Topic 13- Diversity in Forests

Contributors to Diversity

• Relative influence of different groups or organisms

• Understory diversity tends to be the highest in forests

• Soil organisms represent the greatest biodiversity in forests (Soil microbial organisms probably represent tens of thousands of species per gram of soil)

Diversity over geologic time

• The number of families has been increasing though it has been punctuated with several mass extinctions

• Dominant groups have changed over time

• Extinction is as common as origination

• Massive increases in animal diversity were linked to increases in atmospheric O2 from photosynthesis

• Evolutionarily innovations in the diversification of land plants

Valuing Diversity

• Ecosystem Services - Maintaining the ecological fxn of habitats (protect renewable resources, reduce invasion/ insect species, Soil quality/carbon sequestration)

• Future pharmaceutical value

• Promotes human well being

• Intrinsic value of living benefits

Threats to Diversity

• Direct exploitation- humans directly causing extinction or indirectly through reductions in populations that make them vulnerable

• Habitat loss and fragmentation- the greatest threat. Direct impacts of development and land use and indirect effects of climate change

• Invasive species- Potential to out compete native species. Increasingly important threat.

• Climate Change- maybe largest impact in 50-100 years. Change is happening too past for many species to be able to adapt.

Evolution of Plant Lineages

Do we need to know? Idk

Richness

Number of species

Evenness

Abundance or dominant of one species over another

Alpha Diversity

Species diversity within a community at a local scale

Beta Diversity

• Species diversity between two communities or ecosystems

• Larger scale- generally compares species diversity in two communities

Gamma Diversity

• Very large scale where species diversity is compared between many ecosystems

• Range over areas like the entire slope of a mountain

The Shannon-Wiener Index

• Richeness and evenness combined into one number

Other aspects of diversity

• Functional group diversity

• Trait diversity

• Habitat diversity

Diversity at continental Scales

Wet topical forest have 10x as many tress species as moist forests of the northern and southern temperate zones

Diversity patterns within latitudes

• Mountain building has prompted high rates of speciation in the nootropics and in indomalaya

-Thought to be particularly effective at generating new species because it creates a dynamic and complex landscape

-Relatively little mountain building has occurred in Africa over the last 100 or so million years

• Afrotopical diversity may also be low, compared to other tropical hotspots, due to high extinction rates

-Aridification in Africa~23 million years ago could have shrunk species geographic ranges, leading to high extinction rates

• Importnat of mountains & moisture availability and glacial history

Factors that promote diversity

• Community structure and Complexity

-Bird diversity positively related to foliage height diversity

• Disturbance

• Fire

-Reduces species richness where mesophytic, fire-sensitive species colonize the site

-increases diversity in prairies, otherwise woody encroachment and decrease in diversity

Intermediate Disturbance Hypothesis

• Species richness low at high levels of disturbance → Only the most resistant species survive

• Species richness low at low levels of disturbance → Competitive species exclude others

• Mixed result outcomes likely to be dependent on ecosystem type, disturbance intensity as well as frequency

Succession and Diversity

• Diversity high in open site soon after disturbance

• Once canopy closure occurs, diversity decreases as canopy shades out all intolerant understory species

• Once gaps start to appear in an older forest diversity increases again due to the increase in environmental niches

Foundation Species

• Dominant species in an ecosystem

• Drives energy flow and physical structure

• Impact microclimate and structural complexity

• Creates niches and colonization by other species

• Often plants, usually dominant trees

Keystone Species

• Those with a disproportionately large ecological effect given abundance

Umbrella Species

• Those requiring large areas so their protection would protect many others

• Tends to be large vertebrates

Flagship Species

• Those with broad public appeal, whose plight would stimulate public support for conservation

• Endemics, Rare, and Endangered species often serve as flagships

Diversity- Productivity Mechanisms

• Complementary & Facilitation

• Sampling effect

Complementary & Facilitation

• Communities with higher species richness have species that are bale to differentiate their niches

• Reduces competition, allows for more efficient resource use

• Positive effects of one species on another can increase productivity though mutual benefits of species living together

Sampling effect

• More diverse communities are more likely to contain dominant species with high productivity

Diversity and Ecosystem Stability

• Compensatory dynamics hypothesized to underly this association

• Higher species richness- when one species declines, another can takes it place. Driven by stress or environmental variation.

• Most studies from grasslands

• Likely that this will soon be considered an additional benefit of conserving biodiversity

Ecological Forestry

• Ecological research on relationships have begun to impact forestry management practices

-Mimicking natural disturbance in harvest

-promoting structure diversity

-Recognizing the role of soil organism in the regeneration of the stand