Ana Patricia Sandoval-Calderon and Yann Hautier, Utrecht University, discuss their article: Andean grassland stability across spatial scales increases with camelid grazing intensity despite biotic homogenization
Nestled high in the Andes, a vibrant yet fragile ecosystem thrives under the watchful gaze of camelids. These ancient grasslands have been shaped over centuries by the grazing habits of llamas and alpacas, central to the livelihoods of indigenous communities. Yet, modern challenges like intensive land use and shifting environmental conditions potentially threaten the biodiversity and stability of these grasslands. How do these ecosystems respond to such pressures? Our research provides a surprising answer: camelid grazing may act as a double-edged sword by increasing the stability of Andean grassland productivity across spatial scales but decreasing the heterogeneity in plant communities in the landscape.
The puzzle of grassland diversity and stability
Ecologists have long been captivated by the concept of temporal stability—an ecosystem’s ability to maintain consistent productivity despite environmental fluctuations. While grazing is known to influence biodiversity and biomass, its impact on stability has been debated. Some studies suggest that grazing enhances stability by fostering diversity, while others argue that it undermines stability by disrupting plant communities. What has been missing is a broader perspective—one that considers stability not just locally but also across larger landscapes.
Grazing promotes stability but homogenize plant communities
Our study set out to unravel this complexity in the grasslands of Bolivia’s Apolobamba National Park. We explored how grazing intensity and environmental factors shape plant diversity and stability at two spatial scales: within individual communities (local or alpha stability) and among neighbouring communities (landscape or gamma stability). Here’s what we discovered:
- Higher grazing intensity = Greater stability: At both local and landscape scales, areas with higher grazing intensity exhibited greater stability. This was primarily because grazing increased spatial asynchrony. That is, grazing increased the variation in productivity responses among communities, ensuring that declines in one area were offset by gains elsewhere.
- Grazing homogenizes plant species composition: While grazing contributes to stability, it also homogenizes plant species composition across the landscape. This homogenization, characterized by reduced beta diversity (differences in species composition between patches), may have unintended consequences for ecosystem resilience and adaptability. Diverse plant communities often provide complementary functions and enhance productivity, especially under changing environmental conditions.
Why do these results matter?
These findings underscore the dual nature of grazing as both a stabilizing force and a driver of homogenization. The increase in stability across scales highlights grazing’s potential as a management tool to support ecosystem functions. However, the associated loss of beta diversity and its implications for productivity and resilience warrant careful consideration.
Implications for conservation and management
To strike a balance, land managers might:
- Promote heterogeneity in grazing regimes. Rotational or patchy grazing strategies could mitigate homogenization, preserving beta diversity while maintaining stability.
- Monitor ecosystem functions at multiple scales. Understanding local and landscape-level dynamics is essential for assessing trade-offs and optimizing management outcomes.
- Incorporate adaptive management. Regularly adjusting grazing practices based on ecological feedback can help sustain multifunctionality and biodiversity.
Conclusion
The influence of grazing on Andean grassland ecosystems exemplifies the complexity of human-nature interactions. While it promotes stability at multiple scales, the accompanying homogenization of plant communities poses challenges for biodiversity and long-term productivity. By integrating these findings into land management practices, we can better navigate the trade-offs and ensure the sustainable functioning of grasslands in a changing world.
