Commercial picking of Banksia hookeriana in the wild reduces subsequent shoot, flower and seed production.
Abstract
The impact of bloom picking on subsequent flower and cone production, seed bank dynamics and plant architecture was studied in 3 picked and 3 unpicked 13-year-old populations of B. hookeriana, a canopy seed-storing, fire-sensitive shrub, growing on infertile sands in dry-mediterranean scrub-heath near Eneabba, Western Australia. After reaching reproductive maturity at 4 years, bloom picking over the subsequent 9 years reduced plant canopy area and volume by 37% and 44%, respectively, with a 56% reduction in the number of 1-year-old stems, compared with the unpicked plants. A total of 13 255 blooms/ha was picked over the 9 years, accounting for 29% of total production. Cockatoos removed a further 2477 blooms/ha (5% of the total), but removed over 3 times as many blooms in the unpicked plants (7562/ha, 7% of the total). Resprouting was much more likely from cockatoo-damaged stems than from picked stems. Picked plants produced 35% fewer blooms than unpicked plants, but percentage cone fertility and the number of follicles per fertile cone did not differ significantly. Seed production and storage per individual plant were 50 and 57% lower, respectively, in the picked plants. There was a slight increase in total insect-eaten seeds (4%) and a slight decrease in viable seeds (9%) in picked plants, but there were no significant differences in the fractions of seeds released, aborted or non-viable. The reduced seed store following picking could adversely affect post-fire regeneration, particularly if fires were at short intervals followed by an unusually severe summer drought. The study shows the usefulness of demographic studies in guiding management to resolve the conflict between commercial exploitation and the conservation of rare plant species.