Tree diversity is crucial to urban forest management. More diverse urban forests provide habitat for a wider range of organisms, increase resilience to pests and disease and, in cases where native tree species are well represented, contribute to local biodiversity protection. Studies have shown that tree diversity can peak in the low- to mid-density neighbourhoods found in suburban and peri-urban areas, emphasizing the potential for biodiversity enhancement during and after subdivision development. Most studies quantifying tree species composition in suburban areas focus on one or two major drivers of tree diversity, such as land use, socioeconomics and demographics, or the presence of natural features like parks or greenways. Furthermore, relatively little attention has been paid to the drivers of diversity for the variety of land types that make up the entire urban forest, which represent differences in tree planting and establishment practices, ownership, and maintenance. This paper presents an overview of drivers of tree species composition based on the literature, as well as factors that require further study because they play a role in determining the structure of the (sub)urban forest. These factors are examined in the context of four land types: street, residential property, park, and remnant woodland, and are organized under the following major themes: biophysical characteristics, community design, historical paradigms and influences, municipal management, and demographics and cultures. Based on what is known so far, a research agenda is also presented outlining major gaps in research on urban tree diversity in North America (USA and Canada). The information presented in this paper can thus serve as a guideline to inform urban forest management practices and strategically enhance tree diversity.
An index of forest management intensity based on assessment of harvested tree volume, tree species composition and dead wood origin
