To date, there has been no standard sampling design for assessing the created snag component of the YSTDS, but several small-scale field efforts have been launched to evaluate the project.
In 2007, about 5.5 years after topping and inoculating, the created snags were surveyed to assess general condition (living, dead, or fallen), extent of decay (presence of insects and fungus, decay class), and presence of foraging and nesting cavities. Snags showing evidence of nesting activity were re-visited twice between 7 June and 5 July 2007. At each of these return visits, each snag was observed for 20 minutes to determine whether nest cavities were in current use. The same snags were re-visited in 2008, again to document nesting activity. In all, 77 created snags were identified as having nest cavities in 2007; among these, 2 active nests were confirmed in 2007 and 2 others were confirmed in 2008. In addition to these nests in created snags, an additional 5 nests were found in natural snags and stumps. Conclusions from this monitoring were that: the created snags were used for foraging and nesting; inoculation of snags with heart-rot fungi increased the frequency of bark beetle and pouch fungus, and foraging use by birds was greater than for snags created by topping alone; and that the usefulness of snags less than 50 cm dbh for nesting is likely marginal, as demonstrated by the low detection rate of active nests.
In 2009, a brief pilot project was fielded to try to find evidence that mammals were using the created snags. In particular, there was interest in whether northern flying squirrels were using the snags as summer or maternity dens. All snags were examined visually for cavities, and those with cavities large enough were probed with a Tree-Top Peeper, essentially a video camera on a telescoping pole. No mammals were detected using the Peeper. In fact, only a few cavities were large enough to insert the camera; small cavities such as these are not likely to be used by flying squirrels, but may have been used by smaller mammals such as mice or shrews. As a corollary to this work, the condition (live, dead, or fallen) and location of all snags was updated and added to the Forest Science Data Base, and several missing tree tags were replaced.
In 2010, another round of nest activity monitoring was accomplished. In this assessment, all YSTDS stands were systematically surveyed for the presence of cavity-nesting birds between May 15 and July 15, and detected birds were followed in an attempt to locate nest cavities. The protocol combined passive listening and periodic playbacks of 9 cavity-nesting bird species and covered all areas of each stand. Each morning that weather permitted, 2 stands were surveyed for 3 hours each, and each stand was surveyed twice during the season. Actual search time per survey varied from 2.6 to 2.8 hours because a portion of each 3-hour survey was spent following birds to nests and recording data, so results were standardized as nests found per unit of time actively searching. In all, 20 active cavity nests were found. These 20 nests were rechecked every few days to assess nesting success as well as possible; however, most nests were already far advanced when first discovered, and nestlings were gone from most before they were revisited; thus, conclusions about nest success could not be made. Analysis-of-variance provided weak statistical evidence of differences among thinning treatments in terms of numbers of active nests (P = 0.0982). More active nests were found in thinned treatments than in unthinned control stands.
SMALL MAMMALS
Methods for sampling the mammal fauna on the YSTDS changed over the course of the study. In the 1990’s, pre-treatment and immediate post-treatment sampling was focused on sampling of forest floor vertebrates using Sherman live-traps and pitfall traps. In later years, efforts to measure densities of northern flying squirrels (Glaucomys sabrinus) were gradually increased, because of the squirrel’s importance as prey for spotted owls and its larger role as an indicator of forest health generally.
Before thinning, in Oct-Nov of 1991 and 1992, the mammal fauna on the YSS sites was sampled for 8 consecutive nights annually in each stand using conventional square grids of Sherman live-traps (10x10 with 20 m inter-trap spacing) and pitfall traps (5x5 with 20 m spacing; Garman 2001). This effort sampled only a small portion of each YSTDS stand.
The YSTDS sites were trapped again for several years soon after thinning, in 1998, 1999, and 2001 (Garman 2001). To better sample the spatial variability in these post-treatment stands, square trapping grids were replaced by variable-length transects that covered more of each stand. Number of transects per stand varied from 4 to 11 depending on stand shape, but each stand included a total of 100 trapping stations. Distance between traps on each transect was 30 m. Transects were spaced 30 m apart and >50 m from a stand edge. In 1998-99, 1 Sherman live-trap (Model LFATDG) was placed at each station (total of 100 traps per stand), and 1 pitfall trap was installed at every 2nd station (total of 50 pitfalls per stand). In 2001, Tomahawk live-traps (Model 201) were added to the design to specifically target flying squirrels; in each treatment stand, 1 Tomahawk trap was placed on the ground at every 2nd station on alternating transects, so that traps were evenly distributed through the treatment unit (total of 25 Tomahawk traps per stand). In each year of the 1998-2001 sampling effort, all 4 stands within a block were trapped simultaneously for 6-8 consecutive nights during late September to mid-November. It should be noted that these early efforts (1991-2001) also sampled forest floor amphibians, though captures were sparse. More recently, efforts to quantify abundance and diversity of amphibians have been made separately from mammal sampling, and are covered in a separate section of this report.
In 2007-08 (11-13 years after thinning), all stands were resampled, using the same variable-length transects established in 1998 (Manning et al., in review). Trapping occurred for 4 consecutive nights in each stand between late September and late November. Two stands in each block were sampled simultaneously and the other 2 stands in the same block were sampled in the following week. The order for sampling stands within blocks was randomized, and blocks were sampled sequentially. Considerations for the order of sampling among blocks included elevation, seasonal road closures, and proximity to other blocks. One trap was placed at each station. In this phase of the study, we increased efforts to capture flying squirrels by doubling the number of Tomahawk traps deployed. In each stand, Sherman traps alternated with Tomahawk traps along each transect, so that 50 of each were evenly distributed throughout the 100 stations in each stand. Half of the Tomahawk traps were attached to the boles of trees (approx. 1.5 m high), and the rest were placed on the ground; tree and ground placements of Tomahawk traps alternated along transects. To increase capture rates, all traps were locked open and pre-baited once 10 days before the trap session began. During the trapping session, traps were checked twice daily to minimize mortality of trap-prone diurnal species (e.g., chipmunks). Traps were set in the afternoon on the 1st day of each trap session, checked twice each day for 3 days, then checked and closed on the morning of the 5th day; thus, each trap session included 4 nights and 7 capture occasions.
In all years, traps were baited with a mixture of peanut butter, oats, and sunflower seeds. Polyester or cotton fiber insulation was placed in each trap, and traps were placed within weather-resistant covers. Pitfall traps (not used after 2001) were provided with a small shelter, insulation, and food, and were operated as live-traps. All traps were checked daily (twice daily in 2007-2008). Captured rodents were identified to species, weighed, sexed, marked with individually-numbered eartags, and immediately released at the point of capture. Trap mortalities were frozen for later necropsy to confirm species and sex. After trapping was completed, pitfall traps were made inoperable and box traps were removed. All procedures were conducted under protocols approved by the Institutional Animal Care and Use Committee at Oregon State University.
AMHIBIANS
During pre-treatment sampling (1991-1992), pitfall trapping was used to sample both small mammals and amphibians. A 5x5 grid of pitfall traps, with 20-m spacing between traps, was deployed for 8 nights in each of the 16 YSTDS experimental stands. This design yielded a total of 53 individuals of 6 species of salamanders and no frogs or toads (Garman 2001). This amounts to a capture rate of 0.8 salamanders per 100 trap-nights.
During an initial bout of post-treatment sampling (1998-2001), the number of pitfalls was doubled and more evenly distributed throughout each YSTDS stand. This yielded 151 captures of 5 species of salamanders (2.7 captures/100 trapnights), as well as 4 individual frogs and a single toad (Garman 2001).
At the beginning of a second period (2007-2009) of post-treatment sampling, we attempted to continue pitfall sampling using the same design as in 1998-2001. After 3 days of simultaneous mammal and amphibian sampling in Oct 2007, it became clear that we had underestimated the resources required to do the work. Since the capture rate of salamanders was very low (0.67 captures per 100 trap nights), pitfall trapping was halted to concentrate on mammal live-trapping. In lieu of pitfalls for sampling amphibians, time-constrained searches (TCS) were attempted. In each stand, 3 strip plots measuring 50 m by 4 m were laid out. Each plot was searched intensively for one person-hour, by turning over logs, bark, and other debris to expose salamanders. After sampling 12 of these plots, and capturing only 4 salamanders, this work was discontinued because 3 person-hours per salamander was not considered an efficient use of human resources. Another attempt was made by Joan Hagar and Brenda McComb to implement the same TCS design in June 2008, again with disappointing results (2 salamanders in a day of work for 2 people).
It was after this setback that the idea of using artificial cover objects (ACOs) was advanced. ACOs provide a standardized method for sampling of terrestrial salamanders. The board design used is detailed in:
Davis, T.M. 1997. Non-disruptive monitoring of terrestrial salamanders with artificial cover objects on southern Vancouver Island, British Columbia. In Amphibians in decline: Canadian studies of a global problem, D.M. Green, editor. Society for Study of Amphibians and Reptiles, Salt Lake City, UT.
The ACOs were constructed of freshly milled Douglas-fir without any sort of anti-fungal treatment. The thickness of the baseboard was about 5 cm, and the top boards were about 3 cm thick. Three of these devices were deployed within each YSTDS stand in October of 2008 at randomly chosen locations within the mammal trapping transect arrays. Each location was marked with bright orange flagging, and GPS coordinates were recorded and stored.
Sampling from ACOs involves removing the top boards one at a time, and examining any salamanders thus exposed. Next the main (bottom) board is lifted and the ground underneath examined for salamanders. Each salamander is placed in a small plastic bag for weighing and measuring. Weight is measured with a 50-g Pesola spring scale to the nearest 0.5 gram. Snout-vent length (SVL) is measured to the nearest millimeter with a small plastic ruler. These data, along with location, species, and sex (when it can be determined) are recorded on a field sheet printed on water resistant paper.
During the November 2009 checks, salamanders were photographed in order to attempt to later determine sex, but this was not successful. In practice, few salamanders captured on the YSTDS stands have been sexed, other than larger Ensatina which are relatively easy to sex based on lip and vent morphology, and the occasional appearance of visible ova within the females’ abdomens.
After handling, each salamander is carefully placed back into the re-assembled ACO in approximately the position it was found, through the side openings created by the lengths of lath attached to the main board.
