Seedling recruitment patterns over 4 years in an Australian perennial grassland community with different fire histories

Abstract

Summary1 Seedling recruitment was followed from 1993 to 1996 in four remnant Themeda triandra grassland sites in south-eastern Australia subjected to different long-term fire histories (1-, 2-, 4-year fire intervals, unburnt > 10 years). Multivariate analyses were used to separate the effects of site and year on recruitment and community dynamics. 2 Exotic species (mostly annual monocots such as Aira spp., Briza minor and Juncus capitatus ) dominated the seedling flora at all sites in all years. Seedlings of most native species were absent or rare in all years, despite their abundance in the standing flora. 3 Seedling recruitment (richness and density) in the long unburnt grassland was significantly less than in burnt sites in all years. Hence, the seedling floristic composition of this site was substantially different from all other sites on PCA axis 1, which did not differ in all years. 4 Amongst burnt sites, some differences in the annual seedling cohort were evident on PCA axes 2 and 3, but these were due to small differences in the relative abundance rather than the composition of recruiting species. Seedling recruitment was not cued or promoted by fire but rather, seedling density was influenced by, and interacted with, yearly (presumably rainfall) variation. 5 Amongst the native species seen as seedlings, yearly emergence occurred in some cases (14 of 24 species) but always at low densities (< 10 seedlings/0.25 m 2 ). Seedling survival amongst native species varied from nil (0%) to high (> 60%), with most mortality occurring in early summer. 6 The temporal and spatial variation observed in seedling regeneration suggests that long-term native species coexistence may be promoted by differences in the 'regeneration niche'. Seedling regeneration, however, has minimal impact on the short-term dynamic of this community, whose conservation requires maintenance of the existing 'bud-and tuber-bank' of native species.

Seed dynamics of Themeda triandra in the montane grasslands of South Africa

“…The poor representation of grasses in the seed bank (7-38%) contrasts with their dominance in the above-ground vegetation (75-81%). Similar observations were made by Morgan (2001), who found that seedlings of most native species in T. triandra grassland sites in Australia were rare despite their abundance in the standing flora. The absence of a persistent seed bank in South African grasslands highlights the importance of maintaining existing grasslands as a resource of seeds for restoration programmes.…”

Bryophyte Mats Inhibit Germination of Non-native Species in Burnt Temperate Native Grassland Remnants

“…Establishment on disturbed soil mats did not significantly affect seedling mortality, at least for the short duration of this experiment. The effects may have been more pronounced, however, if mortality had been monitored over summer when soil moisture likely becomes more limiting to seedling growth (Morgan 2001). Several studies have indicated that differential long-term survival of herbaceous seedlings can be expected on microsites with soil crusts compared to bare ground areas (e.g.…”

Prescribed burning and understory composition in a temperate deciduous forest, Ohio, USA

“…In fire-prone ecosystems, fire is often followed by a flush of germination from the seed bank (Lemon, 1949;Keeley et al, 2003;Milberg and Lamont, 1995;Morgan, 2001). Seed banks in deciduous forest sites are generally small relative to those of other North American ecosystems (Harper, 1977), and typically include disturbance-oriented annual and perennial herb species (Matlack and Good, 1990;Hyatt and Casper, 2000;Schelling, 2006).…”