The legacy of planting: A century-long experiment in forest development at Lehigh University

As global afforestation and reforestation efforts gain momentum, it becomes ever more important to understand the long-term effects of management strategies on secondary forest development. The Lehigh University Experimental Forest (LUEF) is a unique 5.5-ha forest in eastern Pennsylvania that is well poised to inform these forest management efforts. The forest was densely planted with 22 species of evergreen and deciduous tree seedlings in 1915, which were arranged in 43 distinct monospecific or bispecific plots. The LUEF was then left unmanaged for approximately a century, and therefore provides an opportunity to explore the potential long-term implications of planting on the community dynamics of secondary forest. In this study, the community composition and recruitment history of the LUEF were compared to a nearby non-planted control site in order to contrast the effects of planting versus natural succession alone. Results from this comparative ecological study show a strong legacy of planting on the community composition and structure of the forest, even after a hundred years of unmanaged succession. Although both forests are dominated by black birch (Betula lenta L.) and oak (Quercus spp.), community composition was significantly different between the sites, and the planted forest had greater species richness and evenness. Total tree biomass was also greater in the planted forest, mainly due to significantly higher tree density (number of trees per hectare) in the LUEF. Tree species in the planted forest tended to have a clumped spatial distribution pattern whereas species in the unplanted forest tended to be more randomly distributed. Peaks in recruitment of Betula lenta L. occurred synchronously during the 1930s and 1940s in both forests, although there was spatial variability in recruitment patterns. Within the LUEF, there was great variability in recruitment success of originally planted species, but Liriodendron tulipifera L., Tilia americana L., Acer saccharum Marsh., and Pinus strobus L. were particularly successful at maintaining dominance in their plots. Although spatiotemporal patterns of recruitment of different species within the LUEF were species-specific, all tree species show depressed recruitment in the past few decades, likely due to heavy overbrowsing by white-tailed deer (Odocoileus virginianus). The results of this comparative ecological study highlight the need for careful consideration in choosing forest management strategies, as planting decisions leave century-long legacies on composition, biomass, spatial structure, gap dynamics, and recruitment patterns of secondary forest communities. Especially in shifting climate regimes, the unique character of these forests will likely play a vital role in carbon sequestration, biodiversity conservation, resistance to invasive species, and nutrient cycling.