Terrestrial lichen abundance in relation to stand structure and silvicultural history

Abstract

Terrestrial lichen has been identified as an important factor contributing to suitable woodland caribou (Rangifer tarandus caribou) winter habitat. Conservation efforts to maintain viable populations of woodland caribou in areas where forest management activities take place will require an understanding of the forest conditions that promote suitable habitat characteristics. Two studies were conducted for this thesis. In the first study, terrestrial lichen abundance and stand structure of naturally disturbed and previously harvested forest stands in northwestern Ontario were measured. Terrestrial lichen abundance (% cover) was relatively low and highly variable, but significantly higher in conifer-dominated (4.28 ± 6.83%), than in deciduous (0.60 ± 1.51%) or mixedwood (0.62 ± 1.01%) stands. No significant difference in lichen abundance was found between naturally disturbed (3.14 ± 5.77%) and previously harvested stands (3.41 ± 6.53%). Lichen abundance was significantly greater in stands with non-organic (5.71 ± 7.75%), rather than organic (2.07 ± 4.14%) soil textures. Among non-organic conifer-dominated stands, negative relationships were observed between lichen abundance and canopy closure, basal area, tree height and crown height. In the second study, terrestrial lichen abundance was compared in twenty-four 20 to 40 year-old stands, previously treated with prescribed burning (PB) or mechanical site preparation (MSP). T-test and Mann-Whitney U test results indicated no strong difference in terrestrial lichen abundance between PB (8.95 ± 8.45%) and MSP (2.37 ± 2.03%) treatments, though confounding effects of dominant tree species composition may have contributed to this result. Among the stand structural characteristics measured, canopy closure exhibited the strongest negative relationship with lichen abundance. Negative relationships were also observed between lichen abundance and crown height and basal area. The results of this study indicate that terrestrial lichen abundance is difficult to predict in conifer-dominated stands of northern Ontario. Terrestrial lichen abundance is strongly correlated with overstory structural attributes, which suggests that forest management activities could potentially influence terrestrial lichen abundance by manipulating stand structure to create understory light conditions that are favourable to terrestrial lichen establishment and growth.