Understanding how past agricultural land use and contemporary afforestation affect plant communities is important because both activities are widespread, both activities can dramatically affect biodiversity, and areas that remain for biodiversity conservation are likely to have a history of agricultural use, contemporary afforestation, or both. One mechanism whereby past agricultural land use and afforestation might affect plant establishment is by altering the nature of below-ground competition that seedlings experience, as past agricultural land use may alter soil physical properties and nutrient levels, and afforestation affects the potential for below-ground competition with trees. However, despite the importance of understanding the role of past agricultural land use and afforestation on plant establishment, their roles in affecting belowground competition remain poorly understood. We conducted a large-scale experiment to investigate the role of land-use legacies from cultivation agriculture and afforestation on seedling establishment within the longleaf pine ecosystem. By planting seeds within root exclosures, we measured the strength of belowground competition on seedling establishment and biomass allocation for multiple plant species (Coreopsis major, Vernonia angustifolia, Eupatorium cuneifolium, Silphium compositum) in sites crossing two factors: with or without cultivation land-use histories, and with high or low tree density from afforestation or canopy tree thinning.
Results/Conclusions
Belowground competition strongly limited seedling establishment for 3 of 4 herbaceous understory species (Coreopsis major, Vernonia angustifolia, Eupatorium cuneifolium) and the strength of this effect did not vary with different land-use histories. In addition, seedling establishment was also affected by an interaction between land-use history and tree density, which was especially important immediately after seedling emergence. Coreopsis major and Eupatorium cuneifolium allocated relatively more biomass to stems and less to leaves when tree density was high and Vernonia angustifolia species allocated more biomass to roots only when belowground competition was present in low tree density remnant habitat. Belowground competition, land-use history, and canopy thinning all acted early in the growing season to drive patterns of establishment success, but weakened as the growing season continued. This work highlights the strong role that belowground competition plays in limiting establishment. It also underscores the importance of considering land-use history in restoration management plans as the outcome in sites with low and high tree densities depended on land-use history. Finally, we recommend further investigation of the mechanisms underpinning restoration success during early establishment.