Thomas P. Sullivan

STAND STRUCTURE AND SMALL MAMMALS IN YOUNG LODGEPOLE PINE FOREST: 10‐YEAR RESULTS AFTER THINNING

Management of forested landscapes for biological diversity is a major objective across North America. Perhaps the greatest potential to diversify future forests lies in the vast areas of young second-growth stands which may be managed silviculturally to accelerate ecosystem development. This study was designed to test the hypotheses that large-scale precommercial thinning, at ages 17–27 yr, to various stand densities would, over the 10-yr period since treatment, enhance: (1) productivity of lodgepole pine (Pinus contorta) crop trees, (2) stand structure attributes, and (3) species richness and diversity of forest floor small-mammal communities. Study areas were located near Penticton, Kamloops, and Prince George in south-central British Columbia, Canada, in three forest ecological zones. Each study area had three stands thinned to densities of ∼500 (low), ∼1000 (medium), and ∼2000 (high) stems/ha, with an unthinned juvenile pine and old-growth pine stand for comparison. Understory vegetation was measured ...

Influence of conventional and chemical thinning on stand structure and diversity of plant and mammal communities in young lodgepole pine forest

Abstract Silvicultural practices that provide a wide variety of vegetative composition and structure (habitats) in young stands should help manage for biological diversity across forested landscapes. This study was designed to test the hypotheses that: (i) abundance and diversity of stand structure attributes (species diversity and structural diversity of herb, shrub and tree layers) and forest floor small mammal communities, and (ii) relative habitat use by large herbivores, will increase from unthinned to conventionally thinned to chemically thinned stands of young lodgepole pine (Pinus contorta) forest. Replicate study areas were located near Summerland, Kelowna and Williams Lake in south-central British Columbia, Canada. Each study area had three treatments: a conventionally thinned, a chemically thinned and an unthinned stand. Pre-commercial thinning was conducted in 1993. Coniferous stand structure and understory vegetation were measured prior to thinning in 1993 and 5 years later in 1998. Small mammal populations were sampled intensively from 1993 to 1998. Relative habitat use by large herbivores was sampled in 1998. Our results indicate that chemical thinning of young lodgepole pine stands produced an aggregated pattern of crop trees compared with stands subjected to conventional thinning. Diameter growth of crop trees in the chemically thinned stands was similar to that in the conventionally thinned, but also to that in unthinned stands. Although horizontal stratification (aggregates of trees) was enhanced, vertical stratification (structural diversity of vegetation) was less in the chemically than conventionally thinned stands. Abundance and diversity of understory vegetation and small mammal communities were generally unaffected by stand thinning in these particular installations. Relative habitat use by mule deer (Odocoileus hemionus) occurred in a gradient from highest in the conventionally thinned stand to lowest in the unthinned stand. Habitat use by snowshoe hares (Lepus americanus) tended to have the opposite trend. Moose (Alces alces) exhibited no difference in habitat use among stands. Thus, although there were few differences among treatment stands, chemical thinning could be used to develop an aggregated pattern of crop trees in pre-commercially thinned stands to maintain habitat for herbivores such as snowshoe hares and mule deer. Understory plant and forest floor small mammal communities would be maintained in these stands as well.

Improving research into effects of forest herbicide use on biota in northern ecosystems

Abstract Studies of indirect effects of forest herbicide use on biota have improved dramatically during the last two decades, though further improvements are still needed. Based on our experience, we provide recommendations designed to ensure continued improvements to general field research, including forest herbicide-wildlife research. Specifically, we suggest that researchers should: 1) use a combination of public concerns and existing scientific information to focus research efforts (i.e., the appropriate foundation for this type of research is social and ecological); 2) predict and test social and ecological consequences of herbicide and alternative treatments on components of concern in forested landscapes, using scales (time and space) that are operationally, ecologically, and socially meaningful; 3) understand the ecology of biotic components of interest and their interaction with other components in shared ecosystems; 4) determine the appropriate integrative currency so that a synthesis of effects on ecosystem or economic parameters can be developed; 5) document treatment delivery and consequences for plants targeted for suppression and for improved growth; and 6) appreciate that herbicides could hold the key to a variety of wildlife management and vegetation (habitat) restoration efforts.

Influence of diversionary foods on vole (Microtus montanus and Microtus longicaudus) populations and feeding damage to coniferous tree seedlings

Abstract This study was designed to test the hypotheses that diversionary food would: (1) reduce feeding by voles (Microtus spp.) to lodgepole pine (Pinus contorta) seedlings; and (2) provide a food source without increasing vole populations. Two experiments (A and B) were conducted with montane voles (M. montanus) in old field habitats at Summerland, British Columbia, Canada from 1996 to 1998. A third experiment (C) was conducted with long-tailed voles (M. longicaudus), meadow voles (M. pennsylvanicus), and southern red-backed voles (Clethrionomys gapperi) in young lodgepole pine plantations in forested areas in 1998–1999. Diversionary food was prepared in the form of “logs” composed of alfalfa pellets, wood pellets, or bark mulch mixed with wax and sunflower oil. Vole populations were intensively live-trapped on control and treatment sites. Mean percentage of seedlings eaten per vole was significantly reduced with bark mulch logs during a peak damage period in old field habitat. Alfalfa logs also tended to reduce seedling damage but only for the first month after placement. None of the diversionary foods tested had any effect on mean abundance of vole populations. In forest plantations, seedlings on control sites suffered mortality from vole feeding at levels 2.6–2.8 times higher than those on alfalfa and bark mulch sites. This difference was not statistically significant (P=0.09) but very likely was biologically significant in terms of seedling protection. This result was achieved with Microtus spp. on clearcut sites, but not on patch cut sites where red-backed voles were the most abundant microtine. The concept of seedling protection with these diversionary foods appears sound, but additional research is warranted.

Reinvasion dynamics of northern pocket gopher (Thomomys talpoides) populations in removal areas

Abstract This study was designed to test the hypothesis that continuous removal of northern pocket gophers (Thomomys talpoides) from natural habitats and tree fruit orchards would result in successful population reduction. A secondary objective was a detailed analysis of demographic responses (reinvasion dynamics) of gopher populations in control and removal sites. Pocket gopher populations were intensively live-trapped in replicate control and removal sites in natural and orchard habitats at Summerland and Vernon, British Columbia, Canada. New pocket gophers readily colonized removal sites in the natural habitats, particularly during spring, summer, and fall months. Fewer gophers colonized vacant sites during winter months (⩽1xa0perxa0ha at Summerland and ⩽9xa0perxa0ha at Vernon). Mean abundance of gophers ranged from 15 to 31xa0perxa0ha on control sites. Population increases due to recruitment on control sites were reflected in periods of high reinvasion of removal sites. Spring reproduction and subsequent dispersal of juvenile gophers resulted in high colonization of vacant habitat. The recovery ratio (colonization rate) of gophers in natural habitats averaged 26.9% in summer and 0.9% in winter at Summerland, and averaged 44.2% in summer and 40.4% in winter at Vernon. Recovery ratios to previous densities on removal sites averaged >100% in summer at Summerland and in both seasons at Vernon. A relative recruitment index also followed this pattern at both study areas. New adult gophers that reinvaded removal sites produced young there despite continuous removal of animals. Mean body mass of gophers was significantly higher in control than removal populations at Summerland, but not Vernon. This study is the first intensive live-trapping evaluation of reinvasion dynamics of northern pocket gophers in removal sites. It seems likely that colonization of sites treated with toxicants or kill-trapping will be at least as high as the reinvasion rates recorded in our study. The timing of removals is crucial to achieving an overwinter reduction in gopher abundance.

Long-term responses of mammalian herbivores to stand thinning and fertilization in young lodgepole pine (Pinus contorta var. latifolia) forest

Snowshoe hares (Lepus americanus Exrleben, 1777), mule deer (Odocoileus hemionus (Rafinesque, 1817)), and moose (Alces alces (L., 1758)) commonly occur in young coniferous forests. This study was designed to test the hypothe- sis that large-scale pre-commercial thinning (PCT) and repeated fertilization 15-20 years after the onset of treatments in young lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Wats.) stands would enhance relative habitat use by hares, deer, and moose compared with unmanaged stands. Study areas were located in south-central British Columbia, Canada. Habitat use was measured by fecal pellet and pellet-group counts. Understory vegetation and coniferous stand structure were measured in all stands. Habitat use by deer and moose was highest in heavily thinned stands, probably due to the higher levels of forage and cover provided by understory shrubs and conifers in thinned stands. Habitat use by snowshoe hares was highest in high-density stands, but also in lower-density (£1000 stemsha -1 ) stands where an increase in understory conifers provided essential cover for hares. Managers should consider the long-term nature of understory de- velopment in young stands managed for timber production. Heavy thinning (£1000 stemsha -1 ) will generate suitable understory habitat for these herbivores sooner than conventional PCT at higher stand densities. Resume´ : Le lievre dAmerique (Lepus americanus Exrleben, 1777), le cerf mulet (Odocoileus hemionus (Rafinesque, 1817)) et lorignal (Alces alces (L., 1758)) occupent generalement les jeunes forets de coniferes. Cette etude visait atester lhypothese que leclaircie precommerciale (EPC) et des fertilisations repetees, 10-15 ans apresl e debut des traitements dans de jeunes peuplements de pin tordu latifolie ´ (Pinus contorta var. latifolia Engelm. ex S. Wats.), devraient faire aug- menter lutilisation de lhabitat par le lievre, le cerf et lorignal comparativement aux peuplements non amenages. Les ai- res detudes etaient localisees dans le centre-sud de la Colombie-Britannique, au Canada. Lutilisation de lhabitat a ete ´ mesuree par comptage de feces et de groupes de feces. La vegetation du sous-bois et la structure des peuplements de coni- feres ont etemesurees dans tous les peuplements. Lutilisation de lhabitat par le cerf et lorignal etait maximale dans les peuplements fortement eclaircis, probablement en reponse ades quantites plus elevees de brout et de couvert fournis par les arbustes de sous-bois et les coniferes dans les peuplements eclaircis. Lutilisation de lhabitat par le lievre etait ason plus fort dans les peuplements denses, mais aussi dans les peuplements de faible densite ´ (£1000 tigesha -1 )o uune aug- mentation des coniferes en sous-bois procurait le couvert essentiel au lievre. Les amenagistes devraient prendre en compte le developpement a long terme du sous-bois dans les jeunes peuplements amenages pour la production ligneuse. Une eclaircie severe ramenant la densitedu peuplement a ` £1000 tigesha -1 produira un habitat de sous-bois de qualitepour ces herbivores plus rapidement que lEPC conventionnelle ades densites de peuplement plus elevees. (Traduit par la Redaction)

WEASELS, VOLES, AND TREES: INFLUENCE OF MUSTELID SEMIOCHEMICALS ON VOLE POPULATIONS AND FEEDING DAMAGE

The role of predators, particularly small mustelids, in regulating vole (Mi- crotus spp.) populations has been the subject of much scientific inquiry over the past several decades. From a management perspective, voles cause economic damage by feeding on seedlings planted on cutover forest land in temperate and boreal zones. Because of the close relationship between small weasels (Mustela erminea and M. nivalis) and voles, could the indirect effect of weasel scent disrupt vole populations and reduce their damage to forest plantations? This study was designed to test the hypotheses that synthetic weasel odor would: (1) reduce abundance, reproduction, survival, and movement of montane (Mi- crotus montanus) and meadow (M. pennsylvanicus) vole populations; (2) enhance the ac- tivity of small weasels; and (3) reduce feeding damage by voles to tree seedlings. Study areas were located near Summerland and Gavin Lake in south-central British Columbia, Canada. Vole populations were intensively live-trapped on replicate sites from April 1994 to May 1995 during a peak year in abundance. Synthetic weasel odor was continually present on treatment sites from early summer 1994 to spring 1995. Weasel activity was measured by the number of individuals captured in live-traps and by the number of snow tracks on control and treatment sites. Overwinter mortality to planted lodgepole pine (Pinus contorta) seedlings from vole feeding was measured on all sites in May 1995. Mean vole abundance (n = 4) was similar between control (32-121 voles/ha) and treatment (37-118 voles/ha) sites. Montane voles declined by 17-36% on treatment sites during early summer when trappability of this species declined dramatically at Summerland. This pattern was not observed for meadow voles at Gavin Lake. Recruitment of new voles was generally similar between control and treatment sites. Weasel odor had no effect on reproduction, in terms of number of successful pregnancies and index of early juvenile survival, or on total survival, movements, or body mass of voles. Activity of small weasels appeared to be higher on treatment than control sites at Gavin Lake. Weasel odor did not reduce mortality of tree seedlings caused by vole feeding. This study is the first investigation of the population responses of free-living voles to synthetic odor of the short-tailed weasel, a principal predator of Microtus spp. Our results demonstrate that by the time voles have reached high densities, it is too late to reduce numbers or curtail feeding damage, regardless of weasel odor-induced antipredatory be- havior or enhanced activity of predators. Application of weasel odor during the low phase of the vole population cycle would be a critical test of the hypothesis that small mustelids could lengthen the period of low vole numbers and potentially protect forest plantations from vole damage.

Long-term responses in population dynamics and diversity of small mammals in riparian and upland habitats within an agricultural landscape

Riparian zones in agricultural landscapes provide linear non-crop habitats for a variety of plant and mammal species, and hence are an important component of biodiversity. To date, variable responses of abundance, species richness, and species diversity of small mammals have been recorded in riparian and upland habitats. To address this variability, we provide a detailed analysis of seasonal changes in abundance and diversity of terrestrial small-mammal communities over a 7-year period within an agricultural landscape in south-central British Columbia, Canada. We tested the hypotheses (H) that abundance, species richness, and species diversity of communities of small mammals (H1), and demographic parameters of reproduction, recruitment, and survival of the major species: deer mouse (Peromyscus maniculatus) and montane vole (Microtus montanus) (H2), would be higher in riparian than upland habitats. Mean total abundance of small mammals was higher in summer and winter, and species richness higher in summer, in riparian than hedgerow habitats. Winter population data supported the total and species abundance patterns for small mammals, but species richness was similar, and diversity lower, in riparian than hedgerow sites during winter periods. Deer mice were the dominant species in terms of abundance and reproductive output for pregnancies and recruitment, but not survival, in riparian sites. Montane voles were similar in abundance and demographic parameters in the two habitats. House mice (Mus musculus) preferred hedgerows and wandering shrews (Sorex vagrans) riparian sites. Demographic parameters for deer mice and montane voles indicated that both riparian and hedgerow sites were “source” rather than “sink” habitats, and likely contribute to maintenance of mammal diversity in agricultural landscapes.