Seed dispersal and recruitment limitation are barriers to native recolonization of old‐fields in western Australia

Abstract

Summary1. Native recolonization of abandoned farmland in the wheat-growing region of western Australia is slow to non-existent, even 45 years after abandonment. Instead, old-fields tend to be dominated by non-native annual grasses. The native vegetation in the region is highly fragmented. We predicted that recovery is limited by seed availability and recruitment failure. 2. We compared the seed rain, soil seed bank and extant vegetation of three old-fields and three adjacent native woodland remnants to test our predictions. 3. Seed dispersal limitation was evident at two old-fields: species richness of the native seed in the soil seed bank declined at 50-m increments (i.e. 0 m, 50 m and 100 m) into the old-fields. Species richness of recolonizing native vegetation also declined along this transect. 4. Recruitment limitation was evident at one old-field, probably linked to the few abundant non-native species that dominated the vegetation. These non-natives dominated the seed supply, and tended to germinate more rapidly than the native seeds. 5. In contrast, seed dispersal and recruitment had not limited native recolonization of the third old-field: 91% of the species present in the adjacent remnant had recolonized this old-field. Species richness and abundance of non-natives in the seed supply and extant vegetation were minor compared with that of the other old-fields. Therefore an adequate seed supply of natives, the lack of non-natives and chance natural disturbance events (i.e. cyclone and fire) had probably contributed to this result. 6. Synthesis and applications. Native recolonization of wheatbelt old-fields is contingent upon the unusual coincidence of seed availability, favourable conditions for recruitment and an absence of competitive non-natives. Grasses, annual herbs and Acacia shrubs are dominant among the few native species that have consistently recolonized these oldfields. In most cases, direct seeding and control of non-natives are the minimum requirements for restoration of wheatbelt old-fields to species-rich eucalypt woodlands.

The seed bank of subtropical grasslands with contrasting land-use history in southern Brazil

“…Seed limitation of typical native grassland species and presence of annual non-natives in disturbed old-fields areas has been observed in other studies in the southern hemisphere (Tognetti et al 2010, Standish et al 2007. Our study, together with the few other available studies of the seed bank of subtropical Campos Sulinos grasslands in Brazil, indicates that the large majority of typical grassland species depend on vegetative regrowth from rhizomes or underground storage organs after a disturbance (Fidelis et al 2014), or that are short lived in the soil and that regeneration from the seed bank is not the principal plant strategy.…”

Incorporating novelty and novel ecosystems into restoration planning and practice in the 21st century

“…Chief among the changes that are difficult to reverse are missing soil seed banks, nutrient enrichment, the presence of competitive non-native species, and reduced seed sources and land degradation associated with habitat fragmentation (Standish et al , 2007(Standish et al , 2008. Socio-economically, there is not the current knowledge to recover all facets of the historic ecosystem (e.g., native ground cover), and additionally there is not the needed level of investment to discern methods to do so.…”

“…At the experimental site, ecological and socio-economic thresholds are present which indicated that restoration to historic York gum woodland would likely be prevented (Standish et al 2007). Chief among the changes that are difficult to reverse are missing soil seed banks, nutrient enrichment, the presence of competitive non-native species, and reduced seed sources and land degradation associated with habitat fragmentation (Standish et al , 2007(Standish et al , 2008.…”

Impact of tree species on nutrient and light availability: evidence from a permanent plot study of old-field succession

“…The observed gradient strongly supports the initial floristic composition model by Egler (1954) and the strong and persistent influence of the land use history on the plant community and the pathway of succession, respectively (Koerner et al 1997;Dupouey et al 2002;Bonet 2004;Dölle and Schmidt 2007). Which species dominate during succession can be determined by numerous factors like differences in seed dispersal, interannual differences in seed production (mast years), soil seed bank, germination requirements, relative growth rate, competition with other plant species, as well as various environmental parameters (Hard 1975;Schmidt 1981;Tilman 1988;Zeiter et al 2006;Standish et al 2007).…”