Demography of the invasive woody perennial Prosopis glandulosa (honey mesquite)

1 To assess the effect of annual environmental variability on the long-term population dynamics of the invasive woody perennial Prosopis glandulosa va r. torreyana (honey mesquite), we employed elasticity analyses of annual, m ean and periodic matrix models. Growth, survival and reproduction were reco rded for 1306 individuals in a 1-ha plot over a 4-year period. The volume o f each individual was estimated, and transition matrices with nine size cla sses were constructed. Standard matrix analysis was performed, and the rela tive importance of individual life-cycle components to changes in the finit e rate of population increase (lambda) was determined. 2 Periodic matrix analysis projected a 29% annual increase in population si ze (lambda= 1.29), while annual projection lambda-values varied between 0.9 9 and 1.44. For both methods, elasticity of seedling recruitment was always very low in all 4 years, and the highest elasticities were generally assoc iated with permanence in the same size class. 3 Periodic and annual projections predicted similar elasticity patterns, wi th the relative contribution to a change in lambda of different demographic processes changing between 'good' and 'bad' years. However, annual matrice s identified two bad years, with fecundity and growth elasticity decreasing relative to survival, whereas periodic analysis identified only one such y ear, and elasticity changes were seen only in fecundity and survival.