The Relationship between Attributes of Plants Represented in the Germinable Seed Bank and Stocking Pressure in a Semi-arid Subtropical Rangeland

Abstract

A range of diaspore and mature plant attributes of the species represented in the germinable seed bank of a semi-arid subtropical Queensland sheep rangeland was investigated. The attributes of both the diaspores themselves and the plants that produced them changed as distance from water increased. Close to the water source, species with prostrate or erect growth habit and with low palatability and capsular fruits were common, whereas further from the water source plants with ascending growth habits, high palatability and mericarpic fruits were more frequent. At close proximity to water, species with diaspores that germinated rapidly, were unornamented, with unassisted dispersal and rounded in shape were common, whereas at greater distance from water, species tended to possess diaspores which germinated slowly, were ornamented (possessed awns, barbs, or hairs), with an elongated shape. Longevity of the plants (annual or perennial) was not significantly affected by distance from water. The dormant, vegetative and reproductive phases of plants that are successfully incorporated into the germinable soil seed bank can, therefore, be related to success under the different stocking intensities present at different distances from water.

Spatio-temporal variation in soil seed banks under contrasting grazing regimes following low and high seasonal rainfall in arid Namibia

“…With the structural and compositional changes of the biophysical environment, selections for size traits occur that permit plants to increase in abundance (Osem et al, 2006). For example, high livestock pressure favors annuals, which tolerate or avoid intense grazing and trampling through various adaptations, such as prostrate growth and small seeds, which become easily buried (Navie and Rogers, 1997). During secondary dispersal, seed traits interact with microsite characteristics, thus determining where a moving seed comes to rest (Chambers, 2000).…”

Species, functional groups and community structure in seed banks of the arid Nama Karoo: Grazing impacts and implications for rangeland restoration

“…Accordingly, the annual/biennial life cycle, high abundance of tiny and small diaspores and, consequently, persistent soil seed banks were similarly the most represented plant regenerative strategies irrespective of the grazing regime. However, there was a shift in the abundance of regeneration strategies known to be related to grazing and/or trampling avoidance or tolerance (Aboling et al, 2008;Cornelissen et al, 2003;Navie and Rogers, 1997). Persistence under severe grazing was linked to the trait combination of high seed production, prostrate growth and/or easily buried small and rounded seeds.…”

“…Following Chambers et al (1991), individual diaspore masses were obtained from 90 to 100 oven-dried (48 h at 60 • C) diaspores per species. Diaspore length-to-width ratio was calculated as a measure for shape (Navie and Rogers, 1997) with all appendages or enclosing structures which were assumed to be part of the dispersal unit entering the soil. Although dispersal of all recorded species can be regarded more or less restricted in space in time, lightweight diaspores (<0.1 mg) and such with morphological characters directly interacting with dispersal agents like wind or animals (e.g.…”

Large-scale grazing history effects on Arctic-alpine germinable seed banks

“…Similar trait dominance was found in both stable and increased districts. The general pattern reflected in both seed banks from increased and stable districts seemed to correspond to a more classic overall grazed ecosystem, i.e., small seeds lacking dispersal mechanisms (Navie and Rogers 1997) and mainly of graminoid growth form. Several graminoid species Table 2 Geometric means (and 95% confidence intervals) for the seed density (seeds per m 2 ) per habitat (n) of the different growth forms, and seed traits, i.e., seed mass and diaspore morphology Geometric means are given for each combination of grazing history and region are known for their capacity of compensatory or even overcompensatory growth under grazing pressure (Wegener and Odasz 1997;Bråthen and OdaszAlbrigtsen 2000).…”

“…Changes in seed bank structure associated with grazing could also be influenced by processes related to seed and dispersal unit characteristics, because of their critical role in determining species responses to disturbance (Navie and Rogers 1997;Osem et al 2006). Grazing is known to favor plants with small and round seeds lacking dispersal assisting structures (Eriksson and Eriksson 1997;Navie and Rogers 1997). Thus, in our approach to study the seed bank under grazing conditions, we consider both plant traits (growth form) and seed traits (seed mass and diaspore morphology).…”