Tree Mortality Undercuts Ability of Tree-Planting Programs to Provide Benefits: Results of a Three-City Study

Sarah Widney,Jess Vogt,Burnell Fischer

doi:10.3390/f7030065

Sarah Widney, Jess Vogt + Show 1 more

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https://doi.org/10.3390/f7030065

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Abstract

Trees provide numerous benefits for urban residents, including reduced energy usage, improved air quality, stormwater management, carbon sequestration, and increased property values. Quantifying these benefits can help justify the costs of planting trees. In this paper, we use i-Tree Streets to quantify the benefits of street trees planted by nonprofits in three U.S. cities (Detroit, Michigan; Indianapolis, Indiana, and Philadelphia, Pennsylvania) from 2009 to 2011. We also use both measured and modeled survival and growth rates to “grow” the tree populations 5 and 10 years into the future to project the future benefits of the trees under different survival and growth scenarios. The 4059 re-inventoried trees (2864 of which are living) currently provide almost $40,000 (USD) in estimated annual benefits ($9–$20/tree depending on the city), the majority (75%) of which are increased property values. The trees can be expected to provide increasing annual benefits during the 10 years after planting if the annual survival rate is higher than the 93% annual survival measured during the establishment period. However, our projections show that with continued 93% or lower annual survival, the increase in annual benefits from tree growth will not be able to make up for the loss of benefits as trees die. This means that estimated total annual benefits from a cohort of planted trees will decrease between the 5-year projection and the 10-year projection. The results of this study indicate that without early intervention to ensure survival of planted street trees, tree mortality may be significantly undercutting the ability of tree-planting programs to provide benefits to neighborhood residents.

Highlights

100% of the trees in randomly selected block groups were inventoried in Detroit and Philadelphia, while 52% of trees were re-inventoried in Indianapolis
These street trees can be expected to provide increasing annual benefits during the 5–10 years if the annual survival rate is higher than the 93% annual survival measured during the establishment period
The main management implication of this study is that ensuring the survival of planted street trees is most important for providing future benefits; each dead tree represents a loss of $40–$50 in annual benefits for the city each year after the tree dies, while faster growth only increases the annual benefits per tree by $11.30 at the most (Table 10)

Summary

Introduction

Nonprofit organizations and municipalities plant substantial numbers of young trees, sometimes in large tree-planting or canopy campaigns, to increase the provisioning of these benefits for urban residents (e.g., Philly Plant One Million Campaign (in Philadelphia, Pennsylvania), MillionTreesNYC (in New York City, New York), Mile High Million (in Denver, Colorado), etc.). These entities incur significant costs to plant and maintain trees [8,9], yet there is often little. The benefits planting monitoring to assess whether the the trees survive afterafter planting.

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