We investigated population responses of Microtus longicaudus to cumulative clear-cutting of coniferous forests and to enhanced understory vegetation in young, fertilized pine stands near Summerland, ...British Columbia, Canada. We explored if there was a threshold level of habitat quality arising from a given forest disturbance for M. longicaudus to increase to high population levels and potentially fluctuate in abundance over time. Secondly, we asked if these outbreaks were site-specific or part of a long-term pattern. We tested three hypotheses (H) that populations of M. longicaudus would increase in abundance and potentially fluctuate owing to (H1) the availability of early seral postharvest habitats associated with cumulative clear-cut harvesting; (H2) woody debris piles on clear-cuts; and (H3) have higher mean abundance, reproduction, and survival in fertilized forest sites with enhanced understory vegetation. Mean annual and peak abundances of M. longicaudus were significantly different across the four Periods of cumulative forest harvesting with numbers being highest in the first two Periods. Thus, H1, that long-tailed voles would increase in abundance on new clear-cuts, was partially supported for the first two Periods but not in the later Periods. Constant cattle (Bos taurus) grazing during summer periods over the four decades may have reduced vegetative productivity for voles and damped out population responses on these clear-cut sites, at least in the last two Periods. Woody debris piles on clear-cuts may have increased abundance and generated a population fluctuation, thereby supporting H2. Enhanced abundance of understory vegetation had no effect on mean abundance, reproduction, or survival of M. longicaudus, and hence did not support H3. We conclude that it is site-specific disturbances, particularly in forest management, that generate occasional outbreaks of M. longicaudus, and there does not appear to be any long-term pattern to these discordant fluctuations.
We investigated the responses of meadow vole (
Microtus pennsylvanicus
) populations to cumulative clearcutting of coniferous forests during four
Periods
over a 42-year span from 1979 to 2020 near ...Summerland, British Columbia, Canada. This vole is a common inhabitant of moist meadows, grasslands, and early successional sites after forest clearcutting and wildfire and may damage plantation trees on reforestation sites. We tested three hypotheses (H) that populations of
M. pennsylvanicus
would (H
1
) increase in abundance and potentially fluctuate owing to the availability of early seral post-harvest habitats associated with cumulative clearcut harvesting; and (H
2
) be positively associated with mean cover of herbaceous vegetation on clearcut sites; and (H
3
) be at lower abundance when the long-tailed vole (
M. longicaudus
) is present at higher numbers. Overall, mean abundances of
M. pennsylvanicus
were generally low, and hence differences among
Periods
were not formally significant. Thus, H
1
, that meadow voles would increase in abundance on new clearcuts was not supported, except for
Period 2
with the highest mean density recorded at 14.3 voles/ha. There was some evidence of a 4-year multi-annual fluctuation in 1998 and 2002 in
Period 2
. Mean ground cover of total herbs, grasses, and shrubs were similar in
Periods 2
and
3
. However, meadow vole populations were dramatically different in these two
Periods
, with few meadow voles captured in
Period 3
and then a decline to extirpation in
Period 4
. Thus, H
2
was supported for
Period 2
, but not
Period 3
. Both species of voles were present at similarly low numbers (< 5/ha) with fewer meadow voles in the three years of peak numbers (22–33/ha) of long-tailed voles, and hence this pattern provided weak support for H
3
. The lack of increases in meadow vole numbers post-cutting in
Periods 1
,
3
, and
4
may have been related to very high numbers of
M. longicaudus
in
Period
1
and possibly the advent of cattle grazing and drought conditions in
Periods 3
and
4
. Although the decline in
Microtus
on post-harvest forest sites may be beneficial for pest management and reforestation, such declines may have serious consequences for predator communities, biodiversity, and other ecological functions.
Long-term population dynamics are essentially unknown for the western heather vole (Phenacomys intermedius), a relatively rare microtine species. Our objectives were to provide a description of ...demographic changes in populations of P. intermedius and determine possible causes of these changes. We analyzed four detailed 12- to 22-year data sets that recorded changes in abundance of P. intermedius in a variety of managed forests in south-central British Columbia, Canada from 1993 to 2018. We evaluated three hypotheses (H) that may help explain population changes: heather voles will (H1) have higher populations in sites with (i) abundant dwarf shrubs or (ii) cover of woody debris; (H2) colonize new clear-cuts as dispersal sinks for young voles; and (H3) be at lower abundance when other Microtus species are present at equal or higher numbers. Populations of P. intermedius occurred commonly at ≤ 1 animal/ha (as a density index). However, in favorable habitats such as some new clear-cuts and in “open” pine stands, P. intermedius occurred at mean annual peak numbers of 5–6/ha (as a density index). There were two relatively high populations of P. intermedius in 1994–1995 and 1998, and possibly again in 2002 in the open pine stands. Mean numbers of lactating females and recruits per year tended to follow the pattern of changes in abundance. High populations of P. intermedius occurred in stands with abundant dwarf shrubs in open pine stands but not those with a cover of woody debris structures in clear-cuts, H1, therefore, was only partially supported. A relatively higher proportion of adult than juvenile heather voles on clear-cuts did not support H2: that these harvested sites would be dispersal sinks for young voles. Mean annual numbers of P. intermedius were positively correlated with those of M. longicaudus, at least on clear-cut sites, hence H3 was not supported. Phenacomys intermedius was essentially absent from our closed-canopy mature/old-growth forests but occurred in many managed forest habitats at low abundance (density index of ≤ 1/ha). In early successional habitats after clear-cutting and in open young pine stands this species occurred at moderate abundance and generally appeared stable in numbers across these forest landscapes.
In semiarid regions, the deer mouse (Peromyscus maniculatus) is a major small mammal species occupying perennial grassland habitats that include old-fields, native bunchgrass–sagebrush, and some ...agricultural settings. We investigated population changes in deer mouse populations in perennial grasslands, both natural and old-field, from 1982 to 2003 in southern British Columbia, Canada. Hypotheses (H) predicted that P. maniculatus populations will have (H1) multiannual fluctuations in abundance driven by population increases from extended breeding in summer and winter; (H2) relaxed spring reorganization events in some years leading to higher overall recruitment and survival; and (H3) interspecific competition with montane voles that causes deer mice to be lower in density when voles are higher. P. maniculatus populations in old-field and grass–sagebrush sites had clearly defined periods of high “peak” mean numbers (32–52/ha) and other times of low mean numbers (20–22/ha). Based on mean annual peak density in autumn, deer mouse populations exhibited fluctuations of 3–4 years in both habitats, but this pattern was not always present. The greater numbers of P. maniculatus in high than low years was directly related to population increases from extended breeding seasons and an increased number of lactating females, thereby supporting H1. Spring breeding season declines occurred but were similar or less in high than low years of mean abundance and were relaxed in comparison to forest populations of deer mice in other studies. Thus, H2 was supported for recruitment with high numbers of young-of-the-year breeding and total number of juvenile recruits but for survival was equivocal. Total summer survival was consistently higher in high than low population years but juvenile productivity in all years was poor. Mean abundance of P. maniculatus and M. montanus in old-field sites were highly correlated, and hence H3 was not supported. This latter result is the first, to our knowledge, of P. maniculatus coexisting in a similar pattern of population fluctuations with a Microtus species in a mainland grassland habitat. Higher than average precipitation in the year preceding a peak population of deer mice may have enhanced herbaceous vegetation and contributed to population increases in both habitats. We conclude that the old-field habitat associated with this agricultural setting provides optimum habitat for P. maniculatus and facilitates multiannual population fluctuations in this species.
Mean crown architecture, diameter, and height of crop trees in treatment stands 25 years after pre-commercial thinning. Display omitted
•Stand thinning is a powerful tool to influence future stand ...growth and structure.•Lodgepole pine increases in volume and structures 25years post-thinning.•Heavily thinned (⩽500stems/ha) stands with several old-growth attributes.•Silvicultural trade-off of stand volume gain vs. old-growth attributes.
Acceleration of forest succession to develop late-seral structural characteristics in younger stands may be achieved by silvicultural practices such as pre-commercial thinning (PCT). Young second-growth stands of lodgepole pine (Pinus contorta) range across several million ha of the inland Pacific Northwest of North America and respond positively to various stand treatments. Objectives of this project were that large-scale stand thinning to a wide range of densities, at a 25-year period after PCT, would enhance: (1) productivity and structural features (diameter and height growth, and crown volume and dimensions of crop trees; (2) merchantable volume of crop trees; and (3) development of old-growth structural attributes. Three stands thinned to densities of ∼500 (low), ∼1000 (medium), and ∼2000 (high) stems/ha at age 17years, with an unthinned young pine and old-growth pine stand for comparison, were located near Penticton in south-central British Columbia.
Lodgepole pine grew faster in mean diameter (cm) in the low- (13.89) than either of the medium- (10.2) or high-density (9.2) stands, but mean height growth increment (8.8–9.7m) was similar over the 25-year period since PCT. Mean diameter was 2.2 times greater in the low-density stand than unthinned stand. The medium- and high-density stands also tended to have large diameters (1.7–1.9 times that of the unthinned stand) and crowns, but still with mean heights 5–6m less than trees in the pine component of the old-growth stand. Mean merchantable stand volume (m3/ha) was 1.7–1.9 times higher in the medium- (231) and high-density (257) stands than low-density (137) stand, and comparable to the old-growth pine (225). Mean crown volume (m3) of crop trees was substantially greater in the low- (88) than in the medium- (27) and high-density (31), unthinned (4), or old-growth stands (4 pine only). Mean structural diversity of five layers of coniferous trees was highest in the low- and medium-density stands, with declining diversity from the high-density to unthinned to old-growth stands. In terms of old-growth structural attributes, large dominant trees with substantial crowns, multi-layered canopies of conifers, some canopy gaps, and understory patchiness of herbs and shrubs appeared in the heavily thinned (⩽1000stems/ha) stands at 25years post-thinning. These stands were 42years old at this re-measurement, and hence were not considered “old-growth” but the heavily thinned stands seemed to have some old-growth structural attributes. Silvicultural trade-off of stand volume gain vs. old-growth attributes may be necessary for low-density stands.
Responses of forest-floor small mammals to clearcutting are species-specific with generalists occupying a range of habitats, and specialists persisting on clearcuts for variable periods. We ...investigated the responses in abundance and species composition of small mammal communities to cumulative clearcutting of coniferous forests on a landscape that had four independent clearcutting events (Periods 1 to 4) over a 42-year interval from 1979 to 2020 in south-central British Columbia, Canada. We ask if the small mammal communities have changed significantly over these decades owing to removal of old-growth forest by clearcut harvesting. Hypotheses (H) predicted that the small mammal community would (H1) increase in abundance, species richness, and diversity on new clearcuts owing to the availability of early seral post-harvest habitats from cumulative clearcutting; and (H2) have higher mean abundance, species richness, and species diversity in clearcut than uncut forest sites, owing to availability of vegetative food and cover. A third hypothesis (H3) predicted that abundance of (i) early seral vegetation (herbs and shrubs) and (ii) small mammal populations, will be greater in ungrazed clearcut sites than in those grazed by cattle (Bos taurus). Mean total numbers of small mammals on new clearcuts declined in Periods 3 and 4, and hence did not support the abundance part of H1. Much of this decline was owing to low numbers of the long-tailed vole (Microtus longicaudus) and meadow vole (M. pennsylvanicus). Two generalist species: the deer mouse (Peromyscus maniculatus) and northwestern chipmunk (Neotamias amoenus), contributed to high mean species richness and diversity in Periods 2 and 3 before these metrics declined in Period 4, and hence partly supported H1. The similarity in mean total numbers of small mammals in Periods 2 to 4 did not support the abundance prediction of H2 that total numbers would be higher in clearcut than uncut forest sites. Higher mean species richness (Periods 2 and 3) and diversity (Period 3) measurements on clearcut than forest sites, particularly in the early post-harvest years, did support these parts of H2. The vegetation part (i) of H3 was not supported for herbaceous plants but it was for shrubs. The small mammal part (ii) of H3 that populations would be higher in ungrazed than grazed clearcut sites was supported for abundance but not for species richness or diversity. The decline and near disappearance of both species of Microtus was possibly related to the reduction in plant community abundance and structure from grazing (at least for shrubs) and potentially from drought effects associated with climate change. Loss of microtines from these early seral ecosystems may have profound negative effects on various ecological functions and predator communities.
We livetrapped populations of Microtus montanus from 1982 to 2003 in semiarid perennial old-field grasslands of southern British Columbia. We evaluated two, nonmutually exclusive hypotheses (H) to ...explain their population dynamics: first (H1), that extended breeding during the summer or winter will drive the increase phase of population fluctuations; and second (H2), that density-dependent depression of juvenile survival will be reflected in poor early juvenile survival during high populations. Populations on 2–3 grids of 1 ha were livetrapped at 3- to 8-week intervals in summer and winter except in 5 years of very low populations. Densities ranged from 10/ha to 250/ha. Peak densities occurred in 6 years and an extended low phase occurred from 1999 to 2003. Fluctuations of 3–4 years appeared in our populations but were not always present. Breeding occurred both in summer and winter, and the best predictor of the population growth rate was the fraction of adult females lactating in summer or winter, thereby supporting H1. Juvenile production (number of juveniles/lactating female) varied greatly among years with the mean being over two times higher in low (2.41) than high (1.08) years, thereby supporting H2. There was no clear correlation between population changes and either seasonal temperatures or rainfall, or any combination of these two variables, and no obvious cause of the prolonged low from 1999 to 2003. Thus, both female reproduction and juvenile production drive montane vole dynamics demographically, similar to what is found in other vole species. However, the ultimate cause of these changes remains to be tackled experimentally.
Coarse woody debris on the forest floor contributes to maintenance of forest biodiversity and long-term ecosystem productivity. Down wood is often dispersed over harvested sites during logging ...activities, thereby leaving piles of postharvest debris as “excess” material at landings and roadsides. These wood residues may be burned in most jurisdictions in North America to reduce a perceived fire hazard. The fire hazard debate needs to acknowledge the documented benefits of woody debris retention while striking a balance among biodiversity, bioenergy, and alternative uses for debris, while reducing ignitions by humans. The burning of excess woody debris also creates smoke, causes the release of greenhouse gas (GHG) emissions, and creates human health issues, particularly for vulnerable individuals. The relationship of wildfire smoke to human health problems is well documented. However, there is no scientific evidence showing that postharvest debris piles are ignition points for forest fires, other than those caused by humans. Wood residues from forest harvesting or natural disturbance wood from wildfire and insect outbreaks may be used as renewable biomass “feedstocks” that could help improve energy supplies and reduce GHG emissions. If not marketable, the management of postharvest debris should seek alternative outlets that do not dispose of debris by burning, but still meet fire hazard abatement requirements. The construction of woody debris structures (e.g., piles and windrows) built at the time of forest harvesting and log processing, or later at the site preparation stages, has positive benefits for wildlife habitat and forest biodiversity. A windrow or series of piles may connect patches and reserves of mature forest and riparian areas on clearcut openings. Piles and windrows have consistently provided habitat on new clearcuts for southern red-backed voles (Myodes gapperi) and Microtus voles, as well as a host of other forest-floor small mammal species, at least up to 12 years postconstruction. Woody debris provides important habitat for foraging and cover attributes for marten (Martes americana), weasels (Mustela spp.), and other furbearers. A list of “What to do?” and “When and Where?” with options for construction of woody debris habitats: poorest, good, better, and best are given. In the cases where fire risk from humans is minimized and there are no marketable wood products, eight alternative management scenarios for postharvest woody debris are provided. These include: (1) piles for wildlife habitat; (2) distribution of debris in partial cut forests; (3) machinery to break up and crush debris; (4) protection of riparian zones with barriers for cattle; (5) construction of range fencing; (6) reclamation of landings and skid-trails; (7) soil fertility and reduction in weed competition and drought for planted conifers; and (8) slope stabilization and revegetation. Advantages and disadvantages (if known) are given for each alternative. A flow chart for the fate of excess postharvest woody debris with respect to fire hazard abatement and markets or nonmarkets is given.
Many mammalian species decline on forest sites that are harvested by clearcutting because of a loss of food, cover, and other components of stand structure. Small mustelids are impacted negatively as ...is the southern red-backed vole (
Myodes gapperi
), a principal prey species, that disappears from clearcuts within a year of harvest. These effects may be potentially ameliorated by aggregated retention harvests that leave unlogged patches on clearcuts. We tested three hypotheses (H) that (H
1
) abundance, reproduction, and survival of
M. gapperi
populations, (H
2
) total abundance, species richness, and diversity of the forest-floor small mammal community, and (H
3
) the presence of small mustelids would be greater in large than small patches of retention forest on new clearcuts. We measured demographic responses of
M. gapperi
, total small mammals, and the presence of small mustelids (American marten,
Martes americana
, and small weasels (
Mustela
spp.)) from 2014 to 2016 in replicated treatments of four sizes (ha) of retention patches (means of 0.53, 1.50, 4.13, and 18.73) near Elkhart in south-central British Columbia, Canada. Mean abundance, reproduction, and survival attributes of
M. gapperi
were similar among treatment sites over the 3-year study. Overall mean abundance ranged from 3.5 to 5.3 voles per line in patches while this microtine was extirpated on clearcut sites (i.e., no forest patches). The similarity in population dynamics among the various forest patches across a gradient of increasing patch size of 4.5 to 35.3 times did not support H
1
. Mean abundance, species richness, and diversity of total forest-floor small mammals were similar among treatment sites, and hence did not support H
2
. Although not formally significant, mean species diversity did show a consistent increase from the largest (0.82) to the smallest (1.11) patch size, owing primarily to the presence of several generalist species such as
Neotamias amoenus
,
Microtus
, and
Sorex
in nearby early successional habitat. Small mustelids were present at similar levels among patch sizes, presumably in response to abundance of small mammal prey, and hence did not support H
3
. Although our results were relatively short-term, the detailed assessment of population dynamics of
M. gapperi
indicated that habitat quality was sufficient to maintain this species regardless of patch sizes, ranging from 0.3 to 20.0 ha. Similarly, the total forest-floor small mammal community and presence of small mustelids also followed this pattern. All sizes of forest patches have conservation value and will help to maintain abundance and diversity of forest mammals, both predator and prey species, on clearcuts. Longer-term studies (e.g., at 5- to 10-year intervals) are essential to determine if our results are sustainable in augmenting forest restoration.
We report a 26-year detailed record of changes in abundance and demography of the deer mouse (
Peromyscus maniculatus
) in old-growth coniferous forest in southern British Columbia, Canada, from 1995 ...to 2020. We evaluated three separate hypotheses that may help to explain population changes: (H
1
) large cone crops of coniferous trees will correspond to peak
Peromyscus
density; (H
2
) spring reorganization of individuals within populations will lead to early breeding season declines; and (H
3
) competition between
P. maniculatus
and the sympatric red-backed vole (
Clethrionomys gapperi
) and hence densities of the former will be lower when the latter are higher. Populations of deer mice showed five periods of high numbers with intervals of 3 to 8 years between fluctuations. Mean density ranges were low, growing from 2–3/ha in spring to 8–13/ha in autumn. The mean abundance of
P. maniculatus
in high years was directly related to number of successful pregnancies, total number of juvenile recruits, and a high index of early juvenile productivity. Irregular population fluctuations were related to pulsed food supplies in the form of coniferous seeds, thereby supporting H
1
. Numbers declined in 16 of 26 summers, reflecting poor overall survival and low reproduction (only 69% of adult females lactating and 51% having only one litter; virtually no juveniles matured and bred). Thus, H
2
was partly supported for a reorganization event that led to breeding season declines, and the immediate cause was very poor survival of juvenile mice. The annual peak numbers of
C. gapperi
ranged from 1.5 to 16.9 times higher than numbers for
P. maniculatus
and hence provided only weak support for H
3
. Field experiments are needed to test these hypotheses as mechanisms driving deer mouse populations.
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