Forest Biodiversity Notes

Forest Biodiversity

Species Richness

• Definition: The number of species occurring within a community.
• Characteristics:
  • Simplest measure of diversity.
  • Expressed per unit area sampled.
  • Good expression of taxonomic diversity.

Species-Area Curves

• Purpose: To determine if an area's species richness has been adequately characterized.
• The number of species is plotted against the sampled area.

Species Evenness

• Definition: Equitability in the distribution of individuals among the species within a community.
• Considers both the number and relative abundance of species.

Relative Abundance

• Definition: The number of individuals of a species relative to the total number of individuals of all species living in the community.
• $p<em>i = \frac{n</em>i}{N}$
  • $p_i$ = proportion of individuals of species i
  • $n_i$ = number of individuals of species i
  • $N$ = total number of individuals of all species

Dominance

• Definition: When a single or few species predominate within a community.
• A community dominated by a few species has lower evenness and is less diverse compared to a community where individuals are more evenly distributed across species.

Community Abundance Patterns - The J Curve

• Illustrates the distribution of species abundances in a community.

Diversity Index

• Measure of diversity that accounts for the number of species present and their relative abundance.
• Simpson Index (D):
  • $D = 1 - \sum (p_i)^2$
  • $p_i$ represents the relative abundance of each species.
  • As species richness and evenness increase, so does diversity.
  • D ranges between 0 and 1 (1 represents infinite diversity, 0 represents no diversity).

Calculating the Simpson Index

1. Calculate the total number of individuals.
2. Calculate the relative abundance of each species as
   $p<em>i = n</em>i / N$
3. Square the relative abundances and sum them.
4. Subtract the sum from 1 to obtain the Simpson Index D.

Types of Diversity

• Alpha (Local) Diversity: Species diversity of individual communities.
• Beta Diversity: Variation in species composition among sites (communities) in a geographic area.
• Gamma (Regional) Diversity: Total species diversity across all communities within a geographic area.

Alpha Diversity Considerations

• Quantifying local diversity is difficult.
• Defining community boundaries can be problematic.
• The relationship between diversity and area complicates comparisons between communities/ecosystems of different sizes.
• Local patterns of diversity change over time during succession.

Beta Diversity

• Increasing environmental heterogeneity within a region usually results in increasing beta diversity.
• Differences in environmental constraints across the landscape restrict the distribution of species.
• Mountainous regions generally have more diverse habitats and communities than flatlands

Gamma Diversity

• A comparison of broad-scale patterns can be confounded by time (seasonal changes that affect water temperature, migration patterns).

Keystone Species

• A keystone species has a disproportionate impact on the community relative to its abundance.
• Even though some species are less abundant, they can still be very important!

Foundation Species

• Usually a primary producer that dominates an ecosystem in abundance and influence and provides food and shelter for many other species.
• In many forested ecosystems, the architecture and functional ecology of certain tree species define forest structure and their species-specific traits control ecosystem dynamics.

Loss of Foundation Tree Species

• The loss of foundation species can have significant consequences for the structure and dynamics of forested ecosystems.

Loss of American Chestnut

• Example of the impact that the loss of a tree can have on its environment.

Loss of Oak Trees

• 60% of eastern forest has experienced a decrease in oak (especially in Central Hardwood Region, ~87%)
• Oaks dominate eastern landscapes.
  • Dominant in 68 of 90 forest types.
  • ¼ of all growing stock in eastern forests.
  • Provide food (acorn) and habitat for many wildlife species.
    *Implications of loss of oak for multiple animal species.