A study on Quadra Island indicates wildlife survives group selection logging, but retention of second-growth trees is recommended.
Small clearcut and pushover logging patch cuts in the Morte Lake area of Quadra Island, in northern Georgia Strait, were the subject of a recent study which looked at the effects of group selection logging on wildlife. The study took place over the past five-and-a-half years, and wildlife populations were sampled for two years prior to logging and one year after logging.
According to the study’s report, prepared by biologist Jennifer Balke of nearby Denman Island, there were no substantial effects of the first entry of group selection logging on populations of birds or small mammals sampled in the sites.
However, the study does recommend the retention of mature second growth trees and snags, in patches or buffer strips, to supply future large trees as roosts, cavities, and large coarse woody debris. Such patches or buffer strips of mature second-growth trees and snags would help to “sustain the observed wildlife diversity and abundance through repeated logging entries.”
Balke says, “Where clearcutting emphasizes the production of uniform serial stages and the complete removal of the overhead canopy and standing snags, alternative techniques offer the opportunity to increase the structural diversity of managed forests.” She writes that alternative techniques, if applied with an ecological perspective, may result in the reintroduction of complexity into the forest “by creating or retaining a variety of forest elements, such as snags, large standing trees, and a degree of canopy cover.”
Balke’s report points out that although forest managers are tasked with protecting the biodiversity of the forest and using alternative silvicultural systems, little research has been done on the effects these systems have on wildlife populations in old-growth or second-growth forests in BC.
The wildlife study took place on three 20-hectare sites in the Morte Lake area. Two of the sites were on land managed by TimberWest, as part of Tree Farm License #47. The Quadra Conservancy property adjacent to Morte Lake was used as a control site for the study.
The patch cuts in the study area were between 0.2-to-one hectare in size and were logged in 1995-’96 by local loggers, in a Timber West “Aggregate Inverse J Group Selection Trial.” Clearcutting and pushover logging were the methods used. Douglas fir canopy with moss underfoot and Douglas fir, red alder canopy with sword fern on the ground were the two predominant forest habitat types in the study area.
Biologists Jennifer Blake, Steve Mooney, Graham Suther, and Terri Martin were the four main people who worked on the study, which was funded for the first 4.5 years by the Silvicultural Systems Program of the Ministry of Forests, and for the final year by Forest Renewal BC.
The study was broad in scope, researching not only populations of birds, bats, small mammals, amphibians, and invertebrates, but also surveying coarse woody debris, forest structure, flowering plants, and bryophytes (mosses and liverworts).
Various sampling methods were used, including point counts for winter birds; spot-mapping surveys for breeding birds; call surveys for owls; live-trapping with Sherman traps; pitfalls for small mammals, amphibians, and invertebrates; and ultrasound detection for bats.
Balke used a bat detector. She explained that it picks up echoes when bats are flying overhead echo-locating. “We hear ‘feeding buzzes’ when bats are getting close to moths. Bats consume insects at a phenomenal rate,” she said. The researchers identified bats traveling and looking for food within the forest canopy, and bats using both permanent and small ephemeral water sources.
Seventy species of birds were documented during the course of the study. Winter bird point counts were done monthly from November to March each year, for two winters before logging and one winter after logging. The bird survey recorded species and number of birds by sight, or called at established stations early in the morning.
Thirty-six species of birds were identified using this method, including the downy woodpecker, violet green swallow, and rufus hummingbird. Balke writes, “There were no significant differences in species richness between sites or years for the winter bird species.”
Spot mapping surveys revealed the presence of 62 species of birds during three summers in all sites. Again, there was “no significant difference in the total number of summer bird species between sites and years.” No species detected before logging was absent only from the treatment site (site of patch cuts) after logging. Some of the bird species recorded in the summer were dusky flycatcher, northern flicker, and warbling vireo.
After logging, three new species–white-crowned sparrow, olive-sided flycatcher, and dark-eyed junco-appeared in the treatment site. Balke notes the white-crowned sparrow was a spring migrant, the olive-sided flycatcher was seen on two visits, and the dark-eyed junco was nesting within the site. “The dark-eyed junco likes open areas and tends to occupy recent clearcuts. Humans have created a lot of open habitat and open species birds have become very common,” Balke said.
The most common breeding bird species detected were the American robin, Hammond’s flycatcher, Townsend’s warbler, and the winter wren. These species accounted for between one-third and one-half of the breeding bird population in the study sites. Error! Filename not specified. WILDLIFE STUDY WAS CENTRED IN MORTE LAKE AREA
The biologists recorded four species of owls on the study sites: the barred owl, northern pygmy owl, northern saw-whet owl, and the great horned owl. Balke states, “As [the owls] probably occupied territories larger than the individual sites, differences between sites and years could not be determined.” Owls were detected by playing a tape of owl calls at dusk and listening to the responses.
The report states that four species of birds, detected before and after logging, are on the Provincial Blue List of species considered to be vulnerable and at risk. These species are the bald eagle (year-round resident), Huttons’ vireo (year-round resident), the turkey vulture (summer), and a Vancouver Island subspecies of the northern pygmy owl (year-round resident).
According to Balke’s report, “the only evidence of an ecological impact of the group selection logging on the bird community was the addition of the dark-eyed junco.
“A regular clearcut totally changes the bird population, so it was neat to find out that this didn’t.”
However, the report cautions that the potential effects of future cutting must be considered.
“This study documented the results following the … initial application of the group selection patch-cutting. Additional entries resulting in patch cuts over a greater percentage of the forest may result in more significant changes. As shrubs establish in the patches and new patches are cut, the habitat is increasingly suitable for open and shrub nesting and foraging species. As the young forest develops, it will supply the needs of species that roost, nest, and forage on young trees. But the gradual loss of mature trees means that there are fewer large trees and snags for species that require large cavities for individual or communal roosting and for those species that require large limbs for nesting or roosting.”
The report goes on to say that retaining residual mature second-growth patches, as well as wildlife trees within each patch, will help to maintain the necessary habitat requirements.
The biologists also recorded information about small mammals in the study sites, by using live traps. Trapping took place at intervals of four weeks in summer and six weeks in winter, for two years prior to logging and one year afterward. Trapping sessions consisted of three inspections of the traps over two days. Animals caught in the traps were identified, tagged, sexed, weighed, and released at the point of capture. A mixture of peanut butter, rolled oats and sesame seeds was used as bait.
Five species of small terrestrial mammals were found on the study sites: deer mouse, dusky shrew, northern flying squirrel, red squirrel, and ermine (short-tailed weasel). There were more deer mice than any other small mammals, accounting for between 86-98% of the small mammals trapped. Although there were some differences in mouse density over the study years, none of the differences suggested an effect of logging.
In general, there was no effect of group selection logging on small mammal abundance in the study area. Balke notes that flying squirrels require large trees and snags, so retaining sufficient patches or strips of mature second-growth trees would also benefit this species. The biologists saw raccoon tracks in the treatment site and also recorded the presence of black-tailed deer, gray wolf, and cougar.
Pitfall traps were used to sample amphibians, and incidental observations of reptiles and amphibians were also recorded. Six species of amphibians were detected during the course of the study. These were northwestern salamander, clouded salamander, ensatina, rough-skinned newt, Pacific treefrog, and red-legged frog.
More than twice as many amphibians were recorded in the first year as in other years, but the data was not separated by site; as similar species were recorded in each site, the sample size was small. Amphibians require standing water and moisture found in coarse woody debris, and Balke writes that “it appeared the amount of standing water and moisture … in these sites was sufficient to maintain a variety of amphibian species.”
She notes the effect of group selection logging on the diversity and abundance of amphibians could not be determined, as the amphibian sampling was preliminary and there were no patch cuts near the pitfall trap lines. “Further intensive sampling is required to determine the effects of the present and future small openings on the overall amphibian population and also to determine the effects of pushover logging and traditional clearcutting on amphibians.”
Reptiles sighted included common garter snake, northwestern garter snake, and some unknown garter snake species. The garter snakes were rarely seen under the forest canopy, preferring instead to frequent exposed areas. Balke predicts that the incidence of these reptiles may increase in the patch cut areas.
Invertebrates were also subjects of the study. Slugs, snails, and ground beetles were captured in pitfall traps. The most common slug was the banana slug, which Balke said represents a huge group of invertebrates critical to the decay cycle of the forest. Snails are also critical to the decomposition process of the forest, and ground beetles consume numerous forest pests. No differences in the abundance of these species were detected throughout the course of the study.
The biologists also categorized wildlife habitat in the sites, measuring volumes of coarse woody debris, assessing forest structure, and recording the presence of plants. They identified 104 flowering species, 52 moss species, and 24 liverwort species.
After logging, 20 new flowering species were observed in the treatment site and 11 species were lost. In the control site, 10 species appeared after the nearby logging and 11 were lost. Similar changes occurred with the mosses and liverworts, with little change in the overall numbers of species. Balke notes the changes may be due to the logging, but could also be the result of year-to-year fluctuations in the emergence of some species or of an insufficient sample size to approximate the true species total.
The report states that “overall the results of this study suggest that the effects of the group selection logging on wildlife habitat are minimal”, but calls for further research to explore differences between the impacts in traditional clearcut patches and pushover logged patches.
“As this study only looked at the effects of group selection logging for up to one year after the logging took place, it would be a good idea to look at the sites again later. Patch-cutting appears to offer an approach to logging that retains, at least initially, some of the elements of forest diversity,” said Balke.
* This article first appeared in the Discovery Islander, April 1998