COS 46-2 - Forest patches in urban and agricultural landscapes have lower tree diversity, more non-native trees, and altered forest structure across cities and ecoregions

Monday, August 7, 2023

3:45 PM – 4:00 PM PDT

Location: E146

Coauthor(s)

JS

John Paul P. Schmit

National Capital Region Inventory and Monitoring Network, National Park Service, United States

Presenting Author(s)

LJ

Lea R. Johnson

Division of Science, Longwood Gardens; Department of Plant Science and Landscape Architecture, University of Maryland
Kennett Square, College Park, PA, MD, United States

Coauthor(s)

MB

Matthew Baker

University of Maryland, Baltimore County, Maryland, United States
LD

Lindsay E. Darling

Purdue University, United States
RF

Robert Fahey

Assistant Professor
Department of Natural Resources and the Environment, Center for Environmental Sciences and Engineering, University of Connecticut
Kelowna, British Columbia, United States
DL

Dexter Locke

US Forest Service, United States
AM

Anita T. T. Morzillo

Department of Natural Resources and the Environment, Center for Environmental Sciences and Engineering, University of Connecticut
Storrs, CT, United States
MA

Myla F.J. Aronson

Rutgers, The State University of New Jersey
New Brunswick, NJ, United States
MJ

Michelle L. L. Johnson

USDA Forest Service, Northern Research Station, NYC Urban Field Station
Bayside, New York, United States

Abstract: Forest patches in urban landscapes make outsized contributions to biodiversity, ecosystem function, and human health and well-being. However, urbanization alters environmental conditions that underpin forest health. Most studies of forest health in urban landscapes have focused on individual or few forest patches across single metropolitan regions, but larger spatiotemporal syntheses are needed to understand the condition and potential of these forest systems.

To establish whether attributes of forest patches vary with urbanization intensity and if these effects are consistent across ecoregions, we asked how the landscape context of urban forest patches varied and whether differences in degree of urbanization and other surrounding land cover were reflected in differences in forest tree community composition and structure. We synthesized tree community composition and structure data from nineteen observational studies (n = 4,905 plots) and remotely sensed land cover (within a 1-km radius surrounding each plot) across four metropolitan regions (Baltimore-Washington DC, Chicago, New York City, and Philadelphia) spanning five ecoregions of the Eastern Deciduous Forest of North America. This analysis is the first to examine relationships between landscape context and indicators of forest health across intensities of urbanization in multiple regions.

We found that ecoregions had distinct land cover signatures and forests were surrounded by heterogeneous land cover, confounding simple interpretations of urbanization. However, general patterns of species distribution and forest structure reflected the influence of landscape context. Forest patches surrounded by high levels of canopy cover had species diversity, tree density, basal area, and size diversity equal to or greater than those with greater agricultural or impervious contexts. In contrast, there were few structural differences and similar levels of diversity between forests in highly agricultural and impervious settings. Tree species composition varied among ecoregions as expected, yet forests with similar landscape contexts often shared indicator species. Forest structure and species diversity in urban forest patches were often more similar to those of forest patches in agricultural areas than to patches in forested landscapes. Lower tree diversity, basal area, and size class diversity combined with greater non-native tree abundance in both urban and agricultural contexts highlights commonalities between these intensive anthropogenic landscapes. In both urban and agricultural landscapes, shifts in forest structure and dampened ecoregional diversity present common challenges to forest health and common opportunities for forest stewardship.