Flowering range changes across an elevation gradient in response to warming summer temperatures

Many studies have demonstrated plant response to warming temperatures, both as advancement in the timing of phenological events and in range shifts. Mountain gradients are ideal laboratories for studying species range changes. In this study of 363 plant species in bloom collected in five segments across a 1200 m (4158 ft) elevation gradient, we look for changes in species flowering ranges over a 20-year period. Ninety-three species (25.6%) exhibited a significant change in the elevation at which they flowered from the first half to the second half of the record, with many of these changes occurring at higher elevations. Most of the species exhibiting the changes were perennial plants. Interestingly, though many changes in flowering range were specific to higher elevations, range changes occurred all across the gradient. The changes reported in this study are concurrent with significant increases in summer temperatures across the region and are consistent with observed changes around the globe.     

Early Establishment of a Native Grass Reduces the Competitive Effect of a Non‐Native Grass

Buffelgrass (Pennisetum ciliare (L.) Link), a C₄ perennial bunchgrass native to Africa and parts of Asia, has invaded broadly across the southwestern United States and northern Mexico. Buffelgrass establishment may occur earlier than the natives it displaces which may preempt resource acquisition by native species and contribute to its invasion success. In a greenhouse, buffelgrass aboveground growth was tested against Arizona cottontop (Digitaria californica (Benth.) Henr.), a native C₄ perennial bunchgrass, in pairwise combinations in a randomized complete block factorial design with 10 replications, three neighbor identities (self, other, and no neighbor), and three competition treatments (21‐day younger neighbor, 21‐day older neighbor, and same‐aged neighbor). When compared with control plants, there was no significant effect on aboveground biomass for older Arizona cottontop plants competing with younger buffelgrass plants (p > 0.05). However, when Arizona cottontop plants were of the same age or younger than buffelgrass plants, buffelgrass caused 95 and 88% reductions, respectively, in aboveground biomass (p < 0.05 in both cases). Intraspecific competition between same‐aged Arizona cottontop plants resulted in only 55% decline in aboveground biomass production (p < 0.05), thus interspecific competition with buffelgrass was more intense than intraspecific competition for Arizona cottontop when plants had similar emergence times. These results suggest that establishing native plants immediately following a disturbance event could be a practical technique for restoring or retaining diversity on sites with high potential for invasion by buffelgrass.     

Observations of Coyote-Cat Interactions

ABSTRACT Coyotes (Canis latrans) pose a risk to domestic cats (Felis catus). We captured, radiocollared, and tracked 8 coyotes from November 2005 to February 2006 for 790 hours in Tucson, Arizona, USA. We observed 36 coyote-cat interactions; 19 resulted in coyotes killing cats. Most cats were killed in residential areas from 2200 hours to 0500 hours during the pup-rearing season. Single coyotes were as effective killing cats as were groups (>1) of coyotes. Documented cases of predators killing cats could encourage cat owners to keep their cats indoors and assist wildlife managers in addressing urban wildlife issues.     

Importance of scale in nest-site selection by Arizona gray squirrels

Nests provide a place for individuals to rest, raise young, avoid predators, and escape inclement weather; consequently, knowledge of habitat characteristics important to nest placement is critical for managing species of conservation concern. Arizona gray squirrels (Sciurus arizonensis) are endemic to mountains of southwestern United States and northwestern Mexico. We investigated factors influencing nest-site selection at 4 spatial scales (forest-type, nest-site, nest-tree, and within-canopy placement) to provide ecological information and management recommendations for this sensitive species. Nest densities were 2.6 times higher in riparian than pine-oak woodlands. Nest sites had more large trees, snags, logs, and canopy cover and had lower slope. Arizona gray squirrels selected tall trees with more interlocking trees and tended to place nests adjacent to the main trunk. Regardless of scale, Arizona gray squirrels seemed to select nesting areas for their ability to provide protection from predators and the elements as well as access to food. Consequently, maintaining large trees with closed canopies and downed logs should be considered when determining land management plans. © 2011 The Wildlife Society.     

The regeneration of a protected Sonoran Desert cactus since 1800 A.D. over 50,000 km2 of its range

The tall, branched saguaro cactus (Carnegiea gigantea) is perhaps the best-recognized symbol of the desert. However, little is known about the regeneration and future of the species outside of a few well-studied populations. In 2000, data for 537 saguaros were collected in 30 populations throughout the northern Sonoran Desert. A recently developed technique now provides a mechanism by which to reconstruct individual age at multiple populations. This new technique is based on a general growth curve with a site-specific adjustment factor, which I calculate based on local growth data and a recognized relationship with summer rain. Thus, the year of establishment was estimated for all saguaros in each of the populations individually, followed by the merging of all individuals, to create a single regeneration and survivorship curve for the combined regional dataset. Unlike other studies that only look at regeneration at one site, this is the first study to look at the long-term regeneration of the species over an area of more than 50,000 km², nearly the US portion of its range. The results suggest that over the long term, the population is quite stable, with a favorable period of regeneration in the late 1800s and early 1900s. It is also encouraging that the frequency of individuals that established in the most recent time period is relatively high. However, whether these youngest individuals will persist over the long-term in the face of future extreme freezing events (which can substantially thin populations) is not clear.     

Comparison of Mexican Wolf and Coyote Diets in Arizona and New Mexico

ABSTRACT Interactions between wolves (Canis lupus) and coyotes (C. latrans) can have significant impacts on their distribution and abundance. We compared diets of recently translocated Mexican wolves (C. l. baileyi) with diets of resident coyotes in Arizona and New Mexico, USA. We systematically collected scats during 2000 and 2001. Coyote diet was composed mostly of mammalian species, followed by vegetation and insects. Elk (Cervus elaphus) was the most common item in coyote scats. Mexican wolf diet had a higher proportion of large mammals and fewer small mammals than coyote diet; however, elk was also the most common food item in Mexican wolf scats. Our results suggest that Mexican wolf diet was more similar to coyote diet than previously reported, but coyotes had more seasonal variation. Considering results in other areas, we expect that Mexican wolves will have a negative impact on coyotes through direct mortality and possibly competition. Reintroduction of Mexican wolves may have great impacts on communities by changing relationships among other predators and their prey.     

Characteristics of Mount Graham Red Squirrel Nest Sites in a Mixed Conifer Forest

Abstract: The Mount Graham red squirrel (Tamiasciurus hudsonicus grahamensis) is constrained to the Pinaleño Mountains in southeastern Arizona, USA. The population's endangered status and extensive forest damage from insects and fire warrants a better understanding of habitat variables important for nest site selection. We examined characteristics of cavity (n = 91) and drey (n = 38) nests and compared these to random sites (n = 113). Dreys were found primarily in Engelmann spruce (Picea engelmannii) and corkbark fir (Abies lasiocarpa var. arizonica). Cavity nests occurred primarily in aspen (Populus tremuloides) and corkbark fir. Squirrels selected nest sites with higher canopy cover and more corkbark fir, decayed logs, and living trees. Forest management plans emphasizing thinning must consider how altering these habitat characteristics could affect availability and suitability of tree stands for nesting squirrels.     

The taxonomic status of Astragalus mokiacensis (Fabaceae), a species endemic to the southwestern United States

Astragalus mokiacensis has been a problematic species since it was first described in 1877. Every major revision delimited this taxon differently. A principal components analysis of morphological data from herbarium specimens was used to determine the affinities between type specimens and extant populations ofA. mokiacensis. The taxon recently recognized asA. lentiginosus var.trumbullensis is morphologically similar to the lectotype ofAstragalus mokiacensis. Astragalus lentiginosus var.trumbullensis is herein recognized as a lowelevation minor variant and considered a synonym ofA. mokiacensis. A taxonomic key and complete synonymy are included.     

Soil seed banks in Pinus ponderosa forests in Arizona: Clues to site history and restoration potential

Question: How does the relationship between the viable soil seed bank species composition and the above‐ground vegetation in northern Arizona Pinus ponderosa forests differ under varying historical land use disturbances (low, intermediate, high)? Is above‐ground vegetation correlated to the viable soil seed bank immediately following soil disturbance from restoration thinning treatments? Location: Northern Arizona, USA. Methods: Soil seed bank samples were taken along replicated transects and collected with a 5‐cm diameter bulk density hammer. Samples included a 5 ‐cm diameter O‐horizon sample (at varying depths) plus the underlying mineral soil to a depth of 5 cm. The seedling emergent method was used to quantify seed bank species composition and density. The herbaceous and shrub plant community was quantified along the same transects using the point intercept method. Results: Early‐successional or ruderal species were common in the soil seed bank at all three disturbance sites. Non‐native species, notably Verbascum thapsus, were more numerous (up to 940 seeds/m²) under high disturbance with overgrazing and logging, and less common or absent under low disturbance. Most viable seeds were found in the O‐horizon and the upper 5 cm of mineral soil; there was little correlation between species in the soil seed bank and the above‐ground vegetation. Conclusions: We recommend that restoration plans be geared toward minimizing activities, such as severe soil disturbance, that may promote the spread of non‐native invasive species, and that manual seeding be explored as an option to restore plant species diversity and abundance.