Declines in occurrence of plants characteristic for a nutrient-poor meadow habitat are partly explained by their responses to nutrient addition and competition.

Stefanie Höckendorff,Felicitas Fiedler,Marc Stift,Mark Van Kleunen,Markus Peintinger

doi:10.1002/ece3.7306

Abstract

Species losses and local extinctions are alarmingly common, frequently as a consequence of habitat destruction. Nevertheless, many intact habitats also face species losses, most likely due to environmental changes. However, the exact drivers, and why they affect some species more than others in apparently intact habitats, are still poorly understood. Addressing these questions requires data on changes in occurrence frequency of many species, and comparisons of the responses of those species to experimental manipulations of the environment. Here, we use historic (1911) and contemporary (2017) data on the presence–absence of 42 plant species in 14 seemingly intact Molinia meadows around Lower Lake Constance to quantify changes in occurrence frequency. Then, we performed a common‐garden experiment to test whether occurrence frequencies in 1911 and changes therein by 2017 could be explained by responses of the 42 species to nutrient addition and competition with the acquisitive generalist grass Poa pratensis. Within the 14 still intact Molinia meadows, 36 of the 42 species had declined since 1911. As expected, nutrient addition generally led to increased biomass production of the 42 target species, and competition with P. pratensis had a negative effect. The latter was stronger at high nutrient availability. The more frequent species were in 1911 and the more they declined in frequency between 1911 and 2017, the less above‐ground biomass they produced in our experiment. Competition with P. pratensis magnified this effect. Our work highlights that environmental change can contribute to local extinction of species in otherwise intact habitat remnants. Specifically, we showed that increased nutrient availability negatively affected formerly widespread Molinia‐meadow species in competition with P. pratensis. Our study thus identified a likely mechanism for the decline in occurrence frequency of species in the remaining Molinia meadows.

Highlights

Biodiversity loss, due to global and local species extinctions, is a worldwide problem for different ecosystems and for different groups of organisms (Ceballos et al, 2015; IPBES, 2019; Régnier et al, 2015)
Many factors contribute to extinctions simultaneously, there is general consensus that the recent rates of global and local species losses are primarily caused by human activities (Bauer et al, 2019; Bowler et al, 2019; Vitousek et al, 1997)
Seemingly intact habitat remnants could be compromised by globally acting environmental changes such as increased nutrient loads and climate warming (Steinbauer et al, 2018; Vitousek, 1994)

Summary

| INTRODUCTION

Biodiversity loss, due to global and local species extinctions, is a worldwide problem for different ecosystems and for different groups of organisms (Ceballos et al, 2015; IPBES, 2019; Régnier et al, 2015). 87 km long shoreline of Lower Lake Constance (Germany and Switzerland) as a model to understand potential drivers of change in occurrence of plant species within a single habitat type These Molinia meadows developed on nutrient-poor substrates in the 19th century as a result of annual mowing to collect hay for stables (Peintinger, 2012). The meadows that remain today are protected and constitute one of the most plant species-rich habitats in the Lower Lake Constance region (Lang, 1973; Peintinger, 2012) Despite their protected status and the restored annual mowing, the Molinia meadows are, like many other habitats around the world, still subject to global environmental changes. We addressed the following specific main questions: (a) Are the species that benefit least from nutrient enrichment the ones with relatively high occurrence frequencies in 1911 and/or that showed the strongest declines in occurrence frequency by 2017? (b) Are the species that suffer the most from competition the ones with relatively high occurrence frequencies in 1911 and/or that showed the strongest declines in occurrence frequency by 2017? (c) Does nutrient enrichment aggravate the negative impact of competition?

| MATERIALS AND METHODS

Findings

| DISCUSSION

| CONCLUSIONS