Predictions of where minimal damage to jarrah roots could result in tree death

Abstract

Field observations of Eucalyptus marginata Dorm ex Smith (jarrah) trees on sites infested with Phytophthora cinnamomi Rands showed that sudden and sustained stem shrinkage at 1–3 m preceded crown death. This was interpreted as indicating severe water deficiency in the stem base before the foliage died. Reduced mot 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 sap wood conduction were made in 20 cm‐long segments of large horizontal jarrah roots using gas flow at positive pressure. Conduction. expressed as cm3 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 with increasing vessel number or a decrease in the proportion of tylosed vessels. Observations on roots from trees from two sites, part of each site being infested with P. cinnamomi, indicated that maximum conduction mm−2 along a root was associated with site, not whether or not the site was infested with P. cinnamomi. Our calculations show that conduction in large horizontal roots is not constant, but decreases dose 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. Copyright © 1995, Wiley Blackwell. All rights reserved