G. Allen Rasmussen

Managing Native Invasive Juniper Species Using Fire

Junipers (Juniperus spp.) are native woody shrubs that have expanded beyond their normal historical ranges in the western and southwestern United States since the late 1800s. Most ecologists and resource managers agree that juniper has become a deleterious native invasive plant that threatens other vegetation ecosystems, such as grasslands, through a steady encroachment and ultimate domination. The use of fire in managing junipers is based on a management goal to increase the disturbance return interval and thereby reduce the abundance and/or competitive impact of juniper in an ecosystem. In this paper, we discuss rates of juniper encroachment in relation to presettlement fire regimes, juniper encroachment and soil health, postfire vegetation responses, and long-term potential of different juniper treatment scenarios that involve prescribed fire.

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.

Long-term effects of aeration and fire on invasion of exotic grasses in mixed-brush plant communities.

Abstract Invasion of exotic grasses into grasslands dominated by native plants changes fire cycles and reduces biodiversity. Brush management practices that create soil disturbance, such as aeration, may potentially result in invasion of exotic grasses and replacement of native vegetation. We tested the hypothesis that a long-term effect of aeration and prescribed burning is an increase in exotic grasses. The study was conducted at the Chaparral Wildlife Management Area in the western south Texas plains where four treatments were evaluated: aeration, warm-season burn, aeration followed by a warm-season burn, and no treatment (control). The experimental design was a randomized complete block with four replicates. We estimated percentage canopy cover of exotic grasses, native grasses, forbs, litter, bare ground, and woody and succulent plants in 2007. There was a multivariate main effect among treatments for the dependent variables absolute canopy cover of exotic grasses, native grasses, forbs, litter, and bare ground (Wilkss Lambda F15,179.84  =  2.78, P  =  0.001). Variables that contributed to the significant overall effect included litter (F3,69  =  4.32, P  =  0.008) and native grasses (F3,69  =  6.11, P  =  0.001). The multivariate main effect of treatment was significant (Wilkss Lambda F9,180.25  =  2.04, P  =  0.038) for the relative canopy cover of herbaceous species. Relative cover of exotic grasses was 31% higher (P  =  0.024) in control than in the prescribed burn treatment. Native grasses relative cover was 30% higher (P  =  0.003) in prescribed burn than in the control treatment. We did not detect differences among treatments in the percentage of total woody and succulent plants canopy cover (P  =  0.083). Under the environmental conditions at the time of the study, aeration and/or prescribed burning do not increase exotic grasses.

Developing Monitoring Programs for Livestock Producers

Many official monitoring programs have been developed, but few have been adopted by livestock producers. While these programs have relatively strong support from professionally trained managers, even their implementation is not consistent. New programs must address several important factors if they are going to be used. They must be used to help producers and managers make current decisions relating to their objectives and those broader resource objectives of society. Producers must understand how these broader objectives relate to their specific livestock objectives. These monitoring programs must help make proactive decisions, and be cost effective. Finally attempts must be made to make them flexible to deal with changing objectives that happen over time.