Vegetation is susceptible to multiple types of damage from project development. Plants and natural communities can experience disruption from changes in environmental conditions. Such disruptions could include:
- The accumulation of fugitive dust on leaves, which interferes with photosynthesis
- The alteration of water flows from prior paths, resulting in either too much or not enough water to support the native species
- Contamination of water resources resulting from runoff
- Degradation of soil quality through compaction, which can damage root systems
- Nutrient leaching, which can dredge soils of the minerals plants require to thrive
Human impact on the environment through urbanization often results in water, air, and land pollution that endanger many natural plant and animal species. Development, which changes a sensitive ecosystem, may adversely affect the diversity of species present, the productivity of the system, or the rate of nutrient recycling.
Additionally, development can have direct impacts on vegetation and natural communities, such as by driving through natural communities that support special-status vegetation species, or the accidental removal of not only special-status species, but also species that provide crucial ecosystem services to the larger natural community. When a natural community is disturbed and native species fail to thrive, noxious and invasive weed species often take over and can become dominant in developed areas.
The abundance and survival of both plant and animal species depend upon the existence of a favorable environment and their ability to adjust to man-made conditions. Urbanization has seriously altered natural ecosystems. The Audubon Society, USDA, and other organizations have resources for urban native planting efforts.
Vegetation can also positively affect the quality of a project development by adding aesthetic value and ameliorating the impact of climate change. Trees can help control climate change as they remove carbon dioxide from the air, store carbon, and release oxygen into the atmosphere. Vegetation can also ameliorate the negative effects of climate change; for example, areas with greater vegetative cover stay cooler than other areas in cities suffering from the urban heat island effect and coastal wetlands help absorb and limit the impact of extreme weather events on the coastal communities. Consider not only avoiding the removal of trees on a project site but also adding trees and other native vegetation to the project implementation.
- Will the project create problems by introducing nuisance or non-indigenous species of vegetation that may be ecologically disruptive, be invasive, threaten the survival of indigenous plant habitats, or disrupt agricultural or silvicultural activities?
- Will the project introduce landscape maintenance actions (pesticide usage, fertilization) that may threaten the survival of indigenous plant habitats, or disrupt agricultural or silvicultural activities?
- Will the project damage or destroy existing remnant or endemic plant communities, especially those containing nationally, regionally, or locally rare species (e.g., prairie grasslands, ice-age disjuncts, local soil-type endemics)?
- Will the project damage or destroy plant species that are legally protected by state or local ordinances?
- Will the project damage or destroy trees without replacement and landscaping?
- How much risk does the proposed project face from the impacts of climate change? Will the proposed vegetation management or landscaping plan mitigate those risks (e.g., excessive heat, flooding, degraded air quality), where possible?
Review existing documentation to determine the ecological features of the area. As part of preparing a data file, prepare maps that delineate the locations of endangered or rare species, remnant native plant communities, and existing open space. Also, consider reviewing the following:
- Vegetation maps
- Biotic surveys
- U.S. soil conservation survey’s soils surveys, which include data on woodland productivity
- State and local Threatened and Endangered Species lists
- Natural community databases prepared by state agencies
- The U.S. Fish and Wildlife Service (USFWS) Environmental Conservation Online System (ECOS) critical habitat online ArcGIS mapviewer
- Satellite photography resources
Field observation can help determine the nature, viability, and degree of vulnerability of plant species on the site. Natural sites, sites on slopes, and sites with or adjacent to streams and other bodies of water tend to be more sensitive to development than previously developed sites that have no nearby surface water.
A key factor in measuring the level of ecologic disturbance is the percentage of the site that will be developed or altered. No set formula fits all cases since the level of damage is a function of the sensitivity of the site and the amount of the site to be developed. For example, a condition of high ecological disturbance may result from a project of 30% site coverage on a highly sensitive site to 70% project coverage on a site of low sensitivity. This sort of evaluation requires the skills and experience of a biologist, ecologist, or botanist.
Site vegetation may also be considered factors in critical habitats, related to the Endangered Species Act, as well as prime farmland under the Farmland Protection Policy Act. These factors are addressed separately in the laws and authorities section of the environmental assessment.
Most effective mitigation measures involve modifying project plans rather than altering the ecosystem itself. Strategies can include:
- Clustering development rather than allowing for sprawling areas that form disjointed habitat connections
- Limiting tree cutting to those areas that buildings will occupy
- Establishing buffer areas between construction activities and sensitive areas, including wetlands or communities known to support special-status plant species
- Terracing downhill slopes
- Planting native vegetation in open space areas and selecting native species that provide appropriate ecosystem services to mitigate climate and other impacts
- Incorporating best management practices that ensure that runoff does not substantially alter existing conditions
- Avoiding pavement/concrete near the area that supports substantial native communities