Divergent patterns of abundance and age-class structure of headwater stream tadpoles in burned and unburned watersheds


Wildfire is a potential threat to many species with narrow environmental tolerances like the Rocky Mountain tailed frog (Ascaphlls montanlls Mittleman and Myers, 1949), which inhabits a region where the frequency and intensity of wildfires are expected to increase. We compared preand post-fire counts of tadpoles in eight streams in northwestem Montana to determine the effects of wildfire on A. montanus. All streams were initially sampled in 2001, 2 years before four of them bumed in a large wildfire, and were resampled during the 2 years follo\ving the fire. Counts of tadpoles were similar in the 1\\'0 groups of streams before the fire. After the fire, tadpoles were almost twice as abundant in unbumed streams than in bumed streams. The fire seemed to have the greatest negative effect on abundance of age-l tadpoles, which was reflected in the greater variation in same-stream age-class structure compared with those in unbumed streams. Despite the apparent effect on tadpoles, we do not expect the wildfire to be an extirpation threat to populations in the streams that we sampled. Studies spanning a chronosequence of fires, as well as in other areas, are needed to assess the effects of fires on streams with A. montallus and to determine the severity and persistence of these effects. Resume: Les feux de brousse sont une menace potentielle a de nombreuses especes a tolerance environnementale etroite et en particulier a la grenouille a queue des Rocheuses (Ascaphus montallUS Mittleman et Myers, 1949) qui habite une region m\ les feux de brousse risquent d'augmenter en frequence et en intensite a l'avenir. Nous avons compare les denombrements de tetards avant et apres un feu dans huit cours d'eau du nord-ouest du Montana afin de detenniner les effets des feux de brousse sur A. montanus. Tous les cours d'eau ont ete echantillonnes en 2001, 2 ans avant que quatre d'entre eux aient ete affectes par un important feu de brousse, et ils ont tous ete echantillonnes a nouveau 2 ans apres Ie feu. Les denombrements de tetards etaient sembI abies dans les deux groupes de cours d'eau avant Ie feu. Apres Ie feu, les tetards etaient presque deux fois plus nombreux dans les cours d'eau non affectes par Ie feu que dans les cours d'eau affectes. Malgre cet effet apparent sur les tetards, nous ne comptons pas que les feux de brousse constituent une menace d'elimination des populations dans les cours d'eau que nous avons echantillonnes. 11 faudrait mener des etudes comTant une chronosequence de feux et faire des recherches dans d'autres regions afin d'evaluer les effets sur les cours d'eau it A. montanus et pour determiner la severite et la persistance des effets. [Traduit par la Redaction] Introduction ians, especially considering the recent outbreaks of large wildfires and projections of future fire scenarios in the region (Fagre et al. 2003; Westerling et al. 2006). Headwater stream amphibians, in particular, may be model candidates for indicators of ecosystem stress because their popUlations tend to be relatively stable and negative effects of disturbances are often unambiguous (Hairston 1987; Welsh and OUivier 1998; Lowe et al. 2004). Wildfire creates and maintains much of the structural diversity of forests in western North America (Hessburg and Agee 2003), and thus is an important factor in the distribution and abundance of most fauna (e.g., Smith 2000). There is, however, almost no information on the effects of wildfire on forest amphibians in the region, particularly in the Northwest (Com et al. 2003; Bury 2004), where several endemic headwater stream species are sensitive to landscape disturbances (Corn and Bury 1989; Welsh 1990; Adams and Bury 2002). Effective management policies require better knowledge of direct and indirect effects of fire on amphibReceived 20 April 2006. Accepted 28 August 2006. Published on the NRC Research Press Web site at http://cjz.nrc.ca on 1 December 2006. B.R. Hossack! and P.S. Corn. US Geological Survey, Aldo Leopold Wildemess Research Institute, 790 East Beckwith Avenue, Missoula, MT 59801, USA. D.B. Fagre. US Geological Survey, Glacier Field Station, Glacier National Park, West Glacier. MT 59936, USA. lCorresponding author (e-mail: blake_hossack@usgs.gov). The Rocky Mountain tailed frog (Ascaphus montanus Mittleman and Myers, 1949) is part of a large group of amphibians in the northwestern USA and southwestern Canada that often form the dominant vertebrate assemblage in forested headwater streams (Com et al. 2003). Tadpoles of the more widely studied coastal tailed frog (Ascaphus truei Stejneger, 1899), the sister species of A. montallus (Nielson et al. 2001), are sensitive to disturbance-induced changes to stream habitats (Corn and Bury 1989; Welsh and Ollivier 1998). Limited research on environmental preferences and tolerances of A. montanus tadpoles (Franz and Lee 1970; Bull and Carter 1996; Adams and Frissell 2001) suggests that they are similar to those of A. truei. Ascaphus montanus may be particularly vulnerable to long-term decline after fire and other disturbances because its tadpoles require >3 years Can. J. Zool. 84: 1482-1488 (2006) doi:10.1139!Z06-143 © 2006 NRC Canada

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@inproceedings{Hossack2017DivergentPO, title={Divergent patterns of abundance and age-class structure of headwater stream tadpoles in burned and unburned watersheds}, author={Blake R. Hossack and A. S. Leopold and Paul Stephen Corn and Daniel B. Fagre}, year={2017} }