Ecohydrological controls of natural and restored lichen and moss CO2 exchange on a rock barrens landscape

Abstract

Lichen and moss are the dominant ground cover on the Canadian Shield rock barrens of eastern Georgian Bay, and they provide many ecosystem services. Lichen and moss mats are essential for developing and accumulating soil on the bedrock landscape, and as the mats establish they moderate soil temperature and reduce soil water losses, thereby improving the microclimate for more complex vegetation. In addition to pioneering ecosystem succession, the lichen and moss mats provide essential nesting habitat for turtle species-at-risk. These lichen and moss mats are not well understood on rock barrens landscapes, and as such this thesis aims to increase knowledge of the growth, persistence and restoration approaches for these valuable ecosystem resources. We quantified the ecohydrological controls on the growth of lichen and moss mats by measuring the CO2 exchange of lichen and moss under varying environmental conditions. From these results we determined that key growth periods for lichen and moss were during the wet portions of the growing season (spring and fall), and that growth was limited or non-existent during the dry period (summer). Further, we determined that soil moisture was the most important control on lichen and moss CO2 exchange, and that this relationship differed among cover type (lichen, moss, mix of lichen and moss). Moss was able to continue CO2 uptake at a lower water content than lichen, suggesting that lichen would have a greater decline in productivity under drier conditions. A decline in lichen and moss productivity would also likely lead to a decline in soil development through chemical weathering which, in turn, could affect the availability of turtle nesting habitat. We also used CO2 exchange measurements to compare lichen and moss productivity between natural and transplanted mats. Transplanting in-tact patches of lichen and moss has not been widely studied, and as such we tested this approach on a rock barrens landscape. We determined that natural and transplant productivity did not differ for lichen, and that there were some differences between treatments for mixed and moss plots. We also used the tea bag index method to compare relative decomposition rates between treatments (natural, transplant), where we found that decomposition rates did not differ. Our results indicate that it is feasible to remove lichen mats from the footprint of a planned disturbance such as construction and transplant them successfully to nearby undisturbed areas. This approach would restore the lichen cover and the ecosystem services that lichens provide immediately rather than waiting decades for natural regrowth or fragment establishment. As a whole, this thesis will increase knowledge of both the growth and persistence, as well as the restoration of lichen and moss on rock barrens landscapes. Given that lichens and mosses of these genera grow globally, our findings can be applied widely to enhance and protect lichen and moss mats, and the ecosystem services they provide