Even tiny mountain plants thirst for water
For the flora in the fells, water has many meanings. There can be too much, too little, or just the right amount. It can vary from floods to a period of drought, or streams can erode the substrate the plants grow on. Researchers are increasingly interested in the effect of the water cycle on plants in a changing climate.

– We often think mountain nature is primarily limited by low temperatures, but plants may be short of water even in the fells, says doctoral student Julia Kemppinen.

Small-scale phenomena require local-level observation

Research setup consisting of 387 intensively mapped research plots and it was established in the environment of the Saana fell in Kilpisjärvi.

Diversity of the tundra

The measurements researchers have made reveal that the humidity of the soil varies in the undulating terrain of the fells from one extreme to another even within a few metres. This is reflected in the flora. Soil moisture emerged as one of the most significant environmental variables, determining where each plant, moss, and lichen species may grow. Variability in moisture conditions – dry ridges, small streams and depressions – act to uphold the diversity of the tundra.

– Species distribution modelling revealed that it is especially the local variation of soil moisture that affects the frequency of these three taxonomical groups. The amount of water in the soil also varies temporally, but depending on the site, the effects of temperature and precipitation are different, says Kemppinen.

Mountain streams

In addition to the water conditions of the soil, the researchers have observed the effect of the water in the mountain streams on the plant life. In small meltwater channels, the erosion from the water is greatest during spring, but the effect of melting snow gradually disappears during the summer in the fells.

– Our results show that local water conditions may be more important to some species than the temperature conditions. But what happens when temperatures rise and water becomes more scarce as the snow conditions change? It looks like climate change threatens mountain flora on all sides, says Kemppinen.

The research showed that some species avoid the vicinity of streams, since the streaming water churns up the ground and may even drag small organisms with it. Other species have adapted to the disturbance caused by streaming water and thrive near cold water. The flora that is used to the cool and rainy summers of the fells in Lapland has adjusted to the local water conditions.

– A dry, windyridge is a rough place, where few species do well. However, it may be the only place where drought-resistant lichens can grow, since any plants that might cast shadow on them cannot grow there. At the base of the ridge, on the other hand, water gathers from rain and snow in the small depressions, which may uphold a varied and dynamic plant and moss population, Kemppinen says.

As a part of their research, the scientists mapped the plant life in Kilpisjärvi, in Enontekiö, Finland. Just in the environs of the Saana fell, they found nearly 300 species in their research plots. Mountain plants are small, and if the conditions are suitable, up to 43 different species may be found in one square metre. Even then, a great amount of even smaller moss and lichen can be found among the plants.

Fell nature and its diversity is upheld by water conditions. This is why it is important to understand what happens to the soil moisture in future, when the northern climate warms up. Scientists point out that we need research that crosses the boundaries between sciences. Only through multidisciplinary study can we discover answers to current questions about fell flora and its relation to water.

Research

Kemppinen, Niittynen, Aalto, le Roux & Luoto (2019). Water as a resource, stress and disturbance shaping tundra vegetation patterns. Oikos. DOI: 10.1111/oik.05764

The research was funded by the GeoDoc doctoral programme at the University of Helsinki, Kone Foundation, Societas pro Fauna et Flora Fennica, and the Academy of Finland (project 307761; 286950). The authors want to thank the current and former members of the BioGeoClimate Modelling Lab, who participated in gathering data, and the staff of the Biological station in Kilpisjärvi for their help and support.

More information

Doctoral Student Julia Kemppinen, The BioGeoClimate Modelling Lab
Email: julia.kemppinen@helsinki.fi
Twitter: @juliakemppinen

The BioGeoClimate Modelling Lab, headed by Professor in biogeography Miska Luoto

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