Understory plant assemblages present distinct short-term responses to the clear-cutting of an old-growth spruce forest near an alpine timberline

Abstract

Forest clear-cutting is a prominent disturbance influencing understory plant communities. We implemented a before-after, control-impact (BACI) designed experiment in a high-elevation, old-growth spruce forest in the eastern Tibetan Plateau to understand the response in cover and species richness of the understory plant community and its assemblages, as well as the driving roles of environmental alteration (e.g., radiation, temperature, humidity, and nutrients), physical disturbance (e.g., direct damage by trampling and tree-felling), and interplay effects (e.g., shading or burial from logging residue) during a 2-year period. The decrease in cover for the understory vegetation was predominantly due to a decrease in bryophytes; the grass cover, however, increased. While bryophyte species richness decreased, the total number of understory and vascular plants changed minimally. Furthermore, the environmental alteration drove the increase in grass cover, as well as the cover and species richness decline for bryophytes and its two species groups. It was also found that physical disturbances and interplay effects caused the decrease in cover for bryophytes. The total effects influenced the understory community and bryophytes in terms of cover, but not in terms of species richness. We conclude that the short-term responses of understory vegetation to clear-cutting are distinct across different assemblages due to various mechanisms. Bryophytes are more sensitive than vascular plants, and cover percentage responded more swiftly than species richness to clear-cutting.Key words: understory vegetation, species groups, driving mechanism, physical disturbance, clear-cut logging, Tibetan Plateau.Résumé : La coupe à blanc est une perturbation importante de la forêt qui influence les communautés végétales de sous-bois. Nous avons implanté un dispositif expérimental BACI dans une vieille forêt d'épinette établie en haute altitude sur le plateau tibétain oriental pour comprendre l'impact sur la richesse du couvert et les espèces de la communauté végétale de sous-bois et de ses assemblages de même que les rôles déterminants de l'altération des conditions environnementales (c.-à -d. le rayonnement, la température, l'humidité et les nutriments), des perturbations physiques (c.-à -d. les dommages directs par le piétinement et la coupe des arbres) et des effets d'interaction (c.-à -d. l'ombrage ou l'enfouissement par les résidus forestiers) pendant une période de 2 ans. La diminution du couvert de la végétation de sous-bois a surtout été causée par une diminution des bryophytes. Le couvert herbacé, de son côté, a augmenté. Bien que la richesse en espèces de bryophytes ait diminué, le nombre total de plantes vasculaires et de sous-bois a peu changé. De plus, l'altération des conditions environnementales a entraîné l'augmentation du couvert herbacé et la diminution du couvert et de la richesse en espèces de bryophytes et de ses deux groupes d'espèces. Nous avons aussi observé que les perturbations physiques et que les effets d'i...

The Growth of Two Species of Subalpine Co-nifer Saplings in Response to Soil Warming and Inter-Competition in Mt. Gongga on the South-Eastern Fringe of the Qinghai-Tibetan Plateau, China

“…In summary, strong interspecific competition across this subalpine ecotone for resources and light among understory Sargent spruce may be important influences inhibiting seedling establishment and tree regeneration. All the above-mentioned differences were not observed in Purple cone spruce; this is in accordance with the known shade tolerance of this species [65]. In undergrowth with heavy shading, Sargent spruce tended to decrease its biomass allocation whereas Purple cone spruce showed no significant changes; a fact that might offset the dominant position of Sargent spruce and increase the regeneration opportunity of purple cone spruce, as an associated tree species under competition in the undergrowth community.…”

Latitudinal patterns and environmental drivers of moss layer cover in extratropical forests

“…Forest mosses are well adapted to marginal oligotrophic environments (Bates, 2000), but they are physiologically limited by water availability (Proctor et al, 2007) and sensitive to forest disturbance (e.g., Dovčiak, Halpern, Saracco, Evans, & Liguori, 2006). At fine (microsite) scales, forest moss cover tends to increase with moisture (e.g., Busby, Bliss, & Hamilton, 1978), complexity of the microtopography (Økland, Rydgren, Økland, Storaunet, & Rolstad, 2003) and time since disturbance (forest age; e.g., Liu & Bao, 2014;Zhang et al, 2016). In addition, moss cover tends to decrease with nutrient and light availability (Glime, 2007), and it varies with substrate type (Halpern, Dovciak, Urgenson, Evans, 2014) and canopy composition (Bartels & Chen, 2013;Hart & Chen, 2006).…”

Compositional stability of boreal understorey vegetation after overstorey harvesting across a riparian ecotone

“…The strong influence of bryophytes on post‐disturbance compositional stability is attributable to their strong sensitivity to canopy removal after harvesting (Åström et al. ; Hart & Chen ; Liu & Bao ).…”

“…). By contrast, upland understorey communities, driven mainly by light availability, are relatively species‐poor and dominated by species that require overstorey shading (Nilsson & Wardle ; Hart & Chen ; Liu & Bao ). We therefore expect that upland sites would have a lower compositional stability than streamside communities following overstorey removal by harvesting if high pre‐disturbance biodiversity impedes the establishment of non‐resident colonizing species.…”

“…These conditions, as well as high pH and low moisture content in the thin organic layer following canopy removal, exceed the tolerance of many bryophyte species (Åström et al. ), resulting in bryophyte declines (Hart & Chen ; Liu & Bao ). Bryophytes are highly sensitive to disturbances, and in systems like the boreal forest, where bryophyte species contribute a major proportion to ground‐layer species abundance and diversity in the upland forest understorey than streamside (Hart & Chen ; Dynesius et al.…”