Figure 1. The global distribution of major ecosystems, including (a) a generalized map of the world's major biomes and (b) the location of ecosystems with respect to mean annual temperature and precipitation. Figure 1a was based on the predictions generated by the mapped atmosphere–plant–soil system (MAPSS) biogeography model, courtesy of Ronald Neilson. Some degree of inaccuracy should be expected as a result of errors that are inherent to this type of model analysis. Figure 1b was modified from Whittaker, (1975).

Figure 2. Photosynthetic light response curves for three hypothetical species with varying light requirements. Note the trade-off between maximum photosynthesis at light saturation and the minimum amount of light that can be tolerated (the light compensation point). The shaded regions correspond to the light levels at which each species has the highest growth rate among the three and is likely to out-compete the others. In an ideal forest, the result would be a stratified canopy where total photosynthesis was optimized by species coexistence.

Figure 3. Conceptual diagram showing the major fluxes of nutrients through and within a forest ecosystem. Nutrients enter the system through fixation (N₂), weathering and atmospheric deposition and are lost through leaching and conversion to gaseous phases. The importance of each mechanism varies substantially among nutrients. Cycling within the system is controlled by reabsorption from senescent tissues, production of litterfall, decomposition and uptake. Other mechanisms that facilitate nutrient loss or turnover can include fire and herbivory.

Figure 4. Potential feedbacks between site resource availability, foliar nitrogen concentrations, photosynthesis, leaf lifespan, investment in defence compounds and litter turnover rates. Although these feedbacks can impose strong controls on forest ecosystem dynamics, external forces resulting from disturbance or succession can interrupt and even reverse these cycles.