How Long It Takes for a Forest to Recover after Clear-cutting

Edge Effects and the Effective Size of Old-Growth Coast Redwood Preserves

Photo by Andrew Slack
While it takes mere decades for second-growth redwoods like these to reach impressive heights, it takes can more time for the forest to truly recover. Photo by Andrew Slack.

Walking under the coast redwoods, a casual observer might marvel at how ancient the forest looks—like nothing has changed in thousands of years. But in the wake of the 1849 Gold Rush, explosive demand for lumber devastated what were once vast, ancient redwood forests that stretched from Central California to Southern Oregon. Today, what remains is just 5 percent of the trees’ original 2.2-million-acre range. While it takes mere decades for second-growth redwoods to reach impressive heights, it may take more time for some forest characteristics to recover fully.

Uncut “old-growth” coast redwood forests are complex ecosystems that support not only giant ancient trees, but a diverse community of associated plants and animals. After clear-cutting in coast redwood forests, many small sprouts spring up from the cut stumps. For the first couple of decades, these sprouts, which are still connected to their original root systems, create a dense canopy while they compete for light. The sprouts quickly begin to thin themselves naturally, allowing a few individuals to begin developing into the next generation of giants.

For the sake of redwoods conservation, it’s crucial to understand the patterns of natural recovery in second-growth forests. Researchers at San Jose State University wondered how long it takes for a forest to truly recover after clear-cutting, and decided to approach the question by comparing forests in different age classes.

Their research took place at Big River Watershed in Mendocino, where coast redwood groves range between 15 and 127 years old. They analyzed 360 plots, classifying each as one of five age classes (0-20, 21-40, 41-60, 81-100, or 101-130 years). The team also included three old-growth forests in the study for comparison.

In every plot, the team measured an array of different traits. After clear-cutting, it seemed, certain traits recovered more quickly than others. Second-growth forests in the 41-80 year age class, for example, showed no difference in stand density or canopy cover compared to the old-growth forests. They also showed a similar level of species richness (the number of species present).

Other traits, like having a high level of Shannon-diversity, took longer than forty years to recover. (Shannon-diversity is similar to species richness, but also accounts for the abundance of each species present.) And even in the 101-130-year age class, certain traits had yet to recover. Basal area, which is the cross-sectional area of trees at 4 ½ feet above ground, had not yet reached old-growth equivalence in the second-growth forests, for example.

Surprisingly, the team also found a great deal of variation between old-growth forests. While all ancient forests are often assumed to be populated by enormous trees and similar types of species, tree size and species assemblages were quite different between one old-growth site and the next.

In a similar study, the same first author compared second- and old-growth forests, but focused specifically on riparian areas, the unique ecosystem near rivers and streams. Today, harvesting is restricted in and near riparian areas, thanks to the Z’berg-Nejedly Forest Practice Act of 1973; however, some argue it might be wise to increase the width of protection around streams to help protect threatened salmonid species (fish in the salmon family). Timber operations near riparian areas open up the forest canopy, which increases light levels that can raise water temperature and alter plant life. Logging also disturbs sediment, which can fall into streams and bury spawning areas. Aquatic wildlife relies on fallen trees for habitat, but logging can affect the number of trees that fall into streams.

The team set out to quantify the impacts of logging on forests in riparian areas, in the hopes of informing land managers and policymakers on appropriate boundaries between timber operations and running water.

The team found that older forests had thinner canopy cover, and if a timber harvest happened more recently, more hardwood species like red alder grew in the area. Younger forests and forests with smaller riparian “buffer zones” contained more non-native plants like English ivy, pampas grass, and forget-me-not.

Overall, the team’s research shows that second-growth forests recover naturally in most respects within a century or less, while some old-growth characteristics, such as tree size, can take longer to reach old-growth levels.

Publications Resulting from These Grants

Michels , K. K. H., and W. Russell. 2016. Variation in Old-growth Coast Redwood (Sequoia sempervirens) Reference Sites in Mendocino County, California. Madrono 63:258–267

Russell, W. and K. H. Michels. 2010. Stand development on a 127-year chronosequence of naturally regenerating Sequoia sempervirens (Taxodiaceae) forests. Madrono 57:229-241.

Russell, W. 2009. The influence of timber harvest on the structure and composition of riparian
forests in the Coastal Redwood region. Forest Ecology and Management 257:1427–1433

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