Deer Browsing Cuts Tree Diversity in Half, Even in Sunny Gaps: Study – Wood Central

Report on the Impact of Roe Deer Browsing on Forest Regeneration and Sustainable Development Goals

Introduction

A multi-year study conducted by Julius-Maximilians-Universität Würzburg has identified roe deer browsing as a primary inhibitor of natural tree regeneration in deciduous forests. The research, published in the Journal of Applied Ecology, demonstrates that high deer populations can nullify the positive effects of increased sunlight in forest gaps, thereby posing a significant challenge to achieving key Sustainable Development Goals (SDGs), particularly SDG 15 (Life on Land) and SDG 13 (Climate Action).

Research Methodology

The investigation was structured as a four-year field experiment within the Würzburg University Forest. The research team established a series of 36-square-meter plots to compare tree regeneration under different conditions. The experimental design included:

• Fenced plots to exclude deer.
• Unfenced plots accessible to deer.
• Placement of plots in both open, sunlit canopy gaps and shaded forest understory.

This methodology allowed for a direct comparison of the interacting effects of light availability and ungulate browsing on the establishment and survival of young trees.

Key Findings and Ecological Impact

The study’s results highlight a critical conflict between wildlife pressures and forest ecosystem health, directly impacting biodiversity and resilience.

1. Negation of Light Benefits: The additional sunlight in open canopy gaps, which should promote vigorous and diverse regeneration, failed to offset the negative impact of deer browsing in unfenced areas.
2. Reduction in Species Diversity: Tree-species diversity was effectively halved in unfenced plots. While a wide range of species germinated, only a few were able to grow beyond the 1.3-meter browsing height of roe deer.
3. Homogenization of Forest Structure: Selective browsing leads to a less diverse and more uniform forest regeneration profile, which compromises the long-term stability and adaptability of the ecosystem.

Implications for Sustainable Development Goals (SDGs)

The findings have profound implications for the advancement of several SDGs related to environmental stewardship and climate resilience.

• SDG 15: Life on Land: The research directly addresses targets for sustainable forest management and halting biodiversity loss. The observed reduction in tree diversity is a clear setback for Target 15.5 (protect biodiversity and natural habitats) and undermines efforts under Target 15.2 (promote the implementation of sustainable management of all types of forests).
• SDG 13: Climate Action: By limiting the natural regeneration of diverse and robust forests, high deer populations reduce the ecosystem’s capacity for carbon sequestration and its resilience to climate change. This directly impacts Target 13.1 (strengthen resilience and adaptive capacity to climate-related hazards). A less diverse forest is more vulnerable to climate-induced stressors such as drought and disease.

Conclusion and Recommendations

The study concludes that roe deer browsing is a significant barrier to achieving sustainable forest management and biodiversity conservation goals. The natural potential of forests to regenerate with greater species richness is being suppressed. To align forest management practices with SDG targets, the following recommendations are proposed:

• Implement protective fencing around vulnerable regeneration areas for several years, particularly where deer densities cannot be adequately controlled.
• Integrate wildlife population management into broader forest conservation and climate resilience strategies.
• Continue research into the cascading effects of deer browsing on understory vegetation, soil health, and invertebrate diversity to fully understand the ecosystem-wide impacts.

Reference

Lettenmaier, L., Müller, J., et al. (2025). ‘Light and ungulate browsing interact in shaping future woody plant diversity through natural regeneration’. Journal of Applied Ecology. DOI: 10.1111/1365-2664.70211.

SDGs Addressed in the Article

1. SDG 15: Life on Land

   • The article’s central theme is the impact of roe deer on forest ecosystems, specifically on the natural regeneration of trees and biodiversity. This directly relates to the goal of protecting, restoring, and promoting the sustainable use of terrestrial ecosystems, sustainably managing forests, and halting biodiversity loss. The research highlights how deer browsing is “significantly limiting the natural regeneration of tree species” and leading to a “homogenization of forest regeneration,” which are core concerns of SDG 15.

2. SDG 13: Climate Action

   • The article connects the issue of reduced forest diversity to climate resilience. It states that deer browsing can undermine “efforts to increase species diversity and climate resilience.” Healthy, diverse forests are more resilient to the impacts of climate change. By reducing diversity, deer browsing weakens the forest’s ability to adapt, which is a key concern of SDG 13, particularly regarding strengthening resilience and adaptive capacity.

Specific SDG Targets Identified

1. Target 15.2: Promote the implementation of sustainable management of all types of forests, halt deforestation, restore degraded forests and substantially increase afforestation and reforestation globally.

   • The research provides critical insights for forest management practices. The article notes that the findings have “broad implications for forest management” and suggests a specific management intervention: “affected areas should be fenced for several years to allow the forest’s natural potential for greater diversity to unfold.” This directly addresses the promotion of sustainable forest management and the restoration of degraded forest areas where natural regeneration is failing.

2. Target 15.5: Take urgent and significant action to reduce the degradation of natural habitats, halt the loss of biodiversity and, by 2020, protect and prevent the extinction of threatened species.

   • This target is directly relevant as the article quantifies the loss of biodiversity due to deer browsing. The study found that “tree-species diversity was effectively halved, regardless of light availability.” This demonstrates a significant degradation of the forest habitat and a direct loss of local biodiversity, which this target aims to halt.

3. Target 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries.

   • The article explicitly mentions that the homogenization of forest regeneration due to deer browsing could be “potentially reducing long-term ecosystem resilience.” This connects the loss of biodiversity directly to a reduced capacity of the forest ecosystem to withstand and adapt to climate-related stresses, which is the focus of Target 13.1.

Indicators Mentioned or Implied

1. Tree-Species Diversity

   • This is a direct indicator mentioned and measured in the study. The article states that “tree-species diversity was effectively halved” in unfenced plots. This serves as a clear metric for assessing the impact on biodiversity (Target 15.5) and, by extension, ecosystem resilience (Target 13.1).

2. Rate of Natural Tree Regeneration

   • The entire study is based on measuring the “natural regeneration of tree species.” The experiment compared regeneration in fenced versus unfenced plots, making this the primary indicator of forest health and the success of management practices (Target 15.2). The study monitored which species “managed to grow beyond that vulnerable zone” of 1.3 meters.

3. Ecosystem Resilience

   • While not directly measured in the reported phase of the study, “long-term ecosystem resilience” is an implied indicator. The article warns that the observed homogenization of forest regeneration leads to a reduction in this resilience. The measured indicators, such as species diversity, serve as proxies for this broader indicator of ecosystem health and adaptive capacity (Target 13.1).

SDGs, Targets, and Indicators Analysis

Source: woodcentral.com.au