Interactions among phytophagous insect species colonizing cones of white fir (Abies concolor)

Summary The insect complex colonizing white fir (Abies concolor [Gord. and Glend.] Lindl.) cones is composed of eleven species that can be separated into three feeding guilds: the seed-mining guild, Megastigmus pinus Parfitt, M. rafni Hoffmeyer, Earomyia abietum McAlpine; the cone-and seed-mining guild, Dioryctria abietivorella Grote, Eucosma prob. siskiyouana (Kearfoot), Cydia prob. bracteatana (Fernald), Barbara sp.; the scale-and bract-feeding guild, Asynapta hokinsi (Felt), Dasineura prob. abiesemia Foote, Ressiliella conicola (Foote), Lasiomma abietis Huckett). In three of four study sites the cone crop decreased from one year to the next. As cone crop size decreased there was a concomitant increase in the percent of cones with more than one species. In addition, there was a shift toward an increased co-occurrence of members of different guilds within a single cone. Both positive and negative interactions were detected between selected species-pairs. Present-day competition was only inferred between species-pairs belonging to the cone and seed-mining guild. Decreasing resources over time, combined with increasing insect populations and the absence of acceptable alternate hosts appeared to be important factors for setting conditions conducive to interspecific competition. It is hypothesized, that the aperiodicity of white fir cone crops was important in keeping insect populations below levels which would result in interspecific competition. The possible elimination of aperiodicity in cone crops of white fir, such as might occur in managed seed orchards, may lead to decreased species diversity via competitive exclusion and thereby simplify development of IPM programs.     

Ectomycorrhizal morphotypes of naturally grownAbies firma seedlings

Ectomycorrhizas of naturally grown Momi fir (Abies firma) seedlings were characterized based on morphological features of fungal partners. A total of 128 seedlings were collected over three years (1995–1997) from a 10×30 m plot where occurrences of ectomycorrhizal fungal fruitbodies were monitored for the same period. Thirty-seven morphologically distinct ectomycorrhizal types were distinguished based mainly on the color of ectomycorrhizas and the characteristics of fungal mantles. Type 37 was thought to beCenococcum geophilum because of the jet-black mycorrhizas and the characteristic structure of mantle surfaces. For half of the classified morphotypes, fungal partners were inferred to be the generaLactarius, Russula, andTuber, and unidentified Basidiomycetes, based on earlier references.     

Relationships between change in fire frequency and mortality due to spruce budworm outbreak in the southeastern Canadian boreal forest

Abstract. We present a simple empirical model that allows an estimation of mortality due to spruce budworm (Choristoneura fumiferana) outbreak in relation to fire frequency and site characteristics. The occurrence of a recent spruce budworm outbreak around Lake Duparquet (48° 30’N, 79° 20’W, ca. 300 m a.s.l.) in northwestern Québec permitted a reconstruction of the stand composition before the outbreak, and also of the mortality of Abies balsamea due to the outbreak. The basal area of A. balsamea increases with time since fire in all site types but with increasing values for (1) rock and shallow till, via (2) till and mesic clay up to (3) hydric clay. Mortality (measured as percentage loss of basal area due to the outbreak) increases with time since fire but did not vary with site type. The increasing abundance of A. balsamea with time since fire is mainly responsible for this increase in mortality. Mortality for a specific basal area is, however, lower for the more recently burned stands suggesting a significant residual effect of time since fire. A landscape model integrating mortality due to the outbreak for stands of different age is developed. Both absolute and relative losses of basal area increased with the length of the fire cycles. According to this model, changes in fire cycle could explain a large portion of the spatio-temporal variations observed in outbreak mortality in the southeastern boreal forest of Canada.