Robert G. Wagner

The role of herbicides for enhancing forest productivity and conserving land for biodiversity in North America

Abstract Herbicide technology has evolved with forest management in North America over the past 60 years and has become an integral part of modern forestry practice. Forest managers have prescribed herbicides to increase reforestation success and long-term timber yields. Wildlife managers and others interested in conserving biodiversity, however, have often viewed herbicide use as conflicting with their objectives. Do herbicides increase forest productivity, and are they compatible with the objectives of wildlife management and biodiversity conservation? Results from the longest-term studies (10–30 years) in North America suggest that the range of wood volume yield gains from effectively managing forest vegetation (primarily using herbicides) is 30–450% in Pacific Northwest forests, 10–150% in the southeastern forests, and 50–450% in northern forests. Most of the 23 studies examined indicated 30–300% increases in wood volume yield for major commercial tree species and that gains were relatively consistent for a wide range of site conditions. Meeting future demands for wildlife habitat and biodiversity conservation will require that societys growing demand for wood be satisfied on a shrinking forestland base. Increased fiber yields from intensively managed plantations, which include the use of herbicides, will be a crucial part of the solution. If herbicides are properly used, current research indicates that the negative effects on wildlife usually are short-term and that herbicides can be used to meet wildlife habitat objectives.

Acceptable practices in Ontario's forests: Differences between the public and forestry professionals

We compare and contrast survey responses to statements about 1) environmental values, 2) agreement with forest management goals and approaches, 3) perceptions of risk, 4) trust in science and government, and 5) acceptability of forestry practices between the public and three groups of forestry professionals (government biologists, government foresters, and industry foresters) in Ontario. The survey emphasized issues surrounding forest vegetation management due to the contentious nature of herbicide use. Responses were gathered from a 140-question telephone survey administered from September and November 1994 to 1,500 members of the general public and 201 forestry professionals across the province. Forestry professionals tended to be less supportive of some environmental values and forest management goals, perceive everyday and forestry activities to be less risky, be more trusting of science and government, and be more accepting of forestry activities than the general public. Among the three groups of forestry professionals, industry foresters tended to be most different from the public, followed by government foresters, and government biologists. These differences reveal potential sources of conflict and miscommunication between the public and forest managers. Recognizing these differences can help improve communications with the public about forest management plans.

Morphological characteristics associated with tolerance to competition from herbaceous vegetation for seedlings of jack pine, black spruce, and white pine

Tolerance of bareroot and container-grown seedlings of black spruce (Picea mariana (Mill.) B.S.P.), jack pine (Pinus banksiana Lamb.), and eastern white pine (Pinus strobus L.) to competition from herbaceous vegetation was examined in the first five years after planting on a site in the Great Lakes/St. Lawrence forest of Ontario, Canada. Shoot and root morphological characteristics of various stocktypes were measured before planting and correlated with 5-year survival and growth following control and no control of herbaceous vegetation. For black spruce and jack pine, medium-sized bareroot stocktypes had greater relative 5-year stem volume growth in the presence of herbaceous vegetation than did container stock of either species or large bareroot stock of spruce. Relative volume growth was measured as the ratio of the cumulative stem volume increment in the presence of vegetation (Veg) to that in the absence of vegetation (NoVeg), i.e., the Veg:NoVeg ratio. In white pine, the Veg:NoVeg ratio of volume increment of medium container and large bareroot stocktypes exceeded that of small container and medium bareroot stocktypes. In jack pine, root collar diameter at planting and number of first-order lateral roots were positively correlated with 5-year Veg:NoVeg ratio of volume increment. In white pine, the Veg:NoVeg ratio was also positively correlated with root collar diameter at planting and with root volume. In black spruce, the ratio was not related to pre-plant morphology. Thus, for white pine and jack pine, certain pre-plant morphological features may be useful in forecasting the relative ability of different stocktypes to grow under herbaceous competition conditions in the field.

Population dynamics of small mammals in relation to vegetation management in orchard agroecosystems: compensatory responses in abundance and biomass

Abstract This study was designed to test the hypothesis that habitat alteration with intensive herbicide (glyphosate) treatment would adversely affect the small mammal community in apple orchards. Multiple applications of herbicide were applied to the total orchard floor in two experimental orchards, and this same herbicide regime was applied in a 2-m-wide strip within tree rows only in a third orchard. Intensive sampling of montane vole ( Microtus montanus ), deer mouse ( Peromyscus maniculatus ), and northwestern chipmunk ( Eutamias amoenus ) populations was conducted in replicate control and treatment blocks of apple orchards at Summerland, British Columbia, Canada from 1983 to 1986. Average abundance of voles declined by 53% to 73% on treatment compared to control blocks after the first herbicide application. Vole populations were consistently reduced in response to the herbicide treatment, with average abundance ranging from 2.8 to 28.0 times higher on control than treatment blocks. Voles declined to, or near, extirpation in all orchards during the winter of 1985–1986. Either deer mouse and northwestern chipmunk populations were significantly higher on treatment than control blocks or there was no difference in abundance after the start of the herbicide applications. The average abundance of deer mice ranged from 1.3 to 11.1 times higher, and that of chipmunks ranged from 1.8 to 13.3 times higher, on treatment than control blocks. The high numbers of deer mice and chipmunks on treatment blocks were composed mainly of resident animals. There were no significant differences in biomass of small mammals between control and treatment populations in summer and winter periods in two out of three orchards. There appears to be a ‘compensatory response’ in this small mammal community whereby deer mice and northwestern chipmunks have essentially ‘replaced’ the montane vole on treatment blocks in an orchard agroecosystem. The quality of the altered habitats seemed sufficiently high to support these populations at comparable or higher levels than on controls. The species diversity of plants and animals in orchard agroecosystems should be investigated to determine their role as part of a mosaic of natural and agrarian habitats.

Silvicultural use of herbicide in Sub-Boreal spruce forest : Implications for small mammal population dynamics

Vegetation management in northern coniferous forest ecosystems may have implications for small mammal communities. This study was designed to test the hypothesis that herbicide-induced habitat alteration would reduce small mammal populations in early-successional stages of sub-boreal spruce forest. A secondary objective was to determine the long-term influence of herbicide treatment on reproduction, survival, and growth attributes of deer mouse (Peromyscus maniculatus) and southern red-backed vole (Clethrionomys gapperi) populations. Small mammal populations were intensively sampled in 4 pairs of control and treatment sites dominated by early-successional vegetation (5-10 yr after clearcut harvesting) near Prince George, British Columbia, Canada. Sampling was conducted during 1987 (pretreatment year) 1988-89 (first and second posttreatment years), and in 1991-92 (fourth and fifth posttreatment years). Higher mean numbers of red-backed voles (P = 0.03) and shrews (Sorex spp.; P = 0.001) were present on control than treatment sites during 1988-92. Mean abundance of meadow voles (Microtus pennsylvanicus; P = 0.69) and deer mice (P = 0.20) were similar on control and treatment sites throughout the study. Short-tailed weasels (Mustela erminea) and long-tailed weasels (Mustela frenata) were commonly captured on both control and treatment sites. There were no consistent differences between control and treatment populations in body mass, total biomass, or proportion of adult male and female red-backed voles and deer mice in breeding condition. However, there was a higher mean number of successful pregnancies in control than treatment populations of red-backed voles (P = 0.02) but not deer mice (P = 0.18) during posttreatment years. Mean Jolly-Seber estimates of survival of red-hacked voles (P = 0.01) but not deer mice (P = 0.70) were higher in treatment than control populations. The magnitude of observed demographic effects from herbicide treatment were well within the mean values of natural fluctuations of these variables. Herbicide treatment of areas dominated by early-successional vegetation in northern coniferous forests should be staggered in time and space to allow recovery (2-3 yr) of vegetation and small mammal species sucl as red-backed voles and shrews.