Limiting factors in the desert

In some ways the term “limiting factor” is almost a definition of deserts, because deserts lack one or more essential ingredients for the survival of most kinds of plants and animals.

First, a desert is, by definition, a place with very little available water, either because there is little rainfall, or because it evaporates so fast. It may also be that most of the precipitation is unavailable because it is frozen most of the year, as in the far north or south, or in some high altitude regions.

Some areas may get bursts of moisture, even flooding, but it is episodic and not dependably available most of the year.

Temperature is another limiting factor. Many deserts get too hot for most organisms. Some deserts near the north and south poles are too cold. And yet others have wide swings in temperature.

Wind is another. There are few trees or shrubs to stop the wind. Desert mountains, river-courses or other sheltered areas may harbor small oases in their wind and sun shadows.

One unusual limiting factor is lack of sunlight. This can occur in deserts near the poles.

Especially interesting are the adaptations that plants and animals have developed to deal with these limiting factors. Many of them are what we talk about here.

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Leafing again: the strange case of the ocotillo

One of the odder native residents of the Sonoran desert is the ocotillo bush. It typically consists of several spindly branches, vertically striped and spiny, up to 20 feet tall, that are leafless for long periods, only to sprout thick lines of small leaves within a few days after a rain.

Ocotillo branches with few leaves

Its desert adaptation of dropping leaves and playing possum is so complete that ocotillo plants for sale, in their leafless phase, with their branches tied in a bundle and roots bare, look thoroughly dead.

Ocotillo branches with many leaves

In the spring, they produce numerous red tubular blossoms at the ends of the branches that attract insects and birds of many species. They make great landscape plants because of their sparse sculptural look, and extremely low water requirements, and striking seasonal changes.

Choose native plants for your desert landscape

One way to figure out what plants will be suitable and attractive in your desert landscaping is to go to a nearby natural area and see what is growing wild.

Make sure you select a location that is similar to yours in exposure, dryness and altitude.

Take photos or make a list of plants you find attractive. Never dig up native plants! They are fragile and rare, and in most places it is illegal to do so.  Almost everything you will see is available in plant stores. Photos will also help you arrange your landscaping, showing which plants grow together, and how much space they need.

Then go to the web or in plant books to learn about the plants you have found, or take your photos to a local nursery that specializes in native plants, and decide which are for you.

The variety of desert plants is surprising: cacti, shrubs, vines, spring-flowering annuals, many kinds of perennials. A big virtue of native plants is that they  require little in the way of extra water and plant food, and are easy to maintain.

One thing to keep in mind about native plants–some of them grow very slowly, so it may take a while for your landscape to mature. But there is nothing to match their beauty, and their ability to attract native fauna.

A thorny issue

Related to the last post, it is amazing how many kinds of thorns, bristles, hooks, spikes, prickers, sharp edges, pointed leaves, pointed branches, as well as claws, scales, fangs, spines, and hooves you find in the Sonoran desert, and generally in the arid western USA.

In a contrary kind of way, almost all of these indicate that there’s probably a nice, juicy, succulent hunk of flesh nearby.

But you’ll get hurt if you try to get at it!

Dry rain

Even the simplest things about the desert can be strange.

Rain, for instance.

When you need rain the most, where you need it most, seems to be the place you find it least.

And sometimes it comes unusually close, but never arrives.

An eerie and frustrating example is the dry rain that can occur in the desert west, called “virga.”

In the distance, you will see the clouds form, then curtains of rain finally begin to fall. But the rain disappears in the middle of the sky, between cloud and land.

Leaving you high and dry. Or low and dry.

Virga actually does happen in other regions, and can involve snow as well as rain.

It’s a sight to see, watching the rain come down, but never land on land.