Mountain pine beetles: A century of knowledge, control attempts, and impacts central to the Black Hills

Abstract

This publication chronicles the understanding, controlling, and impacts of mountain pine beetles (MPB) central to the Black Hills of South Dakota and Wyoming from the time they were described by Hopkins in 1902, through the presentation of data from work started by Schmid and Mata in 1985. The plots established by these two men from 1985 through 1994 were subjected to the most intense MPB stress to occur since 1900 in the Black Hills. The differentiation of western bark beetle species is discussed and how the final species designations of MPBs and western pine beetles (WPB) came about. The life cycle of MPBs is described and how it was used to develop direct control strategies. Bark beetles carry from tree to tree with them a suite of mites, fungi, nematodes, bacteria, and other organisms that can be both antagonistic and beneficial to the bark beetle and several of these contribute to the death of the tree. The direct control efforts of peeling, burning, harvesting, and spraying trees with chemicals to kill WPBs and MPBs are described. Both Crater Lake and the Black Hills experiences to directly control MPBs are discussed. The millions of dollars that were spent to directly control both species of bark beetles were futile and indirect methods of tree and stand treatments were tried. In the Black Hills, Schmid and Mata established 46 MPB study plots, of which 39 were useable, beginning in 1985 with tree densities ranging from 44 feet2 of basal area per acre to 199 feet2 per acre. MPB-caused tree mortality commenced on some of the plots in 1985 and maximum tree densities occurring on the plots ranged from 75 feet2 of basal area per acre to 217 feet2. During this time, MPB populations within the Hills expanded and the fate of the trees on each plot is shown. Plots with densities over 150 feet2 of basal area per acre experienced major mortality as early as 1987 and all of the plots with densities of 90 feet2 of basal area per acre or greater experienced major mortality by 2010. Stands and landscapes within the Black Hills with tree densities ranging from 40 to 80 feet2 of basal area per acre showed considerable resistance to MPBs. Most likely these outcomes were related to the disruption of pheromone plumes facilitated by the open canopy conditions. However, there were exceptions to these findings currently and historically and they are discussed. This publication strives to synthesize a large portion of the information produced in the last 115 years on MPBs and provide this context for informing, planning, and executing forest treatments to produce MPB resilient forests. In addition, it tells an intriguing and fascinating story about bark beetles and the people who tried to understand and control them.