How does this relate to forestry?
Forests and trees represent a crucial part of the water cycle. The soil absorbs precipitation that falls from the clouds, and trees draw water from the soil into their roots to support all of their life major processes such as growth, reproduction, and maintenance. As water travels from the roots out to the leaves, water is lost through tiny pores, or stomata, in a process called transpiration. Transpiration and evaporation together comprise total evapotranspiration, the amount of water returned to the atmosphere as vapor to continue the water cycle. Forests use more water than lower-growing types of vegetation, and also produce lower surface runoff, groundwater recharge, and water yield. Tree species and age, forest structure, and harvest patterns influence the amount of water a forest requires. For example, evergreen conifer trees such as pines demand more water than deciduous trees. Young trees require more water than older trees. In the Southeast US particularly water-inefficient tree species include black cherry, dogwood, yellow poplar, basswood, birch, buckeye, and sycamore. Thinning out a forest can help to reduce the water demand by the trees, but increases erosion and produces holes in the canopy which removes shade and shelter for other forest species. Maintaining a developed understory layer to protect soil moisture reduces the water requirements of forests, even if many trees are cutdown to reduce water demands by trees.
As climate change causes greater precipitation extremes and higher temperatures, trees and forests will play an increasingly vital role in the Earth's water cycle. Forests increase water quality by minimizing erosion and intercepting polluted runoff, which may become more important if climate change threatens local water supplies. Forests also produce less chemical and nutrient pollution than equivalent, more intensively managed agricultural operations. Forests can reduce the impacts of floods by absorbing water during periods of abundance and slowly releasing it during dry spells. If planting trees to sequester CO2 to reduce carbon dioxide concentrations in the atmosphere, managers must be sure the treesâ€™ water demand will not worsen regional water shortages during droughtâ€”particularly for fast-growing, short-rotation forest crops such as poplar.
|Figure C: Woodfin Watershed in Western North Carolina is a forested watershed which helps to protect water resources from pollution and is protected by conservation efforts.|
|Image from the Southern Appalachian Highlands Conservancy www.southwings.org|