Groundcover effects on establishment of American chestnut (Castanea dentata) on an experimentally reclaimed surface mine
Existing vegetation cover on reclaimed strip mines may work in two diametrically opposed ways; inhibition and facilitation. Herbaceous groundcover may facilitate desirable tree establishment by ameliorating harsh site conditions through soil shading which aids in moisture retention and temperature control or through nutrient addition via root turnover or atmospheric nitrogen fixation. This same groundcover may also inhibit native tree establishment through competition for limited soil resources or by providing cover for small rodent predators during early succession. Here, vegetation cover levels were manipulated (control, mowing, herbicide) to examine their effects on survival, growth, rodent-damage incidence, and above and below ground biomass of American chestnut (Castanea dentata) seedlings. The research site is located in Belmont County, Ohio and was reclaimed using compaction-reducing techniques designed to aid in hardwood tree establishment. Previous studies conducted at the site have shown this method to be effective at aiding hardwood tree establishment. 180 one year-old seedlings were planted in April 2014 (60 per treatment) with growth, survival, and rodent damage incidence was measured in late October 2014. Logistic regression was used to examine the effects of treatments on survival and rodent damage incidence. Growth rates were compared across treatments using one-way ANOVA.
Vegetation cover level had a significant effect on 1-year survival of American chestnut seedlings (Wald test: Χ 2 = 17.2, df = 2, P < 0.01). Odds ratio of survival showed the greatest increase in the mowing treatment but herbicide treatments also positively increased survival odds but the increase was non-significant. Identity of the dominant type of ground-cover vegetation did not significantly affect seedling survival or growth. Dominant groundcover was determined to be the species with highest percent cover in the square meter surrounding each planted seedling. Growth rates were significantly higher in the mowing treatments compared with the control (F=12.2, df =2, P < 0.02). Incidence of rodent damage did not differ significantly across treatments. These results support previous observations that some level of vegetative cover has a positive effect on seedling survival but the mechanism remains unclear. Environmental measurements (soil temperatures and moisture levels) at the site along with excavations to determine biomass allocation (i.e., are seedlings in higher-cover treatments allocating resources below-ground to increase soil-resource uptake?) will hopefully allow greater insight into the competitive interactions at the site as well as providing important management insights