Elizabeth C. Cole

The role of herbicides for enhancing forest productivity and conserving land for biodiversity in North America

Abstract Herbicide technology has evolved with forest management in North America over the past 60 years and has become an integral part of modern forestry practice. Forest managers have prescribed herbicides to increase reforestation success and long-term timber yields. Wildlife managers and others interested in conserving biodiversity, however, have often viewed herbicide use as conflicting with their objectives. Do herbicides increase forest productivity, and are they compatible with the objectives of wildlife management and biodiversity conservation? Results from the longest-term studies (10–30 years) in North America suggest that the range of wood volume yield gains from effectively managing forest vegetation (primarily using herbicides) is 30–450% in Pacific Northwest forests, 10–150% in the southeastern forests, and 50–450% in northern forests. Most of the 23 studies examined indicated 30–300% increases in wood volume yield for major commercial tree species and that gains were relatively consistent for a wide range of site conditions. Meeting future demands for wildlife habitat and biodiversity conservation will require that societys growing demand for wood be satisfied on a shrinking forestland base. Increased fiber yields from intensively managed plantations, which include the use of herbicides, will be a crucial part of the solution. If herbicides are properly used, current research indicates that the negative effects on wildlife usually are short-term and that herbicides can be used to meet wildlife habitat objectives.

Response of Small Mammals to Clearcutting, Burning, and Glyphosate Application in the Oregon Coast Range

We sampled amphibians on 3 red alder (Alnus rubra) sites 1 year before and 1 and 2 years after the following treatments were applied to each site: (1) control (uncut), (2) clearcut and broadcast burned, and (3) clearcut, broadcast burned, and then sprayed with the herbicide glyphosate. All sites included uncut riparian buffer strips. For 3 of the 6 species with ≥20 captures in pitfall traps, we did not detect changes in capture rates after clearcutting. Capture rates of ensatinas (Ensatina eschscholtzii) and Pacific giant salamanders (Dicamptodon tenebrosus) decreased after logging. Capture rates of western redback salamanders (Plethodon vehiculum) increased the first year after logging, probably because the salamanders sheltered in pitfalls, but effects on populations were unclear. Logging did not significantly alter capture rates of rough-skin newts (Taricha granulosa), Dunns salamanders (P. dunni), and red-legged frogs (Rana aurora). Planning the location and timing of clearcuts or other silvicultural practices over a landscape and retaining riparian buffer strips may be necessary to ensure long-term persistence of Pacific giant salamanders. We did not detect any effects of herbicide spraying on capture rates. Capture rates for rough-skin newts and red-legged frogs were higher in uncut red alder stands than in Douglas-fir (Pseudotsuga menziesii) stands sampled in other studies, an indication that, when red alder stands are converted to Douglas-fir, some alders should be left adjacent to streams to provide habitat for these species and other hardwood associates.

Tall planting stock for enhanced growth and domination of brush in the Douglas-fir region

Two long-term experiments followed development of planted stock of various sizes, origins, and species. In one experiment, multiyear comparisons of container, 2-0 bareroot, and 3-year-old Douglas-fir transplants showed strong positive relationship between initial height and long-term (10–14 years) growth under a range of site conditions with high probability of brush development. In the other experiment, Douglas-fir, western hemlock, and Sitka spruce were planted in salmonberry disturbed by logging 0 and 4 years previously. Half the seedlings were released with glyphosate 6 months after planting. Hemlock and Douglas-fir bare-roots all grew well if planted in a fresh burn, despite rapid regrowth of salmonberry, but virtually all seedlings less than 60 cm tall except Sitka spruce were killed by 4-year-old salmonberry if not released. Release improved growth of seedlings in the fresh burn by 6%, gaining an average of about 0.6 year toward reaching a height of 6 m. Release improved growth of survivors in 4-year-old salmonberry by 51% in height, 72% in diameter, and 325% in volume at age 12. Sitka spruce grew well until damaged by insects. Hemlock growth was equal to or greater than that of Douglas-fir of comparable initial height. In all comparisons, the probability of being overtopped by brush decreased with increasing initial stock height, and the effect of suppression on growth was also inversely related to initial height. Field planting operations may require special logistic measures for the largest stock types.

A comparison of overstory density measures for describing understory conifer growth

Abstract Stand basal area (TBA), hemispherical photographic estimates of canopy coverage (PCC), and visual estimates of canopy coverage (VCC) were used to predict underplanted seedling growth in an experiment on conifer regeneration in two-storied stand management. VCC was the best predictor of western redcedar (Thuja plicata) seedling volume when evenly and unevenly thinned treatments were combined and when unevenly thinned plots were examined separately, while TBA predicted seedling volume better in evenly thinned plots. VCC also was the best predictor of grand fir (Abies grandis) seedling volume when thinning treatments were combined or unevenly thinned treatments were examined separately; VCC, PCC, and TBA predicted grand fir volume in evenly thinned plots about equally well. VCC was more strongly correlated with TBA than was PCC, especially at higher levels of overstory retention in the evenly thinned stands. In unevenly thinned plots, the VCC and PCC estimates were correlated with stand basal area about equally. In unevenly thinned plots, both estimators were better at lower than at higher residual densities. With roughly 41% of variance of growth of individual seedlings explained by VCC, it is a relatively poor predictor for individuals. For large groups of seedlings, however, VCC is a good predictor of a general pattern and considerably better than PCC, on average.

Cavity-nester habitat development in artificially made Douglas-fir snags.

Standing dead trees, or snags, are a source of foraging habitat and nesting cavities for wildlife. We evaluated the efficacy of creating Douglas-fir (Pseudotsuga menziesii) snags (by girdling, silvicide treatment, and topping) and their influence on deterioration rate by describing bark beetle activity, fungal colonization, and use by cavity nesters. To compare the development of artificial with natural fungal infection, we inoculated snags with Fomitopsis pinicola, Fomitopsis cajanderi, Phellinus pini, and Phlebiopsis gigantea. Silvicide-treated and fully topped trees took just over 1 year to die; girdled trees took slightly over 2 years to die. Trees topped at mid-crown that died took almost 3 years. Top breakage began 4 years after treatment. Neither snag-creation methods nor artificial inoculation directly affected bark beetle (Dendroctonus spp., Ips spp.) activity or the presence of externally visible fungal fruiting bodies 4 years after treatment. Native decay fungi, particularly Trichaptum abietinum and Cryptoporus volvatus, extensively colonized snag sapwood. Snag-creation method and artificial inoculation did not appreciably affect woodpecker activity after 4 years. Rather, length of time the snag had been dead had the most influence on bird use. All snags except the living mid-crown topped trees provided foraging habitat and may be a suitable condition for cavity-nest excavation. Pileated woodpeckers (Dryocopus pileatus), hairy woodpeckers (Picoides villosus), and other species excavated and de-barked the created snags during foraging, and possibly during nesting activity.

Vegetation Control and Soil Moisture Depletion Related to Herbicide Treatments on Forest Plantations in Northeastern Oregon

Abstract Reforestation in the Inland Northwest, including northeastern Oregon, USA, is often limited by a dry climate and soil moisture availability during the summer months. Reduction of competing vegetative cover in forest plantations is a common method for retaining available soil moisture. Several spring and summer site preparation (applied prior to planting) herbicide treatments were evaluated to determine their efficacy in reducing competing cover, thus retaining soil moisture, on three sites in northeastern Oregon. Results varied by site, year, and season of application. In general, sulfometuron (0.14 kg ai ha-1 alone and in various mixtures), imazapyr (0.42 ae kg ha-1), and hexazinone (1.68 kg ai ha-1) resulted in 3 to 17% cover of forbs and grasses in the first-year when applied in spring. Sulfometuron + glyphosate (2.2 kg ha-1) consistently reduced grasses and forbs for the first year when applied in summer, but forbs recovered in the second year on two of three sites. Aminopyralid (0.12 kg ae ha-1) + sulfometuron applied in summer also led to comparable control of forb cover. In the second year after treatment, forb cover in treated plots was similar to levels in nontreated plots, and some species of forbs had increased relative to nontreated plots. Imazapyr (0.21 and 0.42 kg ha-1) at either rate, spring or summer 2007, or at lower rate (0.14 kg ha-1) with glyphosate in summer, provided the best control of shrubs, of which snowberry was the dominant species. Total vegetative cover was similar across all treatments seven and eight years after application, and differences in vegetation were related to site rather than treatment. In the first year after treatment, rates of soil moisture depletion in the 0- to 23-cm depth were correlated with vegetative cover, particularly late season soil moisture, suggesting increased water availability for tree seedling growth. Nomenclature: aminopyralid; glyphosate; hexazinone; imazapyr; sulfometuron; common snowberry, Symphoricarpos albus (L.) S. F. Blake.