Greenhouse Effect 1. The upper graph provides air temperature and soil temperature for the tropical, closed-canopy forest, which shows little seasonal variation, and no difference between air and soil temperature. The soil in the sugar maple stand remains warmer through the winter than the air because of the insulating snow layer. Water in Forests Tree roots absorb vast quantities of water to replace that lost by transpiration and that used in metabolic activities. Trees use 500 to 1000 kg of water for each kilogram of dry matter produced.
Tree roots can effectively exploit soil moisture even at relatively low soil-moisture contents.
The mycelia of mycorrhizal fungi may play an important role in the extraction of soil. In spite of the efficiency of most tree root systems, the distribution of trees is controlled to a great extent by water supply. Wherever trees grow, their development is limited to some degree by either too little or too much water. Even in relatively humid areas of the temperate zone, forest soils may be recharged to field capacity only during the dormant season or for a brief time after very wet growing periods. Trees use water because they have to open spongy, wet insides to dry air in order to get CO 2 . 2.