SURVIVAL OF SEVERE DROUGHT BY A NON-SPROUTING CHAPARRAL SHRUB

A 2-yr drought (1975-1977) in much of California provided unusually severe water stress on many native plant species. In this paper we evaluate the effects of this drought on Arctostaphylos viscida Parry, a common non-sprouting chaparral shrub in the foothills of the southern Sierra Nevada. At the peak of the drought, water potentials as low as –74 bars were measured. While only three of 90 shrubs sampled were killed by the drought, all but one showed signs of drought-induced dieback. First and second year post-drought twig growth was significantly greater on shrubs with 90% or greater branch mortality than on those suffering lesser dieback. In all cases, new growth occurred only on surviving branches. Midday water stress measurements showed little difference for shrubs exhibiting high and low levels of dieback. These results suggest that drought survival in Arctostaphylos viscida may depend on a mechanism where certain branches are sacrificed with the surviving ones preferentially receiving available resources. The possibility that this may involve the dieback of below ground roots and/or lack of production of new roots to compensate for lack of root turnover is supported by water stress measurements of adjacent fire damaged shrubs. Implications of possible specialized drought survival mechanisms in non-sprouting shrubs are explored.