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Topical Tropicals 101

We’ve all fallen in love with a beautiful or wonderfully fragrant flowering plant, say a Plumeria, which, of course, we left out on the deck a little too long into late fall or early winter.  Shortly thereafter, our treasured Plumeria resembles week old road-kill.  Plumeria is native to Central America, the Caribbean, and parts of South America, thrives in tropical and sub-tropical climates, but isn’t fond of temperatures below 60°F (15°C).  It’s important to know how best to protect your valuable tender plants, shrubs, and trees when the climate you’re giving them isn’t to their liking.

Let’s first sort out what the terms tropical and sub-tropical actually mean.  Of course, that encompasses multiple definitions.  You didn’t really think it would be simple, did you?  By understanding what these climates are, we can then gain a better understanding of the plants that naturally occur and thrive in them.

The Köppen climate classification system defines five distinct climate groups.  We’ll be looking at just two.  The Tropical/Megathermal group describes regions with an average temperature of 64°F (18°C), and the Temperate/Mesothermal group describes regions with warmest month average temperatures above 50°F (10°C) and winters insufficiently cold to support snow cover.

Tropical climates usually occur at lower elevations, generally occurring within 23.5° latitudinally on either side of the equator.  There are three categories of tropical climates, which are briefly described below:

  • Tropical Rainforest, with an average rainfall of at least 2.4 in (60mm) per month.
  • Tropical Monsoon, where the driest month has less than 2.4 in of rainfall, but more than 4% of total annual rainfall.
  • Savanna, where a distinct dry season occurs, during which the driest month has less than 2.4 in of rainfall and less than 4% of annual rainfall.

The major source of variation among tropical climates is the amount of water available to the plants, animals, and people existing within them.

Sub-tropical climates fall into the Temperate climate group.  There are two subtropical climates:

  • Dry-summer Subtropical, which usually occurs in the western parts of continents between 30° and 45° latitude on either side of the equator.  Dry-summer Sub-tropical climates experience moderate temperatures in winter, with unpredictable, often rainy weather.  Summers in Dry-summer Sub-tropical climates are (surprise!) very hot and dry, except along coastal areas, where temperatures are moderated by cold ocean currents.
  • Humid Sub-Tropical, which occurs mostly in the eastern bits and edges of continents, in the high 20s and 30s latitude on either side of the equator.  As you might have guessed, Humid Sub-Tropical climates enjoy a warm, wet, often suffocating, summer, which is also the wettest season of the year.

Sub-tropical climates are subject to greater variation than tropical climates, with Humid Sub-Tropical climates experiencing extremes of weather in the form of violent thunderstorms or the combination of dry winters with drenching monsoons in summer.  You’ve probably already figured out that here in the Atlanta area, we live in a Humid Sub-tropical climate.

In subsequent posts, we’ll explore what all this means in terms of sustaining a lasting relationship with your warmth-loving plants.

Source:  wikipedia.org article on Köppen climate classification system.

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