“Forest health” is ultimately a metaphor, but it is a phrase bandied about so much that it is unavoidable in this kind of discussion. To be clear, it should be defined.
There are many such definitions in circulation. Some include a clause such as “serves human needs” in the definition. This is clearly convenient to the logging industry, which is probably responsible for promulgating such definitions. Yes, a healthy ecosystem can better withstand exploitation. But to include such exploitation in the definition is cynical, and can only be considered circular reasoning when such a definition is used, in turn, to justify logging.
It makes more sense, instead, to base the notion of forest health on Aldo Leopold's general description of land health: “Health is the capacity of the land for self-renewal.”
A healthy forest, then, is one that can renew itself. That is precisely what our CTPZ has been doing since the Sea Ranch acquired it in 1993. Even the reports commissioned by the advocates of logging confirm this. (See FDQ 5.)
It is commonly asserted that second-growth redwood forests require thinning for their own health. For example, the 2013 McBride report asserts (p. 40) that “The benefits of harvesting ... include ... improve forest health ... ”. In his Appendix to the same report, forester Matt Greene goes into more detail (p. 114):
If forest management is not continued on the property, the growth rates will decline and the forest will eventually begin to stagnate. The amount of dead, dying, and diseased trees within the forest will continue to increase, as will the hazards associated with leaving them standing. The forest will develop a multi-age structure, but it will take much longer than if actively managed. During this time period, which could last for many decades, the fuel load for fires will continue to build up.
Greene does not present any justification for these dire predictions, perhaps because this is conventional wisdom in the logging industry.
But it turns out that there has been very little study, in the case of coast redwood forests, to verify these beliefs. A recent empirical study (Russell et al. 2014) was designed expressly to examine this issue. The study involved second-growth plots in five state parks in the Santa Cruz mountains, where the redwoods have been protected from logging for periods ranging from 80 to 160 years. For reference, five old-growth reference sites were examined as well. The conclusion?
The results of this study indicate that natural recovery is an effective technique for the restoration of coast redwood forests. The overall density of trees declined over time in recovering stands reaching statistical equivalence with old-growth reference sites for most species. The dominance of S. Sempervirens also reached statistical equivalence with old-growth, as did canopy cover, understory cover, and species richness. Associated herbaceous species also trended toward recovery ...
This is a far cry from Greene's prediction of stagnation and death!
An older study (Chittick and Keyes 2007), which is sometimes cited in support of thinning as a restoration technique, is worth examining closely, as the data presented actually also provide evidence for a coast redwood forest's capacity for self-regeneration.
This study compares control plots (untouched) and plots thinned to two different densities in second-growth portions of Redwood National Park, after a lapse of 25 years (thinning was performed only once at the start of the period). The second-growth forest began as primarily even-aged stands, and the thinning was intended to increase redwood dominance and introduce a more variable-aged forest structure. The authors conclude that thinning failed to increase redwood dominance, but did introduce a more variable-aged structure, and the decreased density in the thinned plots favored increases in herbaceous cover of the forest floor. Intriguingly, their raw data also shows significant decrease in density of stems/acre in the control plots, concentrated in smaller (<4" diameter) stems, indicating that self-thinning is taking place; but they do not comment on this in their analysis. They claim instead, in their conclusions (citing no evidence) that the controls will take another 50-100 years to move to the next stage in development.
There is another lesson for Sea Ranch in the Chittick and Keyes study. The technique they recommend is one pass of thinning to establish the desired age structure, and then allowing the forest to develop on its own. This is quite different from the current plan for logging our central forest, which envisions not one thinning pass, but endless recurring logging at frequent intervals.
Interestingly, the procedure recommended by Chittick and Keyes has already been performed in our central forest. As described in the Tunheim report (p. 8) the former owner of this land performed a 40%-50% selective cut in 1991–1992.
Forester Matt Greene confirmed that this selective harvest had precisely the effect desired by Chittick and Keyes: “This multi-age structure [of the CTPZ forest now] much more closely resembles what the original forest would have looked like, pre-European settlement. The main differences today are that the trees are smaller and there are many more per acre.” (Greene appendix to 2013 McBride report, p. 108–109).
This is even more clearly stated in the NTMP itself (p148):
The assessment area contains grasslands, second growth stands within the 40 to 60 year age class with scattered remnant trees that may be up to 100 years old, as well as a 20 year old age class. The mature second growth stands within the assessment area are generally made up of redwood, Douglas-fir, grand fir, western hemlock, sugar pine, bishop pine, tan oak, bay and madrone. This has created the appearance of at least 3 age classes on the property with distinct canopies.
Thus, Greene himself confirms that the existing central forest already has a multi-age structure. As for his “the trees are smaller and there are many more per acre,” the studies cited previously establish that a coast redwood forest resolves these issues naturally, in a few decades, without any need for further violence.
One issue remains that requires intervention: fuels management for fire safety. This was, indeed, the one intervention sanctioned under the original rules established to govern the central forest when the Sea Ranch acquired it. This kind of intervention, however, is radically different from the logging plans being proposed.
We discuss fuels management in the section Managing the Forest for Fire Safety.