Limestone Hills 12-16" p.z.

Description

The historic native plant community is a diverse mixture of perennial grasses, suffrutescent forbs, shrubs, succulents and desert trees. A rich flora of native annual forbs and grasses, of both the winter and summer seasons, exist in the plant community. Periodic, naturally occurring, wildfires were important in maintaining the potential plant community.
North slopes have a chaparral of evergreen shrubs like jojoba, turbinella oak, mountain mahogany, cliffrose, desert buckbrush and canotia. Southern exposures will have a higher percentage of desert shrubs, trees like paloverde and succulents in the plant community. More xeric grasses will dominate southern exposures (aristida, tridens). Grasses on cooler aspects include stipa species and sideoats grama.

Dominant plant species

1. crucifixion thorn (Canotia holacantha), tree

2. blue paloverde (Parkinsonia florida), tree

3. jojoba (Simmondsia chinensis), shrub

4. Sonoran scrub oak (Quercus turbinella), shrub

5. mountain mahogany (Cercocarpus), shrub

6. Arizona cliffrose (Purshia ×subintegra), shrub

7. desert ceanothus (Ceanothus greggii), shrub

8. threeawn (Aristida), grass

9. tridens (Tridens), grass

10. (Stipa), grass

11. sideoats grama (Bouteloua curtipendula), grass

Submodel

Description

Perennial grass canopy cover is reduced due to the interactions of drought, grazing and fire. Desert shrubs and cacti dominate the plant community. Shrub cover exceeds 30%. Annuals, both native and non-native, dominate the under-story. Fire frequency is reduced but the site can still burn, especially after "El Nino" years produce heavy fuel loads of annual grasses and forbs.

Submodel

Description

Shrubs like jojoba, whitethorn acacia, mesquite, ocotillo and canotia, and succulents like prickly pear, cholla and banana yucca can increase to dominate the site in the absence of fire for very long periord of time. Native and non-native annual forbs and grasses dominate the under-story. In "El Nino" years, herbaceous fuels can be sufficient to carry fire through the heavy canopy of shrubs. The major woody shrubs are, however, fire resistant once established. Such fires would remove less tolerant species like cacti and leave intact the sprouting woody plants to become more and more dominant. Extreme rainfall events coupled with the fire, drought and grazing interaction, can lead to rilling of steep slopes. Compaction of soils can occur with heavy trailing from continuous livestock use. Loss of plant cover after repeated fire can lead to accelerated rill erosion under these circumstances.

Dominant plant species

1. jojoba (Simmondsia chinensis), shrub

2. whitethorn acacia (Acacia constricta), shrub

3. mesquite (Prosopis), shrub

4. crucifixion thorn (Canotia holacantha), shrub

5. cholla (Cylindropuntia), shrub

6. banana yucca (Yucca baccata), shrub

7. pricklypear (Opuntia), shrub

Submodel

Description

Non-native annual grasses and forbs like red brome, cheatgrass, and wild oats can invade and dominate areas of the site. These species can, over time, reduce the seed-bank of native annual grasses and forbs. Their presence can increase the fire frequency (of man made fires) especially where roads and urban areas are adjacent to areas of the site. Repeated fires tend to remove fire sensitive species like paloverde, cacti and canotia, and leave fire tolerant species like turbinella oak, mesquite, whitethorn and jojoba.

Dominant plant species

1. red brome (Bromus rubens), grass

2. cheatgrass (Bromus tectorum), grass

3. wild oat (Avena fatua), grass

Submodel