Healthy Trees, Healthy Cities (HTHC) is a partnership between the US Forest Service and The Nature Conservancy that seeks to protect the health of our nation’s trees, forests, and communities. HTHC’s goal is to create a culture of stewardship that engages people in long-term stewardship and monitoring of the trees in their respective communities. Through our mobile app, users can participate in a nationwide citizen science effort studying urban tree health, learn how to care for trees in their community, and track stewardship efforts for trees.

The Healthy Trees, Healthy Cities app can easily incorporate and work with existing tree inventories, and data can be cross-walked across multiple platforms. When an inventory is loaded, the app can auto-populate a user’s Nearby Trees list allowing a user to select a specific tree from the inventory. This insures that any new information is   linked to the correct tree. The app also allows users to add trees, by adopting existing trees not already in the app or by planting a new tree. Once added, the tree and its data become visible to all users and data managers.

Stewardship of trees planted in urban areas is a critical component of longevity (Lu et al., 2010). The Tree Care module of the app allows users to record stewardship activities, with a drop-down menu for the most common options and an open-ended notes section for unlisted activities and for project-specific details. This module can be a resource for local volunteer groups to help track and plan stewardship activities in their areas. The records of tree care can also be linked to tree health data, and can be used to find correlations between tree care and individual and community-wide tree health. The tools available for tree stewardship and the data generated in the app complement the research being done on environmental governance and civic engagement and will assist in research. Future plans include linking data from STEW-MAP to make it easy for local stewardship groups to find and manage the trees they care for.

The health check follows the methods laid out by Pontius & Hallett, 2014, using standardized ocular measurements that match the natural range of values for each variable to species specific distributions and normalize all variables so they can be combined into one continuous decline summary variable. The standardization process translates each value into a probability distribution score based on the mean and variability of values on a species level. In this way, several stress symptoms can be equally weighted, standardized to the same scale and combined into one continuous summary value (Pontius & Hallett, 2014). This continuous summary value is also used to generate a Stress Index value on a 0-10 scale, designed to be more easily translated by everyday users.

During the last century, urban and rural trees have been heavily impacted by introduced pests and pathogens including the chestnut blight (1904), Dutch elm disease (1928), hemlock woolly adelgid (1951), Asian long-horned beetle (1996), and now emerald ash borer (2002). All these pests are non-native and were introduced to North American cities inadvertently. Emerald ash borer was first detected near Detroit, Michigan, in 2002, but it probably arrived in the area in the early 1990s (Siegert et al. 2007). Earlier detection of these pests is the first critical step in developing an eradication strategy. Once populations are established and spreading, earlier detection remains important as we strive to delineate the impacted areas and develop mitigation strategies. 

To create an easy-to-use method for checking trees for pests, tree experts considered the common signs and symptoms of several of the most serious pests currently impacting forests across the United States. With this information, a checklist of the signs and symptoms that would be readily visible to tree surveyors was created. This checklist uses multiple choice and yes/no questions, giving surveyors easy-to-assess questions that can be readily analyzed. Pest checks are automatically linked to species and location data, making searching for patterns, or signs of species-specific pests like emerald ash borer or sudden oak death simple.

The online dashboard for the app is how researchers, tree stewardship groups, and anyone who uses the app can manage data and projects. Projects can be as specific as one block of a city or include trees on a metro-wide scale. Any activity recorded in the app is paired to a tree, allowing users to track activities done to a tree over time. Researchers can track levels of stress in a tree from year to year, and stewardship groups can schedule key tree care – like watering during a drought – and ensure it happens regularly. The dashboard is currently live, and new features will be added over the fall of 2019.