Microhabitat associations of lichens, feathermosses, and vascular plants in a caribou winter range, and their implications for understory development

Abstract

Vegetation-environment relationships are well understood for boreal lichen woodlands, but the mechanistic basis for small-scale understory patchiness (patches dominated by lichen, mosses, and vascular plants), and its implications for the prevalence of niche vs. neutral processes driving understory development, have not been explored. We asked whether predictable vegetation-environment associations exist at the microsite scale, with the goal of informing caribou range management. We sampled canopy and edaphic variables in patches of lichen, feathermoss, and vascular plants in subalpine lodgepole pine (Pinus contorta var. latifolia Engelm. ex S.Wats.) forests, in north-central British Columbia, Canada. Lichens positively associate with microsites that have high light and heat, and low moisture and nutrient availability; vascular plants positively associate with base-cation availability, sulphur and phosphorus availability, fine-textured soils, thick organic layers, and high light; feathermosses positively associate with low light and heat, and nitrogen availability. Understory composition is most strongly associated with canopy characteristics, but is also related to edaphic properties in predictable ways; soil and canopy attributes may further interact to define distinct intra-stand niches. The viability of caribou winter ranges can likely be extended by partially thinning or burning the canopy and organic layers, but the longevity of a lichen-dominant stage may ultimately depend on the soil texture, due to its influence on vascular plant growth.Résumé : Les relations végétation-environnement des forêts boréales à lichens sont bien connues, mais la base mécanistique de la microrépartition du sous-étage à petite échelle (taches dominées par les lichens, les mousses et les plantes vasculaires), et ses implications dans la prévalence de la niche vs. les processus neutres qui contrôlent le développement du sous-étage, n'ont pas été explorées. Les auteurs ont demandé si des associations végétation-environnement prévisibles existent à l'échelle du microsite, afin de mieux gérer les grands pâturages de caribous. Ils ont échantillonné le couvert forestier et les variables édaphiques dans les taches de lichens, d'Hylocomiaceae et de plantes vasculaires dans des forêts de pins lodgepole subalpines (Pinus contorta var. latifolia Engelm. ex S.Wats.), dans le centre-nord de la Colombie-Britannique, Canada. Les lichens étaient associés positivement aux microsites bénéficiant de lumière et de chaleur élevées, et d'une humidité et d'une disponibilité en nutriments faibles ; les plantes vasculaires étaient associés positivement à la disponibilité en cations basiques, à la disponibilité en soufre et phosphore, aux sols de texture fine, aux couches organiques épaisses et à une lumière élevée, les Hylocomiaceae étaient associées positivement à une lumière et une chaleur faibles, et à la disponibilité en azote. La composition du sous-étage était plus fortement associée aux caractéristiques du couvert forestier, mais elle était aussi ...

Boreal coniferous forest density leads to significant variations in soil physical and geochemical properties

“…Overall, because we did not find any difference in the geochemistry and texture of the C horizon between ecosystem types and because our sites developed from surficial deposits (undifferentiated till, dead-ice moraine) of similar origin (glacial), our results, which are in line with those of other studies, suggest a biological influence of vegetation on soil profile development and soil chemistry (Finzi et al, 1998;Haughian and Burton, 2015;Wood et al, 1984). Haughian and Burton (2015) showed that more variability in soil composition could be explained by vegetation functional groups (e.g.…”

“…Haughian and Burton (2015) showed that more variability in soil composition could be explained by vegetation functional groups (e.g. mosses vs. lichens) than by abiotic characteristics (soil texture, topography).…”

“…We suggest the following potential causes for the difference observed in soil between LW and MF ecosystems: (i) the abundance of tree cover could influence soil formation through its direct consequence of canopy openness on soil micro-environmental conditions and drainage; (ii) snowfall rate and snowmelt duration in turn may influence reductive conditions and cause differential dissolution of iron oxides that accumulate in the B horizon (Giesler et al, 2002); (iii) thickness of organic soil layers could create differential insulating properties (Lawrence and Slater, 2007); (iv) because water flow also affects the distribution of chemical elements such as labile P, Fe and Al (Giesler et al, 2002), differences in drainage conditions, slope, moisture and hydrochemical processes under moss and lichen covers (Brown et al, 2010;Haughian and Burton, 2015;Price et al, 1997) could also explain the observed variations in lw and mf soil chemical properties; and, finally, v) lichen surface weathering capacity (Chen et al, 2000;Porada et al, 2014) may be responsible for the higher concentrations of Fe and Al species in LW upper mineral horizons, while a dense moss cover may be less aggressive in mineral weathering; however, because this environment is more productive, it could generate more organic acid and favour a deeper profile development. It has previously been suggested that the two vegetation types considered could be two ecological states and that LW could be an alternative stable state resulting from regional disturbance history (Jasinski and Payette, 2005).…”

“…Differences in canopy openness and groundcover type may lead to variations in soil formation processes. MF soils should develop thicker accumulation (B) soil horizons as more organic matter inputs are provided by the denser vegetation, leading to higher nutrient availability (Bonan and Shugart, 1989;Haughian and Burton, 2015). Conversely, the lowdensity canopy in LW should provide a lower nutrient supply, along with higher light and heat (Haughian and Burton, 2015;Sulyma and Coxson, 2001), leading to different soil microclimatic conditions.…”

“…MF soils should develop thicker accumulation (B) soil horizons as more organic matter inputs are provided by the denser vegetation, leading to higher nutrient availability (Bonan and Shugart, 1989;Haughian and Burton, 2015). Conversely, the lowdensity canopy in LW should provide a lower nutrient supply, along with higher light and heat (Haughian and Burton, 2015;Sulyma and Coxson, 2001), leading to different soil microclimatic conditions. Variations in hydrological processes are to be expected beneath both ground covers as moss layers, which have a high water holding capacity, create a saturated environment that is less favourable to decomposition, whereas lichen layers may maintain soil moisture at lower levels (Bonan and Shugart, 1989).…”