Effects of overstory density and fertilizer supplement on American chestnut seedlings: Preliminary results

Background/Question/Methods

American chestnut (Castanea dentata) used to dominate many hardwood forests of the eastern United States until a non-native fungus, chestnut blight (Cryphonectria parasitica), all but decimated it in the early part of the 20^th century. There is little experimental evidence about the relative survival and growth performance of American chestnut seedlings under different shade levels and in response to fertilization. We planted 400 pure American chestnut bare root 1-0 seedlings at the beginning of the 2009 growing season in three shade levels replicated three times: open, ca. 50% sweetgum (Liquidambar styraciflua) canopy cover, and ca. 34% canopy cover. Additionally, each seedling was randomly assigned one of three foliar spray fertilizer supplement treatments: no fertilization, single fertilization at the beginning of the first growing season, and seven fertilizations over the first two growing seasons. We examined the change in survival and growth in basal area and height in each treatment two years after outplanting.

Results/Conclusions

Seedling mortality at the end of the second growing season was significantly different (p<0.01) among the treatments. American chestnuts in the open had only 12% survival, which was three to four times lower than the survival of seedlings planted under partial sweetgum shade. Due to the reduced number of seedlings in the open, we compared only the growth of seedlings in the two shade levels. The shade level did not affect any of the growth measures (all p>0.11). Fertilizer, however, had a significant effect on growth in relative root collar diameter (RCD, p=0.086) and relative basal area (BA, p=0.074). Seedlings that were not sprayed increased 41% in relative RCD, compared to a 55% increase of seedlings that were sprayed once. Similarly, seedlings that were not sprayed increased 105% in relative BA, while seedlings sprayed once increased significantly more, 161%. Seedlings that were sprayed seven times over the two growing seasons had intermediate values for both, relative RCD and relative BA growth. Additionally, their growth was not significantly different from either the seedlings sprayed once, or the seedlings that did not receive fertilization.