Temporal Overlap Among Feral Horses,Cattle, and Native Ungulates at Water Sources

Feral horse (Equus ferus caballus) populations on public rangelands in the western United States threaten forage production for livestock and wildlife habitat. Interference competition between feral horses and heterospecifics at watering sources can have negative effects on livestock and wildlife. Researchers have documented altered timing and behavior of wild ungulates at water sources when horses were present. The few studies examining these interactions have infrequently occurred within areas specifically managed for feral equids and have not occurred in sites with cattle. We used motion-sensitive cameras at 8 watering sources to document watering activity patterns and construct indices of temporal overlap among feral horses, cattle, elk (Cervus canadensis), mule deer (Odocoileus hemionus), and pronghorn (Antilocapra americana) within the Adobe Town Herd Management Area in southern Wyoming, USA, between June and September 2018 and 2019. Feral horses, cattle, and pronghorn exhibited a high degree of temporal overlap (>79%) in water use, with feral horses and pronghorn exhibiting the highest estimated percent overlap (88.1%, 95% CI = 86.5–89.6%). Mule deer and elk watering activity also overlapped with horses and cattle but to a lesser degree (<55%). Feral horses spent a mean of 16.7 ± 30.5 (SD) minutes during a watering event and were present at a given water source on average 4.5 ± 6.3% and up to 34.9% of the day, which is less than reported in previous studies. Cattle spent on average 23.5 ± 44.9 minutes during a watering event, and were present on average 4.2 ± 7.7% and up to 42.4% of the day at a single water source. Results of generalized linear mixed-effects models indicated that number of conspecifics was the strongest predictor of visit duration for pronghorn and horses; hour of the day and group size of heterospecifics were informative, but less important, variables. There was no difference in peak visitation time for any species between sites of high versus low horse or cattle use. Despite temporal overlap, we did not find evidence of interference competition between feral horses, cattle, and pronghorn. We recommend future examination of interference competition and its biological consequences between introduced and native ungulates at water sources of varying size across sites, equid population levels, and livestock stocking rates. © 2020 The Wildlife Society.     

Bombing and Sonoran Pronghorn: A Clear and Present Danger?

ABSTRACT The United States Air Force (USAF) uses part of Sonoran pronghorn (Antilocapra americana sonoriensis) habitat for bombing exercises (i.e., Barry M. Goldwater Air Force Range [BMGR], southwest AZ, USA) that could be detrimental to the endangered subspecies. To minimize injury or death to Sonoran pronghorn, the USAF and United States Fish and Wildlife Service developed a monitoring protocol that would eliminate live ordnance delivery in the vicinity of pronghorn. From 1998 to 2003, we searched for pronghorn on or near military targets prior to ordnance delivery. If we observed pronghorn within 5 km of a target, the target was closed for ≥24 hours. We monitored bombing ranges on BMGR and closed >5,000 targets for >1,000 days due to military activity. To our knowledge, no pronghorn were killed or injured. We recommend that the monitoring program continue as long as military activity occurs in pronghorn habitat.     

Annual Pronghorn Survival of a Partially Migratory Population

The importance of conserving migratory populations is recognized across a variety of ungulate taxa, yet the demographic benefits of migration remain uncertain for ungulate populations that exhibit partial migration. We hypothesized that migratory pronghorn (Antilocapra americana) would experience greater survival compared to residents by moving longer distances to avoid severe winter weather and access higher quality forage. We used a Bayesian time-to-event approach to analyze the fates of 175 radio-collared adult female pronghorn monitored over 8 biological years (2004–2011) in the Northern Sagebrush Steppe ecosystem. Annual survivorship of migratory pronghorn was 7% higher on average compared to residents but not statistically different. Migratory pronghorn had higher survivorship in summer and winter compared to residents, and few mortalities were observed during the short autumn and spring migration periods. Mortality risk for both movement tactics intensified under more severe winter weather; winter weather severity alone best explained annual pronghorn mortality risk. The top model predicted survival rates to decline on average by 56% over the range of observed winter climatic conditions. To minimize human impacts to pronghorn during extreme climatic events, we recommend working with transportation departments and land managers to enhance pronghorn crossings of roads and railroads, and landholders to modify fences to wildlife-friendly standards. © 2020 The Authors. Journal of Wildlife Management published by Wiley Periodicals, LLC on behalf of The Wildlife Society.     

Use of Museum Specimens to Refine Historical Pronghorn Subspecies Boundaries

Endangered Sonoran (Antilocapra americana sonoriensis) and Peninsular (A. a. peninsularis) pronghorn persist largely because of captive breeding and reintroduction efforts. Recovery team managers want to re-establish pronghorn in their native range, but there is currently uncertainty regarding the subspecies status of extinct pronghorn populations that historically inhabited southern California, USA, and northern Baja California, Mexico. To address this uncertainty, we genotyped museum specimens and conducted phylogenetic and population genetic analyses of historical data in the context of 3 contemporary pronghorn populations. The historical northern Baja California pronghorn share the most ancestry with contemporary Peninsular pronghorn, whereas pronghorn in southern California share more ancestry with contemporary American (A. a. americana) pronghorn. For reintroductions into northern Baja California, the Peninsular subspecies is more appropriate based on museum genetic data. For reintroductions into Southern California, ecological and genetic factors are both important, as the subspecies most genetically related to historical populations (American) may not be well-adapted to the hot, low-elevation deserts of the reintroduction area. © 2019 The Wildlife Society.     

Estimating Coyote Densities with Local,Discrete Bayesian Capture-Recapture Models

Recent advances in noninvasive genetic sampling and spatial capture-recapture (SCR) techniques are particularly useful for monitoring cryptic wildlife species such as carnivores. In southern Arizona, USA, coyotes (Canis latrans) are thought to negatively affect endangered Sonoran pronghorn (Antilocapra americana sonoriensis), although no estimates of coyote abundance or monitoring programs exist. Sonoran pronghorn are provided supplemental feed and water in this region, resulting in areas where pronghorn and other species are congregated. Because of the higher density of artificial water sources for Sonoran pronghorn on the Cabeza Prieta National Wildlife Refuge (CPNWR), we predicted that coyote density would be higher relative to the Barry M. Goldwater Range (BMGR), where artificial water sources are less dense. We used discrete Bayesian SCR models in a local evaluation approach to provide baseline estimates of coyote abundance and understand how coyote density varied between 2 contrasting areas of land use. We identified 106 individuals from scat samples across 3 sessions in 2013 and 2014 and achieved high genotyping and individual identification success rates (~78%). Encounter rates at water catchments were nearly 11 times higher compared to road and trail transects. As predicted, we found that coyote density was on average 2 times higher on the CPNWR (11.2 coyotes/100 km²) compared to the BMGR (5.3 coyotes/100 km²). The local evaluation approach significantly reduced computational time, making the discrete Bayesian approach more practical to implement across a large study area. Our study represents an important contribution towards developing a robust monitoring program for coyotes. We hope that our novel implementation of the local evaluation approach increases the ability of wildlife managers to understand the effects of land use and other ecological influences on large carnivore populations. © 2020 The Wildlife Society.     

Contrasting management paradigms for pronghorn in the arid Southwest and their northern range: a review

Pronghorn (Antilocapra americana), a symbol of western North America, experienced diverging population trajectories since the mid-twentieth century, with northern populations showing signs of recovery while those in the arid Southwest have struggled to persist. We conducted a systematic literature review of papers published through August 2023 to understand 3 questions. What are the habitat conditions needed for pronghorn to persist? What management actions can be taken to foster higher quality habitat? Do these actions differ for populations in the arid Southwest compared to their northern counterparts? Although the fundamental habitat requirements for pronghorn persistence have remained constant since the early 2000s, it has become clear that precipitation is a key factor influencing pronghorn populations in the arid Southwest. The precise mechanisms by which precipitation influences pronghorn population dynamics are not yet clear, whether through the availability of free water, by affecting forage quality, or indirectly via predator-prey dynamics. Although range-wide forage enhancement may be impractical, providing additional free water sources could facilitate greater movement, enabling pronghorn to access more and higher quality forage and areas with lower predation risk. To clarify how pronghorn persisted for thousands of years in this harsh environment, we must gain a better understanding of their historical metapopulation and migratory behaviors in the arid Southwest.     

Factors Influencing Survival Rates of Pronghorn Fawns in Idaho

Pronghorn (Antilocapra americana) occur throughout western North America. In Idaho, USA, following intensive hunting to reduce crop depredations in the late 1980s, pronghorn populations have not rebounded to desired levels. Because neonatal survival in ungulates is one factor limiting population growth, we evaluated cause-specific mortality and the influence of intrinsic and extrinsic factors on survival rates of 217 radio-collared pronghorn fawns across 3 study areas in Idaho during 2015–2016. For intrinsic variables, we determined the sex and body mass index (BMI) for each fawn. For extrinsic variables, we determined the abundance of predators and alternate prey, estimated the normalized difference vegetation index (NDVI) for 1 month pre- and post-parturition, and measured fecal nitrogen and diaminopimelic acid (DAPA). We considered NDVI as a measure of plant productivity, and fecal nitrogen and DAPA as possible proxies of diet quality. We predicted NDVI, fecal nitrogen, and DAPA would be positively related to the nutritional status of females and positively related to fawn survival. We used Program MARK with known fate models to estimate semi-monthly survival rates of pronghorn fawns for the first 4 months post-parturition. During both years, the leading cause of fawn mortality was coyote (Canis latrans) predation (58%), followed by unknown causes of mortality (18%), unknown predation (12%), predation by bobcats (Lynx rufus; 6%), predation by golden eagles (Aquila chrysaetos; 3%), and other (3%). Mean fawn survival for the 4 months post-parturition across years and study sites was 0.42 ± 0.04 (SE; range = 28–62%). The top survival model included BMI, lagomorph abundance, and DAPA and had a model weight of 83.3%. All 3 variables were positively related to pronghorn fawn survival. Because females with increased nutrition generally have heavier fawns, BMI was likely correlated to diet quality, which was supported by the positive relationship between DAPA and fawn survival. We hypothesize that high lagomorph abundance created an alternate prey base to buffer coyotes from preying on pronghorn neonates. We found no influence of measures of NDVI (pre- and post-parturition), fecal nitrogen, or predator abundance on fawn survival. Management actions providing high-quality forage for pronghorn are likely to contribute to production of heavier fawns having the highest chance of survival. © 2020 The Wildlife Society.     

Dispersal of Yearling Pronghorns in Western South Dakota

Abstract: We captured and radiocollared 57 pronghorn (Antilocapra americana) fawns in western South Dakota, USA, during May 2002–2003 and radiotracked them through 15 months of age, by which time all surviving individuals had established a permanent home range. We classified 56% (n = 19) of fawns as dispersers and 44% (n = 15) as residents. Eighty-four percent (n = 16) of dispersers departed natal home ranges in late October and occupied winter home ranges for 102–209 days before dispersing to permanent home ranges during April 2003 and 2004. Dispersal distances from natal ranges to permanent home ranges varied from 6.2–267.0 km. Winter home-range sizes for all individual pronghorns varied from 39.4–509.6 km. Permanent home-range size for all individuals varied from 15.5–166.1 km². Mean 95% permanent home-range size differed (P = 0.06) between residents (x̄ = 97.3 ± 15.1 km²) and dispersers (x̄ = 48.6 ± 16.0 km²), but was similar (P = 0.97) among sexes. Mean dispersal distance from natal to permanent home ranges was similar (P = 0.35) for males (x̄ = 54.2 ± 21.0 km) and females (x̄ = 26.3 ± 19.9 km). We suggest that habitat quality (i.e., patchiness) and pronghorn density, in part, stimulated dispersal. We hypothesize that as habitat patch size decreases, home range sizes and distance traveled during predispersal and dispersal movements by pronghorns will increase.     

Evaluating the interaction of faecal pellet deposition rates and DNA degradation rates to optimize sampling design for DNA‐based mark–recapture analysis of Sonoran pronghorn

Knowledge of population demographics is important for species management but can be challenging in low‐density, wide‐ranging species. Population monitoring of the endangered Sonoran pronghorn (Antilocapra americana sonoriensis) is critical for assessing the success of recovery efforts, and noninvasive DNA sampling (NDS) could be more cost‐effective and less intrusive than traditional methods. We evaluated faecal pellet deposition rates and faecal DNA degradation rates to maximize sampling efficiency for DNA‐based mark–recapture analyses. Deposition data were collected at five watering holes using sampling intervals of 1–7 days and averaged one pellet pile per pronghorn per day. To evaluate nuclear DNA (nDNA) degradation, 20 faecal samples were exposed to local environmental conditions and sampled at eight time points from one to 124 days. Average amplification success rates for six nDNA microsatellite loci were 81% for samples on day one, 63% by day seven, 2% by day 14 and 0% by day 60. We evaluated the efficiency of different sampling intervals (1–10 days) by estimating the number of successful samples, success rate of individual identification and laboratory costs per successful sample. Cost per successful sample increased and success and efficiency declined as the sampling interval increased. Results indicate NDS of faecal pellets is a feasible method for individual identification, population estimation and demographic monitoring of Sonoran pronghorn. We recommend collecting samples >7 days old and estimate that a sampling interval of 4–7 days in summer conditions (i.e. extreme heat and exposure to UV light) will achieve desired sample sizes for mark–recapture analysis while also maximizing efficiency.     

Influence of Precipitation on Pronghorn Demography in Texas

Abstract: Ungulate populations in desert environments are thought to be regulated by precipitation. Pronghorn (Antilocapra americana) populations in Trans-Pecos, Texas, USA, experienced a 70% decline between 1977 and 2001. The causative factors associated with the decline are unknown but appear to be related to drought. We evaluated the relationships between pronghorn abundance and productivity and precipitation (i.e., raw precipitation, Palmer Drought indices) for the Trans-Pecos district of Texas from 1977 to 2004. Pronghorn productivity (range = 305-4,407) and abundance (range = 5,061-17,266) showed high variability. Precipitation was also highly variable, ranging from 18 cm to 57 cm. Pronghorn abundance was positively influenced by precipitation indices (R = 0.790, P < 0.001). The relationship between fawn production and raw precipitation (R = 0.869, P < 0.001) suggested that fawn production may be more closely related to immediate moisture conditions, whereas pronghorn abundance was more influenced by long-term population trends. Management plans for pronghorn populations in more arid regions should include drought contingencies including reduced stocking rates and harvest quotas.     

Soil amendment interacts with invasive grass and drought to uniquely influence aboveground versus belowground biomass in aridland restoration

Water‐holding soil amendments such as super‐absorbent polymer (SAP) may improve native species establishment in restoration but may also interact with precipitation or invasive species such as Bromus tectorum L. (cheatgrass or downy brome) to influence revegetation outcomes. We implemented an experiment at two sites in Colorado, U.S.A., in which we investigated the interactions of drought (66% reduction of ambient rainfall), B. tectorum seed addition (BRTE, 465 seeds/m²), and SAP soil amendment (25 g/m²) on initial plant establishment and 3‐year aboveground and belowground biomass and allocation. At one site, SAP resulted in higher native seeded species establishment but only with ambient precipitation. However, by the third year, we detected no SAP effects on native seeded species biomass. Treatments interacted to influence aboveground and belowground biomass and allocation differently. At one site, a SAP × precipitation interaction resulted in lower belowground biomass in plots with SAP and drought (61.7 ± 7.3 g/m²) than plots with drought alone (91.6 ± 18.1 g/m²). At the other site, a SAP × BRTE interaction resulted in higher belowground biomass in plots with SAP and BRTE (56.6 ± 11.2 g/m²) than BRTE alone (35.0 ± 3.7 g/m²). These patterns were not reflected in aboveground biomass. SAP should be used with caution in aridland restoration because initial positive effects may not translate to long‐term benefits, SAP may uniquely influence aboveground versus belowground biomass, and SAP can interact with environmental variables to impact developing plant communities in positive and negative ways.     

Migration patterns of pronghorn in southwestern North Dakota

Wildlife managers need empirical data about pronghorn (Antilocapra americana) movements in North Dakota to assess whether mid-summer surveys represent occupancy of pronghorn in hunting units during the fall hunting season. Using data from 121 radiocollared pronghorn we evaluated patterns of pronghorn migrations in southwestern North Dakota from 2004 to 2007. Pronghorn exhibited 2 primary movement patterns between summer and winter ranges: migrations >15 km (45%) and movement <15 km (55%). Most migratory pronghorn moved northeast or east in the spring and southwest or west in the fall. Average distance moved for migratory pronghorn was 70.6 km (range = 17.4–253 km). Mean date of pronghorn migration in spring was 20 March (SD = 20 days) and in fall was 22 October (SD = 17 days). Nearly all migratory pronghorn (97%) returned to within 15 km of their previous summer range, whereas only 61% of pronghorn returned to within 15 km of their previous winter range. Most pronghorn moved across hunting and survey unit boundaries; however, only 7 fall migrations occurred between the aerial survey and the hunting season. During years of our study, the mid-summer survey provided representative information about hunting unit occupancy of radiocollared pronghorn for the fall hunting season. © 2011 The Wildlife Society     

Forest floor plant diversity drives the use of mature spruce forests by European bison

The distribution of large ungulates in space is in large extent driven by the availability of forage, which in temperate forests depends on light availability, and associated plant diversity and cover. We hypothesized that the increased number of GPS fixes of European bison (Bison bonasus L.) in usually avoided spruce forests was an effect of higher plant species richness and cover of the forest floor, which developed owing to increased light availability enhanced by spruce mortality. We carried out 80 forest floor plant surveys combined with tree measurement on plots chosen according to the number of GPS locations of GPS‐collared European bison. The mean plant species richness per plot was higher on intensively visited plots (IV) than rarely visited (RV) plots (30 ± 5.75 (SD) versus. 26 ± 6.19 (SD)). The frequency of 34 plant species was higher on IV plots, and they were mainly herbaceous species (32 species), while a significant part of 13 species with higher frequency on RV plots was woody plants (5 species). The species richness of forbs was higher on IV plots, while other functional groups of plants did not differ. Tree stem density on the IV plots was lower than on the RV plots (17.94 ± 6.73 (SD) versus 22.9 ± 7.67 (SD)), and the mean value of Ellenberg's ecological indicator for light availability for all forest floor plant species was higher on IV plots. European bison visiting mature spruce forests was driven by higher forest floor plant cover and species richness, and high share and species richness of forbs. The two latter features may be translated into higher quality and diversity of forage. In spite of morphological characteristics suggesting that European bison is a species of mixed (mosaic) habitats, it seems to be well adapted to thrive in diverse forests.     

Restoration of a Forest Understory After the Removal of an Invasive Shrub, Amur Honeysuckle (Lonicera maackii)

The recruitment of native seedlings is often reduced in areas where the invasive Amur honeysuckle (Lonicera maackii) is abundant. To address this recruitment problem, we evaluated the effectiveness of L. maackii eradication methods and restoration efforts using seedlings of six native tree species planted within eradication and unmanipulated (control) plots. Two eradication methods using glyphosate herbicide were evaluated: cut and paint and stem injection with an EZ‐Ject lance. Lonicera maackii density and biomass as well as microenvironmental characteristics were measured to study their effects on seedling growth and survivorship. Mean biomass of Amur honeysuckle was 361 ± 69 kg/ha, and density was 21,380 ± 3,171 plants/ha. Both eradication treatments were effective in killing L. maackii (≥ 94%). The injection treatment was most effective on large L. maackii individuals (>1.5 cm diameter), was 43% faster to apply than cutting and painting and less fatiguing for the operator, decreased operator exposure to herbicide, and minimized impact to nontarget vegetation. Deer browse tree protectors were used on half of the seedlings, but did not affect survivorship or growth. After 3 years, survival of native seedlings was significantly less where L. maackii was left intact (32 ± 3%) compared with the eradication plots (p < 0.002). Seedling survival was significantly different between cut (51 ± 3%) and injected (45 ± 3%) plots. Species had different final percent survival and rates of mortality. Species survival differed greatly by species (in descending order): Fraxinus pennsylvanica > Quercus muehlenbergii ≥ Prunus serotina≥ Juglans nigra > Cercis canadensis > Cornus florida. Survivorship and growth of native seedlings was affected by a severe first‐year drought and by site location. One site exhibited greater spring soil moisture, pH, percent open canopy, and had greater survivorship relative to the other site (55 ± 2 vs. 30 ± 2%). Overall, both L. maackii eradication methods were successful, but restorationists should be aware of the potential for differential survivorship of native seedlings depending on species identity and microenvironmental conditions.     

Effects of large-scale removal of coyotes on pronghorn and mule deer productivity and abundance

We tested the hypothesis that predation by coyotes (Canis latrans) impacts pronghorn (Antilocapra americana) and mule deer (Odocoileus hemionus) populations. We did so by examining the effects of coyote removal on pronghorn and mule deer populations within 12 large areas (>10,500 km²) located in Wyoming and Utah during 2007 and 2008. Pronghorn productivity (fawn to adult female ratio) and abundance were positively correlated with the number of coyotes removed and removal effort (hours spent hunting coyotes from aircraft) although the correlation between pronghorn productivity and removal effort was not statistically significant (P = 0.08). Mule deer productivity and abundance were not correlated with either the number of coyotes removed or removal effort. Coyote removal conducted during the winter and spring provided greater benefit than removals conducted during the prior fall or summer. Our results suggest that coyote removal conducted over large areas increases fawn survival and abundance of pronghorn but not mule deer. © 2011 The Wildlife Society.     

Brain acetylcholinesterase activity of the American pronghorn antelope <Emphasis Type="Italic">(Antilocapra americana)</Emphasis> collected from the US Army Dugway Proving Ground,Utah

Brain tissue was analyzed for acetylcholinesterase (AChE) activity from 24 American pronghorn antelope (Antilocapra americana) collected on the US Army Dugway Proving Ground (DPG) (latitude 40°13' 52" N, longitude 112°45' 01" W), Tooele County, Utah. Pronghorn antelope from DPG were evaluated against 26 pronghorn antelope collected in Wyoming. The mean AChE activity was significantly greater (P < 0.001) in the Wyoming control group (4.612 ± 0.193 μM/gm brain tissue/min) relative to DPG (4.032 ± 0.621 μM/gm brain tissue/min). The DPG database exhibited a fourfold greater coefficient of variation, a tenfold greater variance, and a threefold increase in the standard deviation when compared to control AChE activity. Furthermore, the 95% confidence interval for the control and for the DPG data were not overlapping; the entire control data set was greater than the mean DPG AChE activity. A post hoc sequential Bonferroni statistical procedure showed two significantly (P < 0.001) distinct subsets in the DPG data. Mean DPG Subset I AChE activity (4.528 ± 0.347 μM/gm brain tissue/min) was indistinct from the mean control AChE value (4.612 ± 0.193 μM/gm brain tissue/min). The mean DPG Subset II AChE activity (3.537 ± 0.387 μM/gm brain tissue/min) differed significantly (P < 0.001) from the mean control AChE activity. The sum of resulting α values from the multiple statistical tests did not exceed the selected α value of P < 0.05, validating the post hoc sequential Bonferroni statistical procedure. Pronghorn antelope represented by Subset II, experienced a 23.3% mean loss of AChE activity suggesting sub-lethal organophosphate (OP) exposure rather than a low level chronic environmental influence was experienced by a population subset of the DPG pronghorn antelope herd. The origin of the DPG sublethal OP exposure and its long-term effects are speculative.     

Increasing drought decreases phosphorus availability in an evergreen Mediterranean forest

Mediterranean ecosystems are water-limited and frequently also nutrient-limited. We aimed to investigate the effects of increasing drought, as predicted by GCM and eco-physiological models for the next decades, on the P cycle and P plant availability in a Mediterranean forest. We conducted a field experiment in a mature evergreen oak forest, establishing four drought-treatment plots and four control plots (150 m² each). After three years, the runoff and rainfall exclusion reduced an overall 22% the soil moisture, and the runoff exclusion alone reduced it 10%. The reduction of 22% in soil moisture produced a decrease of 40% of the accumulated aboveground plant P content, above all because there was a smaller increase in aerial biomass. The plant leaf P content increased by 100 ± 40 mg m⁻² in the control plots, whereas it decreased by 40 ± 40 mg m⁻² in the drought plots. The soil Po-NaHCO₃ (organic labile-P fraction) increased by 25% in consonance with the increase in litterfall, while the inorganic labile-P fraction decreased in relation to the organic labile-P fraction up to 48%, indicating a decrease in microbial activity. Thus, after just three years of slight drought, a clear trend towards an accumulation of P in the soil and towards a decrease of P in the stand biomass was observed. The P accumulation in the soil in the drought plots was mainly in forms that were not directly available to plants. These indirect effects of drought including the decrease in plant P availability, may become a serious constraint for plant growth and therefore may have a serious effect on ecosystem performance.     

Growth and demography of a declining,endangered cactus in the Sonoran Desert

Increases in the incidence and severity of drought threaten the viability of rare plants in arid regions. The endangered Nichol's Turk's head cactus (Echinocactus horizonthalonius Lemaire var. nicholii L. Benson) occurs only in four small, isolated populations in the Sonoran Desert of North America. Since 1995 we have monitored a population in southeastern Arizona (USA). Here we report 23 years of observations on abundance, growth, mortality, flowering and recruitment. Abundance of plants decreased from 132 in 1996 to 40 in 2017, with 100 individuals recruited and 203 dying during the study. Individual plants grew slowly, increasing annually by an average of 0.22 cm (95% confidence interval, 0.18–0.26 cm) in diameter and 0.27 cm (0.20–0.33 cm) in height. Growth was slowest when drought was most severe and slowed as plants reached maximum size. Annual mortality increased markedly across the study period and did not vary with plant size. Annual probability of flowering increased as plants increased in diameter but not in height, and varied with precipitation and drought but not with mean annual temperature. Recruitment was higher when average temperature was higher and the number of recruits per capita increased across the study period. The annual rate of change in abundance averaged −6%, but shifted markedly from −1% during 1995–2008 to −11% during 2008–2017. Our results indicate that the population's decline was not a consequence of failed recruitment but of increased mortality, which we discuss in the context of climate and herbivory.     

Tree growth,mortality, and above-ground biomass accumulation in a holm oak forest under a five-year experimental field drought

A holm oak forest was exposed to an experimental drought during 5 years to elucidate the growth responses of the dominant species Quercus ilex, Arbutus unedo and Phillyrea latifolia. Soil water availability was partially reduced, about 15% as predicted for this area for the next decades by GCM and ecophysiological models, by plastic strips intercepting rainfall and by ditch exclusion of water runoff. The stem diameter increment was highly correlated with annual rainfall in all species, and drought treatment strongly reduced the diameter increment of Q. ilex (41%) and specially of A. unedo (63%), the species showing higher growth rates. Stem mortality rates were highly correlated with previous stem density, but drought treatment increased mortality rates in all species. Q. ilex showed the highest mortality rates (9% and 18% in control and drought plots, respectively), and P. latifolia experienced the lowest mortality rates (1% and 3% in control and drought plots, respectively). Drought strongly reduced the increment of live aboveground biomass during these 5 years (83%). A. unedo and Q. ilex experienced a high reduction in biomass increment by drought, whereas P. latifolia biomass increment was insensitive to drought. The different sensitivity to drought of the dominant species of the holm oak forest may be very important determining their future development and distribution in a drier environment as expected in Mediterranean areas for the next decades. These drier conditions could thus have strong effects on structure (species composition) and functioning (carbon uptake and biomass accumulation) of these Mediterranean forests.     

Effects of young Artemisia rothrockii shrubs on soil moisture,soil nitrogen cycling,and resident herbs

Questions: How do young sagebrush shrubs (Artemisia rothrockii, Asteraceae) affect soil moisture availability? How do young sagebrush shrubs affect soil nitrogen cycling? How does the resident herb community respond to shrub removal in the early stages of sagebrush encroachment? Location: Mulkey and Bullfrog Meadows on the Kern Plateau in the Golden Trout Wilderness, Sierra Nevada Mountains, Inyo National Forest, Inyo County, California, USA. Methods: We removed young encroaching sagebrush shrubs from 3.5 m × 3.5 m plots and compared soil moisture, net mineralization, net nitrification, and herb cover with paired control plots over four growing seasons. Results: On average throughout the experiment, the difference between removal plots and control plots in soil moisture was small. Removal plots were wetter by 1.3 ± 2.0% at 0–30 cm depth, 2.1 ± 3.1% at 30–60 cm depth and 3.1 ± 5.8% at 60–90 cm depth. By contrast, after four years, net mineralization was 32 ± 26% (mean ± 95% CI) lower in sagebrush removal plots, suggesting that sagebrush encroachment increases rates of N‐cycling. Total herb cover was 13.0 ± 6.4% (mean ± 95% CI) higher in plots where young sagebrush shrubs were removed. This difference in cover appeared during the first season in which sagebrush shrubs were removed. Conclusions: Our results suggest that while young sagebrush shrubs do not contribute substantially to meadow drying, they alter N cycling rates, and may indirectly increase the rate of their own encroachment by competitively reducing resident herbs.