The vegetation, environment and occurrence of great gerbils in the survey site

The great gerbil (Rhombomys opimus), a pest rodent distributed in Central Asia, currently has the largest distribution area of all pest rodents in China. R. opimus affects an activity on the environment for two main reasons. On the one hand, R. opimus consumes desert vegetation to such an extent that the vegetation loses water and dies, while its burrowing behaviors significantly decrease surface plant coverage and aggravate regional desertification. On the other hand, R. opimus is the main host of rat plague, leishmaniasis (Leishmania major), and the Karimabad virus, which pose notable threats to human health.

This dataset provides essential monitoring information on the Great Gerbil (Rhombomys opimus) across 46 monitoring sites in Northwest China from 2020 to 2022. It includes data on local vegetation, climate, and the degree of damage observed.

The study sites cover four provinces in northwestern China, i.e., the Inner Mongolia Autonomous Region, Gansu Province, Ningxia Hui Autonomous Region, and Xinjiang Uygur Autonomous Region (36°58’N to 47°71’N and 82°56’E to 108°66’E). Monitoring records for the past several years have confirmed that these areas are the main active areas of R. opimus in China. The study area includes a variety of suitable habitats (e.g., steppe, Gobi, and desert) for R. opimus. These habitats mainly have temperate desert and steppe continental climates, with scarce rain, very dry conditions, strong solar radiation, high temperatures, and vigorous evaporation. 

Within the study area, we selected 46 1-ha sample plots to conduct surveys of the activity levels of R. opimus. All plots were confirmed to have recorded occurrences of R. opimus in 2019, and each plot was spaced at least 100 km2 apart, positioned as far away as possible from human settlements. This arrangement was intended to effectively represent the vegetation and environmental conditions of various R. opimus occurrence areas in China. During the trial period, no artificial disturbances, such as hand trapping or the release of poisonous baits, occurred in these 46 sample plots during the fall (September-November in the Northern Hemisphere) each year from 2020 to 2022. Rodent traps were constructed from medium-sized board clips (8 cm × 15 cm), with every 25 traps arranged in a straight line, spaced 5 m apart, and with a row spacing of 20 m, resulting in a total of 100 traps arranged in 4 rows side by side. The traps were collected after 24 hours of placement, and only the number of captured R. opimus individuals was recorded, without counting other rodent species; any loss of traps was considered an uncaptured rodent. Additionally, damaged plants were randomly selected from 100 shrubs within the sample plots, and only the number of plants damaged by R. opimus was recorded.

Methods
The selection of environmental data was mainly based on our early niche study on R. opimus, which included 14 types: the topsoil gravel content, elevation, topsoil silt fraction, topsoil organic carbon, topsoil pH (H2O), annual mean temperature, precipitation of wettest month, annual precipitation, mean temperature of wettest quarter, precipitation of warmest quarter, mean temperature of driest quarter. The vegetation data were obtained from field surveys at 46 monitoring sites. The age of the vegetation in the living area of R. opimus was summarized, i.e., shrubs less than 5 years old were considered young, shrubs 5-10 years old were considered middle-aged, and shrubs more than 10 years old were considered mature plantings. In this study, the survey of rodents was started in 2020 by using two methods: setting mouse traps and surveying damaged forest trees according to the technical standards of the Chinese industry. For the mouse trap method, the number of caught rodents < 9 was considered mild, 10-19 was considered moderate, and > 20 was considered severe. For the survey of damaged forest method, in surveyed 100 plants, the damage rate < 30% was considered mild, 30-49% was considered moderate, and > 50% was considered severe. Among these two indicators, the one with higher severity was chosen to represent the occurrence of R. opimus in that region. Since vegetation and occurrence are degree indicators, values of 1, 2, and 3 were assigned to represent the progression of shrubs from young to mature and the increase in occurrence from mild to severe.