The introduction of non-native species impacts forest ecosystem functions in urban areas, changing plant community composition, and therefore, the plant-soil relationships that facilitate nutrient cycling integral to ecological functions. In 2007, the city of New York launched the MillionTrees NYC initiative, a large afforestation plan to plant a million trees in the metropolitan area and expand the urban canopy by 2,000 acres to combat invasive species by permanently closing canopy gaps and restoring native vegetation. From 2009-2011, tree saplings were planted in 15m x 15m experimental plots with four different species palettes and planting combinations of herbaceous vegetation and shrubs at 10 urban forests with different soil composition and previously invaded by non-native species (e.g. Rosa multiflora). One meter soil cores were taken to examine soil processes beyond the organic horizon and determine exchangeable nitrate (NO3-) and ammonium (NH4+) pools, net mineralization and nitrification, microbial respiration, microbial biomass carbon (C) and nitrogen (N), and total soil C and N at different depths. This study provides a deep analysis of how soil conditions in urban forests affect N uptake by microbial communities, which lower rates of N transformations and losses from the system that affect plant community development and growth.
Results/Conclusions
The preliminary results show vast differences in soil controls (e.g. pH) and characteristics across sites. Forest soils consisting of well-drained mixture of loamy fill and construction debris, with proportions of coarse fragments (>2 mm diameter) ranging from 10% to more than 75%, including 5 to 10% gravel (2 to 76 mm) have pH ranges from strongly acid to neutral. While forest soils consisting of moderately well to well-drained loam or sandy loam, acidity ranges from strong to moderate. Moreover, sites with construction debris demonstrated high tree mortality, suggesting that soil characteristics strongly influence the ability of plant communities to take up nutrients. In all sites, planted shrubs (e.g. Amelanchier canadensis, Dyospiros virginiana) were more likely to survive (70-100%), with up to 1080% increase in combined root collar area in sandy loam soils, than tree species (e.g Nissa sylvatica, Quercus bicolor). However, tree survivorship at hydric sites are more uniform among different species with high success rates of over 80%. This suggest that shrubs are more likely to grow in degraded soil, this is also supported by high C and N levels (4.5 ppm, 45 ppm respectively) in degraded soils. This suggest that greater availability of C decrease N losses in forest soils.