Forest Investment Account (FIA) - Forest Science Program
FIA Project Y093301

    Long-term trends in amphibians in riparian reserves: are riparian reserves effective for their conservation?
 
Project lead: Richardson, John (University of British Columbia)
Contributing Authors: Richardson, John S.; Wood, Sylvia L.R.
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Description:
Amphibians can be an important component of forest biodiversity, but despite world-wide concerns for amphibian population declines and the possible role of amphibians as sensitive ecosystem indicators, there has been little evaluation of riparian reserves for these species in BC. As part of a riparian ecosystems study at UBC's Malcolm Knapp Research Forest, we have an opportunity to continue a project that was initially funded through FRBC and Habitat Conservation Trust Fund. In this study site there are 9 native species (and 1 introduced species, the green frog). We initiated the study in 1997 just prior to harvesting, and were fortunate to follow these populations until 2004. As amphibian populations can take several years to adjust to changes in their habitat through changes in reproduction and colonisation, it has been shown to take many years to see the results of forest harvest due to these lag effects (from studies in North Carolina primarily). Six sites were laid out, four of which received some harvesting in 1998 (2 clearcut to the stream bank, and 2 with 30 m riparian reserves), along with two control sites. These sites were sampled for amphibians using pitfall trap arrays, and mark-recapture techniques to estimate population sizes for all species. Over 5700 individual amphibians of nine species were uniquely marked at the six sites (tree frogs are not effectively captured in pitfalls). This design allowed for comparisons of the three treatments for amphibian numbers, sizes, movement rates, and species composition. Moreover, this provides for a baseline assessment of amphibian population dynamics and relative abundance in a secure site, for which there are no comparable data anywhere in BC. We propose to continue the evaluation of the rates of recovery on the four treated and two control sites at a less intensive schedule than previously.

Background
Many species of forest amphibians are known to be sensitive to forest harvesting, and a meta-analysis of past studies showed that in general amphibian populations in sites with forest harvesting were about 40% of the numbers in control sites (deMaynadier and Hunter 1995). The extent to which riparian reserves might be effective in maintaining populations and enhancing the long-term persistence of local populations has not yet been carefully tested. Semlitsch and Bodie (2003), based on reviewing the distribution patterns of many amphibians and reptiles, suggested that riparian reserves of about 290 m width, plus an additional 50 m buffer, would be necessary to protect populations of these taxa from forest harvest. A study in coastal Oregon was inconclusive about the utility of partial harvesting in riparian areas as a means to maintain amphibian populations (D. Olsen – unpubl’d results presented at the Oregon Headwaters Co-operative). Amphibians, as a small to meso-scale (i.e., they spend their lives in spatially small areas, and they occur in relatively high abundances relative to large birds and mammals) group of species are good indicators of stand-level consequences of forest harvesting and the effectiveness of riparian reserves to mitigate the impacts of harvesting.

Riparian areas provide unique environments for many species (Richardson et al. 2005, Sabo et al. 2005), although this is better documented for sites that have not been diminished to narrow strips of edge-affected riparian reserves. Although many riparian guidelines make reference (e.g. FEMAT 1993) to the terrestrial wildlife (we use the term to mean all living, wild organisms), there has been relatively little attention given to species other than fish. Species living in the forest may associate with riparian areas for particular resources they provide, or they may be dependent on some aspect of the forest-stream boundary (Richardson et al. 2005). Riparian reserves are effective at mitigating the impacts of forest harvesting on some species (e.g. Cockle and Richardson 2003) and may do so for amphibians as well.
A long-term study of amphibian population changes after logging showed that it took nearly 40 years to recover to control or pre-treatment levels (Ash 1997). Other studies, using synoptic approaches (chronosequences) have shown that many amphibian populations still show depressed numbers decades after harvesting. We do not know if the more temperate conditions as found in coastal BC might reduce the magnitude and persistence of these kinds of effects, and one of our goals is to determine if there is evidence of recovery within a decade of harvesting.

Previous work on our amphibian populations on the study sites indicated reductions in the populations of several species (ensatina, rough-skinned newts, northwestern salamanders), but increases in western red-backed salamanders (Maxcy 2000). Our data set to date represents sampling in each autumn since a year prior to logging in 1998 to 2004. We are seeking to extend the time series and in the process enhance the power to detect changes. Finally, in addition to estimates of relative population sizes, we collect data on size (age) structure, and on recaptures (albeit a relatively low number of recaptures) that allows us to examine changes in population structure, and assemble data on the demography of these species.

Hypotheses
• Estimates of relative abundance (see below) will indicate that populations in clearcut sites are at lower relative abundances than control sites, with the riparian reserve sites intermediate in numbers
• Time trend in numbers on the harvest sites (clearcut, 30 m reserves) will show a trend to returning to similar relative abundances as on control sites
• The populations on the riparian reserve sites will approach relative numbers predicted by the controls sooner than the clearcut sites

We will also provide a time trend as a monitor for these species, the only relatively consistent estimation of amphibian numbers for a full suite of amphibians in BC. This will be of value to agencies responsible for determination of species trends for wildlife, especially those species on the red and blue lists in BC (red-legged frog, tailed frog: western toad is a species of concern).
Related projects:  FSP_Y071301FSP_Y082301

    Deliverables:

Report (85Kb)
Freshwater Biology (2009) 54, 1120-1134 (0.3Mb)

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Updated August 16, 2010 

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