190 Jack-Scott et al.: How Community Group Dynamics Affect Street Tree Survival and Growth own sense of accomplishment (Abbott 1995; Millar 2003; Lee and Hancock 2011). Little empirical research exists, however, examining the traits of planting groups with successful plantings. The most easily defined aspect of success is the sur- vival and health of trees planted. Variability in mortal- ity rates across community groups is complex, with hid- den causes easily overlooked (Abbott 1995). Nowak et al. (1990) found that mortality was highest in neighborhoods with high levels of unemployment, around public housing and apartment buildings (low homeownership), but not as- sociated with race. Dwyer et al. (2002) highlighted the need for further research into the roles of community groups, gov- ernment agencies, and non-profits in street tree survival. The main objective of this study was to provide empirical data on the role of community planting groups in the survival and growth of urban street trees. Community group dynamics such as size, longevity, type (park, public housing, block watch, and more), planting experience (number of trees planted previ- ously), and related neighborhood traits (existing canopy cover, and homeownership rate) were examined. Based on existing research regarding volunteer motivations and group cohesion, it was hypothesized that higher rates of growth and survival would be observed when planted by groups with larger group size, more tree planting experience, and greater group longevity. The same was also hypothesized for groups in neighborhoods with greater existing canopy cover and homeownership rates. Finally, groups with missions in line with urban greening (namely park groups) were hypothesized to have greater growth and survival than those without (i.e., public housing and social service groups). METHODS Site Description Trees surveyed were planted between 1995 and 2007, through the Urban Resource Initiative’s Community Greens- pace program in New Haven, Connecticut. New Haven is located along the northern coast of the Long Island Sound, an estuary of the Atlantic Ocean in southern New England. New Haven has an area of 48.9 km2 and an elevation of 10 m. It has a temperate climate, with average summer tem- peratures in July at 23.3°C and average winter temperatures in January at -1.4°C; receiving a total of 116.8 cm of rain at a steady rate throughout the year. It has a citywide aver- age tree cover of 38% (Pelletier and O’Neil-Dunne 2009). The Urban Resources Initiative (URI) is a non-profit orga- nization that has planted trees in New Haven since it was es- tablished in 1991. Its Community Greenspace program works with groups comprised of interested residents and volunteers on group-initiated planting sites. Groups carry out planting and maintenance with URI tools, planting materials (including trees), mulch, and technical assistance in the form of a trained intern from the Yale School of Forestry and Environ- mental Studies. Intern reports are compiled each year, chroni- cling all tree plantings and locations, forming a unique and valuable database of community-planted street trees. After a number of active years, groups may opt into a designated stewardship program called the Emeritus program, in which they may discontinue planting trees but continue to receive support in the form of tools, mulch, and intern consultations. ©2013 International Society of Arboriculture Sampling Design and Data Collection Reports indicate that between 1995 and 2007, 134 of URI’s Greenspace groups planted a total 1560 trees. In the summer and autumn of 2011, these trees were located and measured for survival and growth indices, including diameter at breast height (DBH) and percent live crown. DBH was divided by the num- ber of years since planting (approximate age of the tree) in order to calculate mean annual growth increment. Percent live crown (the length along the main stem from top height of the tree to the lowest living branch divided by the total height of the tree) was measured using the percent scale on a clinometer (Suunto PM-5, Forestry Supplies, Jackson, Mississippi, U.S.). Both in- dices can be used to evaluate tree vigor and health, with higher rates and percentages indicating healthier trees. Each plant- ing site was also noted as a street (curbside), yard, park, or va- cant lot site—and results were analyzed within each site type. Community group data was gathered from annual intern re- ports, including group size, group planting longevity, group type, group focus, and geo-political neighborhood. Group size signified the average maximum number of volunteers recorded per plant- ing season as having participated with each community group. Group longevity represented the number of planting seasons each group participated in the Greenspace program. Group experi- ence was measured by how many trees the group had planted, both during each planting season and overall. Group types were categorized as apartment, block watch, business, church, neigh- borhood management team, neighborhood resident, park, public housing, school, or social service/non-profit. Based on geo-po- litical neighborhood boundaries, existing tree canopy cover was determined for each group using aerial imagery and GIS. Home- ownership rates were also determined by census block group for each community group using the national decadal 2000 Census. Statistical Analysis Statistical analysis was done using R statistical software and language (Crawley 2007). Trees were analyzed within site type so that street trees were compared to street trees, yard to yard, park to park, and vacant lot to vacant lot. This was done in or- der to minimize potentially covariate biophysical factors (such as available growing space), and highlight the targeted social factors affecting tree survival and growth. Mortality data was analyzed using logistic regression (Takano et al. 2002), and mul- tiple linear regressions were used to analyze mean annual growth increment and percent live crown data (Tomé and Burkhardt 1989). Mean annual growth increment data was normalized us- ing a log transformation. Percent live crown data was normal- ized with an arcsine-square root transformation (street, yard, and park trees), and a log transformation (vacant lot trees) to account for skewed values in the 70%–80% range. A forward selection procedure was done to isolate significant factors, used in regres- sion trees as a visual aid to determine significant interaction effects. Explanatory variables included tree age, tree function (shade versus ornamental), community group planting longevity, group planting experience, group type, existing neighborhood canopy cover, and census block group percent homeownership. RESULTS A total of 1393 trees (89%) were located and measured. The re- maining 167 trees not found were either removed due to con-
July 2013
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
