McComb Ch14: Ecology and Design of Urban Habitat

McComb Ch14: Urban Forests and Wildlife Habitat Management

I. Urban Context and Development

  • Many major world cities (e.g., New York, Boston, Seattle) were developed on formerly forested landscapes.

  • Over half of the world's population now resides in cities or associated suburban areas.

  • The urban–rural continuum describes the expanding gradient of development radiating from a city center.

  • The expansion of urbanization increases the likelihood of human–wildlife encounters, sometimes involving animals typically associated with extensive forests (like bears or moose).

  • Key indicators of urban impact on habitat include building height and density, impervious surface percentage, and road densities, which are often better metrics than just human population density.

II. Wildlife Adaptation and Human Tolerance

  • Cities can provide habitat elements, sometimes serendipitously, for a wide range of species.

  • Some species successfully interpret the "built environment" as suitable habitat.

    • Peregrine falcons use skyscrapers and tall bridges as human-made cliffs for nesting and prey on urban species like pigeons (rock doves) and squirrels.

    • Chimney swifts and Vaux’s swifts use masonry chimneys, adapting from prior use of hollow trees.

  • Human reactions to wildlife vary greatly, from enjoyment to fear or disdain.

  • Effective urban habitat management must engage residents to understand community goals and limits of tolerance for cohabitation.

III. Challenges in Habitat Provision

  • Invasive Species: Cities are focal points for the spread of imported, nonnative species that can displace native species (e.g., European starlings, pythons in Florida).

  • Barriers and Isolation: Impervious surfaces (roads, parking lots, sidewalks) form a maze that limits plant growth and acts as barriers to animal movement. Animals crossing these areas lack cover from predators (pets, coyotes, raptors) and face the risk of being hit by cars.

  • Ecological Traps: Urban habitat patches must be functional and sustainable. If urban patches attract high-priority species but result in low reproductive or survival rates (due to high predation/vehicle risk), they become ecological traps.

  • Liability and Safety: Landowners and park managers face liability issues, which often leads to the systematic removal of key habitat elements.

IV. Limiting Habitat Elements and Management Solutions

Habitat elements that present logistical problems for urban foresters and biologists include:

  • Dead Wood: Dead limbs, dying, or decaying trees are often removed due to the risk of falling on people or property.

    • Solutions: Find low-risk areas; top dead trees (e.g., to 15 feet near sidewalks) to create short snags for cavity nesters and bats. Fallen logs can be placed in parks and greenways for reptiles, amphibians, and invertebrates.

  • Burrows: Sites for burrowing animals are restricted by expansive impervious surfaces and soil compaction. Increases in impervious surfaces reduce potential den sites.

  • Shrubs: Important for nesting, cover, and food. They are often systematically removed along walkways in parks to reduce the risk of muggings, rapes, and attacks.

    • Solutions: Allow shrubs outside safe zones along walkways.

  • Habitat Patches: For diverse animal communities, parks require a full complement of native plants, including a shrub layer, dead wood (snags/logs), and hollow trees, avoiding invasive species.

  • Connecting Patches: Wildlife corridors and urban greenways (potentially serving as walking paths/bikeways) are needed to connect habitat patches.

    • Collaboration among urban foresters, wildlife biologists, landscape architects, and urban planners is necessary to design multipurpose greenways.

  • Innovative Spaces: Green and brown roofs can provide habitat for invertebrates and nesting birds while also mediating stormflow and adding insulation. Designing these roofs to maximize native plant diversity (grasses, forbs, shrubs) can aid biodiversity.

V. Stream and Wetland Management

  • Many urban streams are constrained, channelized, or lined with rip rap, which removes the complexity needed by aquatic species.

  • Increased impervious surfaces lead to contaminants being washed into streams and causes stream levels to fluctuate wildly following rains.

  • Restoration requires a holistic approach across the entire drainage basin, involving multiple landowners and designing new holding areas for stormwater.

  • Stream Restoration Guidelines (Palmer et al., 2005): Restoration must be based on a "guiding image" of a healthy river; achieve measurable ecological improvement; increase self-sustaining resilience; avoid lasting harm; and include public pre- and post-assessment.

  • Wetlands Mitigation and Conservation Banking: Under the U.S. Clean Water Act (Section 404), there is a no-net loss of wetlands policy. Developers offset losses by creating or restoring wetlands, or by purchasing habitat credits from habitat/conservation banks. Conservation banking focuses on replacing lost habitat while considering the ecological context to ensure functionality.

VI. Future Planning and Research

  • Generalized land resource indicators for monitoring land conversion include loss of prime farmland, loss of natural wetlands, loss of core forest habitat, and increase of the impervious surface.

  • Retrofitting habitat into already-built environments is challenging. Possibilities for new corridors/islands include abandoned railways (rails to trails) and the recovery of former industrial sites (brownfields reclamation).

  • Phytoremediation on brownfields creates concerns about contaminants accumulating in plants, potentially leading to a biological trap if animals feed on them.

  • Research is desperately needed in active management of urban areas for wildlife conservation.