Old-Growth Forests of the Santa Cruz Mountains: A Rare and Valuable Resource

by Steven Singer

Old-growth forests in the Santa Cruz Mountains Bioregion are composed of large Coast Redwood (Sequoia sempervirens) and Douglas-fir (Pseudotsuga Menziesii) trees that are hundreds of years old.  Old-growth redwood trees are typically 4 – 10 feet in diameter and 200 – 240 feet tall.  Some trees, on exceptional sites, may be taller than 280 feet, exceed 15 feet in diameter, and may be more than 1,000 years old.   The tallest redwood in the Santa Cruz Mountains is 328 feet high*. 

Old-growth redwood forest is rare in the Santa Cruz Mountains.  About 96 percent of the original old-growth forest has been lost to logging.  Big Basin Redwoods State Park, with about 4,300 acres of old-growth, is by far the largest remaining stand.  Only 11 other stands exist that are larger than 100 acres in size, and six of those are privately owned and not yet protected**.

Second-growth forests make up most of our remaining forest lands.  The redwoods in these forests started as stump sprouts following the clear-cut logging of the late 1800's and first half of the 1900's.  If left to grow for a few hundred years, these forests will slowly recover their old-growth characteristics. 

Old-growth forests can be thought of as natural forests of high biological diversity with their evolutionary and ecological processes still intact and functioning fully.  So-called "managed forests", those where logging takes place at ten to fifteen year intervals, have their ecological development truncated by removing up to 60% of the individual trees in a process called "selective harvest".  The result is a forest of relatively small trees that lack the richness of forest habitats, organisms, and ecosystem functions found in old-growth forests.

Soil Microbes Underground are Essential for Health of Large Trees

Redwoods will not develop normally in soils lacking a healthy soil flora and fauna.  In fact, old-growth forests contain an exceptional diversity and abundance of soil bacteria, fungi, mites, and other micro-organisms.  Unlike tropical rain forests whose biological diversity is found in above-ground organisms (plants, birds, insects, etc.), the old-growth redwood and Douglas-fir forests develop a "hidden biodiversity" of soil organisms- most of which are microscopic in size.  These and other soil organisms, such as mycorrhizal fungi, facilitate such important ecosystem functions as nutrient cycling, water and nutrient uptake by trees, and protection against plant diseases.  This "hidden biodiversity" is absolutely crucial to the long-term maintenance of healthy, productive forest ecosytems. 

The redwood forest's abundant soil flora and fauna is dependent to a large degree on the existence of large logs on the forest floor -- a feature that is often unappreciated by forest land owners.  Large decaying logs provide vital raw materials for the soil organisms that maintain soil fertility and they offer a critical refuge for these same organisms during natural disturbances such as wildfire.  They also serve forest trees as important reservoirs of slow-release energy, nutrients, and water.

Can logging be used as a tool to create old-growth forest conditions?

Many old-growth forest characteristics, like the presence of trunk or limb deformities and the development of massive branch systems, are the result of age and injury and only develop over time.  A typical logging operation will harvest redwoods when they reach 50 - 100 years of age -- at less than 10% of their natural life span, and not leave enough time for these important structural features to develop.

These "farmed" trees never have a chance to develop large limbs, a dead top, or any of the characteristics associated with old age.  Because no redwoods are allowed to grow old and die naturally, there is no replenishment of snags and large down logs on the forest floor.  The small branches and foliage left on the forest floor after logging operations are not nearly as beneficial as are large down logs, since they have lesser amounts of lignin, a critical heartwood component utilized by soil fungi.

How does Wildfire Affect the Old-growth Forest?

Over the course of the millennia, the redwood forest ecosystem has evolved mechanisms to cope with, or even benefit from, natural disturbances like floods, wind storms, or fires.  The natural fire regime of reoccurring low-intensity ground fires does not harm most large trees, and does not favor the development of large catastrophic crown fires that would threaten human lives or structures.  Instead it reduces the risk of a catastrophic crown fire by removing the small trees and shrubs that would fuel such a fire.  To reduce fire hazard, controlled burns that mimic the natural fire regime have been used successfully in the old-growth forests of Big Basin Redwoods State Park for many years.

Does Logging Reduce the Risk of Catastrophic Fire?

Commercial logging is unlike any form of natural disturbance to which the forest has adapted.  Typically, logging removes the saw-mill sized redwoods and leaves the smaller redwoods, hardwoods, and shrubs that present the greatest fire danger.  In fact, in the short term, logging may actually increase the fire hazard by adding massive amounts of "slash", highly flammable dead branches and twigs, to the forest floor.

What Can be Done to Create or Nurture Old-growth Conditions?

People can support old-growth forests by encouraging ecological management of our redwoods forests.  Individual trees in second-growth stands can be manipulated to create the structural deformities (broken tops, deformed branches, hollows, etc.) that normally develop with age.  Where snags are lacking in a stand, a few larger trees can be killed to create new snags.

Wider use of controlled burning will also favor the development of natural forest conditions.  Prescribed burning not only reduces the hazard of catastrophic fire, its use in second-growth forests can speed the development of some old-growth forest characteristics.

Older second-growth forests and those forests with scattered remnant old-growth trees can be purchased and protected from logging.  If protected and allowed to mature, perhaps with the benefit of ecological management techniques such as mentioned above, these forests will assume many old-growth forest characteristics in 50 to 100 years.

Why Should One Care About Old-growth Forests?

Humankind has much to learn from our old-growth forests.  Until the arrival of modern man, these forests have perpetuated themselves and stayed healthy and productive for thousands of years.  The survival mechanisms found in our old-growth forests can teach forest land owners how to manage their forests in a more sustainable manner -- a manner that can not only produce wood products, but also produce fish and wildlife, clean water, and fertile soils for this and future generations.  Indeed, the secrets of the old-growth forest, once revealed, may teach us much about how we can live on this planet without destroying it in the process.

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* Moore, Z.J. and S.W. Singer.  2012 Discovery of the Tallest Redwoods in the Santa Cruz Mountains – Their Distribution and Ecology.  Unpublished report by the authors.
** Singer, S.W.  2012. Unpublished data.