NUTRIENT LOSSES FROM COMMERCIAL PICKING AND COCKATOO REMOVAL OF BANKSIA-HOOKERIANA BLOOMS AT THE ORGAN, PLANT AND SITE LEVELS

1. Losses of dry mass and mineral nutrients (N, P, K, Ca, Mg and Na), occurring through the commercial picking of blooms and their removal b y cockatoos, were quantified at the organ, bloom, plant and population -site levels for three picked and three unpicked populations of Banksi a hookeriana in the scrub-heath of Western Australia. 2. Above-ground dry mass and N and P contents of plants were reduced by 20%, 29% and 3 0%, respectively, from a mean commercial harvest of 29% of blooms over a 9-year period. Cockatoos removed only 1-2% of these during the same period. Removal of cations was in the same order of magnitude. 3. At the site level, losses of N and P from commercial picking were 3103 g ha(-1) of N and 152 g ha(-1) of P over the last 9 years. Removal of 24 0 g ha(-1) of N and 14 g ha(-1) of P by cockatoos was not a loss from the ecosystem as the flower heads were dropped near the plants. 4. Sur face soil nutrients, particularly NH4, NO3, Ca and Mg, and organic C w ere lower in the picked areas, which may indicate nutrient depletion a t the ecosystem level. 5. Bloom concentrations of N were higher by 15% , 32% and 65% for flower heads, leaves and stems, respectively, in unp icked plants, while P tended to be higher for leaves and stems in pick ed plants. Total N content of blooms tended to be higher in unpicked p lants. 6. Seed production was a very large drain on plant nutrients, w ith half of aboveground P and a quarter of N allocated to seeds. Equiv alent picking of cones for their seeds would cause a loss of 35% of P, and 24% of N. 7. Bloom picking not only removed potential nutrient si nks (developing fruits) but also some of the most recent and metabolic ally active leaves. This may have adversely affected the nutrient stat us and/or carbon balance of the plant, reducing subsequent growth, nut rient uptake, and bloom production.