Water and the lack of it shape tundra vegetation patterns

Submitted by editor on 5 March 2019.Get the paper!

Water has a control over vegetation. Whether there is too much or too little of it, it has an impact on the spatial patterns of plants, mosses and lichens. This is evident in arid ecosystems – about but what about cold ecosystems which are considered as temperature limited systems?

Booming tundra heath, where there is plenty of plant-available water, but not too much. What a delicate balance! Photo: Julia Kemppinen

Fennoscandian mountain tundra is dominated by miniature prostate shrubs. But a closer look may reveal over 40 different vascular plant species in a single one square-meter plot. Here, plants are rather tiny, but nothing to compare to the mosses and lichens of this particular region. Solely in our study setting of 378 plots, we found all together 271 species of these three groups.

Rocky streams, the kingdom of mosses. Mosses prefer high water resources, and do not mind a little fluvial disturbance. Photo: Julia Kemppinen

We set out to investigate, just how important is water in its different aspects for these three ecologically and evolutionary distinct taxonomical groups. For this, we collected data on water as a resource, stress and disturbance, i.e. spatial and temporal variation of soil moisture and fluvial disturbance.

Our study setting on Mount Saana in northern Fennoscandia. Blue indicates high levels of soil moisture, yellow the opposite. Soil moisture is truly a fine-scale environmental variable, and this should be taken into account in vegetation research. Figure: Kemppinen et al. (2019) Oikos

Using a species distribution modelling approach, we found that the different water aspects proved to be crucial environmental drivers of fine-scale vegetation patterns. Water acts as a driver of vegetation not only on individual species level, but it also shapes community characteristics. And in this particular system and for these species, the importance of spatial variability of water exceeds the importance of soil temperature.

Some evidence on the fundamental role of water in fine-scale tundra vegetation patterns. GDD = growing degree day; RAD = radiation; SpH = soil pH; CRY = cryogenic processes; BIO = biota; WRE = water resources; WST = water stress; WDI = water disturbance. Figure: Kemppinen et al. (2019) Oikos.

Now we understand just how significant driver water is, even in this ecosystem of cool and rainy summers, where water resources are not scarce at all. It looks like these fundamental components of Arctic ecosystems – vascular plant, moss and lichen communities – will not only show sensitivity to warming temperatures, but they will also respond to altered water conditions.

The plentiful water resources of the high-latitudes are dependent on snow conditions. What will happen to fine-scale plant-available water in the future? Photo: Julia Kemppinen

The next step would be to understand how these fundamental fine-scale water aspects will be shaped by changing winter conditions and rising temperatures. Will there be ecological surprises ahead? How will these tiny tundra organisms cope? Thus, I declare an urgent need of more research on plant ecology and soil hydrology of tundra habitats under our rapidly changing climate.

Written by Julia Kemppinen on behalf of all co-authors



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