This folder contains ASCII text raster files describing the pine density model and yearly aerial detection survey (ADS) data for three study areas: Sawtooth (central Idaho, USA), Chelan (north-central Washington, USA) and Northern Colorado (USA). These data supported analyses presented in

Powell, J.A., M.J. Garlick, B.J. Bentz and N.A. Friedenberg. (2017) Differential Dispersal and the Allee Effect Create Power-Law Behavior: Distribution of Spot Infestations During Mountain Pine Beetle Outbreaks. Journal of Animal Ecology.

Each raster is at 30m resolution, and each pixel is a density in a space-separated ascii file. The top five rows of each file are commented using % (Matlab comment) and contain: number of columns in the raster, number of rows in the raster, UTM for horizontal location of lower left corner UTM for vertical location of lower left corner NODATA value

Separate readme files are in each subdirectory. The zipped file contains:

1 PDF: Crabb_RP_93WWW.pdf (Crabb et al. 2012)

1 general readme: MPB_Spot_ASCIIs.txt

Chelan subdirectory: 20 ADS ASCII tab-separated rasters (2401 x 2067, 9.77MB each) of tree per hectare impact (1990-2009) + 1 pine cover raster (ca 2001) + 1 readme.txt file

No. Colorado subdirectory: 10 ADS ASCII tab-separated rasters (9259 x 8924, 160MB each) of tree per hectare impact (2001-10) + 1 pine cover raster (ca 2003) + 1 readme.txt file

Sawtooth subdirectory: 10 ADS ASCII tab-separated rasters (2076 x 1437, 22.9MB each) of tree per acre impact (1995-2004) + 1 pine cover raster (ca 2001) + 1 readme.txt file

Author ORCID Identifier

James A. Powell 0000-0002-0594-0136



Document Type




File Format


Publication Date



USDA Western Wildland Threat Assessment Center

USDA, Cooperative State Research, Education, and Extension Service (CREES)


Utah State University

Award Number

USDA Western Wildland Threat Assessment Center 09-JV-11221633-240; USDA, Cooperative State Research, Education, and Extension Service (CREES) SBIR 2009-01116

Award Title

Landscape-Scale Enhanced Mountain Pine Beetle and Climate Change Threat Assessment (Western Wildland) and Forest Pest Risk in Dynamic Landscapes (CREES)


Aerial Detection Survey data depicting MPB impact as polygons was converted into ASCII rasters with 30 meter pixels. Pine cover density data from a variety of sources was also projected onto 30 meter scales. Data processing is described in detail in:

Crabb, B.A.; Powell, J.A.; Bentz, B.J. (2012) Development and assessment of 30-m pine density maps for landscape-level modeling of mountain pine beetle dynamics. Res. Pap. RMRS-RP-96WWW. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 43 p. (included in archive).

Scientfic Names

Dendroctonus ponderosae Hopkins

Referenced by

Powell JA, Garlick MJ, Bentz BJ, Friedenberg N. Differential dispersal and the Allee effect create power-law behaviour: Distribution of spot infestations during mountain pine beetle outbreaks. J Anim Ecol. 2018; 87:73–86.


48.10246, -120.26881 40.40913, -105.83095 44.10315, -114.88954



Code Lists

MPB - mountain pine beetle

ADS - aerial detection survey

TPH - trees per hectare

TPA - trees per acre

FIA - Forest Inventory Analysis


Mountain pine beetles (MPB, Dendroctonus ponderosae Hopkins) are aggressive insects attacking Pinus host trees. Pines use defensive resin to overwhelm attackers, creating an Allee effect requiring beetles to attack en masse to successfully reproduce. MPB kill hosts, leaving observable, dying trees with red needles. Landscape patterns of infestation depend on MPB dispersal, which decreases with host density. Away from contiguously impacted patches (low beetle densities), infestations are characterized by apparently random spots (of 1-10 trees). It remains unclear whether the new spots are spatially random eruptions of a locally endemic population or a mode of MPB spread, with spatial distribution determined by beetle motility and the need to overcome the Allee effect. To discriminate between the hypothesis of population spread versus independent eruption, a model of spot formation by dispersing beetles facing a local Allee effect is derived. The model gives rise to an inverse power distribution of travel times from existing outbreaks. Using landscape-level host density maps in three study areas, an independently-calibrated model of landscape resistance depending on host density, and aerial detection surveys (data included in this archive), we calculated yearly maps of travel time to previous beetle impact. Isolated beetle spots were sorted by travel time and compared with predictions. Random eruption of locally endemic populations was tested using artificially-seeded spots. We also evaluated the relationship between number of new spots and size of the perimeter of previously infested areas. Spot distributions conformed strongly to predicted power-law behavior. The spatially random eruption hypothesis was found to be highly improbable. Spot numbers grew consistently with perimeter of previously infested area, suggesting that MPB spread long distances from the boundary via spots following an inverse power distribution. The Allee effect in MPB therefore accelerates, rather than limits, invasion rates, contributing to recent widespread landscape-scale mortality in western North America.


Ecology and Evolutionary Biology


Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.



Additional Files

Powell_README (6 kB)
MD5: 318cbd66a090c1e85307d8efa83103ec (158290 kB)
MD5: 5d0020712b09a0d8e5bf5f33c3a45b4b


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