Whitebark pine forests in British Columbia : composition, dynamics and the effects of blister rust
Date
1998
Authors
Campbell, Elizabeth Marie
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Abstract
The composition, structure and dynamics of forests containing white bark pine (Pinus albicaulis Engel.) were investigated in 53 stands in British Columbia. Mountain pine beetle (Dendroctonus ponderosae) and white pine blister rust (Cronartium ribicola) distribution among stands and incidence (percentage of affected trees) within stands were also examined.
Variation in understory composition among stands was analyzed using non-metric multi-dimensional scaling. Compositional changes were strongly correlated with soil moisture, slope, elevation and longitude. UPGMA agglomerative clustering techniques were used to delineate 11 plot groups representing communities with understories dominated by: Vaccinium membranaceum (Groups A and B); Rhododendron albiflorum/Menziesiaferruginea/Vaccinium membranaceum (Group C); Vaccinium scoparium (Groups D, G, and H); Vaccinium myrtillus (Group E); Phyllodoce empetriformis (Group F); Xerophyllum tenax (Group D; and Juniperus communis (Groups J and K). Analogous communities are reported in the literature for Alberta and the United States. Whitebark pine was most abundant in Juniperus communis communities, in young stands, and at southern latitudes.
White pine blister occurred throughout the geographic range of white bark pine in British Columbia. It was found in at least 37 of the 53 stands sampled but probably occurred in 52 stands. The incidence of white pine blister rust infections ranged from 0-100% among stands. Only 7 of the 53 stands sampled had mountain pine beetle infestations and incidence of infestation in these stands was low ( < I% of trees). Whitebark pine mortality rates ranged from 0-64% over all stands. ANOVA and simple linear regression were used to elucidate patterns in white pine blister rust incidence and mortality. Variation in white pine blister rust incidence or mortality among stands could not be related to variations in regional climatic conditions or other site characters such as soil moisture, aspect, and elevation. Factors influencing the interception of basidiospores by individual white bark pine trees appeared more important. Incidence of infection was greatest in young, open stands and mortality was greatest in stands with low total tree density. Stands with Ribes present also had a greater incidence of infection. Large trees were more frequently infected than small trees but mortality was greatest among small trees.
Most recent fires in whitebark pine forests were stand-replacing, although some small trees survived fire. Whitebark pine, and sometimes lodgepole pine (Pinus contorta), established in abundance shortly after fire. Subalpine fir (Abies lasiocarpa) and Engelmann spruce (Picea engelmannii) also frequently colonized stands following fire but took longer to become abundant. The patterns of successional development following fire disturbance were influenced by the life history characteristics of each tree species, availability of seed sources, the nature of the disturbance, characteristics of the predisturbance vegetation, and characteristics of vegetation in the surrounding landscape. Forests containing whitebark pine developed along three major successional pathways; differences between the three pathways depended on the relative amounts of lodgepole pine establishing in post~fire stands (i.e. , none, some, and abundant lodgepole pine).