Soil moisture matters

Submitted by editor on 8 May 2018.



By Julia Kemppinen

What is soil moisture?

From an ecographical point of view, vegetation patterns are related to soil moisture and its spatial variation. Therefore, soil moisture can be seen as plant-available water. In tundra habitats, plant-available water is restricted on the top-most soil layer as tundra plants have relatively short roots (ca < 30 cm). In addition, varying topography causes soil depth and soil type variation throughout arctic and alpine landscapes. For example, on average the soils in our study area are very shallow (ca < 10 cm), but they vary from ridges barely covered with thin mineral soils to depressions layered with meter-thick peat soils. Peat forms only in water-logged conditions and has the highest soil moisture content of all soil types, but that is completely another story

What is soil moisture? Why is it so important? These questions have haunted me since my bachelor’s thesis. And now they have drove me to do an entire PhD focused on soil moisture and its ecosystem effects.


Not only a vital resource

Our lab collected data for species distribution modelling purposes on three different water aspects from 378 plots in the sub-arctic Scandes. Soil moisture as a vegetation resource (1) was measured in volumetric water content percentage of each plot. The measurements were repeated three times during one growing season, for understanding the stress (2) caused by temporal changes in soil moisture. Besides being a resource and a stressor, water can also be a lethal disturbance (3) to our study organisms. Tundra vascular plants, mosses and lichens are relatively small, not to mention sessile, thus, they are sensitive to earth surface processes, such as seasonal meltwater channels, in which flowing water can wipe them out like field assistants wipe out mosquitos.

On the other hand, some species, such as Saxifraga aizoides (in front), seem to thrive in conditions, in which others cannot simply survive… Complex, isn’t it?

Why is soil moisture so important?

The greatest motivation for our work is climate change and its effects on arctic and alpine ecosystems. The cryosphere and its rapid on-going changes have implications on hydrology and on entire ecosystems. Rising temperatures and sifting precipitation regimes will and have already altered tundra landscapes. On fine spatial scales, usually the fuss is about temperature, but our work shows that also soil moisture matters for tundra vegetation. Our lab has shown that soil moisture varies remarkably from one square-meter plot to another affecting vascular plants from species to community level. Rest of the results are soon to be published, but you can just imagine that I would not be doing an entire PhD on soil moisture, if it was not so important.

The story does not end in the sub-arctic Scandes; we need to understand the relations between soil moisture and vegetation across different ecosystems. We and our colleagues from the University of Pretoria have already taken the next step: replicating this cost-effective study setting to the sub-Antarctic Marion Island and the northern sub-alpine Drakensberg. Who knows – you might run into some soil moisture enthusiasts also in Greenland and Svalbard in the upcoming summer of these high-arctic sites?

julia [dot] kemppinen [at] helsinki [dot] fi

Twitter: @juliakemppinen