PROTECTING TREES DURING DROUGHT

Now is the time to prepare for drought in the landscape, with the future of northern California’s water supply in question some foresight and prevention can go a long way. Trees need ground water to conduct photosynthesis this is an obvious fact that we all learned in school but the reason I bring it up is that people forget in order for a tree to decline some part of the process of photosynthesis has to be interrupted.  Once interrupted, it is secondary or opportunistic insects and diseases that will grow in population, causing increased decline. This is a benefit in forests. Because weakened trees recycle to the earth and provide organic matter and nutrients to the strong trees surrounding.

TREES THAT WILL BE AFFECTED

All trees will be affected, but trees that will be most affected are trees that are in poor health or declining, trees that have been over pruned and trees that have been grown in shallow irrigation, such as in turf grass and in mixed planting beds. Roots need oxygen as well as water and since water has not been scarce for decades, many trees are in irrigation that is frequent and shallow, forcing roots to compete at the surface to exchange gasses and absorb water.  These same roots that are close to the surface will be the first to dry out as rainfall and irrigation are less available, causing root loss and the trees ability to absorb what little water is available.

The key to keeping your trees healthy is prevention and monitoring, and many of these suggestions are not only free but will also save you money and help the environment in the process.

What you can do?

• Mulch – Maintain a 3 – 4” layer of mulch under all of your trees and shrubs. Did you know? The most expensive portion of most landscapes is your lawn! Maintaining lawns causes more pollution than any other part of your landscape! Wood mulch collects carbon!  Remove as much grass under trees as you can and replace with mulch. (See the benefits of mulch below)
  

  Mulch

• Irrigation – Deep water once a week during the hottest times or when trees show signs of stress.  Water evaporates from the surface down, so if you deep water, it will remain in the soil for much longer than if you surface water.  Mulch will increase this water retention.  The best way to water deeply, is slowly with a soaker hose.  This way you can control the irrigation in the root zone and not waste it on areas not needing water.
  

  Soaker Hose Placement

• Do not prune trees in declineor in poor health and in healthy trees do not over prune.  Removing too much leaf matter is always an unacceptable practice, but in times of drought, it could kill a tree.  It reduces the amount of food the tree so desperately needs and reduces the shade in its root zone, which will increase water evaporation.
  

  Over-pruned Tree

• Monitor pest and disease – Pest and disease issues increase during times of drought.  Have one of our ISA certified arborist evaluate your trees and shrubs at the first signs of infestation.  They can make recommendations on treatments before the pest or disease makes any impact on the trees health. (See Pest and Disease information below)
  
  

  Aphids

• Do not use any high Nitrogen fertilizers, slow growth in the crown will compensate for lack of water.  In fact we are only fertilizing trees with mycorrhizae and bio-stimulants.  These are naturally occurring organisms that help strengthen the trees root system. That is good for the tree.  We can slow down the growth even more and increase the trees fibrous roots by applying a tree growth regulator.  For more information on that please have an arborist come out and look at the tree.
• This should be obvious, but you never know.  DO NOT CUT ROOTS, or change grade over root zone.  If there is a construction job or renovation requiring that roots be cut, an ISA certified arborist should always be consulted.  We have a lot of experience in these types of situations.
• If a tree looses all of its leaves, it doesn’t mean it is dead.  Don’t give up on it yet.  Many tree species do this intentionally to save its resources for a better day.  Like next spring.  Increase water frequency and call an arborist.  You can do a little test yourself by grabbing a twig or small branch.  If it is flexible, it is still alive, maybe only barely but it still has a chance.  If the twig snaps when you bend it.  Its dead, but you should still contact an arborist in this matter.

With these tips your trees should make it through a bad summer, but these tips are sound for tree management every year, especially the mulching and water management.  Also don’t plant any trees or shrubs; it is not a good time for establishment.

Further discussion:

Reducing Compition and Selecting the Right Tree for the Right Place – Trees grow most efficiently associated with similar wood types and beneficial organisms, they benefit from the strength that comes with combining root systems and the protection peripheral tree crowns provide in inclement weather, stands of trees help shade and cool root systems and the differences in nutrient uptake from tree to tree is regulated by sharing leaf litter as it returns to the soil. Nature has provided the model for trees to remain balanced with their environment, in our landscape we grow ornamental trees alone with dissimilar plants that compete for resources.More common in commercial settings or large landscapes declining trees use resources that would benefit the sustainable specimen trees, trees in a drought situation that are weak or in severe decline should be removed where it would benefit the surrounding trees, short term considerations during the window of draught like subterranean roots of dead trees can rob nitrogen from the soil during decomposition and of course declining trees will be more susceptible to secondary pest which can be introduced to healthy trees or at a minimum increase population of pests.

Remove trees that are beyond saving that compete for resources and do not provide their fair share, golf course trees, park trees, campus trees where oaks and maple are surrounded with mostly dead mistletoe ridden ash trees can benefit from helping speed up natural selection and condense resources to viable the long term trees. This is valuable in mixed stands where trees beyond saving share stands with viable healthy trees

Lawn – nothing can replace plush green lawn in high use areas or where the kids play but how much of it is visual because it’s the standard. Landscapes with vibrant flowering plants complimenting yellow and purple shrubs growing out of uniform wood mulch are just as aesthetically pleasing and require considerably less maintenance. The amount of chemicals required for preventing or eliminating weeds, combined with high nitrogen that has the potential for runoff and damage to aquatic ecology is not great stewardship of the land.  Less turf grass equals less maintenance and less water usage.

THE BENEFITS OF MULCH

As arborists, our job is to create and maintain favorable environments for trees and shrubs.  While doing so we need to look toward the environment that has achieved perfection in finding the soils that are balanced in nutrient content and filled with beneficial organisms and rich in organic material so that the cycle will continue to produce and support our goals.

Only in nature, amongst the undisturbed cycles, can you find a model worth recreating where trees benefit from the loss of each leaf, twig or branch and works in partnership with fungi, insects and bacteria to ensure nothing goes to waste.  Recycled parts of trees, working with their associates, create layers of protective nutrients that return to the roots while resisting the onset of greedy and invasive weeds that would serve as competition.  As scientists we cannot ignore what has been proven to work, we can only hope to learn from our findings and do our best to duplicate it with as little compromise as possible.

Our landscapes, however, are filled with compromises that work against nature’s process.  We must ensure that our trees do not shed branches on the people that grow them, therefore we prune.  With this in mind, taking away each piece we remove, raking the valuable leaves and small twigs that the winds bring to us for use and then we plant grasses and or plants that absorb more than their share of what is left.

Our only offering back to the soils are processed barks and sterile water.  As the cycle loses its balance, nature does what it is supposed to do by taking the weak and returning it to the earth. The process is slow but constant.

Trees no longer have to live in spite of us. They can thrive because of the lessons we have learned based on the models we know to work.  By taking all parts of the tree and grinding it into a recreation of what nature intended, we can begin the process of getting back our balance.

Simply by adding natural complete mulch, nutrients will return to the soil while it is cooled in the summertime and kept warm in the winter.  Weeds will not go away entirely but will be much fewer in numbers and easier to maintain.  Beneficial organisms will call home where pathogens may have moved in.  This simulation of nature combined with good habits and respect for the soils and the roots that grow in them will minimize the need for pesticides and expensive treatments saving you time and money which you can spend enjoying your trees as nature intended.

MULCH:

• Adds organic matter and humus to soil
• Reduces drastic swings in soil temperature
• Increases retention of soil waters
• Is a food source for earth worms and soil organisms
• Reduces weeds
• Reduces erosion

Mulch by definition is a material that covers soil.  Most of the studies that have shown drawbacks of mulch are done with it incorporated INTO the soil. This is where people confuse it with compost.  Mulch is not compost, although you can compost organic mulch and mulch with compost.  I just wrote that to try to confuse you so stay with me.

Mulch can be made of both organic and inorganic products and should always be used as a top dressing.  There is much debate in our industry over the depths of which mulch should be applied.  Most resources say to mulch at depths between 3-4” whereas my mulch hero, Dr. James Downer, has shown increases in tree growth and vitality with a fresh 12” layer of eucalyptus mulch maintained on avocado crops.

Adds organic matter and humus to soil

A rule of science is that nothing is lost and nothing is gained……. kind of.  What this means is just as you receive the benefits of the nutrients in the things that you eat, so does the soil benefit from what it decomposes. Thus, nothing is lost.  However, nutrients can be lost through volatilization such as NO4 release in standing wood chips…..kind of.

To simplify, organic mulch will incorporate organic material (OM) into the soil and that OM will carry with it what it was built from.  If you were to chip a small fruit tree in its entirety and the leaves had Nitrogen (N), the fruit had Phosphorus (P), and the Xylem had Potassium (K) you would get those nutrients except for what converted to gas during decomposition.  With that in mind, if you look at bark under a microscope you will find that it is mostly dead cells and waxes.  When used as mulch the levels of N, P and K that might have been available in the rest of the tree might not be present or available in the bark.  Even though it is part of the tree, nothing is gained from its association once it is isolated.

Reduces drastic swings in soil temperature

Mulch reduces the soil’s heat index year round by protecting the soil from direct sun exposure in the spring and summer months and trapping radiant soil heat in the winter. The importance of moderate soil temperatures is largely dependent on the crop and the geography of it.  Some trees and their roots do well in higher temperatures, while studies have shown that soil temperature between 93-97° can stunt growth.  Most of the top few inches of soil are affected by sun exposure and mostly in dry soils.  It takes five times the amount of energy to warm water than it does an equal amount of dry mineral particles.

Increases retention of soil waters

Mulch improves soil tilth by incorporating OM while allowing greater holding capacity and improving percolation.  In doing so, soil water helps reduce increases in soil temperature.

Is a food source for earth worms and soil organisms

Earth worms are instrumental in the incorporation of decomposed organic matter into soils. They create tunnels that air and water can move through and help ease soil compaction and disperse OM.  There are many instances where soils would benefit from tilling or mass introduction of organics in places where hard working absorbing roots occupy the soil.  Since mechanical means of incorporating OM are often invasive, it is vital to get the biology of soil working for you.  Mulch creates an ideal environment; moist and organic with moderate temperatures.

Reduces weeds

Many claims have been made of mulch eliminating weeds; this just is not true.  Where there’s a weed, there’s a way.  However, the first rule in weed control should be to select the most effective practice that is not harmful to people or the environment.  Seeds need sunlight to germinate; a consistent layer of mulch can prevent sunlight from reaching the soil.

Reduces erosion

Mulch is used for erosion control for four reasons. The first is to create a “shield” that reduces the amount of soil splashing from forceful downfalls of rain.  Secondly, it prevents soil from slipping when surface water move quickly across it.  The more fine particles, the better the mulch will be at bonding with soil particles.  This bonding creates clumping and requires a larger force to disturb it.  Mulch creates greater infiltration rates allowing a larger holding capacity of water which reduces run off.  Lastly, it creates a better rooting media for absorbing and anchoring roots of plants and trees since roots are an important factor in soil stabilization.

“Don’t be a wimpy mulcher”- Dr. James Downer