I. Extent of ecosystem
A. Walter (1979): Subtropical deserts;
Arid regions of the temperate zone
B. Whittaker (1975): Warm semi-desert scrub (e.g., creosote bush);
Cool semi-desert (e.g., Artemisia, Atriplex, grasses)
C. West (1983): Temperate: Great Basin, Colorado Plateau, Columbia- Snake River Plateau, Wyoming Basin
Sub-tropical: Mohave, Sonoran, Chihuahuan
II. Agents of degradation (Allen 1988)
A. In hot and cold deserts, grasslands and shrublands: domestic grazing, fire, wood harvesting, drought, mining, agriculture
B. Desertification occuring at a rapid rate
III. Restoration strategies (E. Allen. 1995. Restoration ecology: Limits and possibilities in arid and semiarid lands. Pages 7-15 in B. Roundy, E. McArthur, J. Haley and D. Mann (eds.) Proceedings: Wildland Shrub and Arid Land Restoration Symposium. USDA Intermountain Research Station, General Technical Report INT-GTR-315.)
1. Multiple use management
2. Economic vs. conservation value
Rehabilitation has traditionally been defined as planting palatable grasses, perhaps in monocultures, while removing unpalatable shrubs.
3. Restore passively or actively?
Some situations will not wait: mining, overgrazing, erosion, threatened and endangered species
B. Active and passive restoration
1. Passive: Removing stress
Allowing natural succession to occur
2. Active: Management techniques such as introducing propagules, weeding, burning, alleviating compaction, improving: soil moisture, soil nutrients, soil OM
4. Successful and modified trajectories
IV. Limits to restoration
A. Four primary limits: water, invasives, topsoil loss and biodiversity loss
1. Water can be supplied through technological fix;
2. Others, no technological fix.
C. Exotic plant competition
D. Loss of topsoil
V. Seeding of desert grasses. (S. Biedenbender and B. Roundy. 1996. Establishment of native semidesert grasses into existing stands of Eragrostis lehmanniana in southeastern Arizona. Restoration Ecology 4:155-162.)
A. Native desert grasslands have been invaded by native trees and shrubs, plus South African lovegrass (Eragrostis lehmanniana)
B. Causes include grazing, change in fire frequency, climatic change, rabbits and rodents
C. Lovegrasses were introduced in 1930's to revegetate depleted desert grasslands.
Establishes faster than natives.
It is still introduced for forage and erosion control.
Continued spread may lower diversity in native communities.
Can replace native grasses after severe drought.
D. Native grass establishment requirements in relation to E. lehmanniana were measured.
Burn, mow, live-standing E. lehmanniana and dead-standing E. lehmanniana
Sowing dates (June, early August)
E. Summer rainfall period July-September
F. Species: Setaria leucopila (bristlegrass), S. macrostachya (plains bristlegrass), Muhlenbergia porteri (bush muhly), Eragrostis intermedia (plains lovegrass), Bouteloua curtipendula (sideoats grama), Bothriochloa barbinodis (cane beardgrass), Leptochloa dubia (green sprangletop), Digitaria californica (Arizona cottontop)
Planted with no-till drill, one pure live seed per cm., 0.5 cm deep, rows 40 cm apart.
Establishment into live-standing canopy of E. lehmanniana was consistently lacking.
Burning treatment produced highest establishment for most species when post-sowing precipitation was consistent.
Shading by mown, dead or live grass did not make enough of a difference in water availability to consistently increase seedling establishment.
Muhlenbergia porteri failed to establish.
Rainfall closest to sowing date resulted in best establishment.
E. lehmanniana establishment was enhanced by burning and canopy removal.
E. lehmanniana established as well as natives after fire and was more drought-resistant
H. Recommendation: Burn in June and seed either before or after rainfall has begun.
Problem: Native seeds germinate immediately and may dry up, while E. lehmanniana seeds will wait until more dependable moisture is available.
Possible solution: Burn to force expression of E. lehmanniana seedbank. Herbicide after onset of summer rains. Subsequent direct seeding of natives.
VI. Seeding techniques (Frank Munshower.1994. Practical Handbook of Disturbed Land Revegetation. Lewis Publishers, Boca Raton. 265 p.)
A. Drill seeding: drill, cultipacker
B. Broadcast seeding (drops on ground instead of placing in ground)
spreader, seeder with roller or chain to cover seeds
D. Pioneer spp.
immediately prior to period of maximum precipitation, or