Changes in the understory plant community and ecosystem properties along a shrub density gradient

Abstract

Climate warming is projected to alter the vegetation community composition of arctic and alpine ecosystems including an increase in the relative abundance and cover of deciduous shrubs. This change in plant functional group dominance will likely alter tundra ecosystem structure and function. We conducted an observational study to quantify how the understory vegetation community and ecosystem properties varied along a shrub density and altitudinal gradient in a tundra alpine ecosystem in south-west Yukon. Although there was weak association between shrub density and species richness of understory community, there were large differences in functional group abundance between the different shrub densities; forb cover increased at lower elevations with higher shrub density at the expense of cryptogam and dwarf shrub cover. Litter mass, light interception, and soil carbon:nitrogen ratios all increased with shrub density. Sites with shrubs had higher summer soil temperatures, lower summer soil moisture, and lower percent soil nitrogen than the shrub-free site, although there was no difference in available nutrients among sites. This study presents findings from a nonmanipulated, model system where shrubification has been documented and suggests that direct and indirect effects of increasing shrub dominance are likely to affect the surrounding vegetation and abiotic environment controls.Key words: deciduous shrubs, alpine tundra, ecosystem properties, plant functional group abundance.Résumé : Le réchauffement climatique devrait modifier la composition de la communauté végétale des écosystèmes arctique et alpin, notamment par une augmentation à la fois de l'abondance relative et du couvert des arbustes à feuilles caduques. Ce changement dans la dominance de groupe fonctionnel de plantes risque d'altérer la structure et la fonction de l'écosystème toundra. Nous avons mené une étude observationnelle pour quantifier les variations de la communauté végétale en sous-étage ainsi que des propriétés écosystémiques le long d'un gradient de la densité arbustive et d'un gradient altitudinal dans un écosystème alpin de toundra au sud-ouest du Yukon. Même s'il y avait une corrélation faible entre la densité arbustive et la richesse spécifique de la communauté végétale en sous-étage, il existait des écarts considérables au niveau de l'abondance de groupe fonctionnel entre les différentes densités arbustives; le couvert d'herbes non graminéennes s'intensifiait à des altitudes plus basses avec une densité arbustive plus élevée, au détriment du couvert de cryptogames et d'arbustes nains. Quant à la masse de la litière, l'interception de la lumière et le carbone dans le sol: les taux de nitrogène ont tous augmenté avec la densité arbustive. Les aires comportant des arbustes avaient des

Holocene chloroplast genetic variation of shrubs (Alnus alnobetula, Betula nana, Salix sp.) at the siberian tundra‐taiga ecotone inferred from modern chloroplast genome assembly and sedimentary ancient DNA analyses

“…A major contributor to the observed changes is the increase in relative abundance and cover of deciduous shrub species including alder, birch, and willow. This process is colloquially known as shrubification (Crofts et al., 2018; Myers‐Smith et al., 2011). Increased shrub cover alters ecosystem properties.…”

“…Increased shrub cover alters ecosystem properties. Changes in biodiversity and carbon budgets due to shrubification have been reported, potentially affecting climate warming effects (Blok et al., 2010; Crofts et al., 2018; Lantz et al., 2013; McLaren & Turkington, 2010; Myers‐Smith et al., 2011; Myers‐Smith & Hik, 2013). Species richness, for instance, can decline with increasing shrub dominance across the Arctic (Pajunen et al., 2011).…”

“…This has been linked to the competitive exclusion of shade‐intolerant species, in particular lichens and mosses growing under shrub canopies (Pajunen et al., 2011; Walker et al., 2006). On the other hand, low densities of shrubs have been associated with increased understory species richness (Crofts et al., 2018).…”

Woody plants constructing tundra soils

“…Through this 486 hierarchical approach, we controlled for the influence of other possible factors-namely, the 487 topography, wintertime snow depth, and overall vascular plant conditions. Our study benefitted 488 from a hierarchical framework, since previous studies found it challenging to test whether the 489 effects found resulted from changing vegetation properties or from, for instance, the underlying 490 topography (Crofts, Drury, & McLaren, 2018). Thus, we recommend future studies consider SEM 491 in their analyses when investigating hierarchical systems (Lefcheck, 2016).…”

Vascular plant biodiversity of Katannilik Territorial Park, Kimmirut and vicinity on Baffin Island, Nunavut, Canada: an annotated checklist of an Arctic flora

“…Shrub growth response to climate varies with factors such as geography, soil moisture and sea ice decline ( Myers-Smith et al 2015 ; Gamm et al 2018 ; Buchwal et al 2020 ). Shrub expansion is often associated with decreased species diversity in tundra ecosystems and changes in plant community functional group composition ( Cornelissen et al 2001 ; Wilson and Nilsson 2009 ; Pajunen et al 2011 ; Crofts et al 2018 ). Heterogeneous High Arctic tundra landscapes may become homogeneous dwarf-shrub tundra due to climate change ( Stewart et al 2018 ).…”