ARE PROTEA POPULATIONS SEED LIMITED - IMPLICATIONS FOR WILDFLOWER HARVESTING IN CAPE FYNBOS

Little is known about the extent to which plant population growth is l imited by seed production. We studied two non-sprouting Protea species , both entirely dependent on seeds for recruitment after fire, to dete rmine how flower harvesting would affect the size of the next generati on after burning. Five harvesting treatments (0, 25, 50, 75 and 100% i nflorescence removal) were applied, each replicated four times in 10 x 10 m plots. Seedbanks were censused before a late-summer burn for eac h species and each replicate. The mean proportion of seeds surviving t he burn until germination the following spring was 0.46 for Protea rep ens and 0.57 for Protea neriifolia. Of the seedlings that emerged, 90% and 55%, respectively, survived the first summer drought. Flower prod uction in the 9 year old stand was strongly related to population dens ity. Optimal plant-densities for maximum flower production were estima ted as 150 for P. repens and 70 for P. neriifolia. These target densit ies were greatly exceeded by seedling populations surviving the first summer drought in unharvested stands. If future density-independent mo rtality is negligible, the excess represents that part of the seedbank that could have been harvested before the burn without influencing fu ture flower production. We developed a simple static model for setting flower harvesting levels in these seed-saturated populations. The pre dicted harvesting levels (50% of inflorescences in P. repens and 85% i n P. neriifolia) were validated against the experimental harvests. We discuss the sensitivity of harvesting levels to variation in fecundity /density relationships, seed survival through a burn and seedling surv ival until flowering, and the implications for flower harvesting.