Ross Mars writes:
“What we call climate, the daily and seasonal changes in temperature, rainfall and so on, is influenced by the water cycle, and the importance of trees, in providing water to the atmosphere through transpiration and evaporation of water from plant surfaces for cloud formation, cannot be underestimated.
It is imperative that no more forest areas are cleared and that literally billions of trees are replanted, especially on hill slopes, as these play an essential role in the water cycle. We have the ability to change and increase local precipitation patterns simply by planting trees.
Furthermore, greater condensation is possible as trees provide large surface areas for water vapour to condense. Forested mountain areas have permanent fog, mist or cloud on their peaks. In some places, condensation contributes more than rainfall in the total amount of water reaching the Earth.
We can think of a forest of trees as essentially a lake above the ground. Trees often contain more than 80% water and they continue to pump large volumes of water into the atmosphere. Not only do trees store large amounts of water in their trunks and leaves, plant roots also hold water in the soil, usually as a thin film around each root fibre.
Large trees can lose thousands of litres of water each day. Much of the rain and cloud formation comes from the trees in a forest. You can imagine what the effect of forest clearing would have on climate patterns. Fertile land is slowly turning into desert.
Densely-planted trees also soften the force of rainfall and greatly reduce erosion and run-off. In fact, light showers may not even reach the ground and the water [-p.67] remains as a fine mist in the tree canopy, causing a humid atmosphere.” (pp.66-67)
“The term ‘microclimate’ refers to the climate in a particular area which varies in its temperature range, humidity and wind intensity. For example, sheltered garden areas may have slightly cooler daytime temperatures and warm night-time temperatures, reduced wind velocity and higher humidity than other areas nearby or somewhere else on the property – and there may even be significant differences within the same garden.
You can easily create microclimates by building terraces, windbreaks and suntraps, or by planting particular evergreen or deciduous trees.” (p.23)
Ref: Ross Mars (2005) The Basics of Permaculture Design. Permanent Publications: East Meon, Hampshire, UK