Interaction between large herbivore activities, vegetation structure, and flooding affects tree seedling emergence

Abstract

Tree establishment in grazed vegetation mosaics involves a series of early bottlenecks, including seed dispersal, germination, seedling emergence, survival and growth. In a field experiment, we studied seedling emergence of two species with contrasting recruitment strategies, Fraxinus excelsior and Quercus robur, in five structurally different vegetations: grazed and ungrazed grassland, ruderal pioneer vegetation, soft rush tussocks, tall sedge mats and bramble scrub. In a simulation experiment, we studied the interaction effects of pre-emergence flooding (3 weeks of inundation), trampling and grazing (simulated by clipping) of grassland vegetation on the emergence and early growth of both tree species in grass swards. Seedling emergence was enhanced in low swards and sparse vegetation types. Despite different recruitment strategies, the interaction of flooding and trampling of swards enhanced seedling emergence of both species. Grazing of soft rush and tall sedges enhanced emergence of F. excelsior.Clipping grass swards increased early growth of emerging Q. robur. Our results support the hypothesis that natural disturbances of soil and vegetation create microsites for seedling emergence and reduce aboveground competition. In grazed systems however, these results suggest a discordant relationship between successful seedling emergence and subsequent seedling growth/survival during the establishment process in structurally different vegetations.

Biological Flora of the British Isles:Fraxinus excelsior

“…In a variety of grasslands and grazed pastures, while high‐intensity grazing reduces establishment (Hester, Mitchell & Kirby ; Mottet et al . ), low intensity of grazing may facilitate ash invasion by reducing competition but leaving some areas ungrazed providing regeneration niches for ash (Marie‐Pierre, Didier & Gérard ; Van Uytvanck, Milotic & Hoffmann ). Hester, Mitchell & Kirby () found recruitment of ash into sheep‐grazed grassland in Cumbria was greatest in low grazing intensity plots (0.6–1.2 sheep ha −1 ).…”

Can Eucalyptus invade native forest fragments close to commercial stands?

“…The eucalypt seedlings disappeared within a short time frame and after one year, the number of native species seedlings was similar in the plots with exposed soil and in unchanged soil. Changes in soil or vegetation create microenvironments that positively influence germination of seeds and reduce competition above ground (Van Uytvanck et al, 2010). But in tropical conditions, these microenvironments vanish quickly due to the strength of local regeneration.…”

Trampling enhances the dominance of graminoids over forbs in flooded grassland mesocosms

“…Those perturbations exert antagonistic effects upon the structural attributes and the floristic composition of the plant community. Trampling modifies the community structure by flattening out the vertical distribution of the canopy (Edmond 1964; Pellerin et al 2006; Van Uytvanck et al 2010), and changes the floristic composition by favouring prostrate stoloniferous graminoids and rosette forbs (Sala et al 1986; Sun & Liddle 1993; Cole 1995a; Kobayashi et al 1997). In contrast, flooding modifies the community structure by promoting the location of foliage in upper layers of the canopy (Pehrsson 1988; Insausti et al 1999; Striker et al 2005) and subordinating species with rosette and creeping growth forms, which remain mostly submerged and shaded during the flooding period (Insausti et al 1999; Van Uytvanck et al 2010).…”

“…Trampling modifies the community structure by flattening out the vertical distribution of the canopy (Edmond 1964;Pellerin et al 2006;Van Uytvanck et al 2010), and changes the floristic composition by favouring prostrate stoloniferous graminoids and rosette forbs (Sala et al 1986;Sun & Liddle 1993;Cole 1995a;Kobayashi et al 1997). In contrast, flooding modifies the community structure by promoting the location of foliage in upper layers of the canopy (Pehrsson 1988;Insausti et al 1999;Striker et al 2005) and subordinating species with rosette and creeping growth forms, which remain mostly submerged and shaded during the flooding period Van Uytvanck et al 2010). To date, the effects of Applied Vegetation Science 14 (2011) [95][96][97][98][99][100][101][102][103][104][105][106] Applied Vegetation Science Doi: 10.1111/j.1654-109X.2010.01093.x r 2010 International Association for Vegetation Science both perturbations on grassland vegetation have been studied separately.…”