By Dexter Henry Locke, lessandro Ossola, Emily Minor, Brenda B. Lin.
Your yard’s vegetation is similar to your neighbor’s, especially among back yards, larger yards, and in lower-income areas.
In North American cities, residential land uses are often the dominant land use. The non-building area in a residential parcel – the yard – can host substantial amounts of vegetation. The collective environmental impacts of yards, positive or negative, add up to the continental-scale. For example, yard irrigation can influence regional water systems, trees take up and retain carbon, and the excessive application of lawn care products, like fertilizers and pesticides, may harm animals and adversely affect human health.
Vegetation, such as trees and grasses, are unevenly distributed across front and back yards, and we sought to understand how similar yards are to each other when compared to their neighboring yards and neighborhoods using aerial imagery. There are many ways to measure yard similarity, and we compared several measures to account for different definitions of ‘neighborness’.
We found high similarity in vegetation structure among neighbors at both yard and neighborhood scales. This means that yards with low amounts of tree canopy cover are near other yards with low tree canopy cover, and that yards with high amounts of tree canopy cover are near other yards with high tree canopy cover. In higher income neighborhoods, the similarity of tree canopy in yards is lower and larger yards have more in common with respect to vegetation than smaller yards. We also found that how similarity is defined and measured among yards and neighborhoods influences the results. For example, when neighbors are defined as abutting properties (ie sharing a property line), similarity is much higher than using linear distance between properties to define neighbors.
It is possible that neighbors are mimicking each other in how they manage they yard vegetation, either intentionally or subconsciously, which is leading to the patterns of similarity we found. This is important as a better understanding of the social and ecological mechanisms leading to resident emulation could give insights to significantly improve urban forest planning, forestry and greening efforts. Future studies should carefully consider how methods to evaluate urban vegetation structure match, or fail to match, the underlying ecological and social mechanisms shaping residential vegetation.