Effect of forest canopy composition on soil nutrients and dynamics of the understorey: mixed canopies serve neither vascular nor bryophyte strata

Abstract

Question: The effect of overstorey composition on above‐ground dynamics of understorey vegetation is poorly understood. This study examines the understorey biomass, production and turnover rates of vascular and non‐vascular plants along a conifer–broadleaf gradient of resource availability and heterogeneity. Location: Canadian boreal forests of northwest Quebec and Ontario. Methods: We sampled mature stands containing various proportions of black spruce (Picea mariana (Mill.) BSP), trembling aspen (Populus tremuloides Michx.) and jack pine (Pinus banksiana Lamb.). Above‐ground biomass of the understorey vegetation was assessed through harvesting; annual growth rates were calculated as the differences between biomass in 2007 and 2008, as estimated by allometric relationships, and turnover rates were estimated as net primary production divided by the biomass in 2007. Results: Higher aspen presence, linked to greater nutrient availability in the forest floor, was generally associated with higher vascular biomass and production in the understorey. This effect was less pronounced in sites of high intrinsic fertility. In contrast, bryophyte biomass was positively associated with conifer abundance, particularly in wet sites of the Quebec study area. Non‐linear responses resulted in total understorey biomass being lower under mixed canopies than under pure aspen or pure conifer canopies. Turnover rates did not differ with overstorey composition. Conclusions: While resource availability is a main driver of understorey productivity, resources as drivers appear to differ with differences in understorey strata components, i.e. vascular versus non‐vascular plants. Resource heterogeneity induced by a mixed canopy had overall negative effects on understorey above‐ground productivity, as this productivity seemed to rely on species adapted to the specific conditions induced by a pure canopy.

Influences of evergreen gymnosperm and deciduous angiosperm tree species on the functioning of temperate and boreal forests

“…Angiosperms and gymnosperms are not systematically distinguished according to light interception rates (Augusto et al, 2003;Cavard et al, 2011;Yilmaz, Sevgi & Koc, 2012) as it corresponds to different levels of shade tolerance and shading strategies rather than to a functional trait typical of these two groups. Within a given climate, soil temperature is tightly linked to the proportion of sunlight that penetrates the tree canopy and reaches the forest floor, and so to the light interception rate of trees.…”

“…Hättenschwiler & Gasser, 2005), possible allelopathic effects between different organisms including plants and microbes, or other possible feedback loops caused by a change in flora (Barbier, Gosselin & Balandier, 2008;Cavard et al, 2011) or fauna (Deharveng, 1996;Felton et al, 2010) triggered by tree species. In our opinion, particular attention should be paid to some biotic interactions which may be highly complex but can significantly modify ecosystem functioning like litter-fauna interactions (e.g.…”

Sampling Method and Tree-Age Affect Soil Organic C and N Contents in Larch Plantations

“…Therefore, differences in sampling methods do not explain contradictory patterns of SOC and SON variation over time in the studied plantations. As seen in previous reports [9][10][11][12]17,18,20], prior land use, tree species planted, and soil nutrient supply may all affect SOC and SON dynamics after afforestation.…”

“…Additionally, studies examining post-afforestation conditions have reported both the depletion of soil nutrients [4,10,[17][18][19] and the accumulation of soil organic N (SON) with increasing soil organic C (SOC) [9,12,20] over time (e.g., tree age effect). Previous land use, the tree species planted, and soil nutrient supply are thought to explain the contradictions in tree age effects on soil properties after afforestation [9][10][11][12][17][18][19][20]. Furthermore, forest age itself [21], soil depth, and other site-related variations [22][23][24][25] have been used to describe the spatial and temporal changes in nutrient accumulation.…”

“…Soils can range from being a C sink (11 to 238 g·C·m −2 ·year −1 ) [4,[13][14][15]] to a source of atmospheric CO 2 (0.1 to 14.1 g·C·m −2 ·year −1 ) [11,16]. Additionally, studies examining post-afforestation conditions have reported both the depletion of soil nutrients [4,10,[17][18][19] and the accumulation of soil organic N (SON) with increasing soil organic C (SOC) [9,12,20] over time (e.g., tree age effect). Previous land use, the tree species planted, and soil nutrient supply are thought to explain the contradictions in tree age effects on soil properties after afforestation [9][10][11][12][17][18][19][20].…”