HOWEVER, TREE PERFORMANCE IN DRY HABITATS CANNOT BE EVALUATED WITHOUT CONSIDERING CONSTRAINTS WITHIN THE PLANT THAT INFLUENCE CARBON GAIN (EHLERINGER 1994). FOR EXAMPLE, TREES WITH AN EFFECTIVE WATER SUPPLY SYSTEM MAY LACK SPECIFIC ADAPTATIONS FOR CONTROLLING WATER LOSS, RESULTING IN LOW TISSUE WATER STATUS THAT AFFECTS PLANT PERFORMANCE (KRAMER 1980, LEVITT 1980). LOW MAXIMUM STOMATAL CONDUCTANCE AND HIGH STOMATAL SENSITIVITY TO CHANGES IN WATER STATUS MAY BE REQUIRED TO MAINTAIN LEAF WATER POTENTIAL (ΨL) ABOVE A CRITICAL THRESHOLD AND TO AVOID XYLEM CAVITATION (TYREE AND SPERRY 1989, JONES AND SUTHERLAND 1991).