The Residential Urban Forest: Linking structure, function and management
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Vegetation provides a suite of ecosystem functions (e.g., carbon storage) which are partially determined by the forest structure. In urbanizing regions, homeowners play a key role in shaping the structure of the urban forest because residential land is the dominant land use. As cities expand, the influence of single-family residents' land management on urban forest structure and function will increase because most new urban development is in this land use. Yet, we know little about the structure, functions, and dynamics of highly managed residential parcels. I focus on the Seattle Metropolitan Region to examine the patterns of urban forest that emerge from the interactions between biophysical factors and backyard land management attitudes of homeowners and the implications for current and future carbon storage. I use urban gradient analysis and plant functional trait classification systems to (1) characterize the forest structure on single-family residential lots in urban and suburban areas, (2) investigate factors associated with decisions to plant or remove trees and how these management actions have altered and will continue to transform the forest structure over time, and (3) estimate the current and future carbon storage benefits based on reported management actions and considerations. I use two functional plant traits--height potential at maturity and leaf senescence-- selected based on their sensitivity to management decisions and for their role in controlling ecological functions (e.g., carbon cycling). Suburban parcels had more trees than those in the urban area. However, after accounting for parcel size there was no significant difference in tree densities. Compared to suburban residences, urban residential landscapes have significantly fewer trees with large size potential and more deciduous trees with small size potential. Trees with large size potential contribute the majority of the carbon storage benefits, consequently urban residential landscapes store less carbon (as aboveground plant biomass). Surprisingly, the tree planting and removal activities of residents during their tenure resulted in no significant change in tree density. However, increase in total carbon storage in suburban lots will be insignificant from the expected increase in small deciduous trees.
- Urban planning