Ecological dynamics
The redwood's interior range is largely contained within the coastal fog belt. Coastal fog ameliorates the effects of solar radiation on conifer transpiration rates (Daniel, 1942). Research in the redwood region (Dawson, 1998) has indicated that fog drip and direct fog uptake by foliage may contribute significant amounts of moisture to the forest floor during summer months and over the course of the year.
Previous harvesting and the use of fire to treat logging slash have changed species composition on many formerly redwood-dominated sites (Noss et al, 2000). Within many areas of the park, aerial seeding of Douglas-fir has led to a 10:1 ratio of Douglas-fir to redwood (Noss, 2000).
The historical origins of fires within the northern redwood region remain unknown. Lightning-ignited fires are considered rare. However, Native American burning is thought to have played a major role by burning fires from the interior into the redwood zone (Veirs, 1996). Natural fire intervals ranged from 500 to 600 years on the coast, 150 to 200 years on intermediate sites, and 50 years on inland sites. The northern range of redwoods evolved within a low to moderate natural disturbance regime (Veirs, 1979).
Surface fires likely modified the tree species composition by favoring the thicker-barked redwood (Sequoia sempervirens) (Veirs, 1979). Western hemlock's (Tsuga heterophylla) shallow roots and thin bark make it susceptible to fire damage (Arno, 2002). Fires also expose the mineral-rich soil and reduce competition from other plants, thereby increasing the establishment of new western hemlock (Veirs, 1979, Williamson, 1976). Tanoak (Lithocarpus densiflorus) seedlings and sapling-sized stems are often top-killed by surface fire, though larger stems may survive with only basal wounding (Tappeiner, 1984).
Both redwood and tanoak have the ability to re-sprout following fire (Veirs, 1996). After fire, redwood may sprout from the root crown or from dormant buds located under the bark of the bole and branches (Noss, 2000). The sprouting ability of redwood is most vigorous in younger stands and decreases with age. Frequent fire reduces tanoak’s sprouting ability and also tends to keep understories open (Arno, 2002). Fire exclusion would allow for the gradual increase of tanoak in the understory (McMurray, 1989).
A moderate fire could lead towards more of a mosaic in regeneration patterns. Patches of trees would be killed leaving others slightly damaged or unharmed. Douglas-fir (Pseudotsuga menziesii) regeneration would be favored in the large gaps that are created following a moderate fire, potentially leading to a larger proportion of Douglas-fir to redwood for several centuries (Agee, 1993). Without these gaps caused by fire, Douglas-fir regeneration is unsuccessful, and with continued lack of disturbance it may slowly be replaced by redwood as the dominant canopy species (Veirs, 1979, 1996).
Fires will also alter the composition of shrubs and forbs in the understory community. California huckleberry (Vaccinium ovatum) is a common species in both moist and dry redwood environments. It is normally a fire-dependent shrub species, but little is known concerning it's adaptation to fire under low to moderate fire return intervals (Tirmenstein, 1990). Following a fire, California huckleberry will often re-sprout and recover rapidly.
Pacific rhododendron (Rhododendron macrophyllum) is considered sensitive to fire. Following a surface fire, it may reestablish seedlings by sprouting from the rootcrown or stembase (Crane, 1990). After a disturbance such as fire, a decrease in plant cover is common, and will be followed by a gradual increase in cover over time.
Other potential disturbances in the redwood zone include winter storms that can cause top breakage. This breakage may kill individual or groups of trees and create small openings from windfall (Noss, 2000). This would likely favor the establishment of redwood and other shade tolerant conifers. On alluvial sites with periodic flooding, redwood and other colonizing hardwoods would dominate (Veirs, 1996). Where existing redwoods are inundated, new roots would develop in newly deposited silt (Veirs, 1996).
State 1
Reference State - Plant Community 1.1, Redwood and Douglas-fir Forest
Community 1.1
Reference State - Plant Community 1.1, Redwood and Douglas-fir Forest
The reference community for this site is a redwood and Douglas-fir forest. The overstory consists of redwood (Sequoia sempervirens) and Douglas-fir (Pseudotsuga menziesii), with tanoak (Lithocarpus densiflorus) in the sub-canopy. The percentage of redwood composition is generally higher than that of Douglas-fir. Occasionally red alder (Alnus rubra) is present. Western hemlock (Tsuga heterophylla) is present and regenerating in the understory. The estimated age for this community is 200 years or more.
The understory is shrub-dominated with California huckleberry (Vaccinium ovatum), Pacific rhododendron (Rhododendron macrophyllum), and salal (Gaultheria shallon). The cover of grasses and forbs are low.
Community Pathway 1.1a:
Following a block harvest, shrubs and hardwoods will sprout and transition this community to PC 1.2.
Community Pathway 1.1b:
If partial cutting or moderate fire occurs then this community will transition to PC 1.6. Improved seedbed conditions could favor infill of Douglas-fir. Shrubs such as California huckleberry and Pacific rhododendron may increase in cover.
Community Pathway 1.1c:
Blueblossom may dominate the site following block harvesting if a post-harvest burn also occurs, and if a seed source is present. This will lead to PC 1.3.
Forest overstory. The main overstory is dominated by redwood and Douglas-fir, with a minor component of western hemlock.
Tanoak forms a moderate sub-canopy layer beneath the primary overstory. On some sites, an occasional Pacific madrone (Arbutus menziesii) or giant chinquapin (Chrysolepis chrysophylla) may be present.
Average Percent Canopy Cover:
Main canopy
Redwood 30-40%
Douglas-fir 15-30%
Subcanopy
Western hemlock 10%
Tanoak 20-30%
Other hardwoods <5%
Forest understory. The understory is dominated by California huckleberry and Pacific rhododendron. The shrub form of tanoak is present in the understory in varying amounts.
Average Percent Canopy Cover
California huckleberry 25-40%
Pacific rhododendron 20-30%
Tanoak 5-10%
Other shrubs <5%
Table 5. Ground cover
| Tree foliar cover |
60-90%
|
| Shrub/vine/liana foliar cover |
20-40%
|
| Grass/grasslike foliar cover |
0%
|
| Forb foliar cover |
5-10%
|
| Non-vascular plants |
0%
|
| Biological crusts |
0%
|
| Litter |
70-80%
|
| Surface fragments >0.25" and <=3" |
0%
|
| Surface fragments >3" |
0%
|
| Bedrock |
0%
|
| Water |
0%
|
| Bare ground |
0%
|
Table 6. Canopy structure (% cover)
| Height Above Ground (m) |
Tree |
Shrub/Vine |
Grass/
Grasslike |
Forb |
| <0.15 |
– |
– |
– |
– |
| >0.15 <= 0.3 |
– |
– |
– |
– |
| >0.3 <= 0.6 |
0-1% |
– |
– |
5-10% |
| >0.6 <= 1.4 |
– |
10-20% |
– |
– |
| >1.4 <= 4 |
– |
20-30% |
– |
– |
| >4 <= 12 |
0-5% |
– |
– |
– |
| >12 <= 24 |
10-20% |
– |
– |
– |
| >24 <= 37 |
0-10% |
– |
– |
– |
| >37 |
50-60% |
– |
– |
– |
State 2
Plant Community 1.2: Tanoak Shrubland
Community 2.1
Plant Community 1.2: Tanoak Shrubland
Shortly after block harvesting, sprouting will occur from the redwood stumps in the area. The site is quickly covered by rapidly growing shrubs and hardwoods that may dominate the site for a short period of time. Tanoak’s rapid growth will cause it to become the dominant species in the overstory. A dense shrub layer of California huckleberry, rhododendron, and salal will persist in the understory. Douglas-fir seedlings are likely to be present, depending on an available seed source and the degree of ground disturbance, but conifer growth is initially suppressed by brush and hardwood competition. The estimated age for this community ranges from 20 to 200 years.
Community Pathway 1.2a:
Without management this community will transition to PC 1.5 as Douglas-fir and redwood gradually infill and grow. This growth is slowed by the competition from tanoak.
Community Pathway 1.2b:
If an adjacent seed source is present, the infill of Douglas-fir and the sprouting of redwoods would transition this community to PC 1.4. The establishment and growth of Douglas-fir and redwood could be accelerated by brush and hardwood management or chemical treatment which would act to reduce hardwood competition. Tanoak will remain as part of the plant community, leading to a stand of Douglas-fir, tanoak and redwood. Some remnant shrubs of California huckleberry, Pacific rhododendron and salal would remain part of the understory. Douglas-fir may remain as the dominant conifer for a long period of time, with redwoods eventually regenerating in the understory.
Community Pathway 1.2c:
Brush management, chemical control and tree planting may transition this community to PC 1.6 by reducing brush competition and the time period of shrub dominance. Douglas-fir infill from adjacent seed sources could lead to a larger proportion of Douglas-fir to redwood. Overtime, an older multi-story stand of Douglas-fir, redwood and tanoak will develop. Because of tanoak's shade tolerance and persistent behavior to infill, it will remain a stand component indefinitely.
State 3
Plant Community 1.3: Blueblossom Shrubland
Community 3.1
Plant Community 1.3: Blueblossom Shrubland
Block harvesting followed by a moderate post-harvest fire, may lead to an abundance of blueblossom (Ceanothus thyrsiflorus). Blueblossom is a prolific seeder, and the regeneration of seeds stored in the soil tends to be favored following fire. It also readily sprouts when cut (Adams, et al, 1992).Tanoak, California huckleberry and Pacific rhododendron will also sprout and remain part of the plant community. Repeated light to moderate fires would maintain this shrub community. The estimated age for this community ranges from 5 to 15 years.
Community Pathway 1.3a:
Without management, blueblossom could dominate an area for extended periods of time. However, gradual infill of conifers will occur as holes are created from dying brush. Initial conifer growth will be slowed by extreme brush competition, but this community will eventually transition to PC 1.4.
Community Pathway 1.3b:
Brush management and chemical control, in conjunction with conifer tree planting or infill, could transition this shrubland to PC 1.6.
State 4
Plant Community 1.5: Tanoak and Douglas-fir Forest
Community 4.1
Plant Community 1.5: Tanoak and Douglas-fir Forest
Tanoak has rapidly grown in height and is able to dominate large portions of the overstory canopy in this plant community (McMurray, 1989, Adams, 1992). Both redwood and Douglas-fir are established, but growth is inhibited by the competition from tanoak. A modest shrub layer of California huckleberry, Pacific rhododendron and occasionally, salal will remain established in the understory. The estimated age for this community ranges from 20 to more than 200 years.
Community Pathway 1.5a:
Eventually, Douglas-fir and redwood height will exceed that of tanoak, transitioning this plant community to PC 1.4. With time, a multistoried Douglas-fir and redwood plant community with a tanoak sub-canopy would develop. A shrub layer of California huckleberry, Pacific rhododendron and salal remains in the understory.
Community Pathway 1.5b:
The growth of Douglas-fir and redwood could be accelerated by a combination of partial cutting, tree planting and chemical control of tanoak in conjunction with the planting of Douglas-fir and redwood. Redwood sprouts would also be released from hardwood competition. This management would transition the plant community to PC 1.6.
State 5
Plant Community 1.4: Douglas-fir and Tanoak Forest
Community 5.1
Plant Community 1.4: Douglas-fir and Tanoak Forest
During the transition from PC 1.2 or PC 1.3, tanoak’s rapid growth causes it to be the dominate species for a short period of time before Douglas-fir and redwood overgrow it. After Douglas-fir and redwood surpasses tanoak in height, an overstory of Douglas-fir and redwood forms with a sub-canopy of tanoak. California huckleberry, Pacific rhododendron, and salal form the understory shrub layer. The estimated age for this site ranges from 20 to more than 200 years.
Community Pathway 1.4a:
In the early stages of stand development a moderate fire could kill young conifers causing sprouting tanoak to become more abundant for a period of time. This will transition the community to PC 1.5.
Community Pathway 1.4b:
Partial cutting or chemical control of tanoak may release the conifers from competition and could reduce the amount of time needed to develop into the community seen in PC 1.6.
State 6
Plant Community 1.6: Douglas-fir and Redwood Forest
Community 6.1
Plant Community 1.6: Douglas-fir and Redwood Forest
Douglas-fir and redwood dominate the overstory with tanoak in the sub-canopy. California huckleberry and Pacific rhododendron are present in the shrub layer and may become more prominent in openings.
1.6a – With fire exclusion or lack of harvesting, Douglas-fir is unable to successfully regenerate. Redwood continues to become established in the understory and eventually becomes dominant over Douglas-fir. See PC#1.1.
