Comparative size, fecundity and ecophysiology of roadside plants of Banksia hookeriana.
The use of road verges in SW Australia for conservation of indigenous species was investigated in B. hookeriana, a shrub which is a major food source for indigenous animals and valued as an attractive species for tourism and wildflower harvesting. The crowns of roadside plants were on average 2.34 times larger than their non-edge counterparts for a range of ages at five sites with infertile sandy soils. Roadside plants produced 2.51 times more flower heads. Cone weight of roadside plants was 32% greater than in non-roadside plants and they contained 27% more follicles and seeds. The fractions of seeds released and eaten/decayed were similar at both positions. Increased cone production, follicles per cone and seed viability per follicle resulted in a 4.74 times larger seed store in the roadside plants. This greater fecundity was apparently due to greater access to water (non-significantly different or higher transpiration rates, lower pre-dawn tensions and diurnal leaf temperatures) and mineral nutrients (including higher concentrations of N, K and Ca), leading to higher photosynthetic and growth rates. Variable access to resources was confirmed by a bioassay using B. hookeriana seedlings: there was a decreasing gradient in survival and size from the road drain beside the roadside plants through to the non-edge positions.