Biology subjects

Radke, M. F.

Publications and source records attributed to Radke, M. F..

3 recordsLinked to original sources

bioRxiv2022

Effects of Beaver (Castor canadensis) Herbivory and Wildfire on Foliage Density and Woody Debris, San Pedro Riparian National Conservation Area, Arizona

Beaver (Castor canadensis) were reintroduced beginning in 1999 on the San Pedro Riparian National Conservation Area. Herbivory is the most obvious effect from beaver, but little research exists of herbivory effects after reintroduction. Fire processes may also have substantial effects to vegetation, and both beaver and fire are important ecological components for comparing effects and subsequent management decisions. The objective of this research, conducted during 2008 and 2009, was to determine any effects to foliage density caused by beaver herbivory and wildfire as compared to control sites. There were significant differences in foliage density between control, beaver, and wildfire sites, with lower foliage density and greater above-ground heights associated with wildfire sites. Although near the significance level, there were no interactions between control, beaver, or wildfire sites for changes in foliage density at different heights. Mean Fremont cottonwood, Gooddings willow, and seep willow foliage density was significantly different between control, beaver, and fire sites. Fremont cottonwood had significantly higher foliage density at control sites than at fire sites, but not between control and beaver sites or between beaver and fire sites. Gooddings willow density was significantly higher at control and beaver sites than fire sites, with no significant difference between control and beaver sites. Seep willow foliage density was significantly higher at control and beaver sites compared to fire sites, but not significantly different between control and beaver sites. Mean downed and dead wood cover was not significantly different between control, beaver, and fire-influenced sites, between beaver and control sites, between control and fire sites, or between beaver and fire sites. Management implications include more strategic wildfire planning and preparedness, achieved through integrated tamarisk control in the riparian area and use of prescribed fire in upland habitats to reduce fire size and severity that threaten the riparian gallery forest and its ecosystem services.

zoology↗

bioRxiv2022

Dam Site and Vegetation Selection by Reintroduced Beaver (Castor canadensis) on the San Pedro Riparian National Conservation Area, Arizona

Beaver (Castor canadensis) were reintroduced on the San Pedro Riparian National Conservation Area (SPRNCA) after having been extirpated. The two most obvious effects from this keystone species, dam construction and herbivory, have not been studied on the SPRNCA. The purpose of this research was to determine any preference for dam sites, vegetation preferences, or if beaver may travel longer distances for preferred food or dam materials. Individual dams remained or were rebuilt in the same location on average every 2.4 years. Dam building was disproportionate to availability of sites, with beaver more commonly building dams at the confluence of the San Pedro River and tributaries. The size of areas with impacts to vegetation from beaver herbivory averaged 0.34 ha (2.5 ac), containing an average of 40.7 trees. Beaver exhibited a preference for smaller-sized cottonwood (Populus fremontii) trees over larger cottonwood trees and smaller or larger Gooddings willow (Salix gooddingii), both in terms of whether trees were eaten and left standing or felled, and distance beaver travelled from water to the tree. Management implications include continued research on effects of beaver, management of invasive plant species, use of cottonwood genotypes with high tannin levels during restoration projects, further augmentation of beaver, use of beaver-dam analogues, and continued closure to hunting and trapping of beaver.

zoology↗

bioRxiv2022

Effects of Livestock Grazing Exclusion on Perennial Grasses and Woody Species on the San Pedro Riparian National Conservation Area, Arizona

The objective of this study was to determine the effects of livestock exclusion on native and non-native perennial grass richness and frequency, and woody species frequency on the San Pedro Riparian National Conservation Area. A significant increase in species richness of native perennial grass species was noted overall and in retired agricultural fields, supporting the hypothesis of increased species richness with grazing exclusion. There was a significant increase in the number of plots that contained an increase in bristlegrass (Setaria macrostachya Kunth and S. leucopila (Scribn. & Merr.) K. Schum.). No significant change in species richness of non-native invasive perennial grass species was observed. Lehmann lovegrass (Eragrostis lehmanniana Nees) had a significant increase in the number of plots that contained the species, supporting the hypothesis that Lehmann lovegrass expansion would occur in previously uninvaded areas even without current livestock grazing. Velvet mesquite (Prosopis velutina Wooton) exhibited a significant increase in canopy frequency, but velvet mesquite basal frequency showed no significant increase or decrease. Results indicate that past grazing was a primary factor leading to the current distribution and density of mesquite on the SPRNCA because the same basal (i.e. rooted stem) frequency existed prior to and after grazing exclusion. Management considerations include continued grazing exclusion, inventory and monitoring of pollinator plants, continued monitoring of pace frequency transects, use of prescribed fire in uplands, monitoring of soil erosion, and implementation of erosion controls.

plant biology↗