A citizen science approach to monitoring street tree population ecology in Cambridge, MA

Background/Question/Methods

Urban forests provide essential ecological, economical, and psychological benefits for urban dwellers. With urbanization increasing around the globe, we urgently need to better understand how trees respond to the stresses of the urban environment. We established a citizen science program with a dual aim to engage local citizens in scientific research and to assess the demography of street trees in Cambridge, MA. We combine data provided by the City of Cambridge with data collected by 85 citizen scientist participants from 6 one-day expeditions. For young trees planted by the City of Cambridge between 2007 and 2013, we compare survival rates by species and season of planting. As not all trees were planted at the same time, we standardized our comparisons by using Kaplan Meier survival curves and log-rank tests. Finally, we provide guidelines and protocols for implementing similar citizen science programs in other cities.

Results/Conclusions

Between 2007­­ and 2013, the city of Cambridge planted 1850 individual trees, comprising at least 53 species from at least 20 families. Overall survival rate was over 90% for the first three years after planting, but dropped to 73% by the fifth year after planting. Street tree survival rates were equivalent among species native to New England and non-native species (log-rank test, P=0.09). Among the 15 most commonly planted species, Acer rubrum, Quercus palustris, and Tilia cordata were among the best surviving species, whereas Amelanchier arborea, Malus spp., and Syringa reticulata were among the worst survivors. The City of Cambridge planted trees between April and November, but most commonly in May or November. However, survival rates were highest for individuals planted between June and September. We recommend restricting planting to the summer months, and planting fewer of the poor surviving species in the future. The citizen scientists enjoyed their experience and felt more connected to the natural world after participating in our program. Thus programs such as ours benefit scientists, municipalities, and citizens alike.