Leaf Dynamics in an Evergreen and a Deciduous Species with Even-aged Leaf Cohorts, from Different Environments

Abstract

Quantitative phenological measurements were taken for 2 years on Prosopis glandulosa, a deciduous desert tree, and Rhododendron maximum, an evergreen subcanopy shrub of the deciduous forest. Prosopis glandulosa was studied in the Sonoran desert of California while R. maximum was studied in the Appalachian deciduous forest of Virginia. Both species had rapid and synchronous leaf production. However, their leaf mortality was quite different. Prosopis glandulosa leaves died predominantly from the primary and secondary affects of predation. Leaf mortality of R. maximum was due to natural senescence. The difference between the causes of mortality of the two species caused divergent patterns of leaf survivorship. Leaf survivorship on R. maximum resembled survivorship curves of populations with maternal support of offspring, similar to other studies of leaf demography. However, the age-specific leaf survivorship of P glandulosa resembled populations with high offspring mortality due to predation, which is an unusual pattern of leaf demography. The age-dependent arrangements of leaf survivorship on R. maximum remained the same in different habitats. But, the LD50 increased for leaves on R. maximum as the density of the canopy increased. The possible interaction of leaf demographic studies and whole plant growth models is discussed in relation to these short flush species.