Oak/pinyon/juniper woodland on hills and mountains of mixed lithology

On the north side of the Catalinas, a mix of oak, juniper, and manzanita dominate steep slopes built primarily of metasediments (quartzite), igneous rocks (diabase, quartz diorite, granite, rhyolite, and porphyry), and sedimentary rocks (siltstone, sandstone, and limestone). This geologic grab-bag affects the flora, naturally. For instance, bands of mountain mahogany live on limestone strata, while cliff rose seems to favor metasediments.

Overall, this mixed lithology EU is similar to the “oak/juniper/pinyon on granitics”, but steeper: 98% of this mixed lithology EU is steeper than 18% slope, compared to 77% steep slopes on granitics. Steeper slopes amplify the difference between north and south. As can be seen in the photos below, the north is more mesic, with relatively dense cover, while the southern slopes are more arid and open.

Above: Catalinas, Oracle Ridge, looking SSE to Rice Peak, October, 2008, at 6300 ft. The view extends across porphyry, rhyolite, siltstone, and sandstone, across a woodland dominated (at least near the camera station) by three species of oak (silverleaf, Emory, and white) and alligator juniper. Overall tree cover on these north-facing slopes is 25-39%. Patches of ponderosa pine are in the most mesic sites, but it’s an uncommon species.

Above: Catalinas, October 2008, 5400 feet. The view west from the Oracle Control Road, to Dan Saddle along Oracle Ridge. The grassy hills in the middle ground are built of the Apache group, which is predominantly Troy quartzite. The vegetation on the grassy hills is dominated by Emory and white oak, and manzanita; on drier aspects upslope, alligator juniper is also common. Grasses are abundant, especially tanglehead, sideoats grama, and hairy grama, as well as the yellow composite called goldeneye (Heliomeris longifolia). The EU includes the lands to the north (right) of Dan Saddle, the low point along the far ridge; the forested slope in the back left is excluded.

Desired Conditions

Desired conditions are adapted from Madrean encinal woodland, mid-scale desired condition statements in March 2010 Coronado National Forest planning documents.

The size and number of patches of dense trees varies depending mostly on aspect, and to a lesser degree disturbance, soil type, and site productivity. Patch sizes vary, but are mostly tens of acres. Grasses, forbs, shrubs, tree litter, and small trees provide fuel for the natural fire regime with a greater proportion of the ground cover as grasses and forbs as opposed to litter. Vegetation structure in the wildland urban interface (WUI) has a broad mix of different landscapes, such as open areas and scattered groups or clumps of woodland tree species.

Historic Mean Fire Return Interval (Schussman et al. 2006 literature review)

2.5-10 years for Madrean encinal woodland

Primary treatment options (estimated representative project size range):

• Wildland fire: Prescribed fire and/or wildfire to maintain openings, reduce ground fuels, and site prep (1,000 to 30,000 acres per project)
• First-entry mechanical treatments to prepare for fire reintroduction (mastication/crushing, pushing)(up to 2,500 acres per project)
• Fuelwood sales (smaller diameter, including aspens) to reduce fuel loading (up to 300 acres per project)

Supplemental treatment options (estimated representative project size range):

• Thinning to maintain openings and around developments for safety-related fuel reduction (up to 500 acres per project)
• Herbicide treatment for exotics and shrub management to maintain openings (up to 1,000 acres per project)

Other considerations

May be wilderness considerations with treatments

Other Vegetation Classifications: