Defining and assessing urban forests to inform management and policy

Abstract

The context in which trees and forests grow in cities is highly variable and influences the provision of ecological, social, and economic benefits. Understanding the spatial extent, structure, and composition of forests is necessary to guide urban forest policy and management, yet current forest assessment methodologies vary widely in scale, sampling intensity, and focus. Current definitions of the urban forest include all trees growing in the urban environment, and have been translated to the design of urban forest assessments. However, such broad assessments may aggregate types of urban forest that differ significantly in usage and management needs. For example, street trees occur in highly developed environments, and are planted and cared for on an individual basis, whereas forested natural areas often occur in parkland, are managed at the stand level, and are primarily sustained by natural processes such as regeneration. We use multiple datasets for New York City to compare the outcomes from assessments of the entire urban forest, street trees, and forested natural areas. We find that non-stratified assessments of the entire urban forest are biased towards abundant canopy types in cities (e.g. street trees) and underestimate the condition of forested natural areas due to their uneven spatial arrangement. These natural areas account for one quarter of the city's tree canopy, but represent the majority of trees both numerically and in terms of biomass. Non-stratified assessments of urban forest canopy should be modified to accurately represent the true composition of different urban forest types to inform effective policy and management.

Conceptualizing social-ecological drivers of change in urban forest patches

“…An urban forest patch does not include street, yard, and landscaped park treesbeneath which regeneration is discouraged through direct management practicesalthough nearby trees in these contexts may deposit seeds into a forest patch. Our definition includes both wild woodlands as defined by Kowarik and Körner (2005) and Konijnendijk (2005) as well as forests of diverse cultural origins originally planted by people, and aligns with the broad definition of a natural area forest applied by Pregitzer et al (2019) to suggest the need for collective, rather than individual tree management.…”

Estimating carbon storage in urban forests of New York City

“…However, these estimates depend on accurate characterization of tree species, size, density, and growing conditions associated with urban tree canopies. Tree density, basal area and biomass vary markedly among tree canopy types in cities, especially between designed and natural area ecosystems (Pregitzer et al 2019b).…”

Advancing management of urban forested natural areas: toward an urban silviculture?

“…Many cities have begun to use i-Tree Eco and urban Forest Inventory and Analysis (FIA), two plot-based sampling methods, to assess the urban forest at the city scale and provide information about trees across all urban cover types. Although useful for raising public awareness about trees in the city, these sampling approaches are not necessarily effective for characterizing forested natural areas (Pregitzer et al 2019b), or prescribing community-or stand-specific management strategies. Traditional forest inventory sampling strategies often focus on stratifying areas of interest by forest type, stand age, and size class, providing quantitative information for targeted forest management strategies.…”