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Changes in tree stratum

We originally chose the Conservation Woodland for a study site because of its large trees. In some parts the trees are up to 25 m high with diameters of up to 1 m. These are some of the largest trees we have seen in Cumberland Plain Woodland in western Sydney and are likely to be at least 100-200 years old. In some parts of the woodland however the trees are much smaller, evidently where the original trees were cleared during the farming period and young trees have grown since then.

Eucalypt seedling recruitment is generally confined to areas around the canopy of mature seed trees, or within 20 to 30 m of tree canopies This pattern is commonly observed in woodland at Mount Annan. This is because eucalypt seed is small and has no special dispersal mechanism apart from being shed 10-20 m above the ground to be blown a few metres away and may be washed a further few metres across a bare soil surface in rainwater. A lot of seedlings came up following the cessation of grazing in the 1980s and are now trees up to 8 m high.

Interestingly there has been very little subsequent recruitment in the woodland since the 1980s. A few seedling have been recorded in the sample plots but none of these have survived. The only obvious recent successful recruitment has been near the road along a line dug for a water pipe where backfilled soil provided bare soil for the seedling recruitment, trees overhead provided seed, and there was enough rainfall.

Most of the sapling recruitment has been of Grey Box Eucalyptus moluccana and Forest Red Gum Eucalyptus tereticornis, with a small amount of Narrow-leaved Ironbark Eucalyptus crebra. However during the 1990s many adult ironbarks gradually died despite relatively favourable rainfall conditions. We consider that these deaths were a delayed long-term result of the 1980s drought, and the impacts of the increased nutrients and compaction of the soil by stock grazing.

Flowering and fruiting by the woodland eucalypts is very sporadic. At no time could we say that all mature trees of a particular species were in flower, though we would note occasional individual trees flowering. Nor could we note any clear seasonal trends in those individuals that did flower. Fruiting occurs a considerable time after flowering, but again we have not noted any distinctly recurring patterns.

Halo effects around trees

In some areas we noted that the understorey under large trees was different to that nearby. There were more Einadia plants, and weeds such as *Sida rhombifolia. We put this down to these being the site of old stock camps, resting places for animals during hot weather, where nutrients had been locally increased, conditions the Einadia plants would like. However these conditions seem more widespread than we had thought, and a listing of species within about 5 to 10 m of large trees includes the following - 4 species of Einadia, 2 Solanums, *Olea europea subsp. cuspidata and *Sida rhombifolia, grasses rare. These species all have fleshy fruits and are likely to be spread by birds, therefore being concentrated below canopies of large and particularly remnant trees. These effects are most conspicuous under old well-established trees, and may take at least 20 years to become noticeable. First established under isolated trees are the *Olea eurapaea subsp cuspidata, African olive, followed by Einadia species. It is likely that *Olea europaea subsp cuspidata will crowd out other species by its dense canopy and the growth of its own seedlings.

See our image gallery of tree species in the woodland. 

Asterisk * indicates exotic species naturalised at the Australian Botanic Garden.

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