Human land use can leave long-lasting legacies: effects that persist after the land use ends and ecosystems begin to recover. Yet, whether and how ecosystems ultimately recover remains unclear and this leads to uncertainty about the need for, and outcome of, active restoration to promote recovery following human land use conversion. Moreover, studies of land-use legacies and restoration have largely focused specific taxa or abiotic responses; there is a need for synthetic studies to understand the broader implications of past and present-day land use. We conducted a large-scale field experiment to understand the interplay of historical agriculture and contemporary restoration within longleaf pine savannas in the southeastern United States. Our experiment featured a factorial combination of agricultural history (plots with and without a history of agriculture) and restoration tree thinning across 126, 1-ha plots. Within each plot, we measured properties spanning four categories: abiotic conditions (e.g., light availability, temperature, soil chemistry), species richness (soil fungi and bacteria, bees, grasshoppers, small mammals, and plants), abundance (ants, bees, grasshoppers, small mammals, plants), and species interactions (rates of herbivory, pollination, and granivory). For these properties, we asked: 1) What is the legacy of agriculture? 2) What is the response to restoration? and 3) Does a legacy of agriculture alter the outcome of restoration?
Results/Conclusions
Agricultural history tended to increase the abundance of individuals (Hedge's g effect size: 0.36), but had inconsistent effects on abiotic factors, diversity, and interactions. Restoration thinning strongly increased diversity and abundance, with these effects tending to be stronger in remnant plots (without agricultural history; diversity effect size: 1.07, abundance effect size: 1.25) than in post-agricultural plots (diversity effect size: 0.83, abundance effect size: 0.95). Restoration thinning tended to decrease levels of species interactions, with this effect slightly stronger in post-agricultural (-0.43) than remnant plots (-0.32) and had inconsistent effects on abiotic conditions. These results lead to several conclusions. First, agricultural legacies had large effects on individual abiotic conditions but these varied in direction, leading to no net effect for this category. Second, the effects of restoration were generally stronger than were effects of agricultural history, particularly for the diversity and abundance of species, which were strongly positively affected by restoration. Finally, some responses to restoration were stronger in remnant than post-agricultural areas, particularly for species diversity and abundance. These findings illustrate the promise of restoring post-agricultural ecosystems, with benefits spanning a variety of abiotic and biotic properties.