Natural potential vegetation broadly distributed throughout the Boreal and Temperate North American territories is globally studied, basically following the Braun-Blanquet phytosociological methodology. Potential coniferous forests and their respective deciduous secondary woodlands are characterized and systematized according to bioclimatic features, biogeographic distribution, as well as floristic and dynamic patterns. All the potential climactical plant communities are included in a broad, and newly-proposed phytosociological class: Linnaeo americanae-Piceetea marianae, which comprises eight orders, nineteen alliances and sixty-four associations. This monograph also includes a comprehensive compilation of bioclimatic and biogeographic syntheses: The Worldwide Bioclimatic Classification System, the Worldwide Biogeographic Approach at regional level, the Synoptic Biogeographic Approach of America at provincial level and the Synoptic Biogeographic Approach of North America North of Mexico at subsectorial level. Several thematic maps are given (including an attached and newly-proposed biogeographic map of North America), as well as some original vegetation transections (catenas), various original keys to identify the diversity of potential plant communities, a checklist of the characteristic species and plant names used and finally, the bibliographic references. This monograph on North America Boreal and Western Temperate potential natural vegetation follows that previously published (Itinera Geobot. 10: 5-148. 1997) on Mediterranean and Tropical vegetation in Western and South-Western United States North of Mexico (Heteromelo arbutifoliae-Quercetea agrifoliae, Calocedro decurrentis-Pinetea jeffreyi, Prosopido torreyanae-Fouquierietea splendentis and Artemisio tridentatae-Juniperetea osteospermae classes).

North American Boreal and Western temperate forest vegetation: (Syntaxonomical synopsis of the potential natural plant communities of North America, II)

Highlight There is a close relationship between root system characteristics and the relative fire resistance of douglasfir forest zone species in southern interior British Columbia. Susceptible species are usually those that have fibrous root systems or produce stolons or rhizomes which grow above mineral soil. Moderately resistant species usually have fibrous roots with rhizomes which grow less than 5 cm below the mineral soil surface. Resistant species are those that have rhizomes which grow between 5 and 13 cm below the mineral soil surface and those species with taproots which are able to regenerate from below their crowns. Both timber milkvetch and lupine are undesirable range plants and yet both may increase after a fire. Fire has been a significant factor affecting plant composition and forage values on forest ranges of the douglasfir zone in southern British Columbia (Tisdale and McLean, 1957). It has been recognized that relatively few generalizations can be made about fire successions since so many conditions of the soil and living organisms affect the survival and invasion of plant species as a result of burning (Ah&en and Ahlgren, 1960). Nevertheless, in studying range management in southern British Columbia it has been necessary to attempt to predict the plant composition of forested areas following fires. As a result, studies to this end are underway at the CDA Research Station, Kamloops, on both controlled and wild burns. Two main processes are operative in the post-fire succession on any area, namely, regeneration either from underground reproductive structures or viable seed present in the soil and invasion by wind-, animal-, or bird-disseminated seed. The present study is an attempt to predict and explain, to some degree at least, the relative fireresistance of species as influenced by their root structure.

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Fire Resistance of Forest Species as Influenced by Root Systems.

Five vegetation zones were recognized in the Similkameen Valley of southern British Columbia. These zones were largely controlled by elevation primarily as a reflection of climate. The climate becomes progressively more moist from east to west and with increasing elevation. Two habitat types were described in the Artemisia tridentata zone, three in the Pinus ponderosa zone, five in the Pseudotsuga menziesii zone, five in the Abies lasiocarpa zone, and one in the Alpine zone. Some habitat types correlated well with the soils at a great group level. The Pinus—Festuca habitat type was found mostly on Dark Gray soils, the Pseudotsuga—Festuca habitat type on a variety of soils, the Pseudotsuga—Calamagrostis habitat type on Gray Luvisols, the Festuca—Eriogonum habitat type on Black Chernozems, the Abies—Vaccinium—Calamagrostis habitat type on Dystric Brunisols, and the Abies—Vaccinium, Phyllodoce habitat type on Alpine Dytsric Brunisols soils. A key for the identification of the major habitat types is included....

Plant communities of the Similkameen Valley, British Columbia, and their relationships to soils.

Deer and cattle grazing in spring preferred bluebunch wheatgrass plants that had been defoliated the previous fall to those that had not. Deer selected burned plants in greater proportion than grazed plants. Fall grazing by cattle affected the distribution of deer. Deer displayed preference for the fall grazed field after green growth exceeded the height of stubble. The increasing costs of cultural energy and the loss of arable land to urban development will put greater pressure on rangeland to meet future demands for food. The response of rangeland managers can be to increase the efficiency of converting forage into products for human consumption. Studies have shown that utilization of spring forage can be increased by removing litter prior to grazing (Willms et al. 1979) thus shifting the optimum grazing pressure to a higher level. Observations were made on tame deer and cattle in small enclosures. They demonstrated increasing preference for forage from the control, to the clip, to the burn treatment. In order to examine the treatment effects on free-ranging animals, three studies were made. The objectives were: to determine the effects of fall grazing or burning on selection of bluebunch wheatgrass by free-ranging deer or cattle in spring and to determine the influence of fall grazing on the distribution of deer in spring.

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The effects of fall defoliation on the utilization of bluebunch wheatgrass and its influence on the distribution of deer in spring.

This study examines spatially variable stand structure and fire-climate relationships at a low elevation forest-grassland ecotone in west central British Columbia, Canada. Fire history reconstructions were based on samples from 92 fire-scarred trees and stand demography from 27 plots collected over an area of about 7 km2 . We documented historical chronologies of widespread fires and localized grassland fires between AD 1600 and 1900. Relationships between fire events, reconstructed values of the Palmer Drought Severity Index, and annual precipitation were examined using superposed epoch and bivariate event analyses. Widespread fires occurred during warm, dry years and were preceded by multiple anomalously dry, warm years. Localized fires that affected only grassland-proximal forests were more frequent than widespread fires. These localized fires showed a lagged, positive relationship with wetter conditions. The landscape pattern of forest structure provided further evidence of complex fire activity with multiple plots shown to have experienced low-, mixed-, and/or high-severity fires over the last four centuries. We concluded that this forest-grassland ecotone was characterized by fires of mixed severity, dominated by frequent, low-severity fires punctuated by widespread fires of moderate to high severity. This landscape-level variability in fire-climate relationships and patterns in forest structure has important implications for fire and grassland management in west central British Columbia and similar environments elsewhere. Forest restoration techniques such as prescribed fire and thinning are oftentimes applied at the forest-grassland ecotone on the basis that historically high frequency, low-severity fires defined the character of past fire activity. This study provides forest managers and policy makers with important information on mixed-severity fire activity at a low elevation forest-grassland ecotone, a crucial prerequisite for the effective management of these complex ecosystems.

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A. McLean

Papers

The Douglas‐Fir Zone of Southern Interior British Columbia