Ecologically sustainable forestry in redwood ecosystems of the Santa Cruz Mountains

A position statement of the Santa Cruz Mountains Bioregional Council – July 2009

Is the commercial harvest of redwoods as practiced in the Santa Cruz Mountains ecologically sustainable? Local foresters and timber harvest operators often claim that it is. How do we know if this is true? If we can agree that ecologically sustainable forestry, as opposed to sustained yield logging, requires the protection and conservation of such resources as healthy soil, clean water, and natural biodiversity, then forest scientists can best answer this question.

Forest ecologists D.B. Lindenmayer, J.F. Franklin, and J. Fischer (2006) have proposed five major management strategies to protect forest biodiversity while still allowing some timber harvest. These strategies assume two over-riding conditions: (1) that an adequate system of no-disturbance reserves (parks, open-space preserves, etc.) has been provided for, and (2) that exotic invasive plants, animals, insects, and diseases are kept under control.

The authors go on to recommend specific practices for the types of forests that they have studied; some of these practices can be applied to our redwood forests, while others would need to be modified to accommodate the many unique characteristics of redwood. There is no question however that these five broad strategies or actions (listed below) are completely applicable to the redwood – Douglas-fir forests of the Santa Cruz Mountains.

Five Management Actions Required for Ecologically Sustainable Forestry
adapted from Lindenmayer et al., 2006

  1. Maintain connectivity between forest reserves, other forest habitats, biotic communities, and ecological processes at multiple scales through time. In the Santa Cruz Mountains only about 5 % of the original old-growth forest remains and is found in 56 stands. Some of these stands are privately held and can be logged. Of the total remaining old-growth acreage, about 45 percent is in Big Basin Redwoods State Park, which contains about 4,500 acres of old-growth. Of the larger remaining stands, only seven range between 1,000 and 200 acres in size, and the rest are smaller, mostly less than 100 acres. Thus the large majority of old-growth stands left in the Santa Cruz Mountains are too small to fulfill all the important old-growth ecosystem functions unless they are enhanced by buffer areas and connecting corridors of appropriately-managed older second-growth forest. As Ruskin Hartley, Executive Director of Save the Redwoods League has stated about redwoods throughout their range, "connecting protected lands to create larger corridors of wildlife and forest habitat is critical"(Save-the-Redwoods League, 2008).
  2. Maintain the biological and physical integrity of streams, rivers, and wetlands. In the Santa Cruz Mountains most steelhead or salmon streams now have elevated sediment loads and lack an adequate number of larger in-stream conifer logs. Under natural conditions, large logs of redwood and Douglas-fir (which last much longer than alder) will occasionally fall into the channel, or are carried into the channel by upslope debris flows that occur episodically. Once there they provide stable features that create pool habitat for salmonids and help to stabilize the bed and channel from the effects of high stream flows. Unfortunately, historic logging has removed the larger trees from many of our watersheds, and on-going logging continues to remove whatever large trees remain. A lack of such large woody material in channels has been identified by fishery biologists as one of the most important factors limiting steelhead and salmon numbers in our streams. Other land use activities that impair water quality, increase the sediment load, and change the channel configuration of our streams include development, which alters stream flow regimes causing summer flow levels to be decreased and flood flows to be higher, and existing or new roads which can add significant amounts of new sediment to the channel. It is important to control soil erosion, to maintain natural infiltration/runoff relationships, and to restore large logs into rivers and streams where they are now lacking.
  3. Maintain structural complexity within the forest stand. In the redwood – Douglas-fir forests of the Santa Cruz Mountains, this complexity includes such features as trees of different ages, diverse tree species, large living trees, big snags, large down logs, a multi-layered canopy, and horizontal heterogeneity in tree density including some gaps in tree coverage. These features are always present in old-growth redwood – Douglas-fir stands but are typically either completely lacking or scarce in second-growth, third-growth, or fourth-growth stands. In the Santa Cruz Mountains, state law allows forests to be logged repeatedly, every 10 to 14 years, and allows the largest trees to be removed during each cutting cycle, resulting in a loss of structural complexity. To maintain ecological stability, some large trees should be retained forever in the stand. These trees are called "biological legacies" as they carry over some ecologically-important structures and processes into the new forest (Mazurek and Zielinski 2004).
  4. On a broad scale, keep natural landscape heterogeneity such as may be caused by disturbance regimes or variation in environmental conditions (soils, topography, climate, etc.). If feasible, maintain or restore natural disturbance regimes such as ground fires. Hollowed tree trunks (i.e., goose pen trees) are an important habitat feature of natural redwood forests that are dependent on fire for their creation. Management planning should monitor environmental conditions and be adaptive and flexible enough to take into account any future changes that may occur in forest ecosystem functions, as through anticipated changes in climate. The type of disturbance caused by most commercial logging operations does not mimic any type of natural disturbance and is not beneficial for the forest ecosystem.
  5. Logging should be restricted to off-reserve areas, and should, to the extent practical, mimic natural disturbance regimes in "the kinds and numbers of biological legacies left and spatial patterns of environmental conditions" that result from the disturbance. Because old-growth reserves and other old-growth stands in the Santa Cruz Mountains are relatively few in number and generally small in size, "no-logging" buffer zones should be established around them. "No-logging" setbacks from streams and endangered species habitat areas are also important. Tree cutting or manipulation is appropriate in these buffer areas when its purpose is to improve structural complexity and old-growth-like heterogeneity under the guidance of forest scientists. Suitable management practices might include topping of trees for nest sites, girdling large trees to create snags, felling trees to restore wood to channels, felling trees to enhance growth that favors the development of nest site structures on saved trees, and tree removal that creates forest gaps favoring desired understory vegetation.

Literature Cited and Other Sources:

Lindenmayer, D.B., J.F. Franklin, and J. Fischer. 2006. “General Management Principles and a Checklist of Strategies to Guide Forest Biodiversity Conservation”. Biological Conservation 131: 433 – 445.

Mazurek, M.J. and W.J. Zielinski. 2004. “Individual Legacy Trees Influence Vertebrate Wildlife Diversity in Commercial Forests”. Forest Ecology and Management 193: 321-334.

Save the Redwoods League. 2008. “Save-the-Redwoods Celebrates 90 Years of Protecting Ancient Redwood Forests”. Press Release to April 8, 2008.

Singer, S.W. 2003. “Old-growth Forest Stands in the Santa Cruz Mountains”. Unpublished report for Save-the-Redwoods League, San Francisco, CA.