Cynthia J. Zabel

BAT ACTIVITY ALONG INTERMITTENT STREAMS IN NORTHWESTERN CALIFORNIA

Abstract Bats are known to use areas above perennial streams and rivers for foraging and traveling; however, little is known about bat use of smaller streams that flow intermittently. We compared bat activity among 3 size classes of streams and upland sites in a northwestern California watershed during summers 1996 and 1997. Stream size was classified based on channel width. Ultrasonic Anabat II® bat detectors were placed in stream channels and at upland sites, and bat activity was recorded remotely at night. Analysis of bat detector data revealed a significant difference in activity among the 4 habitat types in both years. In 1996, bat activity was greatest along medium and large intermittent streams, was intermediate at small intermittent streams, and was least at upland sites. In 1997, a similar pattern was found, but no significant difference was found in bat activity between small stream and upland sites. To determine species presence, bats were captured in mist nets at stream sites with the highest bat activity. Results are presented indicating differences in number of captures by species between medium and large streams.

Characteristics of fringed myotis day roosts in Northern California

Understanding habitat relationships of forest-dwelling bats has become a wildlife management priority during the past decade. We used radiotelemetry to examine the use of day roosts by fringed myotis (Myotis thysanodes) in a Douglas-fir (Pseudotsuga menziesii) forest in northern California, We located 52 roosts in 23 trees and compared the characteristics of roost sites and structures to random sites and structures. All roost trees were snags in early to medium stages of decay. Bats switched roosts often, and the number of bats exiting roosts varied from 1-88. The most important factor that discriminated roost sites from random sites was 5.4 more snags ≥30 cm dbh at roost sites. Roost sites also had 11% less canopy cover and were 41 m closer to stream channels than random sites. Roost snags were 27 m taller and had diameters 42 cm larger than random snags in the watershed and were 21 m taller and had diameters 30 cm larger than snags nearby the roost. Our results are comparable to findings for other forest-dwelling bat species which conclude that management of day roost habitat requires large numbers of tall snags in early to medium stages of decay.

Forest stand characteristics and reproduction of northern spotted owls in managed North-Coastal California forests

We monitored reproductive success of northern spotted owls (Strix identalis caurina) at 51 sites on Simpson Timber Companys (STC) managed, young-growth forests in northwestern California from 1991 to 1995. We compared habitat characteristics between sites with high and low fecundity at 5 spatial scales (concentric circles of 7. 50, 114, 203, and 398 ha), using 2 stratifications of annual reproductive success (upper 50% vs. lower 50% and upper 25% vs. lower 75% of the proportion of years when ≥1 owlet fledged). Habitat features included number of residual trees per hectare and mean proportion of 6 categories of stand age and 4 categories of basal area. Using the 50th percentile categories, we found there were higher proportions of age class 21-40 years and basal area classes 23-45 and 46-69 m 2 /ha (P ≤ 0.05), but lower proportions of recent clearcuts (0-5 yr) and basal area >69 m 2 /ha (P ≤ 0.05) at sites with high reproductive success. Using the upper 25% and lower 75% categories, we found there were higher proportions of basal area class 23-45 m 2 /ha, lower proportions of 61-80-year-old stands and more residua trees per hectare at sites with high reproductive success (P ≤ 0.05). We also compared random sites to occupied sites via the above parameters, Spotted owl sites contained lower proportions of basal area class 69 m 2 /ha than did random sites (P < 0.05). There was less young forest (6-40 vr) and more forest of age class 41-60 vears at spotted owl than at random sites (P < 0.05). Low prey abundance around spotted owl nest sites, roost sites, or both mav explain why older stands with more basal area were found in higher proportions at sites with lower fecundity. Spotted owls that chose younger stands with smaller trees mav have benefited from higher woodrat (Neotoma fuscipes) availability in young stands. Managing habitat by retaining residual trees and limiting clearcutting to at least 1.1 km bevond lest sites may prove useful in increasing reproductive success of northern spotted owls.

Truffle production in old-growth and mature fir stands in northeastern California

Abstract Few studies have examined fruiting patterns of hypogeous fungi, and relationships between sporocarp production of hypogeous fungi and forest habitat components such as organic soil depth and amounts of decayed wood are poorly understood. We sampled sporocarps of hypogeous fungi (truffles) in four old-growth (>200 years) and four paired, mature (ca 100 years) fir ( Abies spp.) stands during four sample periods in 1993 and three sample periods in 1994 in the Lassen National Forest in northeastern California. Truffles were collected from 4-m 2 circular plots systematically located at 36 grid points per stand during each sample period. Habitat characteristics were measured in 50.3-m 2 circles centered at each grid point in 1993. We found a total of 46 truffle species in 30.4% of the 2016 total plots, and the total standing dry weight of truffles was equivalent to 2.43 kg ha −1 . Total frequency and biomass of truffles and number of truffle species did not differ significantly between stand types in 1993 or 1994, but species composition did. We found no significant associations between measures of total truffle abundance and measures of habitat structure and composition at the 0.25-ha grid scale or at the 50.3-m 2 habitat plot scale. At the scale of the 4-m 2 truffle plot, plots with decayed wood were more likely to have truffles than plots without decayed wood during the final sample period of each year, but the association was significant only in 1993. Mean organic soil depth was greater in plots with truffles than plots without truffles in each sample period in both years, but ranked values were only marginally significant in one sample period. Goodness-of-fit tests to the Poisson distribution indicated that individual truffles had clumped distributions, but we could not reject the null hypothesis of random distribution of truffle collections. Our results indicate that total truffle production had recovered from stand-replacement wildfire in the mature stands, and that total truffle abundance was not strongly associated with habitat characteristics within the range of habitat variation exhibited in these stands. Individual species, however, were associated with old-growth stands and others with mature stands.

SPOTTED OWL TURNOVER AND REPRODUCTION IN MANAGED FORESTS OF NORTH-COASTAL CALIFORNIA

Abstract Northern Spotted Owl (Strix occidentalis caurina) reproduction and turnover (when an owl died or shifted territories, and was replaced by another owl) were monitored at 51 locations on Simpson Timber Company lands, northwestern California, from 1991–1995. We tested for differences in proportions of five stand age classes and reproductive success between Spotted Owl pair sites with (≥1 turnover) and without turnovers. Owl pairs at sites without turnovers fledged more young, showed more consistent reproductive success, and were surrounded by a greater percentage of 21–40-yr-old stands than were owl pairs at sites with turnovers. We hypothesize that pairs with high mate fidelity and survival were more reproductively successful because those pairs had previous breeding experience together. By investigating turnover along with habitat features, we now have an indication of the relative quality of various habitats for Spotted Owls on managed, coastal forests of northern California.