Characterizing Planted Tree Survivorship in the Asian Longhorned Beetle Quarantine Zone in Worcester, Massachusetts

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1 Characterizing Planted Tree Survivorship in the Asian Longhorned Beetle Quarantine Zone in Worcester, Massachusetts John Rogan, Deborah Martin, Arthur Elmes and Michelle Andrews Graduate School of Geography, Clark University, 950 Main Street, Worcester, MA Overview This report draws attention to a unique case within the growing number of city tree-planting programs nationwide; the case of the Worcester region in central Massachusetts where upward of 17 thousand trees have been planted since 2010 to replace those removed in response to the Asian longhorned beetle (ALB) eradication effort. Several governmental agencies including the USDA, the Massachusetts Department of Conservation and Recreation (DCR), and the City of Worcester, as well as a nongovernmental organization called the Worcester Tree Initiative (WTI), were involved in tree planting as a policy response to the infestation and eradication program (Palmer et al. 2014). The DCR was the largest provider of replanted trees, planting about two thirds of the total trees in the program (i.e., about 17,000 trees total between 2010 and present day). Initially, the goal of the DCR program was to plant as many trees as possible in residential areas affected by ALB tree removals (Cahill, pers. comm.). However, this program was soon expanded to provide trees at no-cost in locations that were not directly impacted by the ALB eradication program. The ALB hazard in Worcester notwithstanding, myriad additional factors can influence a given cohort of newly planted urban tree survival vs. mortality. During the first several years after planting (i.e., establishment period (circa 5 years)) trees are most vulnerable to mortality, due to their heightened sensitivity to essential growth requirements and urban stresses. Tree planting site conditions and postplanting maintenance regimes are critical to mitigate mortality of young trees, which is the major driver of urban forest population cycles and tree replacement needs. Biophysical factors impacting urban tree survival vs. mortality include species, size/age, and planting site characteristics. The Clark University Human Environment Regional Observatory (HERO) Program collaborated with the Massachusetts Department of Conservation and Recreation (DCR) in June 2014 to assess the survivorship and condition of the 17,000 trees planted in the Asian longhorned beetle Quarantine zone between 2010 and ,054 trees were sampled for structure, mortality, health and overall condition Figure 1. ALB Field Crew

2 (only trees that had been planted from were surveyed). The tree survey data were analyzed in five phases - geographic/land-use distribution, field data protocol, data distribution, species composition, species/growth form mortality, and future mortality predictive trends. Tree Sampling and Analysis Approach Phase 1 - Tree Sampling Design and Distribution The total number of trees planted by DCR between 2010 and 2013 is 17,000. The Clark University and DCR organizations set a goal to sample a minimum of 1,000 trees over a two-week period in June The two week window was maintained such that the tree health and structure information would be gathered during similar growth conditions, providing a snapshot dataset. The 17,000 tree data set was reduced to 9,000 through stratification by tree species and planting year. This species stratum was randomly sampled to locate a core set of 500 trees. Lastly, the core 500 trees were buffered geographically to encompass as many nearby trees as possible to facilitate efficient sampling. From this group of 1,600, approximately 1,000 were chosen to visit in the field. Overall the field sampling protocol balanced the desire for a random sample, with the need to represent rarer tree species, and with the need to drive to these locations within two weeks. A map of the sampled tree location reveals the trees sampled by Clark University were widely distributed throughout the study area (Figure 2). In terms of land-use, approximately 73% of the trees sampled were located single-family homes, and 9% were contained in institutional land-use such as schools and colleges. Figure 2. Map of planted and sampled DCR trees in the study area, and a graph showing the distribution of the sampled trees by land-use type

3 Phase 2 - Field Plot Sampling Protocol The field sampling protocol was designed by Mat Cahill from the Massachusetts DCR. This protocol considers the Health Characteristics, Mortality Characteristics and Size Metrics for each tree (Figure 3). Figure 3. Example of the field sampling data sheets used in this study Phase 3 - Data Distribution and Analysis 1054 trees were sampled over a broad geographic area and focused primarily on sampling single-family residences. The most common trees in the sample were white fir (7.9%), Northern white cedar, dogwood, blue spruce and serviceberry (Figure 4). The least common trees in the sample were zelkova, scarlet oak, European larch and white oak. Analysis of the entire data set shows that the proportion of shade trees planted increased significantly from Fall 2010 to Spring 2012, at the expense of ornamental trees. Additionally, the analysis revealed that the ornamental trees were preferentially planted in front yards (i.e., dogwood, Japanese lilac and black tupelo) whereas shade trees (predominantly conifers were planted in back yards (i.e., white fir, Eastern red cedar and Northern white cedar).

4 Figure 4. Tree species distribution of all planted trees and sampled trees Most Common Phase 4 - Tree Survivorship Analysis From the sample of 1,054 trees, 75.4% were alive and 24.6% were dead. Of the live trees, 78.4% were in GOOD condition, and 16.5% were in FAIR condition. Only 5.1% of live trees were in either POOR or CRITICAL condition (Figure 5). Considering hardwood vs. conifer growthforms, both showed similar trends in terms of proportion dead vs. alive. The breakdown of survivorship vs. mortality by tree species shows that White Fir had the highest mortality (54%), and was also the most commonly planted tree. In contrast linden, red cedar, dogwood and Japanese lilac experienced mortality of only 10% or less. Serviceberry experienced 26% mortality (Figure 6).

5 Figure 5. Graph showing the proportion of alive vs. dead trees from the sampled data Figure 6. Bar graph showing the proportion of alive vs. dead trees by most common species

6 Phase 5 Mortality Predictions and Ecosystem Services Benefits Analysis and prediction of tree mortality was performed using Fall 2010 (7.3% mortality) and Spring 2010 (10.1% mortality) data, as well as an adjusted mortality rate that accounts for increased tree survivorship through time as trees mature (Figure 7). The adjusted mortality curve indicates that 50% of all trees planted may be dead by 2027 (also known as half-life) (Roman 2014). Figure 7. Mortality graphs indicating a half-life for planted trees in 2027 An assessment of total ecosystem services provided by the replanting cohort (adjusted for mortality rate) over time, in US dollars. The total benefits exceed 10 million dollars. This amounts to a return on investment of $2.29 for every dollar spent to plant the trees. Shade trees offer potential benefits of $250 per tree every year whereas ornamental trees offer $70 per tree every year. The i-tree Tools software was used to calculate these values ( Summary Results of the analysis show that the proportion of ornamental trees planted over the time period decreased significantly compared to shade trees. Ornamental trees were predominantly planted in front yards whereas conifer trees were planted mostly in back yards. Roughly 24% of sampled trees were dead. Of the surviving trees, 78% were in GOOD condition, based on DCR metrics. The breakdown of mortality by tree growth form indicates that 22% of hardwood trees and 30% of conifer trees were dead. According to species, White Fir suffered the highest mortality (i.e., 54%), and it was the most commonly planted tree. Predicted trends indicate that a half-life (i.e., 50% mortality of all trees) is expected in 2027.

7 References itree Palmer, S., D. Martin, V. DeLauer, and J. Rogan, (2014), Vulnerability and Adaptive Capacity in Response to the Asian Longhorned Beetle Infestation in Worcester, Massachusetts. Human Ecology, 42(6): Roman, L.A., (2014), How many trees are enough? Tree death and the urban canopy. Scenario Journal. Scenario p.