What are trees for?

Does that look shady to you?

Hoping to find some information that’s generalizable to the production of tea, I’ve been sporadically reading “The Geography of Wine: How Landscapes, Cultures, Terroir, and the Weather Make a Good Drop.” The author, Brian J. Sommers, has taught a geography of wine course at Central Connecticut University for many years.  I lose patience reading it, as I’m transported to a college lecture hall where the professor talks overlong, desperately grasping at metaphors, trying to hold the attention of jocks and communications majors forced to take a science class.  Also, using the concept of “geography” to envelop such disparate disciplines as soil science and political culture without seeming arbitrary and disorganized takes some boldness that I haven’t seen in this book so far.

Still, I am learning some rudiments of climatology.  I learned that landmasses can’t hold heat as well as oceans, which means that these “continental” climates have wider ranging daily and seasonal temperatures.  (Oceans absorb excess heat when it is hot, and release it when it is cold, producing a moderating effect on temperatures.)  I learned about the Köppen climate classification system, and you can see on the map the humid subtropical areas (light green) where tea is grown.

Unrelated to the book, I happened to be thinking about “shade trees” on tea plantations.  In tropical climates, you will often see tall trees planted among the tea bushes.  Temperatures above 100°F get progressively worse for tea growing, and you frequently hear that the shade these trees provide keeps things cool.  But when I look at pictures of tea plantations, the shade looks pretty sparse.  Could such a small amount of shade really have an effect?  I remember reading a section of Tea: Cultivation to Consumption that studied the effects of shade trees, and the author seemed just as puzzled as I was that a few trees help as much as they do.

Back in the wine book, I was reading about microclimate–physical features that cause localized variations on climate.  I read the line “more wind means more potential for evaporation.”  This was in a section about cold-air drainage, where cold air masses sink to the lowest locations because they are more dense.  Now, in terms of fluid dynamics, a small disruption in a laminar flow can cause a lot of turbulence.  That is to say, if a few trees are planted about a hillside, a flow of wind that encounters them will be broken into eddies and considerably diffused.  Could it be that trees’ principal benefit to a tea garden is that they maintain humid conditions?  I wonder what other positive effects a gentle windbreak might offer.

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