Canadian Forest Service Publications

Abundance of secondary structure in lodgepole pine stands affected by the mountain pine beetle in the Cariboo-Chilcotin. 2009. Coates, K.D.; Glover, T.; Henderson, B. Natural Resources Canada, Canadian Forest Service, Pacific Forestry Centre, Victoria, BC. Mountain Pine Beetle Working Paper 2009-20. 37 p.

Year: 2009

Available from: Pacific Forestry Centre

Catalog ID: 31195

Language: English

Series: Mountain Pine Beetle Working Paper (PFC - Victoria)

CFS Availability: Order paper copy (free), PDF (download)


The extent and abundance of secondary structure was studied in the Cariboo-Chilcotin region of the central interior of British Columbia. Plots were selected from age class 4 and higher pine stands in the Quesnel, Williams Lake, and 100 Mile House Timber Supply Areas. A total of 1,649 plots were established, of which 1,109 were determined to be pine-leading. Secondary structure included all understorey and overstorey trees that survive the current mountain pine beetle epidemic. All lodgepole pine trees 7.5 cm in diameter or greater were assumed to die in the epidemic. The forest health status of a large dataset of individual trees was also summarized. Secondary structure was abundant in all biogeoclimatic zones of the Cariboo-Chilcotin and was consistent with pine-leading stands elsewhere in British Columbia. Conifer seedlings and saplings had a median density of 1800 stems per ha. This varied from a high of 4,700 stems per ha in the Engelmann Spruce-Subalpine Fir zone to a low of 1019 stems per ha in the Sub-Boreal Spruce zone. Across all ecological units, about 70% of sample plots in pine-leading stands exceeded a 1000 stems per ha threshold for understorey conifer seedling and sapling density. Species composition of the understorey tree layer varied considerably in each biogeoclimatic zone. Lodgepole pine was by far the most common understorey tree species in the Montane Spruce and Sub-Boreal Pine-Spruce zones (79% and 74%, respectively). About 34% of all plots had at least 5 m2 ha-1 of secondary structure basal area, varying from 25% in the Sub-Boreal Spruce zone to 57% in the Engelmann Spruce-Subalpine Fir zone. Substantial amounts of the secondary structure basal area were found on non-merchantable stems. The relationship between overstorey pine basal area and non-merchantable secondary structure basal area was poor. Assumptions about non-merchantable secondary structure basal area cannot be based on the proportion of overstorey pine basal area. There was also little evidence to support a relationship between the average piece size of lodgepole pine and the basal area of non-merchantable secondary structure. Across the ecological units, 31%-68% of pine-leading stands currently have secondary structure equivalent to or better than a 20-year-old pine plantation. The forest health of secondary structure was examined. Damage data are difficult to summarize, as not all damage agents are equal. Understorey pine trees (seedlings and saplings) averaged 3.3% infection by mistletoe across all ecological units. Fewer than 10% of all understorey pine trees were damaged, whereas just fewer than 20% of all understorey interior spruce were, though often of a minor nature. Sub-canopy and canopy secondary structure trees (non-pine species) had similar or more damage than the same species in the understorey. The variable levels of secondary structure found in the Cariboo-Chilcotin provide considerable management flexibility. The suitability of managing the secondary structure will depend on the value being considered (e.g., timber supply and hydrological recovery period).

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