Types of Disturbances in the Mojave Desert (and other deserts)

• Linear features (e.g., powerlines, roads)

• Fire

• Off-road vehicles

• Hydrological damage (e.g., Owen’s Lake)

• Abandoned agricultural lands

• Air pollution

• Grazing

• Cactus poaching/mesquite harvest, and so on

Disturbance Effects• Differ among disturbance types (e.g., some just remove vegetation, others remove soil/nutrients

• Some acute (e.g., powerline); others less intense but more widespread (e.g., grazing)

• Alter species composition

• Initiate undesirable trajectories (exotics-fire)

• Destroy soil crusts

• Increase erosion, reducing air quality

• Release carbon to the atmosphere

From Lovich & Bainbridge 1999 supplemental reading

Wallace et al. 1980. The challenge of a desert: revegetation of disturbed desert lands. Great Basin Naturalilst Memoirs 4:216-225.

Principles developed largely from 1960s-70s work revegetating Nevada Test Site

Water clearly critical, but timing and amount per rainfall event just as (or more) important than total quantity

May need to manipulate water, sometimes via catchments and terrain manipulation

Episodic nature of perennial plant recruitment and replenishment of annual plant seed bank

Fertile island structure – concentrated resources, establishment microsites

Some pioneer plants can establish in interspaces

Wallace et al. 1980. The challenge of a desert: revegetation of disturbed desert lands. Great Basin Naturalilst Memoirs 4:216-225.

Animals control survival and growth of many species of plants (jackrabbits, pocket gophers, burros, etc.)

While water clearly often limiting, do not forget about soil nutrients, particularly nitrogen

Must tailor restoration to disturbance type

Photo courtesy of Jessica Spencer

Burro sightings in Lake Mead NRA, 1991-20051

Yellow lines = aerial surveys

ARIZONA

NEVADA

1Map provided by GIS division, Lake Mead NRA

Reference Conditions• As in most ecosystems, depend on objectives/scale/time frame, and nature of degradation

• e.g., blend ORV tracks into surroundings – reference is surroundings – simple trajectory

• Past (e.g., pre 1900s) conditions not necessarily as well known as in some systems, like ponderosa pine forests

• Alternative techniques: charcoal example from Sonoran Desert wetlands

Davis, O.K., T. Minckley, T. Moutoux, T. Jull, and B. Kalin. 2002. The transformation of Sonoran Desert wetlands following the historic decrease of burning. Journal of Arid Environments 50:393-412.

The analysis of sediments from six wetlands (cienegas) in the Sonoran Desert of Arizona, U.S.A., and Sonora, Mexico, document a marked expansion of wetland taxa, particularly woody plants, about 200 years ago at the beginning of the historic period, following a decrease in charcoal percentages and increased percentages of the dung fungus Sporormiella. The presence of charred seeds and fruits of wetland plants in prehistoric sediment establishes burning of the cienega itself. The charcoal decline ca. 250 years ago precedes the first occurrence of the pollen exotic plants at several sites, the change of cienega sediment from silt to peat, and the increase of percentages of the decay fungus Tetraploa. We conclude that prior to the historic period, burning was frequent enough to exclude most woody plants (Celtis, Cephalanthus, Populus, Fraxinus, Salix) from the wetlands and suppress the abundance of bulrush (Scirpus). The cienegas were probably burned seasonally as a management tool to harvest animals and promote agriculture. Prehistoric agricultural utilization of the cienegas is demonstrated by the presence of corn (Zea) and pre-Columbian weeds. This study also records postsettlement (ca. 200 years ago) change of upland vegetation; i.e. an increase in the abundance of Juniperus, Quercus, Larrea, and Prosopis pollen. Historic fire suppression may have permitted the expansion of these non-wetland woody species.

A Beginner’s Guide to Desert Restoration Manual

• Restoration planning (general process same here, as in any other ecosystem)

• Soil salvage and replacement

• Water mgt (incl irrigating plants)

• Plant genetic considerations

• Techniques for plant establishment

Seeding in North American deserts has been cited to be “successful” in only 1 year in 10.

However……

Fall2005

Spring2006

Fall2005

Spring2006

Some general principles• Don’t believe it when people say it never works. Ask for data, justification.

•Don’t overlook the obvious – moisture constrains restoration

• Don’t overlook the less obvious – nutrients, herbivory/granivory can be just as limiting

• Reveg often 1st step – don’t assume success

• Be careful about “restoring” systems that may facilitate exotic species invasion

• Time treatments carefully

• View as jump starting processes

Artificial desert varnish – restore soil color

Anti-fertilizer – a soil amendment designed to reduce soil nutrient availability. A good example is adding carbon as wood chips. Carbon frequently limits microbial activity, so adding carbon results in many nutrients being tied up in microbial biomass and hence unavailable to plants.

Exotic species frequently excel in environments of high nutrients. An idea behind ant-fertilizer is to reduce soil nutrients, potentially giving a competitive advantage to natives. (can search Restoration Ecology for some examples, by searching for carbon addition and so forth).

A problem with the above reasoning is that lowering nutrients may also harm native species.