David B. Wester

Viewpoint: replication, randomization, and statistics in range research.

Appropriate application of significance tests in statistical analyses requires an explicit statement of hypothesis; a clear definition of the population(s) about which inferences are to be made; and a model, a sampling strategy, an analysis, and an interpretation that are consistent with these considerations. In particular, experimental design and analyses must recognize appropriate replication and random selection of experimental units from target population(s). This paper discusses some aspects of these issues in range science research. Textbook examples and examples from range science applications are discussed in parallel in an attempt to clarify issues of randomization and replication in statistical applications.

Purposeful wanderings: mate search strategies of male white-tailed deer

In species where defense of females or resources attractive to females is not an option, males search for mates. How males locate mates is not well understood. Male white-tailed deer (Odocoileus virginianus) are assumed to search widely for females in estrus; but the rut (2–4 weeks) and estrus (1–2 days) are short and males would benefit by having a strategy to locate mates. Because females typically have small home-range sizes and exhibit site fidelity, we predicted males would spend time in small focal areas containing females during rut. We fitted 102 males with GPS collars across 5 breeding seasons in South Texas. During rut, movement rates increased but most males used a small portion (26–34%) of their home ranges. Most males had ≥ 2 small focal areas (18–33 ha) which were revisited every 20–28 h. Because estrus is ∼24 h, males may revisit focal areas to assess female receptiveness. During peak rut, 1 year olds had the lowest movement rates and rates were similar in 2- and ≥ 3-year-old males. However, most 2 year-old males exhibited Levy walks, an efficient search strategy when resources are rare. One-year-old males may not have exerted high effort, whereas most 2 year olds used a different strategy because of competition or lack of experience. Our results provide the first fine-scale description of ungulate mate-searching behavior and how spatial memory may be important for acquiring mating opportunities in species that rove for mates.

Can We Predict Forage Nutritive Value With Weather Parameters

On the Ground The use of easily accessible information to forecast when standing forage may lack nutrients to sustain cattle production could be valuable to the ranching community. Our study was designed to determine if forage crude protein and acid detergent fiber could be reasonably predicted using precipitation, season, and temperature. In south Texas, monthly precipitation in the fall accounted for 63% of the variation in crude protein and 73% of the variation in acid detergent fiber. A better understanding of how forage nutritive value changes over the year can improve strategic supplementation efforts.

Smoke Water and Heat Shock Influence Germination of Shortgrass Prairie Species

Abstract Smoke or heat from fire can act as a cue that affects seed germination. We examined germination responses of 10 plant species (six forbs, two shrubs, two grasses) native to the southern High Plains in the United States, to smoke, heat, and their interaction in a laboratory experiment. Smoke treatments were applied by soaking seeds in 1∶5, 1∶10, or 1∶100 (v/v) Regen 2000® smoke solution for 20 h. Heat treatments were applied by placing seeds in an oven at 50°C or 80°C for 5 min. Nine species responded to smoke, heat, or both. Results showed that smoke can enhance, inhibit, or not affect seed germination. Germination capacities of Gutierrezia sarothrae (Pursh) Britton & Rusby and Astragalus crassicarpus Nutt. were promoted by 1∶5 and 1∶100 dilutions of smoke water, respectively; Coreopsis tinctoria Nutt., G. sarothrae, Salvia reflexa Hornem., Digitaria ciliaris (Retz.) Koeler, and Panicum virgatum L. were inhibited by high and/or moderate concentrations of smoke water either in germination percentage or in mean germination time. Germination percentage of Solanum elaeagnifolium Cav. increased following an 80°C heat treatment. Interaction effects between smoke and heat on germination also were detected. Smoke and heat treatments might be useful as management tools for promoting or suppressing specific target species of shortgrass prairie communities in future habitat management.

Role of Thermal Environment in Habitat Selection by Male White-Tailed Deer during Summer in Texas, USA

Thermal cover may influence habitat selection by white-tailed deer Odocoileus virginianus in subtropical climates with hot summers. We 1) tested the hypothesis that thermal environment is more important in habitat selection at midday during summer than forage quality or quantity and concealment cover and 2) determined whether operative temperature, vegetation height, or woody plant canopy cover (or some combination of these) explain habitat selection at midday. We predicted that during crepuscular periods and at night habitat use increases with increasing forage quality and quantity and concealment cover and is unrelated to thermal environment. Male white-tailed deer were fitted with GPS collars to determine resources selected within habitats during June and July 2008 and 2009. A generalized linear mixed model using logistic regression was used to estimate resource selection functions. We used the first principal component in a principal components analysis (PCA) of forage standing crop, crude protein, and acid detergent fiber (ADF) to create a ‘forage index’. This index and vegetation height, operative temperature and concealment cover, together with their interactions with activity period, were used to develop a priori candidate models. Akaike weights were used to compare candidate models. A model that included the forage index, vegetation height, operative temperature, concealment cover and their interactions with activity period was the best model out of 97 candidate models for explaining habitat selection by adult male white-tailed deer. Male white-tailed deer selected areas with taller vegetation in morning and midday activity periods but selected shorter vegetation during evening and nighttime. Forage quality was important in habitat selection in all activity periods. Male white-tailed deer did not select areas with greater concealment cover during any activity period. A combination of operative temperature, vegetation height, and woody plant canopy cover predicted midday habitat use better than any of these three variables alone. Thermoregulatory behavior in male white-tailed appears to include a combination of seeking cooler environments during midday but at the same time using areas with greater forage quality.

Fire effects on tobosagrass and weeping lovegrass.

Fireline intensity (kW/m) was measured on 61 plots of weeping lovegrass [Eragrostis curvula (Schrad.) Nees.] and tobosagrass [Hilaria mutica (Buckl.) Benth.] burned as headfires and backfires during late winters of 1982 and 1983 in western Texas. Relative humidity, air temperature, wind speed, soil moisture, soil temperature, and fuel moisture were measured at time of burning. Vegetation response was based on plant yield, plant height, and number of seed stalks. Plant responses were not correlated with fireline intensity or any of the environmental parameters measured. Although fireline intensity is an important fire behavior measurement, high fireline intensities did not cause a negative impact on either weeping lovegrass or tobosagrass. Therefore, range managers can conduct high intensity fires to damage or burn down shrubs and not damage these grasses.

Biosolids Effects in Chihuahuan Desert Rangelands: A Ten-Year Study

Arid and semiarid rangelands are suitable for responsible biosolids application. Topical application is critical to avoid soil and vegetation disturbance. Surface-applied biosolids have long-lasting effects in these ecosystems. We conducted a 10-year research program investigating effects of biosolids applied at rates from 0 to 90 dry Mg ha−1 on soil water infiltration; runoff and leachate water quality; soil erosion; forage production and quality; seedling establishment; plant physiological responses; nitrogen dynamics; biosolids decomposition; and grazing animal behavior and management. Biosolids increased soil water infiltration and reduced erosion. Effects on soil water quality were observed only at the highest application rates. Biosolids increased soil nitrate-nitrogen. Biosolids increased forage production and improved forage quality. Biosolids increased leaf area of grasses; photosynthetic rates were not necessarily increased by biosolids. Biosolids effects on plant establishment are expected only under moderately favorable conditions. Over an 82-mo exposure period, total organic carbon, nitrogen, and total and available phosphorus decreased and inorganic matter increased. Grazing animals spent more time grazing, ruminating, and resting in biosolids-treated areas; positive effects on average daily gain were observed during periods of higher rainfall. Our results suggest that annual biosolids application rates of up to 18 Mg ha−1 are appropriate for desert rangelands.

Drought but not population density influences dietary niche breadth in white-tailed deer in a semiarid environment

A premise in ungulate foraging theory is that animals become less selective and expand the breadth of their dietary niche as the availability of palatable forage declines with increasing herbivore population density or drought. Increased niche variation resulting from intraspecific competition is thought to create less similar diet composition and decreased diet overlap between individuals within a population at higher densities than between individuals within less dense populations. These ideas were largely developed in relatively mesic environments and their applicability to ungulate foraging in semiarid environments is unclear. We tested the idea that white-tailed deer (Odocoileus virginianus) contract dietary niche breadth; reduce dietary plant species diversity, richness, and evenness; and become more individualistic in forage choices in response to a fourfold difference in population density (12 deer/km2 versus 50 deer/km2) in semiarid shrubland in Texas, USA. We used the bite count method to determ...

Grassland Bird Communtiy Response To Large Wildfires

Abstract We studied breeding season communities of grassland birds on short-grass and mixed-grass prairie sites during the second and third breeding seasons following two large wildfires in March 2006 in the Texas panhandle, USA. There was an apparent temporary shift in avian community composition following the fires due to species-specific shifts associated with life-history traits and vegetation preferences. Species that prefer sparse vegetation and bare ground on short-grass sites, such as Horned Lark (Eremophila alpestris), benefited from wildfires, while others, such as Western Meadowlark (Sturnella neglecta), that prefer more dense vegetation, were negatively impacted. Mixed-grass sites had species-specific shifts in 2007, two breeding seasons after the fires; grassland bird communities on burned plots were similar by 2008 to those on unburned plots. Avian communities appeared to return to pre-burn levels within 3 years following wildfires. Many of the responses in our study of wildfire were similar to those reported following prescribed fires elsewhere. Prescribed fires appear to have similar effects on the avian community despite differences in intensity and environmental conditions during wildfires.

Influence of Surface Biosolids Application on Infiltration

Biosolids from waste water treatment facilities applied to soils not only add plant nutrients, but also increase infiltration and decrease runoff and erosion. Wet biosolids from New York, NY, were surface applied at 0 to 90 Mg ha−1 dry weight to soils near El Paso, Tex. Simulated rainfall intensities of 16.4 cm hr−1 for 30 minutes applied to 0.5 m2 soil plots yielded initial infiltration rates of ~16 cm hr−1 for all plots. Biosolids applications extended the duration of the initially high infiltration rates. After 30 minutes, infiltration rates for bare soil were 3 cm hr−1 without and 10 cm hr−1 with 90 Mg biosolids ha−1. Applied biosolids, plant litter, surface gravel, and plant base contributed surface cover, which absorbed raindrop energy and reduced erosion. Biosolids increased cumulative infiltration on the vegetated, wet soils more than for the dry or bare soils. Biosolids increased cumulative infiltration from 2 to 6 cm on a bare gravelly soil and from 9.3 to 10.6 cm on a vegetated soil.