166 C. Maisonneuve, S. Rioux Agriculture, Ecosystems and Environment 83 2001 165–175
agriculture that was previously characterized by a mo- saic of pastures, prairies and woodlots was replaced
by a more specialized agriculture aimed at large-scale production, with corn as Zea mays L. the dominant
crop in the south-west. The new agricultural practices developed for this large-scale production has led to
the expansion of cultivated areas, thus exerting an in- creasing pressure on uncultivated portions of the land.
Forests in agricultural landscapes have been reduced and fragmented in numerous small woodlots, and ri-
parian strips which often represent the only remaining corridors for wildlife between these woodlots are also
being threatened.
Riparian strips are not only recognized as impor- tant wildlife habitats for a great diversity of species
Thomas et al., 1979; Small and Johnson, 1986; De- camps et al., 1987; Naiman et al., 1993, but they also
help reduce the impacts of agricultural practices on the water quality of streams by controlling bank erosion,
and by filtering fertilizers, pesticides and sediments from adjacent crops Lowrance et al., 1985, 1986;
Brenner et al., 1991; Gilliam, 1994; Vought et al., 1994 and they maintain quality of aquatic habitats by
regularizing water temperature Karr and Schlosser, 1978. Thus, efforts to integrate the conservation
of riparian strips in the management of agricultural lands should lead to both sound agroecosystems and
environments.
However, many factors contribute to limit the value of riparian strips in agricultural landscapes of
Québec. Under the provincial Protection Policy for Lakeshores, Riverbanks, Littoral zones and Flood-
plains, a buffer strip of 3 m is required for the pro- tection of riparian areas in agricultural landscapes,
whereas 10–20 m are required in urban or forested landscapes. Moreover, the vegetation in these narrow
riparian strips is often maintained at the herbaceous stage through mowing or burning. This practice stems
from the farmers’ belief that such management re- duces the risk of riparian strips becoming shelters
for pest species birds, rodents, weeds, insects. In a recent study made for the Union des producteurs
agricoles Lamarre et al., 1993, pesticide use for weed control was even recommended within riparian
strips. This perception of riparian habitats repre- sents a major obstacle for efforts to integrate wildlife
habitat needs in the management of agricultural landscapes.
The objectives of this study were thus to determine the importance of riparian strips for small mammal and
herpetofaunal amphibians and reptiles communities in agricultural landscapes of southern Québec, and to
verify if there is a basis to farmers’ belief concerning the risk of riparian strips being used as shelters by
rodent pest species.
2. Material and methods
2.1. Study area The study was carried out in the Boyer River water-
shed, located on the south shore of the St. Lawrence River near Québec City. Agriculture is the predom-
inant land use in this watershed, covering more than 60 of its 217 km
2
. Most of the agricultural land is devoted to hay 43 and cereal production 14.
The remaining area of the watershed is covered by woodlots 28, peatlands 4, and edge-transition
habitats 2; abandoned farmland, riparian strips and hedgerows. The watershed comprises a total length
of 345 km of streams, including ditches created to im- prove drainage. Most of the streams circulate in agri-
cultural lands; 67 have agricultural fields on both of their banks, 25 woodlots on both banks, and the re-
maining 8 both a wooded and an agricultural bank.
Most herbaceous and shrubby riparian strips are located in areas where topography permits cultiva-
tion right up to the rim of the streambanks. Mean width of the strips is close to the minimum of 3 m
required by the provincial policy: 3.2 ± 1.0 m for shrubby strips, and 3.7 ± 1.0 m for herbaceous strips.
The wooded strips are located in stream sections where the steepness of the banks impedes cultivation,
and are 19.2 ± 14.0 m wide. Herbaceous riparian strips are mostly covered by gramineous plants like
Phalaris arundinacea, Bromus inermis, and Calama- grostis canadensis, and forbs like Impatiens capensis,
Eupatorium maculatum, Prunella vulgaris, and Fra- garia virginiana. Shrubby riparian strips 3 m high
are dominated by Prunus virginiana, Spirea latifo- lia, Rubus idaeus, Alnus rugosa, Crataegus spp., and
Cornus stolonifera. The most abundant tree species 3 m in wooded riparian strips are Acer negundo,
Salix spp., Fraxinus spp., Acer saccharum, P. virgini- ana, and Populus tremuloides.
C. Maisonneuve, S. Rioux Agriculture, Ecosystems and Environment 83 2001 165–175 167
2.2. Field methods Two methods were used to trap small mammals.
The first one consisted of lines of traps installed par- allel to the streams. A total of 18 sites were selected
to cover a total of 3600 m in each of the habitat types. Each line had a length of 600 m. Museum special
snap traps, Sherman live traps, and pitfall traps 2 l were placed alternately every 10 m. Thus, each line
comprised 20 of each of these traps. Snap traps were baited with peanut butter, and live traps with ap-
ple pieces dipped in peanut butter. Pitfall traps were not baited, but filled with enough water to rapidly
drown mammals. Half of these lines were operated for five consecutive nights during September 1995,
the other half during September 1996. Total trapping effort was thus 1800 night-traps in each of the habitat
types.
Drift fences Corn, 1994; Kirkland and Sheppard, 1994 were used as a second trapping method to
sample amphibians and reptiles, and to make ad- ditional small mammal captures. Drift fences were
installed on the same 18 sites six by habitat type where line trapping had been carried out in the previ-
ous year. Each of the arrays consisted of jute fences 45 cm high and 30 m long installed parallel to the
streams. Four 25 l pitfall traps were installed flush to the ground at every 10 m and with enough water
to immediately drown mammal species. Six funnel traps were also placed alongside the fences, on both
sides, one set between each pitfall traps. Each of the arrays was operated for a total of 22 nights. In 1996
and 1997, sampling was carried out during 14 nights in May, four nights in June–July, and four nights
in September. A trapping effort of 1320 night-traps was thus carried out in each of the three habitat
types.
Except for easily identified species squirrels, chip- munks, weasels captured in live traps, all mammal
specimens were sacrificed and kept frozen until later identification with the use of cranial and dental charac-
ters. Amphibians were identified in the field, marked by cutting a toe in order to consider recaptures in eval-
uation of abundance, and released.
Land use adjacent to each trapping station along line transects was noted. These could be grouped into the
following four categories: cereals, pastures, prairies and fallow lands.
2.3. Statistical analyses Shannon’s index Zar, 1984 was used to measure
diversity within each of the three riparian habitats H =
n log n −
P f
i
log f
i
n 1
where n is the total number of individuals captured for all detected species combined, and f
i
the number of captures for species i.
Hutcheson’s test 1970 was used to compare diver- sity indices between habitat types
t = H
1
− H
2
S
2 H
1
+ S
2 H
2
12
2 where S
2 H
is the variance of the diversity index ob- tained as follows:
S
2 H
= P
f
i
log f
i
− P
f
i
log f
i 2
n n
2
3 Since habitat types with similar diversity indices
may be inhabited by different communities, an overlap index Horn, 1966 was calculated
O = P
f
i
+ g
i
log f
i
+ g
i
− P
f
i
log f
i
− P
g
i
log g
i
n
1
+ n
2
log n
1
+ n
2
− n
1
log n
1
− n
2
log n
2
4 where f
i
is the number of captures of species i, g
i
the number of captures of species j, n
1
the total number of captures in habitat 1, and n
2
the total number of captures in habitat 2. This index varies from 0, when
two communities have no species in common, to a maximum of 1 when all species and relative abundance
are the same in both habitats compared.
The reciprocal of Simpson’s index was used to determine niche breadth Levins, 1968; Colwell and
Futuyma, 1971; Whittaker and Levin, 1975; Brown and Parker, 1982 for each species
W = 1
P p
2 ij
5 where p
ij
is the occurrence rate of species i in habitat j. This rate is obtained as follows:
p
ij
= O
ij
P O
ij
6
168 C. Maisonneuve, S. Rioux Agriculture, Ecosystems and Environment 83 2001 165–175
where O
ij
is the number of captures of species i in habitat j. Since three habitat types were compared, a
niche breadth value of 1 indicates that a species is only present in one habitat type, whereas a maximum
value of 3 indicates that a species is distributed evenly in all three habitat types. This value of niche breadth
can be used as a tolerance index to habitat modifica- tions; species with great niche breadths are considered
tolerant and to modifications of their habitat and vice versa Best et al., 1979; Stauffer and Best, 1980.
Proportions of insectivores and rodents within each habitat type were compared with G-tests Scherrer,
1984: 484. When this test indicated heterogeneity between the three habitat types, multiple comparison
tests Scherrer, 1984: 488 were carried out to de- termine to which habitat this was due. The G-tests
were also used to compare proportions of pest species among the small mammal communities. Two species
were considered as potential pests: Microtus pennsyl- vanicus, and Mus musculus.
Comparison of observed numbers of individual species with numbers expected according to adjacent
land use availability was carried out with G-tests. This test was carried out for species for which at least
20 captures were obtained in the trap lines. Microtus pennsylvanicus and M. musculus were grouped as
pests species for this analysis.
Table 1 Mean, standard deviation S.D. and total numbers of individuals of each species of small mammals captured within each of three riparian
habitat types and number of sites on which they were detected in agricultural landscapes of southern Qu´ebec, 1995–1997 Species
Habitat Herbaceous
Shrubby Wooded
Mean S.D.
Total Sites
Mean S.D.
Total Sites
Mean S.D.
Total Sites
S. cinereus 15.5
6.6 92
6 27.7
7.6 166
6 26.3
5.9 158
6 S. fumeus
0.3 0.5
2 2
0.8 1.5
5 2
4.0 4.2
24 6
Sorex hoyi 0.2
0.4 1
1 0.5
0.8 3
2 0.2
0.4 1
1 B. brevicauda
6.3 2.6
42 6
9.5 4.2
57 6
8.8 3.9
53 6
Condylura cristata 0.7
0.8 4
3 0.5
0.8 3
2 M. pennsylvanicus
4.5 4.0
27 5
3.5 1.3
21 6
2.2 2.6
13 3
C. gapperi 2.2
2.9 13
3 2.3
1.7 14
4 6.2
5.7 37
6 M. musculus
1.2 1.3
7 3
0.3 0.5
2 2
0.8 0.7
5 4
P. maniculatus 0.5
1.1 3
1 10.8
8.6 65
6 Napaeozapus insignis
0.2 0.4
1 1
0.5 0.8
3 2
Z. hudsonius 25.3
7.1 152
6 35.5
14.8 213
6 41.8
13.3 248
6 Tamiasciurus hudsonicus
0.8 1.5
1 1
0.2 0.4
1 1
1.0 0.8
6 4
Tamias striatus 0.3
0.5 1
1 Mustela herminea
0.5 0.8
3 2
1.7 1.5
10 4
0.3 0.5
2 2
Total 344
496 620
3. Results
