# RECORD 51b11fac87d973139852a88a8c12a9cdbf87b57a # TITLE: Hedonic Analysis of Forest Pest Invasion: the Case of Emerald Ash Borer # YEAR: 2019.0 VENUE: Forests DOI: 10.3390/f10090820 # AUTHORS: Xiaoshu Li; T. Holmes; Kevin J. Boyle; E. Crocker; C. Nelson # PAGES: 15 CANDIDATE TABLE PAGES (1-based): [7, 10, 11, 12] # ABSTRACT: The emerald ash borer (EAB) was first detected in North America in 2002, and since its introduction, this invasive pest has killed millions of ash trees. While EAB kills native North American ash trees in all settings, its impacts have been especially large in urban areas where ash has been a dominant street tree, especially in residential areas. While some management costs, such as insecticide treatment, tree removal, or tree replacement, are relatively straightforward to compute, the impact that EAB has had on residential property values is less clear. To better understand the economic cost of EAB in urban settings, we conducted a hedonic property value analysis to evaluate the impact of ash tree damages due to EAB infestation on housing sales prices. This study was conducted in the city of Milwaukee, Wisconsin, which had high stocking levels of ash trees prior to EAB’s arrival. The objectives of the study are to investigate: (1) how EAB-infested ash trees affect property values; (2) whether the benefits from healthy ash trees to property value change after arrival of EAB; and (3) whether healthy ash trees located within infested neighborhoods provide the same benefits as the healthy ash trees located outside of infested neighborhoods. In general, our results show that the EAB outbreak has had a negative impact on home values for properties located in close proximity to the ash tree component of the urban forest. This result holds true for neighborhoods where EAB does not yet pose an imminent threat, and is amplified for neighborhoods where EAB has been detected. Our results highlight the early stages of a dynamic economic process that impacts urban residential property owners subject to the risk of EAB or other tree pests and diseases. In general, we find that forward-looking behavior of residential property owners is capitalized into property values during the process of forest pest infestation. ===== PAGE 1 (score 13, numeric-paren 0, table-words 0, var-words 13) ===== Article Hedonic Analysis of Forest Pest Invasion: the Case of Emerald Ash Borer Xiaoshu Li 1,* , Thomas P. Holmes 2 , Kevin J. Boyle 3, Ellen V. Crocker 4 and C. Dana Nelson 5 1 Center for Health Services Research, University of Kentucky, 740 South Limestone, J515 Kentucky Clinic, Lexington, KY 40536, USA 2 Forestry Sciences Lab, Southern Research Station, USDA Forest Service, Research Triangle Park, NC 27709, USA; tom.holmes@usda.gov 3 Agricultural and Applied Economics Department, Virginia Polytechnic Institute and State University, 430A Bishop Favrao Hall, Blacksburg, VA 24060, USA; kjboyle@vt.edu 4 Department of Forestry and Natural Resources, University of Kentucky, 121 Thomas Poe Cooper Building, Lexington, KY 40546, USA; e.crocker@uky.edu 5 Forest Health Research and Education Center, Southern Research Station, USDA Forest Service, 208 Thomas Poe Cooper Building, Lexington, KY 40546, USA; charles.d.nelson@usda.gov * Correspondence: Xiaoshu.li@uky.edu; Tel.: +86-859-323-7078 Received: 29 July 2019; Accepted: 17 September 2019; Published: 19 September 2019   Abstract: The emerald ash borer (EAB) was first detected in North America in 2002, and since its introduction, this invasive pest has killed millions of ash trees. While EAB kills native North American ash trees in all settings, its impacts have been especially large in urban areas where ash has been a dominant street tree, especially in residential areas. While some management costs, such as insecticide treatment, tree removal, or tree replacement, are relatively straightforward to compute, the impact that EAB has had on residential property values is less clear. To better understand the economic cost of EAB in urban settings, we conducted a hedonic property value analysis to evaluate the impact of ash tree damages due to EAB infestation on housing sales prices. This study was conducted in the city of Milwaukee, Wisconsin, which had high stocking levels of ash trees prior to EAB’s arrival. The objectives of the study are to investigate: (1) how EAB-infested ash trees affect property values; (2) whether the benefits from healthy ash trees to property value change after arrival of EAB; and (3) whether healthy ash trees located within infested neighborhoods provide the same benefits as the healthy ash trees located outside of infested neighborhoods. In general, our results show that the EAB outbreak has had a negative impact on home values for properties located in close proximity to the ash tree component of the urban forest. This result holds true for neighborhoods where EAB does not yet pose an imminent threat, and is amplified for neighborhoods where EAB has been detected. Our results highlight the early stages of a dynamic economic process that impacts urban residential property owners subject to the risk of EAB or other tree pests and diseases. In general, we find that forward-looking behavior of residential property owners is capitalized into property values during the process of forest pest infestation. Keywords: emerald ash borer; property value; forward-looking behavior; urban forests; forest health 1. Introduction The emerald ash borer (EAB) was first detected in North America in 2002, and is thought to have been introduced from Asia by packaging materials [1]. Since its introduction, this invasive pest has spread out from Michigan to over 30 states and killed tens of millions of ash trees. EAB is an invasive wood-boring beetle that can kill ash trees within 2–4 years from infestation, as larvae tunnel into the vascular system of the tree and cut offtranspiration of water and nutrients. Ash trees are Forests 2019, 10, 820; doi:10.3390/f10090820 www.mdpi.com/journal/forests ===== PAGE 7 (score 33, numeric-paren 0, table-words 5, var-words 20) ===== Forests 2019, 10, 820 7 of 15 Table 1. Descriptive Statistics of Property Characteristic Variables (n = 4502). (EAB = emerald ash borer). Variable Means Standard Deviations Description Ln(Sale price) 11.642 0.009 Log transformation of sale price ($2005) Living area 1.462 0.010 1000 ft2 Lot size 7.647 0.106 1000 ft2 Baths 1.900 0.012 Number Bedrooms 3.200 0.012 Number Age 65.000 0.372 Home age at sale; Years Stories 1.200 0.006 Number Air conditioning 67% 0.7% 1 if air-conditioned; 0 otherwise Fireplace 32% 0.9% 1 if has fireplace; 0 otherwise Pool 2% 0.2% 1 if a pool present; 0 otherwise Basement area 1.029 0.005 1000 ft2 Garage area 0.410 0.002 1000 ft2 Distance to highway 2.300 0.030 Kilometers Distance to railway 4.700 0.100 Kilometers Distance to Airport 16.800 0.200 Kilometers Water 1% 0.1% Percentage of land covered by water in 1 km buffer of parcel Trees/Forest % 27% 0.1% Percentage of land covered by trees and forest in 1 km buffer of parcel Grass/herbaceous plants % 27% 0.1% Percentage of land covered by grass & herbaceous plants in 1 km buffer of parcel Ash_parcel 31% 0.7% 1 if ash trees on the parcel; 0 otherwise Ash_buffer0.1 30% 0.2% Percentage of properties located within 0.1 km buffer of parcel that have ash trees Ash_buffer0.5 28% 0.2% Percentage of properties located within 0.5 km buffer of parcel that have ash trees Ash_buffer1.0 27% 0.1% Percentage of properties located within 1 km buffer of parcel that have ash trees EAB_parcel 0.002 0.001 Number of EAB infested ash trees within the parcel EAB_buffer0.1 0.047 0.011 Number of EAB infested ash trees within 0.1 km buffer of parcel EAB_buffer0.5 1.217 0.142 Number of EAB infested ash trees within 0.5 km buffer of parcel EAB_buffer1.0 3.803 0.298 Number of EAB infested ash trees within 1 km buffer of parcel post 0.620 0.007 1 if sale occurred after 2011; 0 otherwise outbreak 0.033 0.003 1 if EAB infested ash tree within 1 km of parcel Within the study area, roughly equal proportions of the land area within 1 km of sales properties were covered by trees/forest and grass/herbaceous plants (27% each; Table 1). Nearly one third (31%) of sales parcels contained ash trees, and similar proportions of parcels within buffers up to 1 km surrounding sales parcels also contained ash trees (27–30% of parcels). These statistics suggest that, in terms of the ash component of the urban landscape, sales parcels were generally representative of other residential parcels within the study area. The summary statistics which describe the spread of EAB are listed in Table 2. These measurements were based on the field surveys consistently conducted over four years. It shows that 16 ash trees were infested in 2012, with 34 infested trees in 2013, 240 infested trees in 2014, and 528 infested trees in 2015 (Table 2). The sizes of the infested ash trees ranged from 3 to 40 inches, with a mean of 17.0 inches. However, very few EAB-infested trees occurred on sales properties. In 2015, there were only four property sales with infested ash trees identified on the parcel. If we assume the sale price could be impacted by the EAB infested ash trees located within a 1 km buffer, there would be 222 property sales impacted in 2015. ===== PAGE 8 (score 10, numeric-paren 0, table-words 2, var-words 6) ===== Forests 2019, 10, 820 8 of 15 Table 2. The Number of emerald ash borer (EAB) Infested Ash Trees and Impacted Properties with Sales. Year Total EAB Parcel Buffer 0.1 km Buffer 0.5 km Buffer 1 km 2012 16 0 1 13 32 2013 34 1 7 29 66 2014 240 0 12 81 164 2015 528 4 34 137 222 Total 5 54 260 484 4. Model Specification 4.1. Traditional Hedonic Model A fixed-effect hedonic model was estimated to address the potential for spatially correlated omitted variables in the model specification. The base model used to estimate the effects of ash trees ln Pit = Ziα + Liβ + Ashiγ + τt + ωi + σit (1) where Pit is the sale price for property i at time t, Zi is a vector of property-specific characteristics and distance measurements, measurements (distance to road, railway, and airport) are included in the model in both linear and quadratic functional forms, τt is the time fixed-effect for the year of sale, ωi is the spatial fixed effect specified based on the zip code of the sales property, and σit is the equation error. This model is estimated for the years 2008–2011 to test the hypothesis that ash trees enhanced residential property values prior to the EAB outbreak. After the outbreak of EAB, the damages from EAB infestation would impact the property sales. In Model 2, we constructed a fixed-effect hedonic model following the previous literature, which linked the forest pest infestation together with property sale values. ln Pit = Ziα + Liβ + EABitδ + τt + ωj + σit (2) The property sale data for estimating Model 2 run from 2012 to 2015. A statistically significant negative coefficient estimate associated with EABit would suggest that the presence of infested trees in the vicinity of residential properties decreases property value. The model is separately estimated for each of the four different spatial specifications—parcel level, and the 0.1 km, 0.5 km, and 1.0 km buffers (Table 1). 4.2. Quasi-Experimental Design A limitation of the Model 2 specification is that it does not provide information on whether the capitalized value of the entire stock of ash trees is affected by the EAB outbreak. After the arrival of EAB, both infested and healthy ash trees had the potential to affect property values. This limitation is addressed in Model 3, which estimates whether a structural change occurred in the capitalized value of ash trees after the arrival of EAB. We construct a difference-in-difference model following the quasi-experiment design, which could test the specific treatment effect by comparing the changes in sale prices before and after the outbreak of EAB between the properties with ash trees in the neighborhood and the other properties in the study area. The property sale data for estimation is from 2008 to 2015. The hypothesis being tested here is that the presence of infested ash trees within a 1 km buffer of the sales parcel provides a signal that other ash trees near the property are at risk of becoming infested in the near future. ln Pit = Ziα + +Liβ + Ashiγ + Ashi ∗posttρ + Ashi ∗outbreakitθ + τt + ωj + σit (3) ===== PAGE 10 (score 204, numeric-paren 162, table-words 2, var-words 20) ===== Forests 2019, 10, 820 10 of 15 Table 3. Coefficient Estimates of Hedonic Model 1, Home Sales 2008–2011 (N = 1710). Variable Parcel Buffer 0.1 km Buffer 0.5 km Buffer 1 km Living area 0.212 *** 0.214 *** 0.215 *** 0.214 *** (0.029) (0.029) (0.029) (0.029) Lot size 0.006 *** 0.004 ** 0.004 ** 0.004 ** (0.001) (0.002) (0.002) (0.002) Baths 0.069 *** 0.070 *** 0.068 *** 0.068 *** (0.014) (0.014) (0.014) (0.014) Bedrooms 0.010 0.008 0.010 0.008 (0.012) (0.012) (0.012) (0.012) Age −0.002 *** −0.002 *** −0.002 *** −0.002 *** (0.0004) (0.0004) (0.0004) (0.0004) Stories 0.082 *** 0.084 *** 0.081 *** 0.083 *** (0.029) (0.029) (0.029) (0.029) Air conditioning 0.105 *** 0.106 *** 0.105 *** 0.105 *** (0.015) (0.015) (0.015) (0.015) Fireplace 0.092 *** 0.089 *** 0.091 *** 0.092 *** (0.016) (0.016) (0.016) (0.016) Pool 0.014 0.007 0.013 0.011 (0.052) (0.052) (0.052) (0.052) Basement area 0.125 *** 0.131 *** 0.124 *** 0.127 *** (0.037) (0.037) (0.036) (0.036) Garage parking area 0.329 *** 0.323 *** 0.325 *** 0.324 *** (0.049) (0.049) (0.049) (0.049) Distance to highway 0.041 *** 0.043 *** 0.044 *** 0.043 *** (0.014) (0.014) (0.014) (0.014) Square Distance to highway −0.007 *** −0.007 *** −0.007 *** −0.007 *** (0.002) (0.002) (0.002) (0.002) Distance to Railway −0.036 *** −0.034 *** −0.032 *** −0.030 *** (0.011) (0.011) (0.011) (0.011) Square Distance to Railway 0.003 *** 0.003 *** 0.003 *** 0.003 *** (0.001) (0.001) (0.001) (0.001) Distance to Airport −0.030 *** −0.030 *** −0.028 *** −0.028 *** (0.006) (0.006) (0.006) (0.006) Square Distance to Airport 0.001 *** 0.001 *** 0.001 *** 0.001 *** (0.0002) (0.0002) (0.0002) (0.0002) Water 0.151 0.132 0.059 −0.009 (0.322) (0.321) (0.323) (0.326) Trees/Forest 1.664 *** 1.514 *** 1.437 *** 1.429 *** (0.206) (0.211) (0.225) (0.220) Grass/herbaceous plants 0.517 *** 0.461 ** 0.440 ** 0.454 ** (0.194) (0.194) (0.196) (0.195) Ash 0.005 0.165 *** 0.757 ** 0.380 *** (0.015) (0.056) (0.095) (0.129) constant 10.678 10.700 *** 10.665 *** 10.539 *** (0.154) (0.154) (0.154) (0.161) Adjust R2 0.7558 0.7570 0.7567 0.7570 Note: *** denotes significant at the 1% level, ** denotes significant at the 5% level, * denotes significant at the 10% level. Standard errors in parentheses. ===== PAGE 11 (score 24, numeric-paren 5, table-words 7, var-words 4) ===== Forests 2019, 10, 820 11 of 15 5.2. After the Outbreak of Emerald Ash Borer (EAB) The presence of EAB-infested trees in nearby locations, combined with media attention given to the growing outbreak, likely raised awareness among city residents that the entire stock of ash trees in Milwaukee was at risk of infestation and death. This type of forward-looking behavior might be detected in sales data, where EAB-infested ash trees are located in relatively close proximity to sales properties. As the impact of nearby EAB-infested ash trees on home sales prices may be rather subtle, a substantial number of observations that possibly include forward-looking behavior would be needed to detect a measurable effect with statistical significance. Within our data, this possibility is suggested, as the number of property sales within 0.1–1 km of EAB-infested trees ranges from 54 to 484 observations, respectively, representing roughly 2–17% of the 2792 sales after the EAB outbreak. Model 2 includes EAB detections in the model specification, and results indicate that residents in the general vicinity of known EAB detections were negatively impacted in terms of property values by the outbreak (Table 4). While results are only statistically significant at the 1 km buffer level, and the impacts per tree on housing price are rather small, this result may reflect an inadequate number of impacted property sales to detect significant impacts for the other buffer levels. However, Model 2 suggests that nearby EAB detections provide a signal to homeowners that ash resources in their neighborhood are at risk of infestation. Table 4. Coefficient Estimates of Hedonic Model 2, emerald ash borer (EAB) Detections, 2012–2015 (n = 2792). Variable Parcel Buffer 0.1 km Buffer 0.5 km Buffer 1 km EAB 0.0006 0.0055 −0.0005 −0.0006 *** (0.054) (0.0060) (0.0005) (0.0002) Adjusted R2 0.7737 0.7738 0.7738 0.7742 Note: *** denotes significant at the 1% level, ** denotes significant at the 5% level, * denotes significant at the 10% level. Standard errors in parentheses. Model 3 provided a more nuanced test of the hypothesis that residential property owners were forward-looking and perceived a risk that healthy ash trees on, or close to, their property may become infested in the future. The results of Model 3 estimation generally indicated that the capitalized value of the entire stock of ash trees located near sales properties decreased as the EAB infestation spread (Table 5). Two measures illustrate this result. First, by summing the coefficient estimates obtained for ash trees over the entire study period (γ) and during the post-outbreak period (ρ), a diminishment in the capitalized value of ash trees is observed that is statistically significant within each of the buffer zones (Sum 1 = γ + ρ). For example, prior to the EAB outbreak, a one percentage point increase in the number of properties containing ash trees located within 0.5 km of sales properties increased property values by about 0.76% (Table 3). However, after the outbreak began, the marginal percentage increase in home value from properties containing ash located in that buffer was only about 0.20%. Both of these parameter estimates are significant at the 0.01 level. Second, adding the parameter estimate for the variable indicating that an EAB infected tree had been located within 1 km of the sales parcel to the previous measure (Sum 2 = γ + ρ + θ) can be seen to further reduce the capitalized value of ash trees. The existence of a healthy ash tree would no longer statistically beneficial to the community. ===== PAGE 12 (score 86, numeric-paren 65, table-words 5, var-words 2) ===== Forests 2019, 10, 820 12 of 15 Table 5. Coefficient Estimates of Hedonic Model 3 for Ash and emerald ash borer (EAB) variables, 2008–2015 (n = 4502). Variable Parcel Buffer 0.1 km Buffer 0.5 km Buffer 1 km Ash 0.007 0.183 *** 0.298 *** 0.393 *** (0.016) (0.049) (0.075) (0.101) Ash*Post −0.002 −0.066 −0.102 −0.204 ** (0.020) (0.056) (0.077) (0.098) Ash*Outbreak −0.021 −0.066 −0.093 * −0.095 * (0.028) (0.048) (0.051) (0.054) Adjusted R2 0.7647 0.7657 0.7658 0.7657 Sum 1 −0.005 0.117 *** 0.196 *** 0.188 ** γ + ρ (0.040) (0.042) (0.064) (0.090) Sum 2 −0.026 0.050 0.103 0.093 γ + ρ + θ (0.043) (0.059) (0.078) (0.100) Note: *** denotes significant at the 1% level, ** denotes significant at the 5% level, * denotes significant at the 10% level. Standard errors in parentheses. In Model 4, which includes the severity of EAB outbreak within a 1 km buffer in the model specification, it is noted that the coefficient estimates for Ash*Outbreak are still negative but no longer significant (Table 6). This is due to a high degree of correlation between this interaction variable (indicating the occurrence of EAB) and the severity of an EAB outbreak (the number of infested trees). Further, the negative effects from EAB-infested ash trees within a 1 km buffer are shown to be significant at the parcel level and all buffer levels. These results suggest that one additional EAB-infested ash tree within a 1 km buffer of a property decreases sales price by 0.1%. Based upon the average home price, this result suggests that the decrease in sales price due to one additional EAB-infested ash tree within a 1km buffer is about $114. Looking at estimates of Sum 1 and Sum 2, it can be seen that these coefficient estimates are similar to those estimates from Model 3 and indicate that the capitalized value of nearby stocks of ash trees diminished after the onset of the EAB outbreak. Table 6. Coefficient Estimates of Hedonic Model 4, Ash and emerald ash borer (EAB), 2008–2015 (n = 4502). Variable Parcel Buffer 0.1 km Buffer 0.5 km Buffer 1 km Ash 0.007 0.182 *** 0.301 *** 0.393 *** (0.016) (0.049) (0.075) (0.101) Ash*Post −0.005 −0.070 −0.104 −0.210 ** −(0.020) −(0.056) −(0.077) −(0.098) Ash*Outbreak 0.001 −0.011 −0.033 −0.044 (0.029) (0.054) (0.058) (0.060) EAB_Buffer3 −0.001 *** −0.001 ** −0.001 ** −0.001 * (0.0002) (0.0003) (0.0003) (0.0003) Adjusted R2 0.7650 0.7659 0.7660 0.7658 Sum 1 −0.011 0.112 *** 0.198 *** 0.183 ** γ + ρ (0.040) (0.042) (0.064) (0.090) Sum 2 −0.010 0.100 0.164 ** 0.139 γ + ρ + θ (0.044) (0.063) (0.083) (0.103) Note: *** denotes significant at the 1% level, ** denotes significant at the 5% level, * denotes significant at the 10% level. Standard errors in parentheses. ===== PAGE 13 (score 8, numeric-paren 0, table-words 0, var-words 8) ===== Forests 2019, 10, 820 13 of 15 6. Discussion and Conclusions In our study, we conducted a hedonic analysis to investigate the impacts of the outbreak of EAB on household property values in Milwaukee, Wisconsin. Our results show that, in general, tree cover was positively capitalized into property values, and that prior to the arrival of EAB, ash trees added a premium to the general value of tree cover. Although this value premium is not found for ash trees located on individual sales parcels, it is consistently found for ash trees located at various buffer distances in surrounding neighborhoods, suggesting that healthy ash trees (as well as tree cover of general types of urban forest) provide a public good that is capitalized into home values. It is suggested that the ash tree premium may be due to their widespread use as street trees within the study area. Notably, the value premium attributed to ash trees throughout the study area (northern 10 zip codes in Milwaukee) is dramatically diminished after the arrival of EAB infestation. This result holds true for the entire study area, whether or not EAB-infested trees were found near sales properties, and suggests that homeowners have forward-looking expectations regarding tree health in their neighborhoods. These expectations are capitalized into diminishing values for ash trees. In general, static models that only evaluate the impacts from existing damages to trees from insects and diseases will likely produce downwardly-biased damage estimates in cases where biological invasions are expanding. Although the capitalized value of ash trees diminished during the study period, our estimates suggest they still contributed positive value to homeowners. This result may reflect the fact that preventive measures, such as the use of insecticides, can protect ash tree health. Or, this result may also reflect the fact that our study was conducted during the early stages of the EAB outbreak. Whether or not ash trees retain a positive capitalized value during the later stages of an invasion is unknown. However, we note that previous research has indicated that once an insect invasion reaches a threshold value, all host trees, regardless of health condition, are capitalized into negative values by homeowners [21]. The fact that our Milwaukee case study represents just one of many urban forested areas impacted by EAB suggests that further analysis of this problem is warranted to help urban forest managers understand the trade-offs between the cost and benefits of protective management activities. While treatment ash trees are implemented on a two-year cycle in Milwaukee, there have not yet been enough trees replanted for the lost ones. The plan is to replace removed ash trees with diverse species of trees that are more resilient to biotic stressors and climate change. In our study, the outbreak of EAB in Milwaukee is still in the early stage. Therefore, we did not consider the replacement programs in the analysis. It will generally take a long time for the newly-planted trees to grow back. The replacement programs should be able to increase property value in the long run. This would also warrant further hedonic study to investigate the benefits from replacement management practices. Our study result is highly flexible and useful for other non-native forest insects and pathogens. In the evaluation studies of these long-lasting effects, more studies examining the dynamic response of property values from invasive species are needed. Not only the tree health conditions, but also the treatment and replacement procedures could impact property sale values, as they could potentially change the expectation of property values based on our analysis results. Tracking the change of property value related to invasive species during all the stages, including infestation, removal, treatment, and restoration, would be useful to guide long-term management plans. The EAB infestation is posing a significant threat of reduction in ecosystem services provided by ash tree canopies. The value estimates from the hedonic model represent the portion of value of ecosystem services provided by ash trees to the family residential properties, including largely aesthetic views, recreational opportunities, and cultural values of trees. Comparing the estimates from ash trees before and after the EAB infestation, we would be able to check the degradation of these ecosystem services. However, the total economic value of benefits from numerous ecosystem services provided by ash trees are not captured in the hedonic study. Further studies are needed to investigate the reduction of value for other types of ecosystem services from EAB infestation, such as carbon sequestration, reductions in stormwater runoff, or wildlife habitat.