I have studied the effects of OTCs on growth of different bryophyte species, seasonal periods and at two different sites (Latnjajaure, Sweden and Thingvellir, Iceland). Bryophytes in the Arctic and Subarctic play a significant role in the primary production, nutrient cycling and species diversity. In the view of predicted climate change it is therefore important to study the bryophytes and their responses to increased temperature.

My results show that:
1. Bryophyte species show different responses to OTC treatments.
2. Single bryophyte species can show different responses to OTC effects on different time scales.
3. The response of the same bryophyte species to OTC treatments varies greatly between sites.

Most bryophytes have an poikilohydric physiology so that growth is mainly limited by water availability or relative humidity. The study results can be explained by (1) bryophyte species have different ecology. (2) A growth measurement during the summer do not have to show the same results as measurements throughout the year. This is because during the warm summer period, the OTC plots may dry out faster and/or more (because of evaporation) than the surroundings, which may cause some species to grow less in the OTCs. During the rest of the year, water is no longer the main limiting factor, and there is no significant differences between treatments. (3) The site differences in bryophyte growth response to OTCs can probably be explained by differences in precipitation. When water is less limiting, the "real" response to an temperature increase is shown.

My results show that bryophytes may have complicated responses to the simple OTC design used within ITEX (e.g. the same species may show different responses, depending on the time scale and site being used). For bryophytes, not only temperature but also precipitation must be considered when studying the possible effects of predicted future climate change. However, today the GCM predictions of precipitation amount and intensities are not fully clear.

The bryophytes are an important and significant part of the communities which most people within ITEX are working with. Therefore, there is an urgent need for more information about the bryophyte responses to predicted climate change (e.g. species specific, between sites, short- and long-term).