Abstract
We examined the effects of a second-thinning harvest with alternative riparian buffer management approaches on headwater stream habitats and associated vertebrates in western Oregon, USA. Our analyses showed that stream reaches were generally distinguished primarily by average width and depth, along with the percentage of the dry reach length, and secondarily, by the volume of down wood. In the first year post-harvest, we observed no effects of buffer treatment on stream habitat attributes after moderate levels of thinning. One of two “thin-through” riparian treatments showed stronger trends for enlarged stream channels, likely due to harvest disturbances. The effects of buffer treatments on salamanders varied among species and with habitat structure. Densities of Plethodon dunni and Rhyacotriton species increased post-harvest in the moderate-density thinning with no-entry buffers in wider streams with more pools and narrower streams with more down wood, respectively. However, Rhyacotriton densities decreased along streams with the narrowest buffer, 6 m, and P. dunni and Dicamptodon tenebrosus densities decreased in thin-through buffers. Our study supports the use of a 15-m or wider buffer to retain sensitive headwater stream amphibians.
Highlights
Forest management practices are a leading concern for world biodiversity
We examined effects on: (1) all species combined; (2) all amphibian species; (3) all fish species—cutthroat trout (Oncorhynchus clarkii), trout species (Oncorhynchus), sculpin species (Cottidae); (4) stream-breeding amphibian species—coastal tailed frog (Ascaphus truei), coastal giant salamander (Dicamptodon tenebrosus) and torrent salamanders (Rhyacotriton spp.), (5) terrestrial-breeding amphibian species—clouded salamander (Aneides ferreus), Oregon slender salamander (Batrachoseps wrighti), Ensatina (Ensatina eschscholtzii), Dunn’s salamander (Plethodon dunni) and western red-backed salamander (P. vehiculum); (6) pond-breeding species—rough-skinned newt (Taricha granulosa), northwestern salamander (Ambystoma gracile) and northern red-legged frog (Rana aurora); and
How wide do no-entry riparian buffer zones need to be to retain sensitive fish and amphibian species or their critical habitat conditions? Do we need a no-entry riparian buffer if we are employing ecological forestry approaches with green-tree retention, rather than clearcut harvesting? To achieve biodiversity goals in managed forests where wood commodity production is a priority, what is the efficacy of an inner streamside no-harvest zone relative to a thinned outer riparian zone? If such an approach has merit for biodiversity objectives, how wide does each of these areas need to be? In some contexts, riparian thinning has been proposed to accelerate the growth of larger trees for future large down wood recruitment; a habitat benefit to both aquatic-riparian and terrestrial species
Summary
Forest management practices are a leading concern for world biodiversity. The International Union for the Conservation of Nature (IUCN) has been tracking species conservation for 50 years, with theirRed List established as the global authority for species status assessments. Amphibians and fishes are two highly vulnerable chordate taxa (32% of amphibian species are globally threatened, and 43% are experiencing declines [1]; 41% of amphibian species are threatened by other criteria [2]; >40% of freshwater fish species are threatened [3]). Both aquatic-dependent taxa are of great concern in forest ecosystems, with many traditional forestry practices, such as clearcut logging without riparian protective areas, listed as major threats to freshwater fishes at the global scale [4]. Forest amphibians have recently been shown to play an important role in forest carbon cycling, facilitating greater carbon storage by reducing leaf litter predators [13]
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