A century-long experiment in forest planting: Preliminary results from the Lehigh University Experimental Forest

Background/Question/Methods

The rediscovery of a 5.5ha experimental forest planted in 1915 on the slopes of Lehigh University’s South Mountain campus provides a unique opportunity to study forest development. The experimental forest was comprised of 43 plots in which a total of 8,000 seedlings of 22 evergreen and deciduous species were planted, with one or two species per plot. To better understand the results of this century-long planting experiment, and assess how differences in the original forest composition may have influenced the subsequent establishment of unplanted native and non-native tree species, we 1) resurveyed and mapped the present-day community composition within the plots, and 2) used dendrochronology to estimate establishment ages for over 800 individuals of the dominant species that were not originally planted.

Results/Conclusions

In 1920, a qualitative assessment of mortality and success was performed, and predicted a starkly different composition than exists today. In fact, only a few of the originally planted species are abundant today (e.g., Liriodendron tulipifera, Acer saccharum), while several non-planted tree species experienced great success (e.g., Betula lenta, Sassafras albidum). However, consistent with general expectations of ecological succession, conifers have decreased in abundance during the past century; this pattern is also evident from historical aerial photographs. Establishment ages demonstrate species-specific patterns of recruitment, with some non-planted species establishing throughout the forest plots within the first few years (e.g., Betula lenta) and other species experiencing later episodes of recruitment (e.g., Sassafras albidum, Acer rubrum, Acer platanoides). However, very few trees established during the past several decades, likely at least in part due to deer browsing. Consistent with this hypothesis, the understory vegetation is dominated by deer-resistant invasives (e.g., Microstegium vimenium, Berberis thunbergii). Plots where planted trees were successful were generally more resistant to invasion of non-planted trees, although exceptions occurred. Understanding the ecological history of this unique planted forest will hopefully inform forest restoration approaches and help us better understand how forest community structure influences invasion.