The Effects of Plant Spatial Arrangement and Landscape Characteristics on the Establishment of Saplings in Community-Managed Agroforestry in Haiti.

摘要

This dissertation presents seven years of research on creating agroforestry systems for ecological and economic benefits in Haiti, where strong population pressures combined with poor resource management have resulted in severe deforestation.;I examined effects of aggregated vs. intermixed spatial arrangements on competitive interactions between slow growing (Cedrela odorata and Swietenia mahogani) and fast growing ( Delonix regia) saplings. After three years, all species showed significantly greater growth in intermixed spatial arrangements, and Cedrela odorata showed improved survivorship. Benefits of intermixed arrangements were significant even when pairing fast and slow-growing species, and demonstrate the importance of fine scale spatial structure in planting design.;I also explored whether remnant adult trees may act as 'nurse trees' and improve the performance of planted saplings of C. odorata, S. mahogani and D. regia. Adult trees increased survivorship, reduced drought deciduousness, and accelerated seasonal growth onset phenology in planted seedlings. Cedrela odorata showed benefits of association with adult trees within a 10 m radius, while drought-tolerant S. mahogani and D. regia showed benefits up to 30 m away, perhaps due to wind- or sun- sheltering microclimatic effects. Adult trees should be considered as potential establishment nuclei for dry forest restoration projects, and even few remnant trees may improve restoration success.;Finally I used monitoring data from 299 community-based reforestation plots planted with 24 dry forest species from 2007-2008 (∼30,000 saplings). I examined the association between sapling survival and topographical, climatic, and landscape level predictors as well as variables related to restoration techniques. The total number of surviving saplings was strongly correlated with more mesic microclimates, including sites with higher precipitation in dry months, northern exposures, and sites containing more adult `nurse' trees. The results support the reforestation best practices of building micro-catchments and planting reforestation plots with diverse mixes of sapling species. Human community association and year effects were also highly significant.;This dissertation research can inform management decisions on where and how to strategically invest in reforestation in Haiti and similar degraded areas, and provide a model for the use of project-based monitoring and evaluation to improve reforestation strategies.