What Is “Drought”
Before we start, we need to understand the definition of ‘drought’. Drought can be defined as a prolonged and exceptional deficit between water supply and demand. In other words, long term conditions of high demand and low supply equals drought.
Many of us in the Southwest have experienced first hand the effects of years of drought, especially those living in California from 2011 thru 2017. With mandatory water restrictions to increased dusty conditions, the drought has altered all of our lives. However, many don’t know just how damaging the drought has been to trees that have been dependent on Mother Nature, both in natural and in domestic settings.
Drought in Natural Setting
First, let’s take the trees that are in natural settings. From the deserts to the mountains, native trees and plants depend on irrigation to not only grow but to defend themselves from outside pestilence.
Hold on a minute. We just heard the phrase ‘defend themselves’. What does that mean? The simple answer is that when trees become stressed by lack of irrigation, they must redirect the energy allocated to defense and apply it to survival. In humanistic terms, you work long days for weeks on end, not getting the proper rest and nutrition, and eventually your defenses are down. The next thing you know, along comes the common cold or flu. You sneeze and sniffle, blowing you nose from time to time and that tells everyone around you that you are sick. Guess what – trees do the same.
Okay, so none of us have ever heard a tree sneeze, but it does release chemicals such as ethanol, acetaldehyde, ethylene and ethane when stressed. These chemicals are catnip for ambrosia beetles, “secondary” bark beetles, and weevils. For our topic we’re going to talk about the secondary bark beetle effect.
The bark beetle attacks the weakest trees first, like the lion on the Serengeti attacks the slowest antelope in the herd. No, the bark beetle doesn’t have a long flowing mane and long tail. Instead, it’s only 1/8” to 3/8” in length. Not particularly daunting in size, right? Don’t let that fool you.
When these beetles team up, they burrow through the vascular system of the tree, cutting off the flow of nutrients to and from the tree.
Have you ever taken a sip through a soda straw that has a hole or slit, only to end up with a mouthful of air? Exactly what is happening here.
Since the tree cannot distribute nutrients throughout the canopy, the furthest extremities will start to die off from starvation, eventually causing the entire tree to die. Meanwhile these bark beetles reproduce, flying off to infect the next victim. Not a pretty picture.
Drought in Urban Setting
Now let’s talk about trees in the urban setting. When the drought became a prolonged event, many cities have imposed watering restrictions in non-essential areas, such as landscaping. To comply with these restrictions, much of the public significantly reduced or eliminated the irrigation to the landscape which effected the trees residing in these areas.
While at first these trees didn’t look as though affected by this reduction, internally they started going through the same stress process as those trees described in natural settings.
These are signs of a tree in stress:
- diminished leaf production
- increased defoliation
- interior thinning/dieback
- smaller leaf size
Remember the bark beetle attacking native trees? They went after similar species of trees, and their cousins went after other varieties. Talk about a full-blown assault on our urban greenscape!
Effects Installing Drought Tolerant Landscaping
Doubling down of the drought water restrictions, many individuals went with native/drought tolerant landscape that required minimal irrigation. Through this process they laid down fake turf or plastic upon which they placed material such as gravel, bark or decomposed granite. This material in essence covered the roots of existing trees, robbing them of oxygen, water and nutrients while baking them under intense heat. Imagine trying to go throughout your day with a plastic bag over your head. I think you get the point.
What You Can Do
Now years into the drought, trees are falling over in our urban living areas. Cars are crushed, houses damaged and the public put at risk. What do we do?
First off, contact an Arborist to look at your trees and give you an assessment of what he/she sees. He/she should ask you questions about the tree just as a doctor asks you questions about your history. This will help him/her provide a better assessment and recommendations.
The effects of the drought will linger for years, if not decades. Make sure you do your part in protecting your trees, all while prevention potential risks to both person and property.