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The recovery plan for the Mexican spotted owl (Strix occidentalis lucida) recommended protection of owl nesting and roosting habitat. Descriptions of rnicrohabitat (less than or equal to-0.04 ha) characteristics associated with suitable nesting sites have been limited for the area of pine-oak forest occupied by this species in Arizona, USA. Therefore, we studied Mexican spotted owl habitat on a 585-km(2) study area on the Coconino Plateau near Flagstaff, Arizona. Mexican spotted owls nested primarily in mature (greater than or equal to45.7-cm diameter at breast height dbh) Gambel oak (Quercus gambelii; 40%) and ponderosa pine (Pines ponderosa; 37%) trees. We examined a plausible set of a priori models using both...
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In the arid southwest of North America, winter precipitation penetrates to deep soil layers, whereas summer "monsoon" precipitation generally wets only surface layers. Use of these spatially separated water sources was determined for three dominant tree species of the pinyon-juniper ecosystem at six sites along a gradient of increasing summer precipitation in Utah and Arizona. Mean summer precipitation ranged from 79 to 286 mm, or from 18% to 60% of the annual total across the gradient. We predicted that, along this summer rainfall gradient, populations of dominant tree species would exhibit a clinal off-on response for use of water from upper soil layers, responding at particular threshold levels of summer precipitation...
    map background search result map search result map Intra- and Interspecific Variation for Summer Precipitation Use in Pinyon-Juniper Woodlands Intra- and Interspecific Variation for Summer Precipitation Use in Pinyon-Juniper Woodlands