| dc.description.abstract | Urban forest patches (UFPs) are small, naturalized areas that persist in the built environment. Previously regarded as self-sustaining “wild” areas, UFPs are gaining attention as valuable resources that can deliver important ecoservices such as air cooling and cleaning, stormwater filtering and absorption, and even associated public health and education benefits. UFPs, however, face challenges that hinder their ability to spontaneously regenerate and consequently threaten their longevity. Preserving UFPs and securing the services they provide necessitates identifying appropriate management methods to establish the next generation of the forest’s trees. Most additions to the urban forest are planted, but in natural areas that approach is expensive, carries an environmental impact and may compromise existing ecosystems. Identifying means to encourage the forest to regrow itself, or naturally regenerate, may be a viable and more appropriate solution.
My research evaluated the viability of Assisted Natural Regeneration (ANR), a restoration approach established in large scale, rural projects, as a management method for small scale, urban forests. ANR engages local community members to offset barriers to regeneration, thus allowing the forest to spontaneously regenerate. In a 2.2-acre forest patch in Washington, D.C., I recruited a team of community volunteers and we collectively deployed ANR by applying site treatments and providing monthly maintenance over two growing seasons to canopy gaps and edges. Our site treatments included clearing, soil disturbance, mulching, and tree planting. For maintenance, each month of the growing season, we clipped non-tree material to below 4” and tagged seedlings for protection and identification.
The site treatments did not significantly differ in their effect on the regeneration of native seedlings (in either count or diversity), but of 48 2x2 meter plots, 85% demonstrated regeneration, for a total of 428 surviving seedlings. Compared with a control site where no maintenance or treatments were applied, the ANR plots recruited an average 2.6 seedlings/m2 versus 0.125 seedlings/m2 in the control plots (ANOVA, F= 9.44, p=.0032, n=60). There was no significant difference in native seedling diversity between the ANR plots and the control plots.
I compared our ANR technique with a traditional planting to evaluate the two methods in terms of social, economic, and environmental costs and gains. The ANR plots yielded more spontaneous regeneration, recruiting an average 2.6 seedlings/m2 versus 1.8 seedlings/m2. The cost per seedling using ANR (absent planted trees) was about $.06; it was $43.22 in the planted area. The ANR plots engaged more than 41 volunteer participants with over 500 volunteer hours, but there was no community participation in the planted area. The ANR plots (excluding those planted with trees) required no watering, but the planted area used 383.3 gallons/m for the trees in the planted area. Planting carries an inherent carbon footprint for transportation and maintenance, but greenhouse gas emissions can be avoided with ANR depending on volunteer locations and transportation decisions. Cumulatively, the data showed that ANR had fewer financial and environmental costs and greater community engagement than traditional planting. | |
