Mountain Pine Beetle Impacts on Carbon Cycling

Science Center Objects

In the Southern Rocky Mountains, an epidemic outbreak of mountain pine beetle (Dendroctonus ponderosae; MPB) has caused forest mortality on a scale unprecedented in recorded history. The impacts of insect-induced mortality have only recently received attention, although other disturbances such as fires and land-use change have a strong influence on carbon sequestration and can result in a net release of carbon to the atmosphere. Ongoing insect outbreaks in British Columbia and the Rocky Mountains are an order of magnitude greater in area than historic outbreaks, and are approaching the extent of area affected by fire. Recent evidence also suggests that a warming climate has allowed some species to expand their range and contributed to increases in outbreak severity and extent and these trends are likely to continue under predicted climate changes.

This study, initiated in 2010, aims to increase our understanding of MPB outbreaks and their biogeochemical impacts. We are working to integrate field and remotely sensed monitoring datasets with vegetation and biogeochemical simulation models to assess and quantify how landscape scale patterns of carbon sequestration have and will change.

Figure 1: Plot of the trees in the study area

Figure 1

Research Objectives:

Objective 1: Quantify changes in biogeochemical cycling in the Southern Rocky Mountain forests in relation to the severity of mountain pine beetle outbreaks

Objective 2: Develop remote sensing approaches for monitoring and assessing broad-scale impacts of MPB outbreaks on biogeochemical cycling

Objective 3: Develop dynamic models to predict how MPB outbreaks will affect long-term forest vegetation succession and structure, and the consequences for biogeochemical cycling

Objective 4: Develop predictive models identifying where future MPB outbreaks are likely, and the resulting impacts on biogeochemical cycling

Approach:

To address the research objectives of this study, a combination of field data, remotely sensed data, and ecosystem, habitat suitability, and biogeochemical simulation models are being used, including:

  • Forest vegetation data collected at 119 plots located in eastern Grand County, CO study area (Figure 1). These data include individual species, status, size, and biomass for large trees, saplings, and seedlings, as well as, downed woody debris, fuel loads, and understory vegetation.
  • Light Detection and Ranging (LIDAR) data to monitor the extent and severity of the MPB outbreak and provide wall-to-wall input data on vegetation structure for modeling efforts.
  • Tree-growth models (Forest Vegetation Simulator) to track vegetation regrowth and changes in biogeochemical cycling and carbon stocks following MPB outbreaks.
  • Habitat suitability models to forecast when and where future MPB outbreaks will occur in response to climate and vegetation change.
Figure 2: Graph of percent of live biomass

Figure 2

Project Status:

In FY2010, field sampling and LIDAR data collection were completed. Initial results indicate that the MPB outbreak caused a 72% decrease in aboveground live biomass (Figure 2).

In FY2011, Tree-growth and succession models were parameterized with field data and used to simulate long-term (200-year) changes in carbon storage using the Forest Vegetation Simulator (FVS). Initial results suggested that standing live carbon would return to pre-outbreak conditions by 2060-2070.

Figure 3: Graph of standing live carbon

Figure 3

In FY2012, additional simulations were completed to compare and contrast impacts of the MPB outbreak with a scenario assuming no outbreak had occurred and another scenario simulating a severe wildfire. Results of these additional simulation, suggest that the impacts of the MPB outbreak on carbon stocks in standing-live biomass was nearly as severe as a wildfire (Figure 3). However, carbon and vegetation recovery after the MPB outbreak is more rapid than after wildfire because of the large amount of advanced regeneration present in forests affected by MPB.