Forest Research: Open Access
Open Access

Abstract

Bark Beetle Demography in Sierra Nevada Mixed Conifer: Variability and Influencing Factors

Walker RF, Swim SL, Fecko RM, Johnson DW and Miller WW

Multiple forest health variables were examined in an eastern Sierra Nevada mixed conifer stand, principal among them bark beetle demography. As indicated by pitch tube counts, California white fir (Abies concolor var. lowiana [Gord.] Lemm.), the predominant species, was colonized prodigiously compared to Jeffrey pine (Pinus jeffreyi Grev. and Balf.) and sugar pine (Pinus lambertiana Dougl.). Across host species, pitch tube abundance was positively related to white fir prevalence and negatively related to tree species diversity. Bark beetles preferentially attacked trees of small to medium DBH in white fir and sugar pine. Attack intensity in small Jeffrey pine was positively correlated with stand basal area and biomass and that in sugar pine of medium size was positively correlated with basal area also. Minor mistletoe infestations were detected in white fir along with incense-cedar (Libocedrus decurrens Torr.) and California red fir (Abies magnifica A. Murr.), with bark beetle colonization in the smallest and largest white fir positively related to the percentage of this fir thus infested. Mortality in white fir and Jeffrey pine irrespective of size was positively correlated with the pitch tube count in the largest white fir regarding the former and with total tree count regarding the latter.