Abstract
Restoration of second-growth riparian stands has become an important issue for managers of redwood (Sequoia sempervirens [D. Don] Endl.) forest reserves. Identifying differences between old-growth and second-growth forest vegetation is a necessary step in evaluating restoration needs and targets. The objective of this study was to characterize and contrast vegetation structure and composition in old-growth and unmanaged second-growth riparian forests in adjacent, geomorphologically similar watersheds at Redwood National Park. In the old-growth, redwood was the dominant overstory species in terms of stem density, basal area, and importance values. Second-growth was dominated by red alder (Alnus rubra Bong.), Douglas-fir (Pseudotsuga menziesii [Mirbel] Franco), and redwood. Understory species were similar in both forests, with several key differences: Oxalis oregana Nutt. and Trillium ovatum Pursh had greater importance values in the old-growth, and Vaccinium parvifolium Sm., Dryopteris spp. and sedges Carex spp. had greater importance values in the second-growth. Notable differences in structure and composition suggest that restoration practices such as thinning could expedite the acquisition of old-growth characteristics in second-growth riparian forests.
Highlights
The silvicultural manipulation of second-growth stands to expedite the acquisition of old-growth forest characteristics, has emerged as a top priority for managers of forest reserves in northern coastal California [1,2,3,4]
Upland second-growth stands that emerged after the clearcutting of old-growth redwood forests are often characterized by conditions that foretell stagnation: very high tree densities, presence of non-native tree species, and suppressed stand growth and development [5,6,7]
The old-growth basal area was more than 6 times the second-growth, 396.1 m2 haí1 and 61.6 m2 haí1, respectively (P < 0.003; Table 1)
Summary
The silvicultural manipulation of second-growth stands to expedite the acquisition of old-growth forest characteristics, has emerged as a top priority for managers of forest reserves in northern coastal California [1,2,3,4]. Of equal importance are the region’s riparian forests that connect upland forests with adjacent aquatic ecosystems. Second-growth riparian stands are believed to inadequately replace old-growth in their provision of important aquatic ecosystem services to streams and rivers, such as canopy shade, nutrients from arboreal detritus, structure and habitat from large woody debris, and stream bank stabilization [8,19,20,21]. Headwater streams are especially influenced by adjacent riparian vegetation in surrounding forests via shading and inputs of nutrients and organic matter [10,19,22]. Headwater streams comprise more than 80% of the cumulative channel length of northern California coastal watersheds, and 89% of streams within Redwood National
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