteristics.