Intraspecific competition in honey mesquite: Leaf and whole plant responses

Abstract

Leaf and whole plant responses of honey mesquite (Prosopis glandulosa Torr.) to intraspecific competition were compared under low (LD) or high (HD) stand density in a semi-arid region of north Texas. The HD trees occurred within a stand of 300 trees ha-1. The LD trees occurred in areas of the dense stand that were thinned to 80 trees ha-1 with no neighbors within 10 m of study trees. Tree size was similar in each treatment at study initiation. Five years after thinning, tree height, canopy volume, basal stem diameter, leaf area, and leaf area index were significantly greater in LD than HD trees. No differences in leaf predawn water potential, stomatal conductance, and photosynthesis were found between LD and HD trees during growing seasons 4 or 6 years after study initiation. Results indicate resources necessary for growth of individual mesquite plants were limiting under increased stand density and suggest the occurrence of intraspecific competition. Limitations were manifest at the whole plant level via modification of tree size and leaf area per tree, and not through adjustment of leaf physiological processes. The limiting factor appeared to be soil water. Daily water loss tree-1 was 2.5 to 4 times greater in LD than HD trees, and ranged from 119 to 205 kg and 46 to 59 kg in LD and HD trees, respectively. Projected daily water loss by mesquite at the stand level was similar between treatments, however, and ranged from 9,500 to 17,700 kg ha-1.