Journal of Herpetology, Vol. 30, No. 3, pp. 385-398, 1996

Habitat Correlates of the Southern Torrent , Rhyacotriton variegatus (Caudata: Rhyacotritonidae), in Northwestern California1

HARTWELL H. WELSH, JR. AND AMY J. LIND

Pacific Southwest Research Station, USDA Forest Service 1700 Bayview Dr., Arcata, California 93’521, USA

ABSTRACT.-Asystematic stratified sampling design was used to quantify the habitat relationships of the southern torrent salamander, Rhyacotriton variegatus, in northwestern California. We sampled 53 first to third order streams, each surrounded by at least 5-7 ha of relatively homogeneous forest or harvested forest habitat. Measurements of 121 attributes of the forest and stream environment were recorded in conjunction with area-constrained aquatic sampling for . A subset of 68 variables, grouped into 11 ecological components including attributes at the landscape, macrohabitat, and microhabitat scales, was used in a hierarchical analysis of habitat associations. Results from discriminant and regression analyses indicated that this occurs within a relatively narrow range of physical and microclimatic conditions and is associated with cold, clear headwater to low-order streams with loose, coarse substrates (low sedimentation), in humid forest habitats with large conifers, abundant moss, and HO% canopy closure. Thus, the southern torrent salamander demonstrates an ecological dependence on conditions of microcli- mate and habitat structure that are typically best created, stabilized, and maintained within late seral forests in northwestern California.

The southern torrent salamander (Rhyacotri- metapopulation structure of R. variegatus in ton variegatus) (previously R. olympicus variega- northwestern California and estimated the spe- tus) is the southernmost member of the family cies occurs in isolated sub-units at a frequency Rhyacotritonidae, comprised of a single genus of 0.07 populations per km. with four species endemic to the Pacific North- Few quantitative data exist on the habitat af- west (Good and Wake, 1992). Rhyacotriton var- finities of R. variegatus (see Corn and Bury, 1989; iegatus occurs in aquatic habitats in conifer- Bury et al., 1991). Anecdotal and general ac- dominated forests at elevations below 1449 m counts indicate that R. variegatus occur in springs, (L. Diller, pers. comm.) in the coast ranges from seeps, small streams,and margins of larger Mendocino County, California to the Little Nes- streams. They avoid open water and seek the tucca River and Grande Ronde Valley of north- cover of moss, rocks, and organic debris in shal- western Oregon (Nussbaum et al., 1983; Steb- low, cold, percolating water (Anderson, 1948; bins, 1985; Good and Wake, 1992; Leonard et Nussbaum and Tait, 1977; Nussbaum et al., 1983; al., 1993). Welsh and Lind (1992) examined the Stebbins, 1985; Bury, 1988; Bury and Corn, 1988; Corn and Bury, 1989; Welsh, 1990; Bury et al., 1991; Good and Wake, 1992; Leonard et al., 1993). Substrate conditions described for this species ‘This article was writtenand preparedby U.S. Gov- consist of water flowing through gravel, pebble, ernment employees on offi cial time, and it is therefore and cobble with little fine sediment. Habitat use in the public domain andnot subject tocopyright. differs slightly between the adult and larval life 386 H. H. WELSH AND A. J. LIND stages of R. variegatus. The larvae are entirely potheses, and can, by itself, produce strong and aquatic. Adults, although primarily aquatic, will useful inferences about real habitat relation- occasionally use adjacent moist riparian and for- ships (see controlled experience studies; Waters est microhabitats in the wet season (pers. obs.). and Erman, 1990). Recent research in northwestern California Site Selection.-Sites were distributed system- revealed that R. variegatus was found at signif- atically across the range of R. variegatus within icantly more sites in late seral forests (old- northwestern California using a stratified de- growth) than in early seral stages (Welsh and sign, with a random component, at four nested Lind, 1988; Welsh, 1990), but the number of levels: (1) biogeographic, (2) geographic (town- sites sampled was small and these results re- ship and section), (3) seral stage, and (4) mini- quire confirmation. Corn and Bury (1989) re- mum essential microhabitat, ported higher densities and biomass of this sal- Level one was defined by the known range amander in streams in uncut forests compared of the species in California based on published with logged forests in western Oregon. accounts (Stebbins, 1985) and included portions Rhyacotriton variegatus has a naturally patchy of two bioregions: the North Coast and Klamath distribution in northwestern California, show- (Welsh, 1994). Levels two and three consisted ing a strict association with headwaters and low of systematic selection of alternating town- order tributaries (Welsh and Lind, 1988, 1992). ships, randomly choosing sections therein, and This salamander is a State “species of special selection of forest stands in from one to four concern” (Jennings and Hayes, 1994) due to the seral stages within each section. These criteria following factors: (1) distributional limits im- were instituted across most of the range de- posed by this habitat specificity; (2) an unusu- scribed at level one, and up to 1115 m based on ally high degree of genetic heterogeneity among elevational limits known to us at the time (1989) sub-populations (Good and Wake, 1992); (3) the (Stebbins, 1985; unpubl. data). All sampling oc- apparent association of this species with late curred on public lands (state and federal parks seral attributes; and (4) the rapid loss of late and Forest Service) within the drainages of the seral forests due to timber harvesting (Thomas Smith, Klamath, Trinity, Mad and Van Duzen et al., 1988). A petition recently accepted by the Rivers of the Siskiyou, Klamath, and Coast Range U.S. Fish and Wildlife Service for listing R. var- Mountains. Sites occurred from near the Ore- iegatus as threatened under the Endangered gon border as far south as southern Humboldt Species Act, cites these same factors (Federal and Trinity counties, California (latitude 40°22’ ), Register, 1995). A better understanding of the and east from the Pacific Ocean to western Sis- habitat relationships of this salamander might kiyou and western Trinity counties (longitude explain their absence or lower abundance in 123’25’). We sampled in mixed conifer-hard- early seral forests and provide a basis for man- wood forests dominated by Douglas-fir (Psei- agement alternatives that could reverse the re- dotsuga menziesii) and redwood (Sequoia semper- duction in its numbers due to forestry practices. virens). We used forest age (the mean of three The objectives of our study were: (1) to ex- corings from the dominant size class of coni- amine and quantify the habitat associations of fers) to represent seral stage. Up to four stands R. variegatus at multiple spatial scales through- were selected in each section when available out the mixed conifer-hardwood forests of (one each clearcut [0-30 yr], young [31-99], ma- northwestern California; (2) to clarify the na- ture [l00-200], and old-growth [ +200]). Stand ture of the apparent relationship with forest ages sampled ranged from one year old clear- succession; and by meeting the first two objec- cuts to a 941 yr old redwood stand. Sampling tives, to (3) provide information critical for sites were located in at least 5-7 ha of contig- evaluating the potential impacts of continued uous forest or clearcut (no edge habitat) with habitat alterations on this species. uniform forest structure and tree species com- position (relatively homogeneous stands). MATERIALS AND METHODS Our sampling design for R. variegatus differed The general sampling design and the strategy from the design previously described (Welsh of analysis used here have previously been de- and Lind, 1995) primarily at the fourth level, scribed (Welsh and Lind, 1995). However, this that of selecting sites within stands with min- study differs considerably from our earlier work imum essential microhabitat (MEM). The intent in the details of both sampling and analysis. was to maximize time, effort, and the usefulness Here we provide a general outline of methods, of data sets by not sampling for salamanders at with particular emphasis on those details that sites with an extremely low probability of oc- pertain to our study of R. variegatus. While this currence. Therefore our sampling universe at research is exploratory and correlative, and not the fourth level was limited to first to third designed to demonstrate cause and effect, such order streams. An acceptable site had to contain an approach is vital for developing testable hy- at least 10 m2 of perennial aquatic habitat in a RHYACOTRITON VARIEGATUS HABITAT USE 387 natural watercourse. This 10 m2 could be any prior to multivariate analyses. Variables with a configuration of seep, spring, or stream chan- high number of zero values across sites (~70%) nel, but the entire area had to consist of aquatic were also removed because they could not be microhabitat. We used two hydrophilic plant normalized, and we believe that they were not species (California spikenard [Aralia californicus] likely to affect salamander distribution or abun- and chain fern [Woodwardia fimbriata]), or the dance. Initial measurements of general locator presence of populations of macroinvertebrates variables (landscape scale), forest structure such as stoneflies (order Plecoptera) and Dob- (macrohabitat scale), and microhabitat vari- son fly larvae (Corydalus sp.), as evidence of pe- ables, resulted in a total of 121 variables (see rennial water. Final site placement was deter- Welsh [1993] for the complete list and details mined by the most direct approach from the on measurements). Aquatic microhabitat cate- nearest trail or road access. All sites were lo- gories followed McCain et al. (1990) except we cated at least 75 m from any high contrast forest combined all pool types into two categories and edge. We selected sites with a variety of stream defined two additional categories: seep and microhabitats (McCain et al., 1990) but avoided splash zone (Table 1). Seeps were defined as centering the 10 m2 sites on deep pools or high shallow (<2 mm), slow-flowing water through gradient/discharge habitats (e.g., waterfalls or rock substrates; splash zones were defined as cascades) because the use of such habitats by wetted areas with no measureable flow or depth. Rhyacotriton conflicted with literature accounts. Aquatic substrate composition was character- However, these microhabitat types did occur ized in two ways: (1) as a visual estimate of the peripherally at many sites and were sampled percent of the search area in ten substrate cat- and included in our analysis. egories (e.g., gravel, pebble, cobble; sizes follow Sampling.-Fixed area aquatic searches Platts et al., 1983); and (2) as a percent of a 4000 (Welsh, 1987; Bury and Corn, 1991) (see also cm3 sample of streambed substrate, taken from quadrat sampling [Jaeger and Inger, 1994]) were a representative site just above each 10 m2 search conducted during daylight at each site to de- area, dried, sifted into five size classes and termine numbers of present. All but weighed (listed by actual size, see Table 1). We two sites were sampled during the summer (June performed preliminary descriptive analyses to to October) of 1989 to minimize seasonal effects. assess the normality of the distributions of all One or two searchers worked side by side to variables, and deviations were corrected by ap- thoroughly search a 10 m2 plot. Each plot was propriate transformations (Sokal and Rohlf, systematically searched, from downstream up, 198 1). Variable reduction procedures resulted with all pebbles, cobbles, and boulders turned in 68 independent variables for our multivar- and finer substrates carefully hand sifted down iate analyses (Table 1). to the armoured streambed or to a depth of 15 Statistical Analyses.-We employed discrimi- cm, unless we saw a salamander escape deeper, nant analysis and regression for statistical anal- in which case we pursued it. We captured both yses. Used together, these techniques can reveal larvae and adults. We assume our capture rates aspects of the habitat that may be limiting for are correlated to absolute densities and provide a species and also indicate those aspects that us relative densities that are valid for compar- might be managed to maintain or increase an- ing R. variegatus numbers amoung sites. imal numbers (this complimentary approach is Measuring Biotic and Abiotic Parameters.-We discussed in more detail by Welsh and Lind selected habitat variables for measurement us- [1995]). Life stages were combined for both ing three criteria: (1) parameters that reflected analyses. In our multivariate analyses we as- structural, compositional, and microclimatic as- sumed that univariate normality implied mul- pects of the forest and stream environment rel- tivariate normality (we did not test multivariate evant to R. variegatus as indicated by previous normality directly). research; (2) parameters that would indicate For the multivariate analyses we grouped change in structure and composition of the for- variables into ecologically meaningful subsets est resulting from common management prac- (ecological components) on the basis of simi- tices such as timber harvesting and reforesta- larity of spatial scale and vertical stratum of the tion, or natural successional events such as fire, forest environment (Table 1) (cf. Bingham and landslide, or flood; and (3) variables that incor- Sawyer, 1991; Welsh and Lind, 1995). We then porated aspects of the forest and stream envi- ran separate analyses on each component. This ronment reflecting three scales of spatial or- approach is a biologically sound and method- ganization: landscape, macrohabitat, and mi- ologically valid way to increase the sample size crohabitat. to variables ratio, which promotes a more sub- Our approach was to initially estimate a wide stantive analysis when dealing with a large range of parameters, and then eliminate highly number of independent variables (James and redundant variables using correlation analysis McCulloch, 1990). 388 H. H. WELSH LINDAND A.

TABLE 1. Hierarchical arrangement’ of ecological TABLE 1. Continued. components (see text) represented by 68 measure- ments of the forest and stream environment taken in “Lichen-B conjunction with sampling for the southern torrent *Moss-L salamander (Rhyacotriton variegatus). * Leaf_L *Aquatic habitat-L Dominant Rock--B l Spatial scales are in descending order from coarse *Co-dominant Rock B to fine resolution (see Wiens, 1989). Level I relation- F. Forest Climate ships (biogeographic scale) were not analyzed be- Soil temperature cause all sampling was within the species range. Air temperature 2 C = count variable which is numbers per hectare; Relative humidity B = Braun-Blanquet (1932) variable which is % cover Solar index4 in 0.1 ha circle; L = Line transect variable which is % canopy closed percent of 50 m line transect; P = % of 102m sala- Soil relative humidity mander search area. Small trees = 12-53 cm DBH IV Microhabitat Scale (diameter at breast height), large trees 1 53 cm DBH. A. Aquatic habitats 3 Based on mean of cores from three trees in dom- *Run-P inant size class on site; classes used = 12-27 cm, 27- *Waterfall-P 53 cm, 53-90 cm, 90-120 cm, and +120 cm DBH. *Backwater pool-P 4 Solar index is an estimate of annual incident solar *Edge-P radiation based on latitude, slope, and aspect (Frank *Splash Zone-P and Lee, 1966). Seep-P 5 Particle sizes from Platts et al. (1983); as a percent Scour pool-P of sample (see text for procedure). Riffle-P *Variable was transformed for statistical analyses. B. Coarse aquatic substrates5 Sediment 2-16 mm II. Landscape Scale Sediment 16-32 mm A. Geographic relationships “Gravel-P Pebble-P Latitude (degrees) *Cobble-P Longitude (degrees) *Boulder-P Elevation (m) Decayed vegetation_P Slope (%) Aspect (degrees) C. Fine aquatic substrates5 III Macrohabitat or Stand Scale *Sediment <0.063 mm *Sediment 0.063-0.5 mm A. Trees: density by size Sediment 0.5-2.0 mm Small conifers-C2 *Silt-P *Small hardwoods-C *Sand-P Large conifers-C *Non-filamentous algae-P ‘Large hardwoods-C Cemented-P Forest age (years)3 *Detritus-P B. Dead & down wood: surface area & counts D. Aquatic conditions Logs-B Water pH ‘Stumps-B Water temperature All logs decay_C *Discharge (cm/sec) “All logs sound-C *Mean channel width C. Shrub & understory composition (> 0.5m) “Mean channel depth *%Canopy (over stream) *Understory conifer-L *Number of Dicamptodon Understory hardwood-L *Large shrub-L Small shrub-L Height II vegetation-B (0.5-2m) A two-group discriminant analysis (DA) (SAS “Bole-L Institute, 1990) was performed for each ecolog- D. Ground-level vegetation ( < 0.5m) ical component (Table 1) using a stepwise pro- cedure to select variables. We tested the null ‘+Fern-L *Herb-L hypothesis that a given variable does not add *Grass-L any additional discriminatory power. For mod- Height I vegetation-B (O-O.5 m) el-building, a variable was entered if its P value E. Ground Cover for the partial F statistic was (0.10. This mod- Litter depth (cm) erate alpha-level reduces the chance of type II *Exposed soil-B errors and is more appropriate for detecting ecological trends (Toft, 1991). A linear discrim- RHYACOTRITON VARIEGATUS HABITAT USE 389 inant function was then determined based on standard non-linear (logarithmic, exponential, the variables selected. Welsh and Lind (1995) and second order polynomial) curve-fitting. In detail the method used for testing the assump- the regression analyses those variables with the tion of homogeneity of variance-covariance best R2 (smallest mean square error) were re- structure among groups required for DA, and ported and discussed. detail the logic for presenting all results here in the form of linear functions only. RESULTS Resulting models were then tested at alpha We sampled 53 sites for Rhyacotriton variegatus 50.05 using a jackknife procedure (SAS Insti- (see map in Welsh and Lind, 1992). Thirty-three tute, 1990) to evaluate classification success. sites had salamanders, with a total of 208 cap- Cohen’s Kappa (Titus et al., 1984) was computed tures (173 larvae and 35 adults). Densities at for each test to indicate classification success these sites ranged from one to 50 animals in 10 compared with chance. In classification tests m2, with a mean of O&B/m2 (SD = 0.89). based on the discriminant functions, we as- Discriminant Analyses.-Discriminant analy- sumed our random systematic site selection pro- ses of 11 ecological components (Table 1) yield- cedure yielded a proportion of sites with and ed significant results for eight of 11 sets of vari- without salamanders that reflects the true pro- ables (Table 2). Elevation was the only land- portion. Therefore we adjusted the prior prob- scape-scale variable that discriminated between abilities of group membership accordingly (pri- sites with and without salamanders (Table 2); ors proportional) (SAS Institute, 1990). with sites supporting salamanders more com- We performed an ‘all-possible-subsets’ re- mon at lower elevations. Jackknife results for gression analysis (APS) of each microhabitat- this model were poor (only 56.6% correct) in- scale ecological component (Table 1). This was dicating that it failed to discriminate between followed by an APS on the combination of vari- sites at a rate much better than chance. ables derived from the individual microhabitat Five of six components at the macrohabitat- components to derive a composite model. We scale yielded significant models: trees, dead and used only sites with salamanders for these anal- down wood, ground-level vegetation, ground yses. Our logic here was that given their small cover, and forest climate (Table 1). These were size, low vagility, and extreme philopatry, it all single variable models, with large conifers, would probably be variation at the microhabi- stumps, grass, moss, and percent canopy closed tat-scale that would yield the most information each proving to be a significant indicator of about habitat aspects that influence differences whether or not R. variegatus occupied a site (Ta- in numbers of R. variegatus. The alpha level was ble 2). More large conifers, moss, and higher set at ~0.05. We also used regression in an ex- canopy closure were indicative of sites with sal- ploratory mode to examine relationships in our amanders, while more grass and stumps were data. Selected variables derived from the DA or indicative of sites without salamanders; classi- APS were examined using simple linear and fication success results were significantly better

TABLE 2. Two-group stepwise discriminant analyses of 53 sites’ sampled for the southern torrent salamander (Rhyacotriton variegatus) across its range in northwestern California. Independent variables were grouped for separate analyses by ecological component (Table 1). Models were tested for classification success (% correct) with a jackknife procedure; I? values indicate the classification success of each model compared with chance based on Cohen’s Kappa statistic (Titus et al., 1984).

1 Missing valuesfor 3 sites resulted in a sample size of 50 for the calculation s of models at the microhabitat scale. * Indicates amodel with heterogeneous variance-covariance matrices.

Mean greater for Model sites with Model Model jackknife score salaman- Scale variable(s) P % (P value) ders Landscape: Elevation 0.03 56.6(0.48) no Macrohabitat: Large conifers: 0.002 75.5(0.0003) yes Stumps 0.009 47.9(0.043) no Grass* 0.000 1 79.3(0.0002) no Moss 0.0017 62.3(0.139) yes % canopy closed* 0.015 69.8(0.048) yes Microhabitat: Splash zone* 0.053 62.0(0.50) yes Cobble 0.044 65.4(0.17) yes Sediment <0.063 mm and % cemented 0.02 69.3(0.035) no 390 H. H. WELSH AND A. J. LIND

TABLE 3. Multiple component discriminant model. All variables derived from the analyses of the ecological components (Table 2) were combined in a two-group discriminant analysis (across all scales and ecological components) to derive a multiple component model of the habitat of the southern torrent salamander. Standardized structure coefficients indicate the relative contribution of each variable to the discriminant function (Rencher, 1992); signs are opposite to that of the true relationship between salamander presence and a particular variable. This model has heterogeneous variance-covariance matrices.

Standardized structure Step Variable F-Statistic P coefficient %grass 27.23 0.0001 0.670 Large conifers 6.88 0.0117 -0.442 % cemented 4.63 0.0367 0.666 % sediment <0.063m 3.08 0.0861 -0.461 Elevation 4.95 0.0313 0.410 Splash zone % canopy closed Moss Stumps % cobble Wilks Lambda = 0.425; F (df = 5, 44) = 11.88; P = 0.0001 Jackknife success (%) = 80.80; Cohen’s Kappa = 0.567; P = 0.0001

than chance for all but the ground cover model ence of R. variegatus (as seen by DA), regression (moss) (Table 2). analyses revealed that these same variables were Three of four ecological components at the generally not good predictors of variation in microhabitat-scale (Table 1) produced signifi- salamander numbers among sites. A bivariate cant models: aquatic microhabitats, coarse scatterplot of one variable, canopy closure, re- aquatic substrates and fine aquatic substrates vealed an interesting pattern. The majority of (Table 2). The aquatic microhabitat model con- sites with salamanders were found in areas with sisting of the variable “splash zone”, indicated 80% or higher of canopy closure (Fig. 2). The more of this microhabitat occurred where sal- two outliers (Fig. 2) were cold springs (10.8 C) amanders were present. This model, however, on clearcut sites with north-facing aspects and was not a good indicator of presence based on relatively high elevations (884 m and 1029 m). the classification test, with results no better than The 95% confidence interval (C.I.) indicated that chance. The coarse substrates model consisted the true mean percent canopy closure for all of the variable cobble, indicating sites with a greater percent of this substrate size were more likely to contain Rhyacotriton. This model had a jackknife success of 65.4%, not significantly lz?l sites with sites without better than chance (Table 2). The fine substrates II model, the only model in the DA to contain more than a single variable, consisted of sedi- ment <0.063 mm and percent cemented (Table 2). This model indicated that sites with sala- manders contained greater amounts of the very finest sediments (comprised primarily of organ- ic material), and lower substrate cementedness. Jackknife classification for this model was 69.2%, 4 -2 0 2 4 6 significantly better than chance. low N- % grass ______) high The DA of the 10 variables from the signifi- many f------large conifers -*few cant component models yielded a composite low - % cemented -> high model with five variables, representing three high MY% sediment < 0.063 mm __I) low spatial scales, and four ecological components low f------elevation -*high (Table 3, Fig. 1): percent grass, large conifers, percent cemented, percent sediment < 0.063 FIG. 1. Frequency curves (kernel method; Silver- man [1986]) of canonical scores for sites with (N = mm, and elevation. Classification success for this 33) and without (N = 20) the southern torrent sala- model was 80.8%, significantly better than mander (Rhyacotriton variegatus) based on the com- chance (Table 3). posite habitat model (Table 3). Values of variables Regression Analyses.-Although ten of 68 hab- (i.e., high or low) represent trends relative to canon- itat variables were useful predictors of the pres- ical scores.

RHYACOTRITON VARIEGATUS HABITAT USE 393 tions, especially in warmer parts of northwest- (Table 4). Southern torrent salamanders, despite ern California at the southern end of the range their name, showed a strong negative relation- of R. variegatus, are probably a life requisite giv- ship with fast (riffle) or deep (scour pool) micro- en its physiological limitations (Ray, 1958; habitats. Diller and Wallace (1996) reported a Brattstrom, 1963). positive relationship between salamander num- The DA of the dead and down wood and bers and riffle habitat. This contrary result may ground-level vegetation components also in- derive from the fact that Diller and Wallace dicated the importance of late seral forest struc- confined their sampling to first order streams ture for R. variegatus, but in a contrary fashion. while we sampled in first to third order streams. These models demonstrated that higher num- Riffles have different characteristics depending bers of stumps and more grass, respectively, on stream size. This species is too small (16-52 indicated a lack of salamanders at a given site mm SVL; Welsh and Lind, 1992) to be well suit- (Table 2). Stumps and grass are characteristic of ed physically for life in fast currents, and occurs open, logged or burned sites where conditions primarily within the streambed substrates of were seldom conducive to salamander survival shallow, slow-flowing parts of streams. The se- because air and water temperatures were high, lection of shallow water also has been hypoth- relative humidity low, and protective cover was esized as a response to predation by Pacific giant usually lacking. Grass can also be abundant in salamanders (Dicamptodon tenebrosus) (Stebbins, drier, more open forest areas which are also 1953; Nussbaum, 1969). The APS of aquatic con- usually unsuitable for this salamander because ditions did show a weak negative relationship of microclimatic conditions. with D. tenebrosus, but this model failed to meet While the five macrohabitat variables from the precribed alpha level (Table 4). However, the DA were good predictors of general site this relationship merits further research be- conditions for R. variegatus, none was a good cause D. tenebrosus is known to feed on Rhyaco- predictor of variation in abundance, suggesting triton, and Welsh (1993) reported a significant that such variation results from changes in at- quantitative model for D. tenebrosus that showed tributes at a finer scale of resolution. Given the a positive association with both numbers of extreme philopatry (Nussbaum and Tait, 1977; Rhyacotriton and numbers of larval tailed Welsh and Lind, 1992) and the narrow physi- (Ascaphus truei). ological limits of R. variegatus (Ray, 1958; Bratts- Both the DA and APS of the coarse aquatic trom, 1963), we believe that relationships at the substrates component demonstrated positive microhabitat-scale are more critical to an un- associations with cobble-size substrates, but the derstanding of the ecology of this species. DA model had poor classification success and Microhabitat Scale.-Of the four microhabitat- the APS of the single variable cobble was not scale variables that produced significant dis- significant (Tables 2 and 4). These results in- criminant models (splash zone, cobble, sedi- dicated that cobble alone was not a good pre- ment <0.063 mm, and percent cemented) only dictor of the presence or abundance of R. var- the fine aquatic substrates model yielded a sig- iegatus. However, the APS analysis indicated that nificant classification test result (Table 2). Per- salamander numbers were significantly greater cent splash zone produced contradictory results when the coarse substrate was comprised of a between the DA and APS (Tables 2 and 4); sites combination of cobble and fine to medium grav- with salamanders present had significantly more el (sediment 2.0-16 mm; Table 4). We believe a of this microhabitat compared to sites without combination of different sizes of coarse sub- salamanders, but salamander abundance varied strates provides the greatest amount and variety negatively with splash zone. This outcome is of interstices for foraging, while providing many probably the result of fewer captures in areas smaller escape spaces for cover from potential dominated by splash zone, indicating it is a mi- aquatic predators. crohabitat indicative of areas that support this The DA result, indicating a positive relation- species, but not one that they actually use often. ship with the smallest sediment class (<0.063 Cobble substrate was a weak predictor in both mm) and a negative relationship with substrate analyses. The fine substrates DA model de- cementedness, appears contradictory (Table 2). scribed two characteristics that appear to be es- However this species’ association with shallow, sential for R. variegatus presence; low cement- slower-flowing water (often occurring along edness and fine organic material (sediment stream margins where fine sediments tend to <0.063 mm) (see below). settle out) and preference for coarser substrates The APS analysis proved far more informa- (which provide more exploitable interstices) re- tive about relationships at the microhabitat scale sults from its’ selection of microhabitats that than did the DA. Percent seep habitat was the offer the best combination of cover and food best single microhabitat variable for predicting resources. The very finest sediments are com- salamander abundance where they did occur prised of primarily organic materials that con-

RHYACOTRITON VARIEGATUS HABITAT USE 395

TABLE 5. Suitable habitat model for the southern torrent salamander (Rhyacotriton variegatus).

Variable mean or range References

Landscape-scale variables Latitude: 38”59’-45’7’ Good and Wake, 1992; ‘MVZ 65797. Longitude: 123”25’- 124’24’ Good and Wake, 1992; Jennings (does not include disjunct populations in and Hayes, 1994. north central Douglas Co., Oregon, and south central Siskiyou Co. California Elevation: O-1469 m (4820 ft) L. Diller, unpublished data. Macrohabitat-scale variables Vegetation series: Conifer-dominated forests This paper; Welsh, 1993. (Douglas-fir or redwood) Seral stage: Associated with mature This paper; Welsh, 1993; to old-growth structural attributes, except coast. Diller and Wallace, 1996. # Conifers 253 cm 6-54+ (n t 1 S.D.) This paper: Welsh, 1993. (21 inches) DBH/Ha: (95% C.I. 22-38 or more) Total Canopy (%): 72-100 (z k-1 S.D.) This paper; Welsh, 1993. (95% C.I. 83-95) Forest structure and Low numbers of cut stumps This paper; Welsh, 1993. ground level veget- low % cover of grass, and ation: high % cover of moss. Microhabitat-scale variables Aquatic habitats: springs, seeps, lst-3rd order This paper and citations streams in the introduction. <50% dominated by cobble (64-256 mm): 15-46% (ji * 1 S.D.) This paper; Welsh, 1993. (95% C.I. 25-36%), with mix of coarse substrates (cobble, pebble, gravel) Substrate cementedness tolerated: 3-47% (R * 1 S.D.) This paper; Welsh, 1993. (95% C.I. 18-33%); low fines (sand), with fine organic particles (<0.063 mm) often present Aquatic conditions Seep or other shallow, This paper; Welsh, 1993. slow-flowing habitats with cold, clear water Water temperature 6.5-15.0 This paper; Waters and range (“C): Welsh, unpublished data. l Museum of Vertebrate Zoology, University of California, Berkeley.

directly to greater terrestrial and aquatic micro- 1988) of this highly specialized salamander on habitat complexity (Sedell and Swanson, 1984; the lands in their care. Harmon et al., 1986; Bisson et al., 1986). The Forest Management Considerations. -Diller and deep duff layer and decomposing wood also Wallace (1996) reported R. variegatus presence store and filter precipitation and help maintain on harvested, commercial, redwood and Doug- lower stream temperatures and a cool, moist, las-fir forestlands in coastal areas of northern and stable forest floor and streamside microcli- Humboldt, and Del Norte Counties in northern mate in these older forests (Brown and Krygier, California. They reported a density of 0.28/m2 1970; Beschta et al., 1987; Maser et al., 1988; (range = 0.09 to 5.0/m2; N = 14) from random Chen et al., 1993a). We summarize the niche of streams with known populations. In our com- R. variegatus in a multi-scaled, suitable habitat parable sampling from across most of the range model (Table 5). This model has practical ap- in California, we found a mean density of plication as a tool to discern potential habitat 0.68/m2 (SD = 0.889/m2; range 0.1 to 5.0/m2; N (see Morrison et al. 1992). It can be used by = 33). Both studies lacked pre-harvest data so forestland owners and resource managers, it is not possible to establish whether the lower within the range of this species, who wish to relative densities on commercial forestlands are make informed land management decisions that the result of harvesting. will maintain functional populations (Conner, Diller and Wallace (1996) reported significant 396 H. H. WELSH AND A. J. LIND relationships between R. uariegatus presence and because the required watercoarse protection stream gradient, aspect, and geologic type (con- zone width for typical headwater habitats is solidated vs. unconsolidated). We found no very narrow (15 m) and may not maintain ap- concurrence in our analyses with slope or as- propriate microclimate, especially at interior pect. We also believe that Diller and Wallace’s sites. Also this zone is not designated as a “no analysis of geology was not done at an appro- harvest” area but is only an equipment exclu- priate scale. Landscape scale maps of geology sion zone, allowing the removal of up to 50% do not depict unique small-scale lithologies. of the canopy. In addition, the current rules are These salamanders can occur in relatively small open to interpretation, such that the canopy can patches of habitat that may be within, but dif- be reduced to 50% of pre-harvest canopy after ferent from, the gross geologic map units. In each entry, so multiple entries along a stream any event, we interpret Diller and Wallace’s will leave less canopy each time. We believe the relationships with stream gradient, aspect, and California State Board of Forestry is remiss in geologic type, to be the result of logging, and not providing strong protection and enforce- evidence of its negative impacts on populations ment for headwater habitats in order to protect of this salamander. High gradient streams, those this salamander and other affected aquatic com- on north-facing slopes, and those on less ero- munities downstream (cf. Vannote et al., 1980). sive geologic types, would be more likely to Acknowledgments.-We wish to thank Lisa Ol- sustain populations of R. uariegatus post-harvest, livier, Dana Waters, Dori Borjesson, Gary Perl- compared with streams on low gradients, south- mutter, and Anders Mikkelson for their help facing slopes, or unconsolidated geologies, be- with the field work. James A. Baldwin, Jerry cause of differences in characteristics of sedi- Allen, and Barry R. Noon advised us on statis- ment transport and microclimate (e.g., Corn and tical methods. We thank Lowell Diller, Norm Bury, 1989). While R. variegatus clearly still oc- Scott, Lisa Ollivier, and three anonymous re- curs on private timberlands in the north coastal viewers for providing helpful comments on zone, Diller and Wallace (1996) noted that this earlier drafts. We thank the California Depart- species has been impacted in their study area ment of Forestry and Fire Prevention and the by alterations to low gradient stream reaches USDA Forest Service for partial funding of this and possibly to springs and seeps. Our study, research. We are most grateful to Barry R. Noon, with a proponderance of interior sites, indicat- Michael J. Morrison, Don C. Erman, William F. ed that logging impacts are probably more pro- Laudenslayer, Harry W. Greene, and Sharyn B. nounced in interior areas which lack the ame- Marks for their encouragement, support, and liorating effects of the mild coastal climate. Data advice. This paper is based on a dissertation from coastal areas further south (southern Hum- submitted by the senior author as partial ful- boldt and Mendocino counties) indicate that fillment of the requirements for a Ph.D. degree such ameliorating effects may not be sufficient in the Department of Environmental Science, to maintain populations post-harvest in those Policy, and Management, University of Cali- areas (Welsh, unpubl. data; Brode, 1995). fornia, Berkeley. Diller and Wallace (1996) also suggest that the presence of R. variegatus across their study area is evidence that current California forest LITERATURE CITED practice rules provide adequate protection for ANDERSON, J. D. 1968. Rhyacotriton and R. olympicus. this species on coastal forestlands in Humboldt Catalogue of American and Reptiles and Del Norte counties. We believe that the 68.1-68.2. inverse relationship they report with forest age BESCHTA, R. L., R. E. BILLY, G. W. BROWN, L. B. HOLTBY, and the presence of R. variegatus suggests that AND T. D. HOFSTRA. 1987. Stream temperature and aquatic habitat: fisheries and forestry inter- past forestry practices were more detrimental actions. In E. Salo and T. Cundy (eds.), Streamside to this species than are current practices. How- Management: Forestry and Fishery Interactions, ever, Diller and Wallace (1996) did not directly pp. 199-232. Proc. Sympos., Inst. of Forest Re- study or test the effects of current forestry prac- sources, Contrib. 57, Univ. Washington, Seattle. tices relative to past practices. We believe that BINGHAM, B. B., AND J. 0. SAWYER, JR. 1991. 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