Treesearch

To investigate whether Northern Goshawk (Accipiter gentilis) reproduction is food-limited, we evaluated the reproductive output from 401 goshawk breeding opportunities on the Kaibab Plateau, Arizona during 1999¨C2002. Concurrently, we estimated densities of 10 goshawk prey species (seven birds, three mammals) using distance sampling. We then assessed the relationship between goshawk productivity (number of fledglings produced) and prey density within and among years by relating the contribution of individual prey species and total prey density to goshawk productivity. We also estimated the...

We used mark-recapture methods to monitor Northern Goshawks (Accipiter gentilis) and their nests over 12 yr in an increasing sample of breeding territories (37 in 1991 to 121 in 2002) in northern Arizona. As many as 8 yr of repeated nest searching were required to identify the population of breeders, as individuals skipped egg-laying on territories for up to 7 consecutive yr. Extensive temporal (within territory) and spatial (among territory) variation in reproduction and a high annual frequency of movements among dispersed alternate nests in territories made finding and monitoring...

Actinorhizal plants are nodulated by the symbiotic, nitrogen-fixing actinomycete Frankia. The genus Alnus in the family Betulaceae is one of the 25 genera in 8 families of angiospermous plants that are actinorhizal. Arizona alder (Alnus oblongifolia Torr.) occurs in isolated populations associated with the watersheds of Madrean Sky Islands in the southwestern United States between 4,500 and 7,500 ft in elevation. We have found root nodules on alder trees from Oak Creek Canyon and from the Santa Catalina Mountains (southeastern and central Pima County to Oak Creek in Coconino County,...

Much has been learned about the oak (encinal) woodlands of the southwestern United States in recent years. Ecological, hydrologic, and environmental characterizations have been obtained through collaborative efforts involving a large number of collaborators. This state-of-knowledge has been presented in a variety of publications and presentations. However, comparable characterizations of the companion oak savannas are needed to help in enhancing the knowledge of all oak ecosystems in the Madrean Archipelago region. Oak savannas differ from oak woodlands in that they are more open in their...

The National Oceanic and Atmospheric Administration Contingent Valuation panel recommended that a response category be included along with the vote in favor and vote against options associated with a referendum contingent valuation question that allows individuals to express lack of a well defined opinion. However, the recommendation did not include guidance on how to analyze such responses. In this article, we describe the results of a carefully designed split sample experiment that allowed for comparison of a standard dichotomous-choice referendum treatment to a treatment that included...

Using independent observations of actual and potential evapotranspiration at a wide range of spatial scales, we provide direct observational evidence of the complementary relationship in regional evapotranspiration hypothesized by Bouchet in 1963. Bouchet proposed that, for large homogeneous surfaces with minimal advection of heat and moisture, potential and actual evapotranspiration depend on each other in a complementary manner through land-atmosphere feedbacks. Although much work has been done that has led to important theoretical and conceptual insights about regional actual evapotransp...

Since the 1990s, numerous authors have expressed concerns about lack of conceptual clarity in research on place. Some authors suggest that place research has failed to evolve into a systematic and coherent body of knowledge. We believe recent critiques do not adequately characterize the state of knowledge in place research, but responding to the issues raised requires investigating epistemological foundations of place research traditions. Specifically, seeing systematic coherence requires a pluralistic world view that understands place, not as a single research tradition but as a domain of...

The Coronado National Forest proposed amending its 1986 Land and Resource Management Plan to conform to the 2001 Federal Wildland Fire Management Policy. This Policy emphasizes fire’s essential role in maintaining natural ecosystems and allows a broader range of management options for wildland fires. Under the current Forest Plan, fires must be suppressed in areas outside of congressionally designated Wildernesses, Wilderness Study Areas, and Research Natural Areas. The proposed amendment would allow fire managers’ discretionary use of a spectrum of fire management alternatives, from...

To examine potential responses of sky island ecosystem pattern to projected climate changes, we used topographic and climatic data to develop a predictive model of plant community distribution in Saguaro National Park East, AZ. Increasing temperatures led to an upslope movement of communities and increased the area of desert scrub at the expense of montane conifer forest while increasing precipitation led to the opposite response as growth constraints imposed by arid conditions were lessened. Specific combinations of temperature and precipitation change created more or less extreme...

Moisture limitations have led researchers to believe that semiarid soils are not significant consumers or producers of trace gases, and these regions are often overlooked in greenhouse gas inventories. We are studying environmental influences on soil fluxes of methane (CH4) in southeastern Arizona. We found negligible CH4 consumption in the very dry pre-monsoon period, but the first moisture pulses stimulated soil CH4 flux. Thereafter, significant CH4 consumption was found through the summer and winter months. The soil CH4 consumption averaged 471 ± 278 µg CH4 m-2 d-1 throughout the year,...