Effects of previous tree harvesting on productivity and photosynthetic pigments of mosses in a boreal black spruce forest

Nimmo, Victoria (2016) Effects of previous tree harvesting on productivity and photosynthetic pigments of mosses in a boreal black spruce forest. Masters thesis, Memorial University of Newfoundland.

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Abstract

The harvesting of forests across Canada is known to affect the carbon fluxes of these ecosystems over large scales, but little is known about the potential range of longer term effects on the bryophytes which cover the forest floor. This study aimed to investigate seasonal productivity of common moss species (Hylocomium splendens, Ptilium crista-castrensis, Pleurozium schreberi, and Sphagnum subnitens) from black spruce boreal forest sites which had previously been clearcut in Western Newfoundland, Canada, in comparison to the same moss species in adjacent intact forests. Tests focused mainly on the photosynthetic rates and photosynthetic pigment concentrations of the species, and found contrasting results. Feathermosses tested in the post-harvest areas had greater photosynthetic rates in the more open habitats, but the decreased rates of growth coupled with the higher vapour pressure deficits measured in these areas suggests that they were often under moisture stress and were unable to capitalize on their light environment. Sphagnum was able to better retain water in these open areas, and had a smaller treatment effect. The light responses of all three feathermosses were such that saturating light levels were greater in the more open post-harvest blocks, and concentrations of photosynthetic pigments decreased as light was no longer a limited resource. In contrast, Sphagnum was able to increase maximum photosynthetic rates in the post-harvest blocks, and fewer effects of treatment were found when measuring photosynthetic pigments, again suggesting that Sphagnum shoots were more capable of mitigating water loss and associated effects. All the test species were found to have naturally increased shoot densities in the post harvest blocks, presumably an attempt to mitigate the negative effects of a more challenging micro-environment. Overall, mosses were found to be capable of maintaining a substantial ground cover within the post-harvest areas, but did display a range of changes to characteristics and traits which could potentially alter their proportional contribution to the carbon fluxes in a harvested area.

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