Kyle Rodman: Rocky Mountain forests & bark beetle outbreaks

Throughout April, we are featuring the articles shortlisted for the 2022 Harper Prize. The Harper Prize is an annual award for the best early career research paper published in Journal of Ecology. Kyle Rodman’s article ‘Rocky Mountain forests are poised to recover following bark beetle outbreaks but with altered composition‘ is one of those shortlisted for the award.

⭐️ About me

I was born in Colorado and spent a lot of my childhood camping, canoeing, and skiing with my family in the mountains near our home. When I was in high school, my first job was as a seasonal employee with an environmental non-profit (the Rocky Mountain Field Institute) in Colorado Springs, which then turned into a longer-term position that set me on the path of working in the environmental field. Among other projects, we spent a lot of time working in post-fire landscapes, attempting to slow the movement of sediment into reservoirs that served as the primary water source to nearby farms and cities. All of these experiences made me immensely interested in forests, ecological disturbances, and land management issues. I pursued graduate studies at Northern Arizona University and the University of Colorado Boulder, before doing a postdoctoral research position at the University of Wisconsin – Madison. I now live in Flagstaff, Arizona, where I work for the Ecological Restoration Institute, a federally funded institute with about 25 permanent employees. Our mission is to conduct research on forests of the western United States, with the goal of informing more effective management of these important ecosystems. In my current role, I am a forest ecologist and biogeographer, and I use a range of tools for research, from remote sensing and GIS to field research and tree-ring methods. I’m particularly interested in quantifying the effects of disturbances such as wildfire and bark beetle (Curculionidae: Scolytinae) outbreaks in forests, and understanding the role that they might play in re-shaping ecosystems across the earth.

Figure 1: Map of the study area and sampled field plots (white circles) in the Southern Rocky Mountains, USA (grey polygon). Colors (orange to purple) indicate the remotely sensed severity of bark beetle outbreaks from 1997 to 2019.

🌲 About the shortlisted article

Like many parts of Europe and North America, forests of the US Rocky Mountains have experienced rapid and widespread changes due to outbreaks of native bark beetles. Though these insects are the size of just a single grain of rice, they work together to overwhelm the defenses of trees across entire forested landscapes. In fact, a handful of bark beetle species have killed nearly four billion trees across the western United States in just the past two decades. These outbreaks are due to warming temperatures and increasing aridity, which enhance survival and reproduction of many bark beetle species and also reduce the ability of trees to defend themselves. Bark beetle activity has now largely subsided in the Rocky Mountains, but their effects have left behind forested landscapes that are substantially different than those that were present just 20 years ago.

In 2022, we published a study in the Journal of Ecology which sought to answer the question – What comes next for these landscapes? The study combined field data collected for 16 past studies in particular parts of the US Rocky Mountains. We used these data with process-based and empirical statistical models to better understand how three species of bark beetle (Dendroctonus ponderosae, Dendroctonus rufipennis, and Dryocoetes confusus) have altered the structure and composition of Rocky Mountain forests. While bark beetles have caused tree mortality across ~20% of all forests in the region, they primarily colonize larger trees of their preferred host species. For this reason, many smaller trees and non-host species are left behind, even under the most severe outbreaks.

Our study illustrates that these surviving trees are often sufficient for forests to regain a structural state similar to what was present before outbreaks. Likewise, the remaining trees are growing rapidly following outbreaks, which may maintain the role of these forests as an important carbon sink. Notably, tree species composition has shifted across the region due to beetle-caused tree mortality, which may set the stage for future outbreaks of other insects and pathogens. This study provides a detailed picture of the effects that bark beetles have had across forest landscapes with a diversity of tree species and environmental conditions.

Figure 2: Shifts in live (a) size structure and (b) species composition in field plots affected by bark beetle outbreaks throughout subalpine forests in the Southern Rocky Mountains, USA. In (a), circles give the quadratic mean diameter (QMD) for each species before (1990s) and after (2010s) major outbreaks, including all trees and saplings (≥ 1.4 m in height). In (b), stacked bars show the percentage of field plots in which a species was dominant (i.e., greatest live basal area) pre-outbreak, post-outbreak, and in the future (based on 30-year runs of the Forest Vegetation Simulator); ribbon widths show the portion of plots following each trajectory. “No Trees/Saplings” plots had no individuals ≥ 1.4 m in a given period.

Find Kyle on Google Scholar.

Read the full list of articles shortlisted for the 2022 Harper Prize here.

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