Characteristics of Mediterranean-Type Ecosystems

Modern mediterranean-type ecosystems (MTEs) are shaped by key ecosystem drivers that affect their function. The most important of these drivers are climate, topography, soils, and fire. There are important geographical, climatic, and fire histories that are crucial to understanding these systems. Mediterranean-type climate (MTC) is defined as a cool wet winter (winter-wet) and a warm dry summer, which is a unique pattern of seasonality and one that is rare globally. All of the MTC regions have nutrient-poor soils, particularly as related to nitrogen (N), and some also have extensive phosphorus-poor soils. There is considerable variation both within and between regions in their degree of nutrient impoverishment of soils. Through these shared ecosystem drivers, selection has operated within each ecosystem to shape the communities and the organisms within them. This has resulted in the communities and organisms displaying similar structures and processes.

Traits associated with nutrient impoverishment and shade-tolerance in tree juveniles of three Bornean rain forests with contrasting nutrient availability

In this study, we tested the hypothesis that functional traits associated with nutrient impoverishment contribute to enhancing shade-tolerance (survival at low light) for the juveniles of canopy tree species in Bornean rain forests. To test the hypothesis, survival and functional traits (biomass allocation, leaf dynamics and foliar nutrient concentration) were investigated as a function of light conditions for saplings of 13 species in three forests with different levels of nutrient availability. As predicted by the hypothesis, the species in the severely nutrient-poor site (a tropical heath forest on nutrient-poor soils) showed greater shade-tolerance (>91% survival for 8 mo at 5% global site factor) than in the other two sites (mixed dipterocarp forests) (54–87% survival). Across the species, greater shade-tolerance was associated with a higher biomass allocation to roots, a slower leaf production and a higher foliar C concentration, which are considered as C-conservation traits under nutrient impoverishment. These results suggest that the juveniles of the canopy species occurring on nutrient-poor soils can enhance shade-tolerance by the same mechanisms as the adaptation to nutrient impoverishments. Tree species in nutrient-poor environments may be selected for surviving also in shaded conditions.