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

Citation

Rodman, Kyle et al. (2021), Data from: Effects of Bark Beetle Outbreaks on Forest Landscape Pattern in the Southern Rocky Mountains, U.S.A., Dryad, Dataset, https://doi.org/10.5061/dryad.1rn8pk0sn

Abstract

Since the late 1990s, extensive outbreaks of native bark beetles (Curculionidae: Scolytinae) have affected coniferous forests throughout Europe and North America, driving changes in carbon storage, wildlife habitat, nutrient cycling, and water resource provisioning. Remote sensing is a crucial tool for quantifying the effects of these disturbances across broad landscapes. In particular, Landsat time series (LTS) are increasingly used to characterize outbreak dynamics, including the presence and severity of bark beetle-caused tree mortality, though broad-scale LTS-based maps are rarely informed by detailed field validation. Here we used spatial and temporal information from LTS products, in combination with extensive field data and Random Forest (RF) models, to develop 30-m maps of the presence (i.e., any occurrence) and severity (i.e., cumulative percent basal area mortality) of beetle-caused tree mortality 1997-2019 in subalpine forests throughout the Southern Rocky Mountains, USA. Using resultant maps, we also quantified spatial patterns of cumulative tree mortality throughout the region, an important yet poorly understood concept in beetle-affected forests. RF models using LTS products to predict presence and severity performed well, with 80.3% correctly classified (Kappa = 0.61) and R2 = 0.68 (RMSE = 17.3), respectively. We found that ≥ 10,256 km2 of subalpine forest area (39.5% of the study area) was affected by bark beetles and 19.3% of the study area experienced ≥ 70% tree mortality over the twenty-three year period. Variograms indicated that severity was autocorrelated at scales < 250 km. Interestingly, cumulative patch-size distributions showed that areas with a near-total loss of the overstory canopy (i.e., ≥ 90% mortality) were relatively small (< 0.24 km2) and isolated throughout the study area. Our findings help to inform an understanding of the variable effects of bark beetle outbreaks across complex forested regions and provide insight into patterns of disturbance legacies, landscape connectivity, and susceptibility to future disturbance.

Methods

Data were collected using a range of techniques. Field data include 239 field inventory plots of live and dead forest structure in sites affected by bark beetles c. 1990s to 2010s. Spatial data include spectral indices derived from Landsat time series, calculated using the Google Earth Engine implementation of the LandTrendr temporal segmentation algorithm.

Data were processed by summarizing the total live and dead tree basal area in each field plot, and converting these numbers to percent basal area mortality. LandTrendr products were extracted to each field plot by summing the magnitude of all identified spectral declines from 1996-2019 for each spectral band/index at each field plot location.

For information on data processing, see "README.md" and refer to the original paper.

Usage Notes

We place no restrictions on the use of these data. See "README.md" and original paper for usage notes. Please contact the study authors with any additional questions regarding the use of these data.

Funding

National Science Foundation, Award: 1030845

National Science Foundation, Award: 1262687

National Science Foundation, Award: 1262691

National Science Foundation, Award: 1634163

National Science Foundation, Award: 1637686

National Science Foundation, Award: 1853520

National Aeronautics and Space Administration, Award: NNX16AH58G