the central Sierra Nevada jerseys

zngmqk19 · Wysłany: Nie 16:10, 20 Mar 2011 Temat postu: the central Sierra Nevada jerseys

Less is known about California and Mexican spotted owls' relationships to patch size. In mixed-conifer forests of the central Sierra Nevada,[link widoczny dla zalogowanych], [link widoczny dla zalogowanych] 1,129 acre (457 ha) areas used by California spotted owls were not significantly (P=0.547) larger habitat patches than random areas [71]. However, in a model of California spotted owl dynamics and reserve design, persistence was greater when reserved areas were arranged in fewer larger patches than when they occurred in more smaller patches [72]. Nest stands in study areas throughout California averaged 100 acres (40.5 ha) [45]. A review suggests that during winter, smaller forest patches may be used than in the breeding season [4].
Although the results are mixed, spotted owls may be negatively impacted by fragmentation and isolation. This has most often been observed at scales from 500 (200 ha) to several thousand acres. In Douglas-fir/hardwood and mixed-conifer forests of northwestern California, northern spotted owl nest sites were significantly (P<0>0.05) different [56]. A similar pattern was observed in Douglas-fir forests of northern California, with no significant associations between northern spotted owl frequency and percent clearcut or total edge at large (2,500 acre (1,000 ha)) scales. Northern spotted owl frequency also had no significant association with distance to a clearcut or total length of edge within the plot at small scales (25 acre (10 ha)). However, at the stand scale, northern spotted owl frequency was negatively associated with a measure of the percentage of the stand's perimeter that bordered clearcuts (P<0.1). Although several measures of fragmentation did not differ (P≥0.14) between northern spotted owl and random areas at a large scale in the Olympic Peninsula in Washington, a measure of northern spotted owl habitat isolation was significantly (P<0.01) lower in 8,038 acre (3,253-ha) circles centered on pair locations than in random circles [70]. Effects at large scales were observed in mixed-conifer and Douglas-fir landscapes in southwestern Oregon. Northern spotted owls in fragmented areas had lower densities,[link widoczny dla zalogowanych] less home range overlap between members of the same pair, higher home range overlap between members of neighboring pairs, and greater incidence of mate changes than owls in study areas with clumped habitat [10].