This study evaluated the hypothesis that urban-tree planting increases neighborhood gentrification in Portland, Oregon. We defined gentrification as an increase in the median sales price of single-family homes in a Census tract compared to other tracts in the city after accounting for differences in the housing stock such as house size and number of bathrooms. We used tree-planting data from the non-profit Friends of Trees, who have planted 57,985 yard and street trees in Portland (1990–2019). We estimated a mixed model of gentrification (30 years and 141 tracts) including random intercepts at the tract level and a first-order auto-regressive residual structure. Tract-level house prices and tree planting may be codetermined. Therefore, to address potential endogeneity of tree planting in statistical modeling, we lagged the number of trees planted by at least one year. We found that the number of trees planted in a tract was significantly associated with a higher tract-level median sales price, although it took at least six years for this relationship to emerge. Specifically, each tree was associated with a $131 (95% CI: $53–$210; p-value = 0.001) increase in tract-level median sales price six years after planting. The magnitude of the association between the number of trees planted and median sales price generally increased as the time lag lengthened. After twelve years, each tree was associated with a $265 (95% CI: $151–$379; p-value<0.001) increase in tract-level median sales price. Tree planting was not merely a proxy for existing tree cover, as the percent of a tract covered in tree canopy was independently associated with an increase in median sales price. Specifically, each 1-percentage point increase in tree-canopy cover was associated with a $882 (95% CI: $226–$1538; p-value = 0.008) increase in median sales price. In conclusion, tree planting is associated with neighborhood-level gentrification, although the magnitude of the association is modest.

这项研究评估了俄勒冈州波特兰市城市植树促进社区中产阶级化的假设。我们将中产阶级化定义为在考虑了房屋面积和浴室数量等住房存量的差异后，与城市其他地区相比，人口普查地区的单户住宅中位数销售价格的上涨。我们使用了非营利组织“树木之友”的植树数据，该组织已在波特兰种植了 57,985 棵庭院树和行道树（1990 年至 2019 年）。我们估计了高档化的混合​​模型（30 年和 141 个区域），包括区域级别的随机截距和一阶自回归残差结构。区域层面的房价和植树可能是共同决定的。因此，为了解决统计模型中植树的潜在内生性，我们将植树数量滞后了至少一年。我们发现，一块土地上种植的树木数量与较高的土地平均销售价格显着相关，尽管这种关系至少花了六年的时间才出现。具体来说，每棵树在种植六年后与区域级中位销售价格增加131 美元（95% CI：53-210 美元； p值 = 0.001）相关。随着时间滞后的延长，种植树木的数量与销售价格中位数之间的关联程度通常会增加。12 年后，每棵树与区域级中位销售价格增加 265 美元（95% CI：151-379 美元；p 值<0.001）相关。植树不仅仅是现有树木覆盖率的代表，因为树冠覆盖的土地百分比与中位销售价格的上涨独立相关。具体来说，树冠覆盖度每增加 1 个百分点，中位售价就会增加882 美元（95% CI：226-1538 美元； p值 = 0.008）。总之，植树与邻里阶层的高档化有关，尽管这种关联的程度不大。