Defoliator outbreaks track with warming across the Pacific coastal temperate rainforest of North America

The biogeography of irruptive insect herbivores is determined by host availability and climate conditions. As such, outbreak distributions are sensitive to climatic change, especially across large latitudinal gradients. Here, we investigate the outbreak distributions of two understudied defoliators, hemlock sawfly (Hymenoptera; Neodiprion tsugae) and western blackheaded budworm (Lepidoptera; Acleris gloverana), that have both recently impacted the greatest land area recorded across the Pacific coastal temperate rainforest since the establishment of aerial survey programs. We compiled polygon-based estimates of insect damage collected by aerial observers, forest inventory, and downscaled climatic data to develop gridded estimates of bioclimatic conditions across the extent of the Pacific coastal temperate rainforest, including the continental United States, British Columbia, and Alaska. We leveraged these data to develop ensemble machine learning models with the goal of predicting the ou..., Data
Aerial surveys
We compiled aerial detection survey data describing the extent of tree damage from insects and diseases. These data were collected by aerial observers in fixed-wing aircrafts by the United States Forest Service (i.e., Alaska and the western Continental United States (CONUS); United States Detection Survey Data) and the British Columbia (BC) Ministry of Forests (British Columbia Overview Survey Data). We calculated the presence/absence of outbreak populations of hemlock sawfly and western blackheaded budworm by intersecting annual polygon and point detection survey data with a 0.25 km2 grid. Grid cells that contained any visible defoliation were listed as affected. Aerial detection data were available for different time periods in each region of our analysis (Alaska: 1989-2022, BC: 1960-2022, CONUS: 1997-2022).
Forest Structure
We compiled forest structure data from raster-based estimates of hemlock (spp.) and spruce (spp.) basal area over Alaska and CONUS (per acre; ..., Packages-All analyses were conducted in R (version 4.2.0). Integral packages included: tidyverse (wrangling; (Wickham et al. 2019), terra (geospatial formatting; (Hijmans 2024), sf (geospatial formatting; (Pebesma 2018), stars (geospatial formatting; (Pebesma and Bivand 2023), and mlr (machine learning framework; (Bischl et al. 2016)., # Defoliator outbreaks track with warming across the Pacific coastal temperate rainforest of North America

Authors:

Michael Howe1,3, Elizabeth E Graham2, and Kellen N Nelson1

1 Juneau Forestry Sciences Laboratory, Pacific Northwest Research Station, USDA Forest Service, 11175 Auke Lake Way, Juneau, AK 99801

 2 Forest Health Protection, State, Private, & Tribal Forestry, USDA Forest Service, 11175 Auke Lake Way, Juneau, AK 99801

 3 Oak Ridge Institute for Science and Education, Oak Ridge, TN 37830

Corresponding author: [[e-mail]](mailto:[e-mail]).

 File list:

defol_data.tiff

Ecography_clean.Rmd

defol_df.csv

grid.hemlock.gpkg

akse.gpkg

na.map.gpkg

File Descriptions:

Ecography_clean.Rmd -- Analysis script. Contains code for models.

defol_data.tiff -- Spatial data for analysis.

defol_df.csv -- Tabular data for analysis.

grid.hemlock -- Spatial data that corresponds to defol_df

na.map -- Spatial data that serves as the basemap for Figure 1.
...