# Vegetation and Landscape Shift After Beaver Settlement in a Mountainous Area

## TL;DR

Beavers in a mountainous area changed the landscape and vegetation over 25 years by building dams and creating ponds, increasing biodiversity and altering plant communities.

## Contribution

The study documents long-term landscape and vegetation changes caused by beavers in a mountain valley using a unique series of vegetation maps.

## Key findings

- Beaver activities increased streambed length by 9.5% and created ponds exceeding 2200 m².
- Vegetation patchiness increased, with moist and wet plant communities expanding from 76.8% to 89% of the area.
- Fresh vegetation and grey alder communities declined, while new communities like Filipendulo-Geranietum emerged.

## Abstract

Beavers significantly influence their environment, particularly in areas close to their habitats. This effect is especially notable in mountain streams, where their presence may not be immediately obvious. Their activities, such as dam construction, led to landscape changes in the small mountain valley in the Eastern Carpathians between 1994 and 2022. These included the creation of ponds and migration corridors, the number of which can vary from year to year. An indirect impact of beavers was the alteration in the length of the streambed, which increased by 9.5% due to the formation of meanders. The ponds created by beavers can exceed 2200 m2, contributing to local humidity levels. As the water accumulates behind the dams, soil moisture increases, resulting in changes in vegetation around the watercourse. Our findings, based on a unique series of vegetation maps, point to a decrease in fresh vegetation, the extent of moist and wet plant communities, a modification of their distribution within the valley, and an increase in vegetation patchiness. Over time, a dynamic vegetation mosaic can be observed that supports biodiversity.

Beavers are classified as ecosystem engineers because their activities can significantly alter environmental conditions. Vegetation and landscape changes, based on a series of vegetation maps and satellite images between 1994 and 2022, were studied in a mountain valley of a protected area in the Polish part of the Eastern Carpathians. Eighteen plant communities were identified before the beavers were released, with moist and wet communities covering 76.8% of the area. After 25 years of beaver presence, the vegetation changed: fresh communities decreased from 23% to 10%, and communities with grey alder disappeared. At the same time, the moist and wet communities expanded and new ones developed. Overall, the share of these communities increased to 89% of the area, with the dominant tall herb Filipendulo-Geranietum and Menyanthes trifoliata community. A distinctive feature was an increase in vegetation patchiness with a corresponding decrease in the evenness index. Landscape analysis revealed a 9.5% increase in the length of the streambed and fluctuations in the number of beaver ponds (11–25) and migration corridors (4–20). The number of corridors increased as the availability of grey alder decreased. The total area of the ponds exceeded 2200 m2, indicating their significant role in water retention and modifying microclimatic conditions.