STRUCTURAL RESPONSE OF MEDITERRANEAN WOODLAND SPECIES TO DISTURBANCE: EVIDENCE OF DIFFERENT DEFENSE STRATEGIES

ABSTRACT

This paper examines the structural response to disturbance of two common species, Quercus calliprinos and Phillyrea latifolia, in a dry Mediterranean woodland in Israel. Disturbance was represented by (a) a continuous diffuse effect as a result of browsing during a 5-year period, (b) a discontinuous concentrated disturbance caused by a single massive thinning and pruning treatment, and (c) a combination of thinning and browsing. Q. calliprinos responded to browsing by increasing leaf toughness and the number and sharpness of leaf spines. Leaf shape was also affected. P. latifolia, on the other hand, showed much less structural adaptations, but responded to both continuous and discontinuous disturbance by intensive shoot regrowth. It appears that while Q. calliprinos has developed complex defense mechanisms to continuous disturbance such as browsing, P. latifolia has employed a different strategy which may be better adapted to massive concentrated disturbance (wood cutting, fire), since under such conditions rapid “recapture” of space by vigorous lateral growth can be an advantage. It is concluded that different defense strategies can point to the dominant disturbance sources against which they have been developed. The multiple-source disturbance so typical of the Mediterranean ecosystems (heavy grazing, frequent fires, and wood cutting) is a probable reason for the coexistence of two distinct defense strategies within the same woodland stands. Other differences (tannin content, tree regrowth pattern) also support this hypothesis.