Photosynthetic Systems of Mediterranean-Climate Shrubs and Trees of California and Chile

The growth forms of the dominant plants found in Chile and California within mediterranean-type climates are similar. As the length of the drought increases, communities dominated by evergreen trees are replaced by evergreen shrubs, then drought-deciduous shrubs, and finally drought-deciduous shrubs and succulents. The shrubby evergreen elements generally have extensive root systems, a long photosynthetic period, but low photosynthetic capacities. The drought-deciduous shrubby elements have high carbon fixation rates but short periods of activity and generally shallow roots. The evergreen systems expend energy for a certain degree of drought tolerance for the gain of potential year-round production. In regions of long drought periods, the potential seasonal carbon gain of evergreens decreases and they are no longer at an advantage over drought-deciduous elements. The highly drought-resistant but slow-growing succulents can persist in communities where water, and not light, is the primary limiting factor.