Factors limiting the recruitment of Eucalyptus salmonophloia in remnant woodlands .3. Conditions necessary for seed germination

Characteristics of the germination strategy of Eucalyptus salmonophloia F.Muell. are described and whether the germination niche is limiting recruitment of E. salmonophloia seedlings in remnant woodlands is discussed. Germination in E. salmonophloia proceeds with favourable soil temperature and water conditions on a variety of substrates. However, at temperatures above and below the optimum for germination (25 degrees C), enforced dormancy occurs and germination is retarded. In these situations, dormancy is simply overcome when temperatures return to optimum. Evidently, seeds can remain moist at sub-optimal temperatures for prolonged periods without losing viability. Furthermore, E. salmonophloia seeds are capable of withstanding a cycle of wetting and drying with undiminished germination capacity. Conditions suitable for germination occur at the beginning of the winter wet season in south-western Australia when soil temperatures are still suitable and soil moisture and atmospheric humidity are frequently high. These germination characteristics minimise the chances of seeds germinating at times when the probability of seedling establishment is low (e.g. summer). This is particularly important because E. salmonophloia only establishes a temporary soil, seed-reserve following large scale disturbances, and therefore the opportunities for recruitment may be quite rare. In remnant woodland when ants were excluded and a soil seed-bank was created artificially, seeds germinated but no seedlings survived. This suggests that the destruction of seeds by ants during inter-disturbance periods is having little effect on recruitment because seedlings are unlikely to establish. Unfavourable conditions for germination are unlikely to be responsible for the lack of E. salmonophloia seedling recruitment in remnant woodlands. Further research is needed to identify the factors critical for seedling establishment; changes in resource availability following large-scale disturbances and associated tree death are important in this respect.