3.2.5. Vegetation

One of the most dramatic microclimate changes I’ve ever experienced was to transition from a redwood forest to landscape with no forest. In the forest, it was cool and moist. The breeze was gentle and the soil was soft and cushiony.

Immediately outside the forest, the land was typical California drylands scrub. Hot, dusty, brown (mid-summer), and bone dry. The temperature difference could have been as much as 20F, both day and night.

At night, the redwood forest stays warmer than the dry, open air of S California which can drop 30+ degrees at night. There is almost no humidity without the trees. The trees create their own rain! The humidity is so great in stands of redwoods that a friend of mine who lived there found mushrooms growing out of shoes she had left on the porch.

These trees don’t just create rain for themselves, but can provide rain to the land around them. The bigger the stand of trees, the more moisture goes to other areas. This is one reason it’s important to maintain large old growth forests. There are many ways in which trees can create significant microclimate changes, whether singly or in a forest.

Trees, because of their energy exchanges, can create significantly different microclimates that are much more conducive for the survival of some plants. Citrus, in Florida, has been found to freeze less and be more disease resistant when growing under an oak tree or in an oak forest. There are thousands of wild citrus trees growing in forests throughout Florida, some of them decades old and still quite healthy and copious fruit producers.

One way to use vegetation as a microclimate is to create a suntrap. This is a stand of windbreak trees protecting a grove of fruit trees for instance in a U shape. One can add a water feature for additional thermal mass (water holds heat and releases it slowly during cold nights. It can also create more frost and snow because of moisture.

Microclimate caused by large bodies of water is called "lake effect" and varies depending on what side of the lake you're on and other factors). I’ve seen tropical fruit trees grow a zone higher than they would normally survive, using this method.