Arthur R. Tiedemann

Solution of forest health problems with prescribed fire: are forest productivity and wildlife at risk?

Advanced forest succession and associated accumulations of forest biomass in the Blue Mountains of Oregon and Washington and Intermountain area have led to increased vulnerability of these forests to insects, diseases, and wildfire. One proposed solution is large-scale conversion of these forests to seral conditions that emulate those assumed to exist before European settlement: open-spaced stands (ca. 50 trees per ha), consisting primarily of ponderosa pine (Pinus ponderosa Laws.) and western larch (Larix occidentalis Nutt.). We question how well presettlement forest conditions are understood and the feasibility and desirability of conversion to a seral state that represents those conditions. Current and future expectations of forest outputs and values are far different from those at presettlement times. Emphasis on prescribed fire for achieving and maintaining this conversion raises questions about how well we understand fire effects on forest resources and values. We consider here potential effects of prescribed fire on two key aspects of forest management—productivity and wildlife. Use of large-scale prescribed fire presents complex problems with potential long-term effects on forest resources. Before implementing prescribed fire widely, we need to understand the range of its effects on all resources and values. Rather than attempting to convert forests to poorly described and understood presettlement seral conditions, it would seem prudent to examine present forest conditions and assess their potential to provide desired resource outputs and values. Once this is achieved, the full complement of forest management tools and strategies, including prescribed fire, should be used to accomplish the desired objectives. We suggest a more conservative approach until prescribed fire effects are better understood. # 2000 Elsevier Science B.V. All rights reserved.

The influence of topography on male and female fitness components of Atriplex canescens

The influence of environmental heterogeneity on components of male and female fitness is examined using Atriplex canescens growing on steep slopes and alluvium at the slope base as a model system. Female fitness is estimated as the grams of fruit produced per plant and the grams of fruit per gram leaf tissue. Male fitness is estimated as the grams of stamens produced, the number of pollen grains dispersed to a given distance, and the potential number of grams of fruit sired taking into consideration the number and distribution of mates and competing pollen donors. The influence of increased plant size on male and female fitness components, the cost of reproduction (as measured by biomass, joules and nitrogen) on a gross level and a per offspring basis are also examined. The results indicate that the female function is more limited on the slope than the male function. The efficiency of pollen dispersal (the number of pollen grains per unit donor plant volume dispersed to a given distance) is enhanced by growing on slopes. Males become less efficient at dispersing pollen as they increase in size, while the efficiency of female reproduction (grams of fruit per volume or gram leaf tissue) is unaffected by increasing plant size. The cost to a male of siring a gram of fruit is about the same as the cost to a female of producing the gram of fruit. Implications for the evolution of sexual lability and dioecy are discussed.

Responses of desert grassland vegetation to mesquite removal and regrowth

Abstract The purpose of this study was to determine the long-term response of understory vegetation in the desert grassland of southeastern Arizona, USA, to removal and regrowth of mesquite Prosopis juliflora (Swartz) DC. var. velutina (Wooton) Sarg. trees. The study involved 3 treatments applied to mesquite in 1966; mesquite left intact (MI), mesquite removed (MR), and mesquite removed, sprouted, and regrown (MRS). Vegetation responses to 2 litter treatments, litter intact (LI) and litter removed (LR), also were examined. Cover of understory vegetation and juvenile mesquite (< 1.5 m height) were measured in canopy and open (intercanopy) locations. Major changes between 1967 and 1991 were increased cover of juvenile mesquite, shrubs, halfshrubs, bush muhly Muhlenbergia porteri Scribn., and Lehmann lovegrass Eragrostis lehmanniana Nees., and a decline in cover of Arizona cottontop Digitaria californica (Benth.) Chase, and plains bristlegrass Setaria macrostachya H.B.K. Arizona cottontop, plains bristlegras...

Rapid analysis of total sulphur in soils and plant material

SummaryThe Leco high-frequency induction furnace technique was adapted for rapid titrimetric analysis of total S in soils and plant material. Accuracy and precision were tested by standardizing soils and plant material and by measuring recovery of known amounts of inorganic and organic sulphur standards from these. Recovery ranged from 86 to 90 per cent and differed between soils, depending on organic matter and N content.

Economic assessment of ungulate herbivory in commercial forests of eastern Oregon and Washington, USA

Four forest stands in eastern Washington and Oregon, USA, containing exclosures to prevent or impede ungulate herbivory, were modeled to forecast timber yields and soil expectation values (SEVs) at harvest. Contrasts of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) growth and yield inside and outside exclosures show that ungulate herbivory may either promote or depress tree volume growth. Projected income from stands with more intensive stocking management and with inclusion of regulated livestock herbivory was higher than that of less intensively managed stands without livestock for scenarios with projected rising stumpage price levels for 2040. Under an assumption of future stumpage prices held constant at 1990 levels, the reverse was true. Ungulate herbivory plus planted stock and prescribed fire in site preparation provided the highest stand value at two sites. Sites without prescribed fire fared better when fenced to prevent livestock or big game herbivory. The results illustrate that ungulate herbivory alone is not the determinant factor of the economic yield of stands, but ungulate herbivory can have substantial impact on site productivity when used in conjunction with prescribed fire, stocking control, and species selection.

Economically optimal private land grazing strategies for the Blue Mountains of eastern Oregon

The Oregon Range Evaluation Project implemented 3 levels of grazing management intensities (strategies) on private land pastures in the Blue Mountains of northeastern Oregon. Prior to implementing each management strategy, a coordinated resource plan was prepared and a benefit-cost analysis on each practice and pasture was performed. The goal was to achieve the largest economic return from grazing for each strategy implemented. Returns above variable costs were used to select the optimal grazing sfrategy for the ecosystems represented. The commodity production strategy was found to be optimal in all ecosystems over a wide range of interest rates, management costs, and beef prices.