PREDICTIONS OF WHERE MINIMAL DAMAGE TO JARRAH ROOTS COULD RESULT IN TREE DEATH

Field observations of Eucalyptus marginata Donn ex Smith (jarrah) tree s on sites infested with Phytophthora cinnamomi Rands showed that sudd en and sustained stem shrinkage at 1.3 m preceded crown death. This wa s interpreted as indicating severe water deficiency in the stem base b efore the foliage died. Reduced root conduction might be an important factor leading to tree death. Measurements of conduit length in stems and roots showed that c. 15% were 1 m long and the remainder 40-50 cm long. Qualitative measurements of sapwood conduction were made in 20 c m-long segments of large horizontal jarrah roots using gas flow at pos itive pressure. Conduction, expressed as cm(3) gas flow mm(-2) min(-1) increased with increasing distance from the tree bole. This increase was associated with an increase in vessel cross-sectional area, not wi th increasing vessel number or a decrease in the proportion of tylosed vessels. Observations on roots from trees from two sites, part of eac h site being infested with P. cinnamomi, indicated that maximum conduc tion mm(-2) along a root was associated with site, not whether or not the site was infested with P. cinnamomi. Our calculations show that co nduction in large horizontal roots is not constant, but decreases clos e to the base of a jarrah tree, so that damage close to the bole will have the greatest effect on water movement to the foliage.