Land use history, canopy thinning and consumers interact to affect seedling establishment

Background/Question/Methods

Legacies of historical agriculture have persistent and dramatic effects on plant community composition decades to centuries following abandonment. Furthermore, much of the land that is recovering from historic agriculture is in fire-maintained ecosystems that are concurrently experiencing fire suppression. Agricultural land use history and canopy closure related to fire suppression could have interactive effects on plant community composition because both factors are known to regulate seedling establishment, an important determinant of plant community composition, and they have a high degree of spatial overlap throughout North America. Furthermore, interactive effects of land use history and canopy cover on seedling emergence could be either direct, by altering microsite conditions, or indirect by altering the abundance or foraging behavior of seed and seedlings predators.  However, few studies have addressed these factors because of the difficultly of implementing large-scale, multi-factor experiments.  Here, we combined local and landscape experiments to examine the role of land use history (non-agricultural or post-agricultural), canopy thinning (thinned or unthinned), and local consumer exclosures (full exclosures or pseudo-exclosures) on seedling emergence of four species of Asteraceae in longleaf pine woodlands.

Results/Conclusions

We found that two to three of these factors interacted to affect seedling establishment of all four species. Seedling emergence of all four species was affected by the consumer exclosures, although consumer effects always depended on the thinning or land use history treatments. The consumer effects we documented are likely driven by foraging behavior of the dominant consumer guilds (insects or rodents) and availability of alternative resources in the different treatment combinations. Although we found large qualitative differences among species, three of the four species had the greatest establishment in the non-agricultural, thinned, full consumer exclosure treatment combination. Averaging across all other treatments, establishment was greater in non-agricultural than in post-agricultural woodlands, whereas both canopy thinning treatments produced similar establishment rates. By comparing seedling establishment in non-agricultural and post-agricultural woodlands combined with factorial canopy and consumer manipulations, our results provide insight into how consumers interact with landscape features to structure plant communities in contemporary landscapes.  Because canopy thinning and seed additions are common strategies to restore groundlayer vegetation, including many Asteraceae species in the longleaf pine ecosystem, our results can inform restoration practices.