Some ecological trends in vessel characters

Abstract

Data on vessel arrangement, grouping, diameter, perforations, element length, wall thickness and helical thickenings are presented for the woody flora of Israel and adjacent regions. Within this flora the arid, Mediterranean, hygrophylic and synanthropic components are compared with each other and with information on woods from the tropical rain and monsoon forest flora of Java and the mesic cool temperate flora of North West Europe. In these floristic comparisons, vessel element length decreases from mesic to xeric vegetations and within mesic floras from tropical to cool temperate or arctic latitudes. Other characters show complex trends and individual ecological categories show very wide, overlapping ranges of wood structural possibilities. The arid flora shows the highest proportion of species with a combination of numerous narrow, and wide vessels in their wood; a high degree of vessel grouping is also most common in this ecological category. Tropical species surviving in wadis of the Negev and Sinai desert do not show this syndrome but resemble their relatives from less xeric conditions. The wood of arid species in general appears to be at least as well adapted to efficient water transport (high values for maximum vessel diameter) as to safety (provided for by numerous, narrow vessels). Vessel walls tend to be thickest in the arid flora. Spiral thickenings are most common in the Mediterranean and temperate floras and are quite infrequent in both the arid subtropical flora of the Middle East and the mesic to seasonally dry tropical flora. Factors underlying the trends observed can only partly be retraced to ecological tendencies within genera; partly they appear to depend on the predominance of species belonging to specialised families in extreme habitats like the desert.