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INFLUENCE ON BIODIVERSITY ON CANOPY PROCESS IN A HARDWOOD PLANTATION FOREST ECOSYSTEM
thesisposted on 28.04.2021, 23:52 by Taylor M Nelson
Increased biodiversity generally enhances terrestrial ecosystem productivity. While niche-use efficiency is thought to drive the biodiversity-productivity relationship, the mechanisms within niche-use efficiency are not well understood. A potential mechanism for niche-use efficiency is nutrient-use efficiency. To measure nutrient-use efficiency, we calculated nitrogen-resorption efficiencies (NRE) because nitrogen is an important growth limiting nutrient for forest productivity. We used a plantation implemented as a full factorial design that included two levels of competition, implemented as different planting densities (one- and two-meter planting densities), and three diversity levels (monocultures, two-, and three-species plantings) that included three hardwood tree species (northern red oak (Quercus rubra), black cherry (Prunus serotina), and American chestnut (Castanea dentata). For our nitrogen-resorption efficiency data, we found that NRE increased as diversity and planting density decreased, but the magnitude of the response varied among species. This outcome suggests that while increased diversity likely provides a release from intra-specific competition, different combinations of species will play a critical role in shaping biodiversity-productivity relationships. Forest nutrient cycling can also be influenced by herbivory. To address the effects of forest diversity on herbivory rates, we monitored rates of foliar damage along with foliar nitrogen content. To measure foliar nitrogen content, we collected spectral data from early, midseason, and late season foliar samples. To assess foliar damage, we collected and imaged leaves from two canopy positions in order to measure late season foliar area and estimate pre damaged foliar area. We found that diversity and foliar nitrogen content have a positive relationship, and diversity does influence canopy damage but the effects vary among species and density. Upon further analysis, we found that foliar nitrogen content and canopy damage are correlated. Meaning individual trees showed a release from intraspecific competition, which lead to an increase in available nutrients and higher canopy quality, showing that stands with higher canopy quality experienced higher levels of damage.