# Predicting the Potential Geographical Distribution of Scolytus scolytus in China Using a Biomod2-Based Ensemble Model

## TL;DR

This study predicts the future spread of the bark beetle Scolytus scolytus in China using climate models, highlighting the need for biosecurity measures to prevent Dutch elm disease.

## Contribution

The study introduces an ensemble model using Biomod2 to predict the beetle's distribution under current and future climate scenarios in China.

## Key findings

- Currently, only 37,883 km2 in China are marginally suitable for Scolytus scolytus.
- Future climate scenarios predict a significant expansion of suitable habitats, especially in coastal regions.
- Medium and high-suitability zones may emerge by mid-century under high-emission climate scenarios.

## Abstract

The bark beetle Scolytus scolytus, a major vector of Dutch elm disease, threatens elm trees globally. Our study employed advanced ecological modeling to assess its potential distribution across China under current and future climate conditions. The results reveal that while most of China currently offers only marginally suitable habitats (37,883 km2), concentrated primarily in eastern coastal areas, climate change may significantly expand these ranges. By the mid-21st century, moderate-suitability zones could grow substantially, particularly under high-emission scenarios, with new risk areas emerging in central and southern provinces. These projections emphasize the growing invasion risk and underscore the urgency for strengthened border biosecurity, targeted surveillance in vulnerable regions, and proactive management strategies to safeguard China’s ecologically and economically important elm resources.

Dutch elm disease is one of the most devastating plant diseases, primarily spread through bark beetles. Scolytus scolytus is a key vector of this disease. In this study, distribution data of S. scolytus were collected and filtered. Combined with environmental and climatic variables, an ensemble model was developed using the Biomod2 platform to predict its potential geographical distribution in China. The selection of climate variables was critical for accurate prediction. Eight bioclimatic factors with high importance were selected from 19 candidate variables. Among these, the three most important factors are the minimum temperature of the coldest month (bio6), precipitation seasonality (bio15), and precipitation in the driest quarter (bio17). Under current climate conditions, suitable habitats for S. scolytus are mainly located in the temperate regions between 30° and 60° N latitude. These include parts of Europe, East Asia, eastern and northwestern North America, and southern and northeastern South America. In China, the low-suitability area was estimated at 37,883.39 km2, and the medium-suitability area at 251.14 km2. No high-suitability regions were identified. However, low-suitability zones were widespread across multiple provinces. Under future climate scenarios, low-suitability areas are still projected across China. Medium-suitability areas are expected to increase under SSP370 and SSP585, particularly along the eastern coastal regions, peaking between 2041 and 2060. High-suitability zones may also emerge under these two scenarios, again concentrated in coastal areas. These findings provide a theoretical basis for entry quarantine measures and early warning systems aimed at controlling the spread of S. scolytus in China.