Winners and Losers of Tundra : Long-term Plant Community Responses to Fertilization and Dominant Species Removal in Subalpine Tundra

Sammanfattning

Nutrient enrichment and species removal experiments are crucial for understanding how plant communities respond to increased nutrient availability in nutrient-poor ecosystems under climate change, and how shifts in dominant species may be involved in those responses. This study investigated the long-term effects of fertilization and dominant species removal on subalpine tundra vegetation in northern Sweden. Using data collected in 2025 from a long-term field experiment initiated in 1989, I assessed vegetation cover, species richness, and Shannon diversity of vascular plants and bryophytes after 36 years of fertilization and 26 years of dominant species removal treatments. The two dominant species at the site, Deschampsia flexuosa and Empetrum hermaphroditum, showed contrasting responses to nutrient addition, with Deschampsia cover increasing and Empetrum cover generally decreasing. Additionally, fertilization strongly reduced bryophyte and lichen cover, confirming their vulnerability to nutrient enrichment. These patterns are consistent with earlier phases of the experiment and reflect a shift from resource-conservative species toward resource-acquisitive species under increased nutrient availability. I found only partial support Contrary to my hypothesis that nutrient enrichment would reduce plant species richness and Shannon diversity, I found only partial support, as vascular plant diversity showed no response, while bryophyte diversity was strongly reduced. The effects of dominant species removal were weak and inconsistent with my hypotheses, suggesting that long-term vegetation change at this site is driven primarily by direct effects of nutrient enrichment rather than indirect effects mediated by dominant species removal. Overall, these findings demonstrate that the nutrient enrichment continues to shape plant community composition after more than three decades, highlighting the importance of long-term studies for understanding plant community dynamics.