Within-Stand Distribution of Tree Mortality Caused by Mountain Pine Beetle, Dendroctonus ponderosae Hopkins

Abstract

The mountain pine beetle (MPB) (Dendroctonus ponderosae) is a bark beetle that attacks and kills ponderosa pine (Pinus ponderosa), among other pine species throughout the western conifer forests of the United States and Canada, particularly in dense stands comprising large trees. There is information on the stand conditions that the insect prefers. However, there is a paucity of information on how small-scale variation in stand conditions influences the distribution of tree mortality within a stand. I examined the small-scale distribution of ponderosa pine basal area pre- and post a mountain pine beetle infestation, and used geostatistical modeling to relate the spatial distribution of the host to subsequent MPB-caused tree mortality. Results indicated increased mortality in the denser parts of the stand. Previous land management has changed historically open low-elevation ponderosa pine stands with aggregated tree distribution into dense stands that are susceptible to mountain pine beetles and intense fires. Current restoration efforts are aimed at reducing tree density and leaving clumps of trees, which are more similar to historical conditions. The residual clumps, however, may be susceptible to mountain pine beetle populations. Land managers will want to be cognizant of how mountain pine beetles will respond to restoration treatments, so as to prevent and mitigate tree mortality that could negate restoration efforts.

Geostatistical Analysis of the Spatial Variation of Chrysolina aeruginosa Larvae at Different Stages in Desert Ecosystems

“…The degree to which insects exhibit aggregation is influenced by various factors, such as vegetation cover, species interactions, plant characteristics, pest abundance, anthropogenic disturbance, landscape composition, and geographic area [5,[33][34][35][36][37][38][39][40][41]. Changes in vegetation cover in desert regions, which provides rich food resources and suitable habitats for desert insects, inevitably affect insect population patterns [42,43].…”

Restoration and fuel hazard reduction result in equivalent reductions in crown fire behavior in dry conifer forests

“…For example, certain wildlife species prefer the continuous vertical foliage created by tree groups with a multi‐layered canopy and mixture of tree sizes (Reynolds et al, 1992 ; Stephens et al, 2014 ), while such groups may be viewed as hazardous from a fire behavior perspective due to the vertical continuity of crown fuels (Graham et al, 2004 ; Johnson & Kennedy, 2019 ). Similarly, large groups of trees were a common component in some historical forest structures (Clyatt et al, 2016 ) but may also increase the risk of MPB mortality (Buonanduci et al, 2020 , Negrón, 2020 ), drought stress (van Mantgem et al, 2020 ), and torching potential (Ritter et al, 2020 ). These conflicting considerations speak to the complexity associated with the implementation of these approaches and suggest the need to carefully consider the various trade‐offs.…”

Effects of Bark Beetle Outbreaks on Forest Landscape Pattern in the Southern Rocky Mountains, U.S.A.

“…Typically, bark beetles persist at low population levels and attack damaged or weakened trees (i.e., endemic conditions); outbreaks are initiated by population irruptions that require abundant susceptible hosts as well as suitable climate conditions [3,15,16]. Beetles in the genera Dendroctonus and Dryocoetes, which are responsible for much of the recent tree mortality in U.S. Rocky Mountain forests, preferentially target denser stands with larger trees, higher stem density, and greater host-tree abundance [17][18][19][20]. Given a suitable landscape, outbreaks may be incited by warm temperatures and drought conditions which increase tree susceptibility to attack and enhance larval development and overwinter survival [20][21][22][23].…”