Forest Ecology and Management 124 (1999) 35±43 Riparian management and the tailed frog in northern coastal forests Linda Dupuis*,1, Doug Steventon Centre for Applied Conservation Biology, Department of Forest Sciences, University of British Columbia, Vancouver, BC, Canada V6T 1Z4 Ministry of Forests, Prince Rupert Region, Bag 5000, Smithers, BC, Canada V0J 2N0 Received 28 July 1998; accepted 19 January 1999 Abstract Although the importance of aquatic environments and adjacent riparian habitats for ®sh have been recognized by forest managers, headwater creeks have received little attention. The tailed frog, Ascaphus truei, inhabits permanent headwaters, and several US studies suggest that its populations decline following clear-cut logging practices. In British Columbia, this species is considered to be at risk because little is known of its abundance, distribution patterns in the landscape, and habitat needs. We characterized nine logged, buffered and old-growth creeks in each of six watersheds (n 54). Tadpole densities were obtained by area-constrained searches. Despite large natural variation in population size, densities decreased with increasing levels of ®ne sediment (<64 mm diameter), rubble, detritus and wood, and increased with bank width. The parameters that were correlated with lower tadpole densities were found at higher levels in clear-cut creeks than in creeks of other stand types. Tadpole densities were signi®cantly lower in logged streams than in buffered and old-growth creeks; thus, forested buffers along streams appear to maintain natural channel conditions. To prevent direct physical damage and sedimentation of channel beds, we suggest that buffers be retained along permanent headwater creeks. Creeks that display characteristics favoring higher tadpole densities, such as those that have coarse, stable substrates, should have management priority over less favorable creeks. Measures should also be taken to minimize ®ne sediment inputs from roads and stream crossings. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Riparian; Headwater; Creek; Gully; Buffer; Amphibian; Tailed frog 1. Introduction growth of any frog in North America, metamorphos- ing in four years in the northern portions of its range, The tailed frog, Ascaphus truei, warrants conserva- and attaining sexual maturity at six to eight years of tion priority. It is the most primitive frog in the world age (Daugherty and Sheldon, 1982; Brown, 1990). (Nussbaum et al., 1983), and the only species in the The tailed frog also has highly specialized habitat Ascaphidae family; its closest relatives reside in New requirements: headwater creeks that must ¯ow year- Zealand (Family: Leiopelmatidae). It has the slowest round because of the long larval developmental period (Nussbaum et al., 1983). The creeks must be cool to *Corresponding author. Tel.: +1-604-898-4770; fax: +1-604- accommodate this species' narrow temperature toler- 898-4742 ance. For example, the eggs require temperatures of 58 E-mail address: [email protected] (L. Dupuis) to 18.58C, the narrowest range of all North American 0378-1127/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0378-1127(99)00051-1 36 L. Dupuis, D. Steventon / Forest Ecology and Management 124 (1999) 35±43 frogs (Brown, 1975). Creeks must also have low levels and is characterized by a mean annual precipitation of ®ne sediment, and a high water velocity (Welsh and of 1295 mm, with maximum rainfall and instanta- Ollivier, in press). neous discharges in the fall. The mean daily tempera- Its high degree of specialization renders the tailed ture in late summer (July and August) is 16.28C, and frog vulnerable to local extirpation or to population can reach 36.28C. Temperatures are below freezing declines following disturbances; at least 75% of Brit- from November to March. ish Columbia's watersheds, hence streamside riparian zones, have been partially developed (Bunnell and 2.2. Experimental design Dupuis, 1993). A number of studies in the United States have reported tailed frog population declines The study was a retrospective examination of creeks following clear-cut logging (Noble and Putnam, 1931; subjected to one of three logging treatments: (a) uncut Metter, 1964; Corn and Bury, 1989; Welsh, 1990; (old growth) forests; (b) clear-cuts (0±15 years) with Bury et al., 1991; Welsh and Lind, 1991), possibly unbuffered creeks; and (c) clear-cuts (0±15 years) with resulting from increases in water temperature. Brown 5±60 m forested buffers. and Krygier (1970) reported a mean annual tempera- We selected three permanent creeks of each treat- ture increase of 158C in a small watershed in Oregon's ment within six drainages (experimental blocks; Coast Range, one year after logging. Similarly, stream total 54 creeks): Shannon Creek, Carpenter Creek, temperatures increased by up to 3.28C in the summer Kleanza Creek, Copper River, Trapline Creek, and following logging in the Carnation Creek watershed of Clore River. This regional strati®cation helped control northern British Columbia (Holtby, 1988). Declines for potential differences among drainages. Creeks have also been attributed to increasing levels of ®ne ranged from 0.5 to 6.4 m in wet width (1.0±15.0 m sedimentation in streams following clear-cut logging in bankfull width) and 200±660 m in elevation. Most and road building activities (Corn and Bury, 1989; road-accessible creeks within each drainage were Welsh and Ollivier, in press). surveyed, thus the sampling density was high and The following study reports the ®rst effort to docu- likely representative of larval populations and distri- ment the tailed frog's habitat needs in the more north- butions within each drainage. ern portions of its range, in western Canada. The The term creek as used here is applied as a general objectives were to (1) summarize the creek features termforsmallwatercoursesgenerally¯owingingullies. which determine habitat suitability for tadpoles at Gullies are V-shaped channels, con®ned or incised northern latitudes, (2) assess the potential effects of withinnon-¯uvialmaterials(glacialtill,rock,etc.),with logging operations by contrasting the density of larvae banks of at least 40% slope. Gullies generally occur in in forested and logged headwater creeks, and (3) the steep, headwater areas of a watershed. Streams, by evaluate the potential bene®ts of riparian buffer strips contrast, ¯ow within alluvial materials (materials of as a management option. their own deposition) and are found further downstream in the watershed (Ministry of Forests and Ministry of 2. Methods Environment, 1995a). The creeks in this study were almost exclusively ¯owing in gullies. 2.1. Study area 2.3. Amphibian sampling The study area is in the Nass and Bulkley Ranges of the Hazelton Mountains east of Terrace, BC (latitude We sampled from 24 July to 24 August, 1994. The 548100, longitude 129800). The relief is rugged, with density of tailed frog tadpoles within a creek was a peaks ranging from 1980 to 2286 m in elevation and count of all the individuals encountered during active valleys draining into the Skeena River. The mountains searches of three systematically placed 5 m reaches, of are underlain by a complex assemblage of igneous, which the ®rst was randomly situated. Reaches were volcanic and sedimentary rocks (Holland, 1976). 50 m apart from one another. The study falls within the Coastal Western Hemlock Searches were thorough and included an initial scan Biogeoclimatic Zone (Meidinger and Pojar, 1991), of the surface for active animals, followed by an in- L. Dupuis, D. Steventon / Forest Ecology and Management 124 (1999) 35±43 37 depth search of all the creek substrates: hand-raking by an analysis of residuals. Differences in mean sand and gravel, upturning cobbles and small tadpole density by treatment were tested by a rando- boulders, sweeping large boulder surfaces by hand, mized block ANOVA design, with drainage as the and scanning the moist banks. Surveys began at the blocking factor. This design uses the block±treatment downstream end of the reach, and proceeded in 1 m interaction as the error term (Zar, 1984). increments. Dip nets (of 1 mm mesh) were held immediately downstream of searchers to catch dis- 3.2. Relationship of creek parameters with tadpole lodged animals. A ®nal visual sweep of the reach often density revealed individuals which escaped detection during the dismantling of rif¯es. When the search was com- Univariate correlation was initially used to examine pleted the creek bottom was re-assembled. Tadpoles relationships between creek variables. A principal were measured, and returned to the top portion of the component analysis was then conducted to examine reach. which of the variables explained most of the vari- ance in the data. A multiple regression was done on 2.4. Creek characterization components with an eigenvalue greater than one, to test for their effect on tadpole numbers. The creek For each creek, we measured: water temperature characteristics de®ning the signi®cant components (8C), aspect (quadrants), average gradient (degree and were then determined based on their component percent), wet width (m), bank width (m), gully depth loadings, in conjunction with the initial correlation (m) and substrate composition (% cover). Substrate coef®cients. was classi®ed as sand (<2 mm), pebbles (2±64 mm), Only creeks without missing values were used cobbles (64±256 mm) or boulders (>256 mm), as for analysis. An level of p < 0.10 was deemed described by Howes and Kenk (1988). Substrate appropriate for testing differences, as this mode- was also categorized as rubble (angular material), rate provides a more sensitive test for the detec- gravel (round material), or mixed (rubble and gravel). tion of ecological trends (Toft and Shea, 1983; Toft, Fine organic debris (detritus) was recorded, as low (0± 1991). 2 mm deep, in <10% of the reach substrate), medium (0±2 mm deep, in 10±50% of the reach substrate), high 3.3. Effect of logging treatment on creek (on >50% of the substrate, coloured water column), or characteristics extreme (opaque water column).