Site Inventory: Biological Attributes

Chapter 6: Site Inventory: Biological Attributes

6.1 Introduction

  • The site inventory process is organized into three separate chapters.

    • This separation is considered useful yet artificial in practice.

  • Landscapes consist of both biotic (living) and abiotic (non-living) components.

  • The structure and ecological function of landscapes are influenced by:

    • Biological factors

    • Cultural factors

    • Physical factors

  • Example of these influences:

    • Cultural landscape corridors can act as barriers for ground-dwelling animals or as vectors for diseases and invasive species.

    • Built features like roads and utility corridors can isolate populations of endemic species, risking local and broader extinctions.

6.2 Ecological Communities

  • Definition: An ecological community is a group of interacting species existing in the same location.

  • Influence on ecological communities:

    • Complex interactions among:

    • Climate

    • Soils

    • Topography

    • Natural disturbances

    • Organisms

  • Communities are often identified based on dominant plant species, which can be dominant due to size or abundance.

  • Examples of North American communities:

    • Beech-maple-hemlock community

    • Oak savanna community

  • Ecotones:

    • Defined as the spatial boundaries of communities.

    • Important for mobile animals seeking shelter and food.

6.2.1 Habitat Fragmentation

  • Human activities (agriculture, forestry, urban development) have altered landscapes in Europe and other civilized regions dramatically.

  • Such activities result in:

    • Habitat destruction

    • Habitat fragmentation and disconnection

  • Importance of natural corridors:

    • Facilitate movement between habitats, crucial for maintaining biodiversity and ecosystem connectivity.

  • Protection Priorities:

    • Large, contiguous natural areas, especially riparian corridors, should be prioritized.

  • Leaving natural areas untouched may not guarantee biodiversity; small isolated patches may lose species due to development barriers.

  • Many species require multiple habitat types for essential life stages (e.g., reproduction, migration).

  • Mapping tools:

    • U.S. Geological Survey provides land cover information.

    • The National Land Cover Dataset (NLCD) and aerial photographs aid in detailed land cover mapping.

6.2.2 Exotic Species

  • Thousands of species have adapted to human-altered habitats since European settlement.

  • Many introduced species have become naturalized, including:

    • Megafauna: Horses, pigs

    • Megaflora: Eucalyptus and melaleuca trees

    • Other Exotic Plants: Kudzu (vine), Brazilian pepper (shrub)

  • Approximately 50,000 species of exotic plants, animals, and microbes are causing considerable ecological changes in the United States.

  • Nearly half of threatened or endangered species are at risk due to invasive nonnative species.

  • Economic impact of exotic species control in the U.S. exceeds $6 billion annually.

  • Example of an invasive species:

    • Melaleuca tree in the Everglades, initially planted to dry wetlands.

  • Definition:

    • Habitat refers to where an organism lives, while the ecological niche describes an organism's role and relationships within its ecosystem.

  • Examples of intentional introduction of species:

    • Eucalyptus in California

    • Melaleuca in the Everglades

  • Importance of preserving native habitats:

    • Riparian areas and wetlands serve functions such as stormwater management and biodiversity protection.

6.2.3 Wetlands

  • Historical Context:

    • Since the early 1600s, over half of the original wetland acreage in the contiguous United States has been lost due to agricultural and urban development.

  • Federally defined wetlands are based on the following criteria:

    • Hydrology

    • Vegetation

    • Soils

  • Classes of wetlands (Cowardin et al., 1979):

    • Marine

    • Estuarine

    • Riverine

    • Lacustrine

    • Palustrine

  • Functions of wetlands that benefit humans:

    • Wildlife nurseries

    • Stormwater runoff storage

    • Aquifer recharge areas

  • Wetland Banking:

    • A process of creating new wetlands to compensate for those destroyed but it faces criticism for not matching biodiversity or altering hydrological regimes.

6.3 Trees

  • Trees provide numerous ecological, economic, and social benefits:

    • Reduce heating and cooling costs

    • Increase property values

  • Factors affecting economic value:

    • Size of the tree

    • Species type

    • Condition of health

    • Location

  • Functions of trees that benefit design:

    • Shade provision

    • Visual amenity

    • Reduction of undesirable views

  • Importance of protection during construction:

    • Common damages include soil compaction, bark scraping, and disruption of root zones.

  • Tree preservation ordinances increasingly protect trees during development processes.

  • Tree mapping:

    • Inventory of species, size, and locations, often using GPS.

6.4 Wildlife

  • Wildlife populations are often discontinuous, comprising several metapopulations.

  • Local extinctions are common, emphasizing the need for viable habitats for recolonization.

  • Benefits of conserving wildlife habitats:

    • Natural pest control by bird species

    • Aesthetic enjoyment for humans

  • Mapping endangered species distribution under the Endangered Species Act (ESA) assists conservation efforts.

6.5 Conclusion

  • Landscape ecology is critical for understanding landscapes and making environmental decisions.

  • Increased awareness of environmental quality correlates with human health and demand for accountability in land development.

  • Mapping and evaluating biological attributes is essential for protecting ecological integrity during site planning.