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USDA Bark Beetle



Bark Beetle Outbreaks

OBJECTIVE: Determine the unique ecological roles that bark beetle outbreaks play in forest ecosystem structure and function.

The relationship between host forests and D. ponderosae has co-evolved over countless millennia. In pre-European times, this relationship was most likely characterized by what Mattson (1996) has termed a "normative outbreak," a term which he used to describe outbreaks of a native insect that are "part and parcel of the normal plant biology." Post-European emphasis on the economic production of western forests has altered this normative relationship in two important ways. First, through interference with natural, co-evolved disturbance regimes, we have dramatically altered forest landscapes from their pre-European condition.

These changes in forest ecosystem structure and function have created conditions which seriously debilitate the capacity of the host to defend itself. Secondly, for various reasons post-European forest management has often attempted to maintain a status quo of current stand conditions that extends beyond the natural cycle of forest regeneration and renewal. The result of both management practices has been the same: vast acreages of highly vulnerable forests and the concomitant shift of normative outbreaks to maladaptive outbreaks where the insect is operating outside the natural range of adaptive variability. In order to formulate effective management tools for bark beetle disturbances we first need to more fully understand the ecological role that bark beetle disturbances play in the critical process of forest regeneration and subsequent successional trajectory.

In order to accomplish the goal of building an ecological knowledge base necessary for adaptive management, we first need to know what the historic (pre-European) range of natural variability was. We also need to understand and appreciate the ecological functions that bark beetle outbreaks perform in nutrient cycling and other critical ecosystem processes. Healthy forests result from disturbance legacies, and the legacy of a bark beetle disturbance is different than that from other natural (e.g. fire) or artificial (e.g. clear cut) disturbances. We need to more fully understand the unique legacy following a bark beetle disturbance by itself and acting in consort with other agents of natural disturbance, such as fire. The legacies of different disturbance agents have different consequences for various values such a recreation, wildlife, and ecosystem processes. Finally, we need to modify and link models developed under Problem 1 in order to evaluate and test long-term and large-scale alterations in disturbance regimes that may occur as a result of global change (both climate and land use).

Although we have initiated preliminary investigations regarding Problem 2, our current levels of funding are inadequate to fully support the research that is justified by the importance of these ecological issues to formulation of forest management plans. In order to adequately address this research problem, the addition of 1 project scientist (a specialist in insect ecology) and one Masters degree (in Forest Entomology) level technician is needed.

Accomplishments planned for the next 5 years:

Goal: Provide information that will allow discrimination between circumstances in which bark beetle disturbances provide positive, negative or neutral impacts on long-term sustainability and productivity.

(1) Begin characterization of the natural range of variability for bark beetle outbreaks.)

(2) Evaluate the long-term impacts of bark beetle management activities on stand structure and function.

(3) Establishment of long-term comparative studies of the impacts of bark beetle outbreaks under different management scenarios.


Forest and Woodland Ecosystems Science Program

Rocky Mountain Research Station and the USDA Forest Service, Logan Utah 84321

Webmaster: Jim Vandygriff


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