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3. Photosynthesis
Light and water are both critical to the process of photosynthesis
Trees compete for light by growing upwards, producing the tall forest canopies found in tropical rain forests. Tree architecture has evolved to enable the maximum possible interception of light.
The mean annual temperature (although not its variability) is roughly similar in the tropical rain forests of the Congo Basin, the savanna grasslands of east Africa and the Sahara desert, yet the amount of plant matter being produced is vastly different. Here, and across the tropics, the total biomass is mainly controlled by the availability of freshwater, usually as rain.
How critical is water to photosynthesis?