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We compared abundances of seven species of forest rodents among three types of fir ( Abies concolor and A. magnifica ) forest: unlogged old-growth, unlogged mature, and shelter-wood-logged old-growth. Small mammals were livetrapped during summers 1991 and 1992 in four grids within each type of forest; grids were located in the Lassen National Forest in northeastern California. Shelterwood-logged forests had been logged 6–7 years previously. Differences in capture rates between unlogged, old-growth and shelterwood-logged, old-growth forests suggest that logging led to significant increases in populations of golden-mantled ground squirrels ( Spermophilus lateralis ), yellow pine chipmunks ( Tamias amoenus ), and lodgepole chipmunks ( Tamias speciosus ) but may have led to reduced populations of western red-backed voles ( Clethrionomys californicus ). Capture rates of Douglas' squirrels ( Tamiasciurus douglasii ), Allen's chipmunks ( Tamias senex ), and deer mice ( Peromyscus maniculatus ) did not differ significantly between unlogged and shelterwood-logged forests. Capture rate of T. douglasii was significantly greater in mature forests than in old-growth forests in 1992, but we did not detect significant differences between old-growth and mature forests for the other six species. These results illustrate how opening of the canopy and disturbance of the forest floor can lead to significant changes in patterns of abundance of forest rodents.

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.

The northern flying squirrel (Glaucomys sabrinus) is the primary prey of northern spotted owls (Strix occidentalis caurina) and California spotted owls (S. o. occidentalis) throughout much of the owls' ranges. Flying squirrel abundance patterns, however, are poorly documented. Using capture-recapture techniques to estimate density, we compared flying squirrel densities among 3 types of fir (Abies spp.) forests in Lassen National Forest, northeastern California. We compared densities between 3 each of old and shelterwood-logged fir stands in 1990 and among 4 each of old, shelterwood, and young fir stands in 1991-92. Shelterwood stands had been logged and had undergone site preparation 5 years prior to our study. In 1990 flying squirrel density was greater in old (? = 2.76 squirrels/ha, SE = 0.55) than in shelterwood (? = 0.31 squirrels/ha, SE = 0.11) stands (P = 0.005). In 1991-92 density varied (P = 0.001) among the 3 stand types, averaging 3.29 squirrels/ha (SE = 0.63) in old, 2.28 squirrels/ha (SE = 0.18) in young, and 0.37 squirrels/ ha (SE = 0.17) in shelterwood stands. Body mass of adult males and females and recapture rate did not differ (M, P = 0.438; F, P = 0.983; P = 0.218, respectively) between old and young stands, and percent juveniles captured was greater (P = 0.052) in old than in young stands. Diet analyses were consistent with other studies and indicated that sporocarps of hypogeous fungi were a common food source. Frequency of hypogeous sporocarps was correlated (r s = 0.860, P < 0.001) with flying squirrel density, but cavity density and understory cover were not (P = 0.344 and 0.217, respectively). Flying squirrels were not old-growth specialists; however, low densities in shelterwood stands suggest that heavy logging and intensive site preparation negatively affected flying squirrel populations.

We examined the relationship between nest site availability and density of secondary cavitynesting birds by blocking cavities in an oak-pine (Quercus spp.-Pinus sp.) woodland. In 1986 and 1987 we blocked 67 and 106 cavities, respectively, on a 37-ha plot. The combined density of secondary cavity-nesting birds did not decline in either year by a greater proportion on the treatment plot than on a control plot, indicating that cavities were not limiting. In habitats where timber management has not substantially reduced availability of natural cavities, managers should not assume nest site limitation; natural nest site availability should be evaluated before implementing nestbox programs designed to increase populations of secondary cavity-nesting birds. J. WILDL. MANAGE. 54(2):239-245 Knowledge of factors that limit species' abundances is needed to formulate management guidelines and to predict effects of habitat alteration. Nest site limitation of secondary cavity-nesting birds (SCNB), i.e., cavity nesters that do not excavate their own cavity, is often assumed rather than hypothesized (e.g., von Haartman 1957, Hilden 1965, Thomas et al. 1979). In his paper on the evolution of the cavity-nesting habit in birds, von Haartman (1957: 339) stated, "In the case of hole-nesters it seems obvious that the number of holes, and not the amount of food, mostly acts as an ecological limiting factor, determining the maximum number of nesting pairs.", Much of the evidence indicating nest site limitation has come from European nestbox studies (see von Haartman 1971 for review). Bruns (1960) reported that densities of some European SCNB species have been increased 5-20 times by adding nestboxes. Natural nest site availability throughout much of Europe, however, has been substantially reduced by long-term intensive forest management (Bruns 1960, Haapanen 1965, Slagsvold 1978). Many North American studies have documented nestbox use (e.g., Hamerstrom et al. 1973, McComb and Noble 1981, Savard 1988). However, we are aware of few controlled nestbox experiments, i.e., studies in which preand posttreatment densities were estimated from bo h treatment and control plots (Brush 1983, Brawn and Balda 1988). Dahlsten and Copper (1979) also used nestboxes to study population characteristics of SCNB's, but they did not obtain premanipulation estimates of abundance on nestbox and control plots. Nestbox use does not necessarily indicate nest site limitation; use can be merely compensatory rather than additive (see van Balen et al. 1982, Nilsson 1984a, Gauthier and Smith 1987). Our objective was to test the hypothesis that breeding densities of SCNB's are limited by nest site availability at a site where the number of cavities was essentially unaffected by man. Rather than test the hypothesis by increasing n t site availability with nestboxes, we reduced ne t site availability by blocking cavities. D. A. Duncan provided much support and assistance throughout this study. We thank J. C. Lovio and B. R. North who censused the plots in 1987. Thanks also to S. P. Duncan and W. A. Patrick at the San Joaquin Experimental Range and J. D. Stuart at Humboldt State University. Our study was partially funded by the U.S. Forest Service Pacific Southwest Forest and Range Experiment Station, the California Integrated Hardwood Range Management Program, the North American Bluebird Society, and Sigma