Ecological dynamics
This ecological site is characterized by open slopes dominated by pinemat manzanita (Arctostaphylos nevadensis), with less than 25 percent tree cover. Tree species include California red fir (Abies magnifica), western white pine (Pinus monticola), mountain hemlock (Tsuga mertensiana) and Sierra lodgepole pine (Pinus contorta ssp. murrayana).
The soils on this site are limited by bedrock contact between 10 to 40 inches and have very coarse textures with very low water holding capacities. In addition, this site is often situated on southern slopes and/or on convex topographies that drain rather that hold water. Trees do not establish well on these sites because they are unable to tap into deeper water sources and the seasonal water supply is quickly drained away, transpired or evaporated.
Pinemat manzanita is characteristic of dry cold sites on well drained soils. Pinemat manzanita is considered to be important for soil stabilization, especially on steep slopes, and is known to recover quickly following a disturbance such as fire. Reproduction techniques employed by pinemat manzanita include sprouting and establishing from seed. Seeds require treatment before germination, with digestion by animals or fire cracking the seed coat (Hurteau, 2009). Hurteau reports that pinemat manzanita has an obligate relationship with mycorrhizal fungi. These fungi are important for water and nutrient uptake. Expanded root systems provided by mycorrhizal fungi help plants extract water from the soil, especially during drought conditions. Plants assist the fungi by providing carbohydrates from their photosynthetic processes. The research is unclear on whether mycorrhizal fungi in sites with a well established shrub field will aid or inhibit conifer regeneration.
Extensive cover of pinemat manzanita can create competition for water in the upper soil profile, especially during the dry summer months (Rose, 2003). This does not affect trees already established on the site as they are deeper rooted and able to utilize moisture stored deeper in the profile, but it is problematic for seedling establishment. Initially a high percentage of shrub cover may aid seedling germination by providing shelter and protection. Ultimately, however, very few seedlings will persist on a shrub dominated site due to increased competition for soil moisture. A combination of competition from the shrub component and relatively shallow soil will prevent this site from becoming forested.
State 1
Natural State
This state represents the natural state and conditions for this ecological site. There is not an altered state.
Community 1.1
Pinemat manzanita dominated slope with scattered trees
Figure 4. Glaciated Mountain Slopes
Community phase 1.1 is the reference community for this ecological site. It consists of scattered mature trees with an extensive understory of pinemat manzanita (Arcostaphlyos nevadensis). Tree species include western white pine (Pine monticola), California red fir (Abies magnifica), mountain hemlock (Tsuga mertensiana) and Sierra lodgepole pine (Pinus contorta ssp. murrayana).
Large scale disturbances do not regularly occur on this site, creating the potential for plant community 1.1 to remain relatively unchanged for decades and possibly centuries.
Forest overstory. Mature trees are scattered around the site, with less than 25 percent total canopy. Representative overstory canopy cover is: California red fir (Abies magnifica), 3 percent; western white pine (Pinus monticola), 4 percent; mountain hemlock (Tsuga mertensiana), 2 percent; and Sierra lodgepole pine (Pinus contorta var. murrayana), 1 percent.
Forest understory. The understory is dominated by pinemat manzanita (Arcostaphylos nevadensis) with about 60 percent cover. It is separated by patches of open ground with a light cover of grasses and forbs growing mostly within the pinemat manzanita canopy. The herbaceous community accounts for about 8 percent total cover.
Table 5. Annual production by plant type
| Plant type |
Low
(kg/hectare) |
Representative value
(kg/hectare) |
High
(kg/hectare) |
| Shrub/Vine |
280 |
453 |
628 |
| Tree |
– |
17 |
39 |
| Grass/Grasslike |
– |
6 |
11 |
| Forb |
– |
2 |
8 |
| Total |
280 |
478 |
686 |
Table 6. Ground cover
| Tree foliar cover |
1-25%
|
| Shrub/vine/liana foliar cover |
35-90%
|
| Grass/grasslike foliar cover |
0-5%
|
| Forb foliar cover |
0-5%
|
| Non-vascular plants |
0-2%
|
| Biological crusts |
0%
|
| Litter |
35-80%
|
| Surface fragments >0.25" and <=3" |
0-50%
|
| Surface fragments >3" |
0-35%
|
| Bedrock |
0-10%
|
| Water |
0%
|
| Bare ground |
0-10%
|
Table 7. Canopy structure (% cover)
| Height Above Ground (m) |
Tree |
Shrub/Vine |
Grass/
Grasslike |
Forb |
| <0.15 |
– |
– |
0-1% |
– |
| >0.15 <= 0.3 |
– |
– |
0-9% |
0-3% |
| >0.3 <= 0.6 |
0-1% |
35-90% |
– |
– |
| >0.6 <= 1.4 |
0-1% |
– |
– |
– |
| >1.4 <= 4 |
0-4% |
– |
– |
– |
| >4 <= 12 |
0-2% |
– |
– |
– |
| >12 <= 24 |
5-15% |
– |
– |
– |
| >24 <= 37 |
– |
– |
– |
– |
| >37 |
– |
– |
– |
– |
Community 1.2
Patchy cover of pinemat manzanita with regenerating shrubs and trees
Community phase 1.2 exists after a disturbance creates openings in the shrubs for regrowth. If the correct conditions were present, a fire could remove a large amount of the vegetation on this site. Pinemat manzanita is known to respond favorably following a fire. Heavy recruitment from seed has been documented after fire (Howard 1993). This suggests that seeds lay dormant in the soil until a fire occurs, prepping the seed for germination and providing an opening for establishment. Species richness could increase following a fire since seeds stored in the soil would take advantage of reduced competition from the shrubs.
Forest overstory. Mature trees remain scattered around the site, but some may have been removed by fire, reducing the canopy cover slightly. Species include California red fir (Abies magnifica), western white pine (Pinus monticola), mountain hemlock (Tsuga mertensiana) and Sierra lodgepole pine (Pinus contorta var. murrayana). Tree regeneration will be relatively slow due to limited seed sources availability and competition for resources with pinemat manzanita.
Forest understory. Large patches of regenerating pinemat manzanita (Arcostaphylos nevadensis) and increased herbaceous cover follow disturbance.
Pathway 1.1a
Community 1.1 to 1.2
1.1a- A lighting strike could burn small areas of pinemat manzanita or strike individual trees, creating open areas and an opportunity for seedling and shrub regeneration.
Pathway 1.2a
Community 1.2 to 1.1
1.2a- With time pinemat manzanita re-colonizes open patches on the ground. Trees establish where the opportunity exists.
