Technical Report - Ministry of Forests

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Project Number: Y062138
ANNUAL PROGRESS REPORT
2005-06
Project Title: Use of Diversionary Foods to Reduce Seedling Damage by Voles
Contact Information:
Thomas P. Sullivan
Dept. of Forest Sciences
Faculty of Forestry,
2424 Main Mall,
University of BC,
Vancouver, B.C. V6T 1Z4
E-mail: tomsu@interchange.ubc.ca
Phone: 604-822-6873 Fax: 604-822-9102
Abstract
Voles of the genus Microtus and Clethrionomys are considered to be major
mammalian pests in coniferous and deciduous tree plantations in North America. Voles
may feed on bark, vascular tissues, and sometimes roots of trees, particularly during
winter months when alternative food sources are limited. This damage may result in
direct mortality from girdling and clipping of tree stems or reduced growth of surviving
trees that have sub-lethal injuries. In terms of conservation and sustainability of
temperate forests, feeding damage may limit regeneration of appropriate tree species in
certain forest ecosystems, become costly to reforest these stands in time for Free
Growing Status, decrease net productive forested area, and result in loss of Mean
Annual Increment. Feeding damage appears to be associated with high populations of
voles in early successional habitats that develop after harvesting. The problem is
widespread throughout the southern and central interior of B.C.
The use of diversionary food is an ecologically favourable way to reduce feeding
damage by voles during those months when alternative natural foods are in short
supply. A diversionary food needs to be palatable so that voles will eat it in preference
to coniferous tree seedlings. However, the food must not be overly nutritious such that
it enhances vole reproduction or survival. The diversionary food being utilized in this
project consists of alfalfa, canola oil, and bark mulch with wax as a cohesive aggregate.
The project will monitor vole populations, and test this technique to decrease mortality
of trees from winter damage by voles, over a 3-year period. If trials are successful, this
will result in increased plantation survival, thereby directly providing positive benefits to
sustainable forest management.
After year 2 of 3, vole populations have been monitored for two years, since the
time of harvesting, to follow how these rodents respond to successional change and
reach densities capable of serious feeding damage to newly planted trees. In particular,

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in 2005 during the second year after harvesting, the long-tailed vole (M. longicaudus) is
most common (20-30 animals/ha), with the meadow vole (M. pennsylvanicus) also
preferring this seral stage but at numbers of 1-2 animals/ha. For red-backed voles (C.
gapperi), in the year after harvesting, mean numbers are as high as 10/ha. However,
their numbers declined dramatically at 2 years after harvesting. The heather vole
(Phenacomys intermedius) occurs at numbers < 5/ha. These early stages after
harvesting provide ideal habitat for many species of small mammals, in addition to
voles.
In two overwinter trials, to date, diversionary food (“mouse pucks”) has protected
newly planted trees compared with control trees. These results were not formally
significant (Trial A; P = 0.09; Trial B; P = 0.08). However, they are very likely
biologically significant, particularly if we examine the effect of (a) the relationship of
successional age to number of voles (older cutblocks have greater vegetative
development and hence higher vole populations) and (b) the potential impact of the food
supply being exhausted. These factors helped direct the design of Trial C (overwinter
2005-06) which is evaluating different densities of mouse pucks (including both lower
and higher amounts of diversionary food) in 1-year-old cutblocks with newly planted
trees.
Introduction
The problem of feeding damage to forest and agricultural crops by herbivorous
small mammals has a long history in temperate and boreal ecosystems of North
America and Eurasia (Moore, 1940; Myllymäki, 1977; Byers, 1984; Getz, 1985;
Conover, 2002). In forestry, voles of the genera Microtus and Clethrionomys are
considered the major mammalian species affecting coniferous and deciduous tree
plantations in North America (Sartz, 1970; Radvanyi, 1980; Bergeron and Jodoin, 1989;
Sullivan et al., 1990), Europe (Hansson, 1985; 1991), and Asia (Shu, 1985; Sullivan et
al., 1991). Populations of some species of voles tend to have cyclic fluctuations in
abundance in northern latitudes (Krebs and Myers, 1974; Taitt and Krebs, 1985;
Körpimaki and Krebs, 1996; Boonstra et al., 1998). It is primarily during overwinter
periods when high populations of these microtines feed on plantation trees. Voles feed
on bark, vascular tissues (phloem and cambium), and sometimes roots of trees. Direct
mortality may result from girdling and clipping of tree stems.
Abundance of Microtus populations and degree of damage is usually highest in
early successional habitats that develop after forest harvesting by clearcutting
(Hansson, 1989; 1991; Sullivan and Sullivan, 2001; Sullivan et al., 2001) and in old
fields (perennial grasslands) undergoing afforestation (Radvanyi, 1980; Bergeron and
Jodoin, 1989; Ostfeld and Canham, 1993; Ostfeld et al., 1997). Grasses, herbs, and
shrubs in these habitats provide food and cover for voles (Batzli, 1985; Ostfeld, 1985).
In terms of conservation and sustainability of temperate forests, feeding damage may
limit regeneration of appropriate tree species in certain forest ecosystems, become
costly to reforest these stands in time for Free Growing Status, decrease net productive
forested area, and result in loss of Mean Annual Increment.
Feeding damage appears to be associated with high populations of Microtus spp.
Some Microtus populations tend to have cyclic fluctuations in northern latitudes with a

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peak every 3 to 5 years, although these periods may be interspersed with annual
fluctuations in abundance (Taitt and Krebs, 1985). Clethrionomys populations occupy a
variety of habitats from early-successional forest to tundra for C. rufocanus in Europe
and Asia (Shu et al., 1985; Sullivan et al., 1991), to mature and old-growth forest for the
southern red-backed vole (C. gapperi) in North America (Merritt, 1981). Southern redbacked
voles appear not to have cyclic fluctuations in abundance compared with other
species of Clethrionomys (Fuller 1985; Hansson and Henttonen 1985).
Because of these habitat preferences, Microtus occur frequently on forested
areas harvested by clearcutting, up to almost 10 years after logging . Conversely, the
red-backed vole appears to decline in abundance within 1 or 2 years after clearcut
logging in western North America. There has been much research on the importance of
habitat heterogeneity in population dynamics of small mammals. Clearcutting of forests
yields relatively homogeneous early-successional habitats. Alternative harvesting
practices such as group seed-tree and patch-cutting systems produce heterogeneous
habitat patterns compared with clearcutting. To date, severe feeding damage by voles
has been reported to seedlings planted on large (> 100 ha) openings created by
harvesting (e.g., near Golden, Summerland, Invermere, Quesnel, Houston) or wildfire
(e.g., Silver Creek Fire, Salmon Arm). However, the population fluctuations of Microtus
are generally unknown in these areas, and it appears that vole populations may be high
on some sites every year.
The population fluctuations of Microtus are unknown around the Golden area,
and in the Columbia Valley, in general. However, it appears that vole populations may
be high on some sites every year. Two species of Microtus, the long-tailed vole (M.
longicaudus) and the meadow vole (M. pennsylvanicus) are implicated as major
consumers of tree seedlings. A third species, the heather vole (Phenacomys
intermedius) is also present in these small mammal communities but exists at low
abundance (< 5 animals/ha). Populations of the southern red-backed vole occur
primarily in mature stands of timber but may spill over into recently cut areas for 1-2
years after harvest. It is likely that these voles already lived on the forested site prior to
logging and continue there for a few years afterward, possibly feeding on lodgepole pine
seed from cone slash. Red-backed voles disappear from harvested sites by 2 years
post-logging, probably because their preferred food source, hypogeous fungi, are in
short supply.
Application of diversionary food is an alternative management practice that has
shown promise in alleviating damage to forest and agricultural crops by montane (M.
montanus) and long-tailed voles without the detrimental side effects of toxicants that are
used to reduce the target pest population (Sullivan and Sullivan, 1988; Sullivan et al.,
2001). These diversionary food studies used “bark mulch logs” to provide an overwinter
food source for voles that would be more palatable than apple trees (Malus domestica)
or planted lodgepole pine (Pinus contorta) seedlings, but of a similar or lower nutritive
value than natural foods. The objective was to provide an artificial diversionary food
that would be more palatable than tree bark and vascular tissues but not be nutritious
enough to maintain or increase population size of voles.
Provision of diversionary food is a method of habitat modification designed to
temporarily satisfy part, or a majority, of the food requirements of a problem species in a

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localized area (Howard, 1967; Sullivan, 1979). In laboratory studies, Hansson (1971)
reported that voles (M. agrestis) did not girdle tree stems if green vegetation and small
twigs supplemented a diet of laboratory food pellets. In subsequent studies, voles
preferred various oil- and sugar-impregnated sticks (Hansson, 1973), and meadow and
montane (M. montanus) voles preferred sticks impregnated with soybean oil compared
with sucrose and sorbitol (Sullivan and Sullivan, 1988). Preliminary evidence from
small-scale trials in young apple (Malus domestica) orchards suggested that a
combination of bark mulch, soybean oil, and wax reduced feeding damage by voles to
apple trees (Sullivan and Sullivan, 1988). Similarly, use of diversionary food
formulations in forest plantations resulted in seedlings on control sites suffering mortality
from voles at levels 2.6-2.8 times higher than those on food sites (Sullivan et al. 2001).
None of the diversionary foods tested had any effect on mean abundance of vole
populations (Sullivan et al. 2001). These studies suggested that certain foods, which are
more palatable than tree bark and of similar or lower nutritive value than natural foods,
may have potential for reducing tree damage by voles.
If coniferous tree seedlings are subsistence overwinter food for voles, then it may
be possible to provide an artificial diversionary food that is more palatable to voles than
tree bark and vascular tissues, but not necessarily nutritious enough to maintain or
increase population size. However, several studies have documented the positive
influence of supplemental food on vole population dynamics (Cole and Batzli, 1978;
Taitt and Krebs, 1981; Boutin, 1990).
Objectives for the 3-year study are:
(1) Determine the population fluctuations of vole species on recently harvested areas in
the Golden Timber Supply Area.
(2) Test the hypothesis that protection of seedlings with diversionary foods will not
affect vole populations or other members of the small mammal community.
(3) Test the hypothesis that provision of diversionary food logs, on a large (operational)
scale, would reduce feeding damage to lodgepole pine seedlings by voles.
Methods
Population Monitoring:
Vole populations (and other forest floor small mammal species) are sampled at
4- to 6-week intervals from May to October each year. Trapping grids (1 ha) have 49 (7
x 7) trap stations at 14.3-m intervals with one Longworth live-trap at each station
(Ritchie and Sullivan 1989). Traps are supplied with whole oats, and cotton as bedding.
Traps are set on the afternoon of day 1, checked on the morning and afternoon of day 2
and morning of day 3, and then locked open between trapping periods. Forest floor
small mammal species sampled by this procedure include the meadow vole, long-tailed
vole, heather vole, southern red-backed vole, deer mouse (Peromyscus maniculatus),

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northwestern chipmunk (Tamias amoenus), montane shrew (Sorex monticolus),
common shrew (S. cinereus), and short-tailed weasel (Mustela erminea). Abundance
estimates of each species will be derived from the Jolly-Seber (J-S) stochastic model
(Seber 1982) when there are sufficient data. Species richness and diversity of the
overall small mammal communities will be calculated using the estimated abundance of
each species for a given sampling period and averaged over the number of sampling
periods for each year.
Diversionary Food Treatments:
Diversionary food “mouse pucks” were prepared during the period May to
September 2003, 2004, and 2005 at the Applied Mammal Research Institute
manufacturing facility. Diversionary food treatments were established in October on
those selected sites with substantial vole populations. Diversionary food mouse pucks
were applied to new plantations at a given density per ha. The location of 100 sample
pucks per ha were marked by staked flags to determine overwinter consumption by
voles on each site. Planted trees were marked by different coloured flags to sample for
evidence of feeding damage during the overwinter period. One hundred sample
seedlings (lodgepole pine) were chosen randomly on each site. Clipping of terminal
and lateral shoots will be recorded for each sample seedling in the spring (April-May).
Removal of the terminal shoot will be considered mortality unless another vigorous
lateral shoot is available to replace it.
Trial A was initiated in September 2003 when five replicate control and treatment
paired sites were established: two pairs at Glenogle Creek, two pairs at Redburn Creek,
both on LP Engineered Wood Products Ltd. sites; and one pair at Caribou Creek, TFL
15 (Tembec). The size of these paired sites ranged from 2.6 to 16.4 ha. All sites were
selected on the basis of operational scale, reasonable proximity to one another, and
availability of sites that were 1- to 2-years post-harvest with substantial vole populations
(e.g., > 30 voles/ha). All sites were far enough apart to be statistically independent.
Diversionary food mouse pucks were applied at a rate of 1,200 pucks per ha. Damage
to tree seedlings and consumption of diversionary food was evaluated in April-May
2004.
Trial B was conducted in 2004 with six replicate control and six replicate
treatment sites (each 8 ha) established to test diversionary foods as a means to reduce
feeding damage to seedlings by voles. Five control-treatment pairs were set up at
Glenogle Creek (LP Engineered Wood Products) and one control-treatment pair was set
up at Caribou Creek (TFL 15, Tembec) in September 2004. Diversionary food was
applied at 1750 pucks per ha on all six treatment sites in October 2004. Efficacy of
treatments and survival of planted seedlings on all sites was measured in April-May
2005.
Trial C was conducted in 2005 with three replicate control and three replicate
food sites (each 5 ha) on the six CP 821-44, 46, 47, 48, 49, and 50 blocks at Glenogle
Creek. Each food block was divided into three 5-ha units. Within each 5-ha unit,
mouse pucks were distributed uniformly at one of three densities: 1050, 1750, and 2800
pucks/ha. The remaining three blocks acted as controls. Efficacy of treatments and
survival of planted seedlings on all sites will be measured in April-May 2006.

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Statistical Analysis:
A one-way analysis of variance (ANOVA) was used to determine the effect of
diversionary food on percentage of tree seedlings eaten (mortality) and attacked (sublethal
damage) in Trial A (2003-04 winter) and Trial B (2004-05 winter). Proportional
data were arcsine-transformed prior to analysis (Zar 1999). In all analyses, the level of
significance was at least P = 0.05. This same analysis will be used in evaluating the
results of Trial C (2005-06 winter).
Results and Discussion
Objective (1) was initiated in 2004 with three installations (CP 825-1, 825-5, and
821-2) to follow population fluctuations of the four species of voles in the area: the longtailed
vole, the meadow vole, the southern red-backed vole, and the heather vole from
the time of harvesting through the early years of planting and vegetative succession.
The long-tailed vole is most common (20-30 animals/ha) on these cutblocks, in 2005
during the second year after harvesting, with the meadow vole also preferring this seral
stage but at numbers of 1-2 animals/ha (Figs. 1 and 2). For red-backed voles, in the
year after harvesting, mean numbers are as high as 10/ha. However, their numbers
decline dramatically at 2 years after harvesting (Fig. 2). The heather vole occurs at
numbers < 5/ha. These early stages after harvesting provide ideal habitat for many
species of small mammals, in addition to voles (Figs. 1 and 2)
Objective (2): the effects of diversionary feeding on vole populations and other
small mammals; was evaluated in the overwinter of 2003-04 into spring 2004.
Diversionary foods had little effect on mean abundance of voles (Microtus) (Fig. 3). The
observed increase, from before to after the food addition, was likely more related to
successional development of vegetation than the actual diversionary food. The
response of total small mammals also followed this pattern (Fig. 3). The two major
seed-eaters, the deer mouse and northwestern chipmunk, do not feed on the
diversionary food. Thus, their changes in abundance, particularly the increased deer
mouse numbers, are likely related to successional development of vegetation as well
(Fig. 4). Numbers of red-backed voles and heather voles were quite low (< 5/ha) and
no trends from before to after the food application could be determined.
Objective (3) included Trials A and B. Trail A was evaluated in May 2004.
Results for Trial A are illustrated in Fig. 5 where in 3 of 4 locations (replicates 1, 2, and
4), with significant feeding damage by voles, the presence of diversionary food reduced
damage to trees. This difference was not statistically significant (F 1,2 = 9.52; P = 0.09),
but likely is biologically meaningful. The lack of a difference between control and
treatment sites in replicate 5 at Caribou Creek was difficult to explain.
Results for Trial B at Glenogle Creek (Fig. 6) are illustrated in Fig. 7. Seedlings
survived better with food than those without, but only in those cases where the food was
not exhausted. At Caribou Creek, seedlings with food had a 93% survival compared
with those without food at 43% survival. ANOVA results (n=6 replicates) (F 1,5 = 4.86; P
= 0.08) were not formally significant, but clearly there is biological significance,
particularly if we examine the effect of (a) the relationship of successional age to

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number of voles (note replicate E in Fig. 6) and (b) the potential impact of the food
supply being exhausted. This latter factor helped direct the design of Trial C which is
evaluating different densities of mouse pucks (including both lower and higher amounts
of diversionary food).
Acknowledgements
We thank the Forest Science Program (Ministry of Forests), Louisiana-Pacific Canada
Ltd., and Tembec Industries Ltd. for financial and logistical support for this project. S.
King and T. Andrews have been particularly helpful in assisting with this project.
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