Worldwide, glaciers are shrinking at an unprecedented rate, bringing major ecological and societal cascading consequences. Although the opening glacier forelands provide an opportunity for novel alpine ecosystems to develop, in these oligotrophic and high-altitude environments ecological processes are slow. For example, it can take hundreds of years to observe soil horizons, and the establishment and organization of novel plant communities are complex processes. As a result, the novel proglacial ecosystems might be impoverished: soils display low fertility and reduced water retention capacity, and biotic communities are highly subject to extinction risks.
In the Cordillera Blanca in northwestern Peru, like everywhere else, the local populations are the first ones to experience the negative consequences of accelerated glacier retreat. Acid rock drainage (ARD) poses a threat to water security and has been associated with glacier retreat in various river catchments in the region. Previous research has linked water acidification to the progressive exposure of the sulfide-rich pyrite, previously covered by the perennial ice. In the Olleros subwatershed within the Cordillera Blanca, the local communities have experienced extensive effects, including the disappearance of trout, decreases in crop yields because of burnt crops due to the very acidic water pH, and an increase in diseases within the population likely resulting from the presence of heavy metals in the water. This story is not specific to the Olleros subwatershed, as it is common to numerous Quebradas of the Cordillera Blanca.
Just as ARD threatens local livelihoods, events such as the extinction of animal and plant species and the modification of ecosystems will endanger emerging proglacial ecosystem services (biodiversity, carbon sequestration, and water provision).
Experimental approaches to study pedogenesis and vegetation colonization after glacier retreat are crucially missing, and management strategies that favor the conservation and protection of proglacial landscapes are nearly nonexistent. So, in response to this, and to the needs of the local community, in 2019 we set up a collaborative experimental approach at the foot of the Uruashraju glacier in the Cordillera Blanca.
From 2019 to the present, we closely collaborated with the Llama 2000 Asociación, the local community of farmers who own the llamas, and Huascarán National Park, to test a novel adaptation strategy to glacier retreat by introducing llamas in the Uruashraju glacier foreland. We set up a complete block design with four monitoring blocks — i.e., four llama plots and four control plots — in an area deglacierized between ~1979 and 1995. Each plot includes 8 permanent subplots (1x1m) that we have surveyed yearly between 2019 and 2022. We also studied the evolution of soil fertility (e.g., texture, soil organic carbon, and soil nitrogen), plant functional traits (leaf nitrogen and LDMC), and the viability of the seeds present within the llama dung piles of the experiment.
Our results are novel and promising. In only 3 years, they showed that likely due to the latrine behavior of the llamas, soil fertility increased significantly. We measured higher soil organic carbon and soil nitrogen in the presence of the llamas. Similarly, in the llama plots the vascular plant cover increased by 57% between the second and third year of experimentation. The presence of the llamas, through the physical effect of grazing, has likely reduced the competition between vascular plants, which in turn might favor the establishment of specialist species in the proglacial area. In accordance with this, we identified four new species that were not present in 2019.
The study of the seeds present within the llama dung, and their viability, reveals that five of the 12 seed species identified still maintain their germinative power. The llamas have the potential to disperse seeds of different plant families and types from lower elevation or neighboring valleys to the proglacial habitat, and thus act as seed transporters by endozoochory. Since llamas move regularly between vegetation communities for foraging and ranging, both endo and exozoochorous dispersal might provide an important mechanism for colonization.
In conclusion, the presence of llamas might help to overcome several of the main constraints of primary succession after glacier retreat: low soil fertility, dispersal limitation, and competition between species.
Our findings may have implications for the conservation and management of novel proglacial ecosystems around the world. Locally, our study supports the goal of national and local efforts in re-introducing native Andean camelids. And the experimental protocol designed in this study will allow long-term monitoring to continue to assess the changes observed in our three-year study and discover what changes may happen at longer timescales.
We deeply thank the Llama 2000 Asociación for its collaboration and help in the field, as well as Huascarán National Park for its support, without whom it would not have been possible to develop this research project.