Terrestrial Bryophyte and Lichen Responses to Canopy Opening in Pine-Moss-Lichen Forests

Abstract

Pinus contorta-dominated montane forests of western Canada with relatively dense tree canopies have ground layers with abundant bryophytes, especially the feather mosses (Pleurozium schreberi and Hylocomium splendens), while those with more open canopies are dominated by species of reindeer lichens, especially Cladonia arbuscula s.l. and C. rangiferina s.l. Woodland caribou (Rangifer tarandus caribou), which are a threatened species in Alberta, prefer open, Cladonia-dominated forests for their winter food supply. This study investigated if opening the canopy by thinning mature montane forests of the Canadian Rocky Mountain foothills would change the abundance of lichens and bryophytes. In 1997, forests were thinned by removing 20%, 40%, and 60% by volume. In 2016, 19 years after treatment, we re-surveyed a subset of these plots (n = 97) for lichen and bryophyte abundance and species richness by utilizing the amount of canopy opening at the plot level as our prime gradient. We then used ordination to determine the relationship of control plots to treatment plots. In uncut forest, the control plots were highly variable, but were mostly dominated by feather mosses, with little or no bare ground. Feather moss abundance was lower in treatment plots when compared to control plots, while cover of bare ground was greater. Overall, 19 years after treatment, we found that, in treatment plots, lichen abundance remained stable or slightly increased, feather mosses decreased markedly, and unoccupied space was double that of the control plots. We conclude that the canopy opening had little effect on understory and ground layer diversity, but considering species abundance (1) bryophytes have not recovered after canopy opening, (2) populations of reindeer lichens increased marginally, but have not colonized areas left bare from bryophyte dieback, and (3), after 19 years there, remains unoccupied areas of bare ground in plots with a reduced canopy cover. Our study demonstrated that, with canopy cover reduction resulting from forest thinning operations, the ground layer diversity is maintained, but recovery of ground layers in old-growth pine-dominated forests is not promoted. Therefore, timber harvest that partially opens the tree canopy is unlikely to benefit caribou by augmenting or accelerating winter food availability and habitat suitability for caribou.

Plant and soil nitrogen in oligotrophic boreal forest habitats with varying moss depths: does exclusion of large grazers matter?

“…Mosses together with lichens and ericaceous dwarf shrubs form the boreal forest (taiga) floor vegetation, which is partly controlled by wildfires and consequent succession where lichens dominate early and mosses and dwarf shrubs later in the successional sequence (Nilsson and Wardle 2005). However, at smaller scales, these plants alternate depending on microclimate: in comparison to mosses and dwarf shrubs, lichens are more abundant in drier microclimatic habitats sustained by soil properties and forest canopy structure (Haughian and Burton 2018;Vitt et al 2019). Furthermore, mosses and lichens respond to ungulate grazers, such as reindeer (Rangifer tarandus L. caribou in North America), whose decimating impacts on lichens are well established across taiga and tundra (Bernes et al 2015;Köster et al 2015;Horstkotte and Moen 2019;Uboni et al 2019).…”

Quantification of Lichen Cover and Biomass Using Field Data, Airborne Laser Scanning and High Spatial Resolution Optical Data—A Case Study from a Canadian Boreal Pine Forest

“…Terricolous macrolichens can form extensive mats on the boreal forest floor, and in some cases become the dominant understory vegetation in mature open pine stands [1]. In the boreal forest of Northern Alberta, Canada, a heterogeneous patchwork of lowlands and upland forests form a mosaic of suitable and unsuitable habitat for ground lichens.…”

“…In the boreal forest of Northern Alberta, Canada, a heterogeneous patchwork of lowlands and upland forests form a mosaic of suitable and unsuitable habitat for ground lichens. Since these terricolous macrolichens have specific growth requirements and are slow growing, these lichens are easily outcompeted by bryophytes and vascular plants in more mesic upland sites [1]. Likewise, flooding and water table fluctuations associated with peatland forests negatively impact lichens through reduction of available habitat [2].…”

“…Likewise, flooding and water table fluctuations associated with peatland forests negatively impact lichens through reduction of available habitat [2]. In the driest habitats, such as well-drained upland forests dominated by jack pine (Pinus banksiana), a naturally low production of vascular plants and a more open canopy structure can facilitate conditions for the dominance of ground lichens [1]. Terricolous reindeer lichens of the genus Cladonia can form large mats, particularly in open pine stands, where they often dominate the forest floor.…”

“…Previous work by Dunford et al [2] identified a relationship between lichen cover and biomass for Northeastern Alberta, but this work occurred only within peatland environments and thus may not represent lichen biomass for other land cover types. While spectral data can predict lichen presence well, it may not accurately depict lichen growth, which is related most to light availability associated with the structure of the overstory canopy [1]. Airborne laser scanning (ALS) data provides accurate, 3-dimensional representations of vegetation structure, including estimates of canopy (horizontal) cover, tree height (vertical structure), and understory shrub or ground cover [15].…”