Work

How to characterize the decline of natural Pinus sylvestris var. Mongolica forests on sandy land?

Year: 2025

Type: article

Abstract: In recent years, the natural Pinus sylvestris var. mongolica (Mongolian pine) forests on the Hulunbaier sandy lands have experienced significant decline, with a clear expanding trend. While, the decline is generally attributed to combined disturbances from both human activities and climate change, a detailed understanding of the underlying mechanisms first requires defining the key decline characteristics, including the minimum detectable decline size (area), decline severity grades, and their spatial distribution patterns. In this study, we employed a random forest algorithm to evaluate the vegetation indices derived from multispectral unmanned aerial vehicle (UAV) imagery for assessing the decline of natural Mongolian pine forests. The species-area curve method and an upscaling approach were used to determine the minimum detectable decline size and to map the spatial distribution of decline patterns, respectively. The results indicated that the Green Normalized Difference Vegetation Index (GNDVI) is an appropriate indicator (VGNDVI) for quantifying the decline of natural Mongolian pine forests. The minimum survey area for reliable decline assessment was determined as 3.24 ha. Based on GNDVI thresholds, we classified the decline severity into three levels: Severe-Decline (VGNDVI < 0.57), Mild-Decline (VGNDVI = 0.57 - 0.63), and Normal (VGNDVI >0.63). The classification criteria (VGNDVI < 0.57, 0.57–0.63, and > 0.63, respectively) were established by selecting multiple representative trees at each level and extracting their vegetation index values to determine the threshold ranges. Over the survey area (7.71 × 104 ha), 8.25 × 102 ha (1.07%) exhibited an unhealthy state (i.e., VGNDVI < 0.63), of which, the area of severe level (VGNDVI < 0.57) was 1.22 × 102 ha, displaying a scattered distribution pattern. These findings provide critical baseline data on the decline status of natural Mongolian pine forests, supporting future mechanistic and management studies.

Source: Global Ecology and Conservation

DOI: 10.1016/j.gecco.2025.e03955