Response of Sahara mustard (Brassica tournefortii) to water addition and soil disturbance

Invasive exotic species can have a significant impact on the structure, function, and diversity of ecological communities. Sahara mustard (Brassica tournefortii) is one of the top exotic invasive species spreading through the southwestern deserts of North America. In arid environments, it is well documented that species abundance is sensitive to rainfall (Beatly 1974, Ernest et al. 2000). In the Mojave Desert, winter precipitation can trigger massive germination events (Beatly 1974). As a winter annual, Sahara mustard may have a positive response to winter precipitation by germinating, growing, and reproducing before native annuals, monopolizing soil moisture and nutrients, and potentially changing native plant community structure and ecosystem processes. To better understand Sahara mustard’s ecology in Mojave Desert habitats, we conducted a field experiment to document the effects of water additions and soil disturbance on Sahara mustard density and native plant assemblage. In addition, we performed a soil seed bank study to compare above ground plant community and soil seed bank composition of study sites. Our experimental treatments were designed to provide favorable conditions for seedling emergence; therefore, we expected to record a greater emergence number in treated than control plots

Monitoring live fuel moisture using soil moisture and remote sensing proxies

Live fuel moisture (LFM) is an important fuel property controlling fuel ignition and fire propagation. LFM varies seasonally, and is controlled by precipitation, soil moisture, evapotranspiration, and plant physiology. LFM is typically sampled manually in the field, which leads to sparse measurements in space and time. Use of LFM proxies could reduce the need for field sampling while potentially improving spatial and temporal sampling density. This study compares soil moisture and remote sensing data to field-sampled LFM for Gambel oak (Quercus gambelii Nutt) and big sagebrush (Artemisia tridentata Nutt) in northern Utah. Bivariate linear regression models were constructed between LFM and four independent variables. Soil moisture was more strongly correlated with LFM than remote sensing measurements, and produced the lowest mean absolute error (MAE) in predicted LFM values at most of the sites. When sites were pooled, canopy water content (CWC) had stronger correlations with LFM than normalized difference vegetation index (NDVI) or normalized difference water index (NDWI). MAE values for all proxies were frequently above 20 % LFM at individual sites. Despite this relatively large error, remote sensing and soil moisture data may still be useful for improving understanding of spatial and temporal trends in LFM

Early Post-Fire Recovery on a Heavily Visited Mojave Desert Burn: Red Rock Canyon near Las Vegas, Nevada

Wildfire has become widespread in southwestern USA deserts. In a record 2005 fire season in the Mojave Desert, for example, more than 385,000 hectares burned (Brooks and Matchett 2006). This burned area is approximately 3% of the entire Mojave Desert. Fueled in large part by exotic annual grasses, these fires burned desert ecosystems thought to have only burned infrequently historically. Burns now occupy significant portions of desert landscapes, posing prominent management challenges. Improving our understanding of plant recovery on desert burns is important for evaluating future fire hazard, whether natural revegetation will meet management objectives, and for planning active revegetation if this becomes a management goal. Desert burns may afford an opportunity for intervention in the grass-fire cycle immediately following a burn if exotic grass competition is temporarily reduced while available nutrients liberated by the fire increase. However, post-fire recovery of plant communities is not a well understood process in desert ecosystems

Early post-fire plant establishment on a Mojave Desert burn

Fire has become more extensive in recent decades in southwestern United States arid lands. Burned areas pose management challenges and opportunities, and increasing our understanding of post-fire plant colonization may assist management decision-making. We examined plant communities, soils, and soil seed banks two years after the 2005 Loop Fire, located in a creosote-blackbrush community in Red Rock Canyon National Conservation Area in southern Nevada’s Mojave Desert. Based on a spring sampling of 20, 0.01-ha plots, live + dead cover of the exotic annual Bromus rubens averaged nine times lower on the burn than on a paired unburned area. Perennial species composition shifted from dominance by late-successional native shrubs (e.g., Coleogyne ramosissima) on the unburned area, to dominance by native perennial forbs (e.g., Sphaeralcea ambigua, Baileya multiradiata) on the burn. Species richness of live plants averaged 26% (100 m2 scale) and 239% (1 m2 scale) greater on the burn compared to the unburned area. Only 5% of Larrea tridentata individuals resprouted, compared to 64% of Yucca schidigera and baccata. Fire and microsite (interspace, below L. tridentata, or below Yucca) interacted to affect several 0–5 cm soil properties, with higher pH, conductivity, and total P and K on burned Yucca microsites. Bromus rubens density in 0–5 cm soil seed banks was four times lower on the burn, and its distribution among microsites reversed. Below-shrub microsites contained the most B. rubens seeds on the unburned area, but the least on the burned area. Intense fire below shrubs may have increased seed mortality, an idea supported by .3-fold decreases we found in emergence density after heating seed bank samples to 100uC. Our study occurred after a post-fire period of below-average precipitation, underscoring a need for longer term monitoring that characterizes moister years

Mojave Applied Ecology Notes Spring 2008

Post-fire restoration, fire chronosequence study, Joint Fire Science update, Weed Sentry program and DNWR survey

Identification of Fungal Colonies on Ground Control and Flight Veggie Plant Pillows

The Veggie system focuses on growing fresh produce that can be harvested and consumed by astronauts. The microbial colonies in each Veggie experiment are evaluated to determine the safety level of the produce and then differences between flight and ground samples. The identifications of the microbial species can detail risks or benefits to astronaut and plant health. Each Veggie ground or flight experiment includes six plants grown from seeds that are glued into wicks in Teflon pillows filled with clay arcillite and fertilizer. Fungal colonies were isolated from seed wicks, growth media, and lettuce (cv. 'Outredgeous') roots grown in VEG-01B pillows on ISS and in corresponding ground control pillows grown in controlled growth chambers. The colonies were sorted by morphology and identified using MicroSeq(TM) 500 16s rDNA Bacterial Identification System and BIOLOG GEN III MicroPlate(TM). Health risks for each fungal identification were then assessed using literature sources. The goal was to identify all the colonies isolated from flight and ground control VEG-01B plants, roots, and rooting medium and compare the resulting identifications

Mojave Applied Ecology Notes Summer 2008

Soil climate project, rare plant monitoring, JFS update, granivory and Sahara mustar

Mammalian Cell Toxicity of the Photoproducts of Octyldimethyl Para-aminobenzoic Acid

Solar tracking is related to moving the solar panels in such a way that its solar panel always points toward the sun which results in maximum output. The goal of this research was to modify and improve a two-axis solar tracking system. The rotation of the module is controlled by a rotational motor and the tilt is controlled by a linear actuator. The motion and direction of these two motors is controlled by an Arduino code which compares the electrical current going through four mini solar collectors (used as sensors) mounted in orthogonal pairs at the top of the PV panel. If a solar collector has a higher current reading, then it is exposed to more sunlight, so the panel is adjusted until all of the mini solar collectors have nearly the same current output, and thus are receiving the same amount of sunlight. Testing of the designed system was performed alongside an identical, stationary solar panel, which allows for a direct comparison between the electrical outputs of the two solar panels.https://digitalworks.union.edu/steinmetz_posters/1012/thumbnail.jp

Watercourse-Upland and Elevational Gradients in Spring Vegetation of a Mojave-Great Basin Desert Landscape

Springs in arid lands provide critical habitat for a variety of species and functions to humans, yet the ecology and management needs of springs to maintain these values are poorly understood. To examine plant communities along spring watercourse-upland gradients, we sampled 12 springs at low (desert) and high (forest) elevations on the Desert National Wildlife Refuge in the Mojave and Great Basin Deserts in southern Nevada. In contrast to the commonly reported positive relationship between native and exotic species richness in sampling studies, we did not find strong correlations (r² < 0.05) between native and exotic richness at any distance from watercourses. Additionally, exotic species cover was lower nearest (0 and 2 m) watercourses than at uplands 20 m from watercourses, which also differs from the hypothesis that watercourses are more heavily invaded than uplands. Exotic species were more pervasive at low-elevation compared to high-elevation springs, but the proportion of total plant cover comprised by exotics was still small (0.03 – 0.06) at low-elevation springs. Species distributions and ordinations suggested that compositional watercourse-upland gradients were often readily detectable, but the composition of springs was individualistic. Some springs contained wetland species such as Juncus saximontanus, while other springs contained species of dry-site affinity. This study also illustrated challenges associated with estimating reference conditions for arid-land springs, as there are no known data prior to the development (i.e., modifying surface flow) of the springs and no known unmodified springs on this landscape.Keywords: exotic species, seeps, wetlands, riparian, conservatio

Temperature Drives Epidemics in a Zooplankton-Fungus Disease System: A Trait-Driven Approach Points to Transmission via Host Foraging

Climatic warming will likely have idiosyncratic impacts on infectious diseases, causing some to increase while others decrease or shift geographically. A mechanistic framework could better predict these different temperature-disease outcomes. However, such a framework remains challenging to develop, due to the nonlinear and (sometimes) opposing thermal responses of different host and parasite traits and due to the difficulty of validating model predictions with observations and experiments. We address these challenges in a zooplanktonfungus (Daphnia dentifera–Metschnikowia bicuspidata) system. We test the hypothesis that warmer temperatures promote disease spread and produce larger epidemics. In lakes, epidemics that start earlier and warmer in autumn grow much larger. In a mesocosm experiment, warmer temperatures produced larger epidemics. A mechanistic model parameterized with trait assays revealed that this pattern arose primarily from the temperature dependence of transmission rate (b), governed by the increasing foraging (and, hence, parasite exposure) rate of hosts ( f ). In the trait assays, parasite production seemed sufficiently responsive to shape epidemics as well; however, this trait proved too thermally insensitive in the mesocosm experiment and lake survey to matter much. Thus, in warmer environments, increased foraging of hosts raised transmission rate, yielding bigger epidemics through a potentially general, exposure-based mechanism for ectotherms. This mechanistic approach highlights how a trait-based framework will enhance predictive insight into responses of infectious disease to a warmer world