Tom Whitham, Peter Price, Kitty Gehring, Joe Shannon, Adrian Stone, Talbot Trotter, Alicyn Gitlin and Larry Stevens

EXAMPLES OF IMPACTS ON BIODIVERSITY

DROUGHT EFFECTS ON NON-FORESTED COLORADO PLATEAU ECOSYSTEMS

Casual observations on 2002 drought impacts on 5 common desert

plant species in northern Arizona (Stevens, unpub. Data).

Grand Canyon Wildlands Council, Inc.

Long-term sawfly populations on willows closely track the Palmer Drought Severity Index (PDSI). 67 other herbivore species on willows are predicted to exhibit the same pattern. (Price & Hunter unpubl)

Ash and sediment runoff damage streams for many years.

In Kanab Creek, 24 miles downstream of the 1996 Bridger-Complex Fire, macroinvertebrate biomass was reduced 65-75% and biodiversity was reduced 90% for 7 years.

Tree Rings Predict Arthropod Species Richness & Abundance

Mycorrhizal mutualists increase with intermediate stress, but decline at high stress levels.

The southwest has the highest proportion of native fishes that are

threatened or endangered. Droughts, increased demands on water

use and fires are likely to make this worse.

PREDICTIONS

1. Extreme drought is a bottleneck event that results in increased extinction of rare species, especially those dependent upon rare habitat types impacted by drought (e.g., springs & riparian).

2. Human impacts on the environment (i.e., increased water use and fire hazards) make droughts far more severe such that a 100 year drought may effectively become a millenium-level drought.

3. Short and long-term effects of drought may switch such that species that initially benefit may subsequently decline. The same holds true for management decisions, especially ones focused on individual species, rather than the community or ecosystem.

4. Marginal or edge habitats that suffer chronic stress can be barometers of change and may be crucial to preserve as sources of extreme genotypes that may be best adapted to changing environments.

MAJOR GAPS IN OUR KNOWLEDGE

1. Lack of long-term studies emphasizing community responses to stress and drought.

2. Lack of protected long-term study sites where observational and experimental studies are emphasized.

3. A general lack of a community perspective as most efforts focus on individual species.

Management Implications

1. Need to plan for droughts that last decades or more.

2. Need to minimize human impacts that exacerbate the effects of drought.

3. Need special emphasis on rare habitat types that are especially sensitive to drought. For example, controlled fires during drought may place riparian habitats at unacceptable risks.

4. Especially important to manage for the community and ecosystem.