Low Thinning as a Forest Restoration Tool at Redwood National Park

Abstract A growing interest in the restoration of young second-growth forests by managers of reserves in the redwood region has led to a need to evaluate restoration-based silvicultural strategies. This case study assessed the effectiveness of low thinning as a forest restoration tool via analysis of stand structure at Redwood National Park's Whiskey Forty Forest Restoration Study. The second-growth stand had more than 5,500 trees ha−1 and 57.0 m2 ha−1 basal area and consisted chiefly of three species: Douglas-fir (the dominant species), redwood, and tanoak. Low thinning reduced stand density but also reduced species richness by eliminating scarce species. Seven years after thinning, growth was enhanced (33.6% gain in basal area), and mortality was minor (3% of all stems); however, Douglas-fir remained competitive in the upper canopy. Its average basal area increment was less than redwood's, but its radial growth was equal and its rate of basal area growth was greater in the years following thinning. We conclude that the thinning improved stand conditions but did not fully satisfy restoration goals and that other thinning methods, such as variable-density thinning, are likely to be more effective at promoting redwood dominance.