Biomes – an area of land with specific environmental conditions that is home to animals and plants adapted to those conditions
The greatest diversity of orchids are found in tropical and subtropical regions of the world. These are areas with a lot of rain and warm average annual temperatures. Epiphytic orchids are almost exclusively found in these biomes because their roots grow out into the air where they have no soil or media to moderate temperature or protect them from water loss. Meanwhile, cooler climates are home to terrestrial orchids that can survive harsh winters with their roots and rhizomes safely buried under ground.
Rainfall and temperature are the most common environmental factors used to define biomes.
These environmental factors are largely controlled by where on the planet the biome is located. Tropical biomes are found right along the equator, while subtropical biomes are a bit further away from the equator.
For a more information, check out the charts below!
Because most scientific articles and texts are published using metric units, I spruced up this graph to include imperial units (inches and Fahrenheit) so my fellow Americans could follow along. (Figure adapted from Whittaker, R.H. Communities and Ecosystems. New York: Macimmilian, 1975; and Rickefs, R.E. The Economy of Nature. New York: W. H. Freeman, 2000.)
This graph, called the Whittaker Biome Model, breaks down common biome types over a range of temperatures and rainfall levels. For instance, from this graph we can estimate that a tropical rainforest receives 80-160 inches of rain per year with an average temperature of ~70-85°F.
This graph also tells us a little bit about the organisms (plants, animals, insects, etc.) that live in those areas. For instance, an epiphytic orchid might grow well in a tropical rainforest or a tropical seasonal forest because the temperatures stay warm all year round and both receive sufficient rainfall. However, a grassland or desert would be too dry for an epiphytic orchid while the taiga and temperate deciduous/coniferous forests would be too cold.
Sometimes there are overlaps between biomes that would make this graph very confusing, so not every biome is represented here. For example, this graph doesn’t identify subtropical rainforests, but we can still talk about them in terms of their rainfall and temperature. Subtropical rainforests are characterized by receiving a lot of precipitation, at least 30 inches. They also tend to be cooler than tropical rainforests, although the temperature rarely goes below freezing. Orchids living in subtropical rainforests will be more tolerant of cooler, drier conditions.
This map of the planet is colored for biomes, rather than countries. If you look carefully you’ll notice that there are lateral bands/zones of particular biomes. From equator to poles, it goes: Tropical rainforest – tropical grassland – desert – temperate forest – taiga – tundra. This makes sense because we know that average annual temperature decreases as we move away from the equator.