Living in a vibrant city like ours, trees combat the unique urban stressors of pollution, road salt, vehicular exhaust and nutrient deficient soils. In addition to the environmental stressors of hot summers, water availability and land type, transplanted trees are incredibly vulnerable in the first three years while they are re-establishing their root system.
That’s where the Survival Study comes in.
Casey Trees designed a study that analyzes 51% of the trees we’ve planted since 2003, allowing us to track the success of different practices and programs over time. This data informs us on what we plant, where we plant, how we care for trees, and so on.
What we have learned from digging deeper
Over the past few weeks we have delved further into the Survival Study data, looking specifically at trees’ survival rate based on species, the type of space it is planted in, and root type. We analyzed how these different traits impact the health of the trees we plant, but examination of these traits individually are not good predictors of overall survival. We will be digging further into the data in order to better understand the other factors that explain differences in survivability.
For example, in Part 2: Space Type, we found that planting strips had a 98.4% survival rate while road medians had a 94.7% survival rate. We speculated it had something to do with ease of access to the tree, but that’s all it is – a speculation. Casey Trees loves data, so we won’t present scientific conclusions until we are sure about it. In order to do that, we will compare space type to the type of tree planted in medians and planting strips. Another cross analysis will compare space type to the entity responsible for maintaining the trees to determine if there is a correlation between the two.
This data is crucial to helping us propose hypotheses and draw conclusions to better our practices and give trees we plant the best chance at a long, healthy life.
Where do the missing trees go?
With each year of data we collect, we are able to draw more conclusions and improve the overall survival rate of our trees. If we discover a tree is removed legally or missing (removed illegally), it makes tracking a tree’s health over time impossible. However, these trees are not rendered useless to us when they disappear.
These trees provide us valuable data because of where they used to be. Homeowners are assumed to have removed the tree because it had died, whereas trees on public land are assumed to have been removed due to construction or development. Tree damage or removal due to construction and development has been a topic of great interest here at Casey Trees in part because it has such a significant impact on D.C.’s trees – in fact, it is the main detriment to their health and longevity.
Year after year, we build on the information we have and gradually gain a more complete picture of the state of our urban canopy. As we continue the analysis of data collected during the summer of 2015, we are already gearing up for the 2016 Survival Study. We will be visiting the same trees we collected data on in 2015 in addition to half of the new trees planted over the past year.
Be on the lookout for our interns clad in bright neon t-shirts this summer as they bike to every corner of D.C. to assess over 5,000 of our trees!