A single range-expanding species reshapes alpine ecosystems and their belowground diversity
Range expansion and alpine ecosystems
Around the world, species are shifting their ranges in response to climate change. In particular, the range-expansion of foundation species can transform recipient communities and ecosystems, however, the potentially pervasive effects on ecological processes and diversity remain poorly documented.
For my MSc at Concordia University, I aimed to document the ecological impacts of range expanding trees (a quintessential foundation species) on alpine ecosystems in Patagonia, Argentina.
To do so, I focused on below-ground fungi, who are well suited for taking the “pulse” of changing ecosystems given their rapid turnover and implications in a wide variety of ecosystem processes. Specifically, I used an ongoing invasion of a foundation species (Pinus contorta) as a natural experiment to infer the effects of range-expanding species on the abiotic environment and the diversity of below-ground fungal communities associated with the roots of resident understory plants.
Lodgepole pines (Pinus contorta) as seen here in the background have successfully co-invaded treeless ecosystems all over the globe along with their obligate fungal symbionts such as the yellow Suillus luteus seen here in the foreground. In Argentina, these mushrooms are often harvested to be eaten, dried, and sold, and comprise a significant portion of local economies.
We found that individual range-expanding pines create distinct abiotic “islands” with cooler and wetter soils and alter soil nutrients compared to the surrounding alpine tundra ecosystem (Fig. 1)
These changes in abiotic conditions do not impact the richness or composition of plant communities but do greatly increase plant cover.
Surprisingly, even without significant changes in plant diversity, we observe a decrease in the alpha diversity of fungal mutualists and an increase in the alpha diversity of fungal pathogens during later stages of range expansion, potentially driven by changes in soil phosphorous, soil moisture, and plant cover (Fig. 2)
Furthermore, changes in gamma below-ground diversity mirrored local patterns of alpha diversity while beta diversity was only minorly affected by range-expanding pines, suggesting that local habitat amelioration/deterioration rather than changes in among-patch heterogeneity underpin changes in below-ground diversity at broad scale.
Figure 1 — a) Illustrated examples of alpine ecosystems at various stages of invasion by Pinus contorta. b) Different in environmental conditions and plant diversity across stages of range expansion.
Figure 2 — Difference in fungal richness across different stages of range expansion for all fungi, decomposers, mutualists, and pathogens.
Our results show that range-expanding foundation species have the potential to create novel ecosystems, altering abiotic conditions and reshaping below-ground diversity across spatial scales, and that these impacts likely begin only a few years after initial spread and establishment.
As climate change leads to poleward and upward shifts in the distributions of organisms around the world, understanding how and when range expanders restructure and reorganize ecosystems may prove critical to designing successful conservation decisions.