UFMPs for Post-Natural Disaster

September 9, 2016

In last week’s post, we explored how prevention such as root channels and pruning in urban forests can go a long way preventing injuries and lessening the costs of damage when natural disasters are on the brink. This week, we’ll cover the second part – what to do after the disaster.

Tree on car Urban Forest

A tree fallen onto property after a natural disaster.

 Restoring trees properly after a natural disaster is imperative for a strong recovery in an urban forest as well as a community. This restoration can last anywhere from two to five years and sometimes even longer for large or severely damaged mature trees. This means it typically requires more than one pruning to repair these strong tree structures. With this, we must remember that patience is a virtue when dealing with storm-damaged trees.

To restore these damaged trees, a response plan is used. The plan covers actions and systems that are used after a disaster that causes damage to the urban forest. A response plan is typically be divided into five parts:

I. Response Plan for Immediately after a Storm

The number one focus of treatment immediately after a storm is removing hazards and cleaning tree canopies of broken limbs and dead stubs. This does not include major pruning that alters the tree’s structure. Trees use energy stored in the wood to recover from damage and produce new growth; therefore, during the cleanup process, the least amount of live wood possible should be removed. Never top the trees or cut the entire canopy back to stubs, that is a recipe for another disaster!

topped_trees_in_brading_avenue_-_geograph-org-uk_-_1226503

An example of a tree overly topped after a storm.

The University of Florida has provided a great step-by-step guide in how to respond immediately after a storm.

Step 1. Get help with removing potential hazards.

It is important that there are qualified workers for situations that may be unsafe. For example, if a limb has fallen near power lines, make sure that a qualified line-clearance arborist treats the situation. Working near electricity is highly dangerous, and may result in a fatality for workers who do not follow proper safety procedures. Other hazardous situations include large hanging limbs or leaning trees that could fall on a person, hit a house, or damage other potential targets if they go down.

Step 2. Stand up and stake small fallen trees, and provide irrigation as needed for stressed trees.

Roots can dry out quickly for small fallen trees. Some research has shown that staked trees with a trunk diameter greater than about 4 inches tend to blow down again in later storms. This may not be worth the time and expense for restanding. The reason for this appears to be that severed roots on bigger trees do not regenerate new roots as well as small (one inch diameter or less) roots do. It is important to note that large severed roots can start to decay or rot, making the tree unstable. These trees should be treated as new plantings and staked with the help of a professional.

Step 3. Clean tree canopies

The purpose of canopy cleaning is to remove potential hazards like dead and cracked branches and broken limbs. Canopy cleaning also includes making smooth pruning cuts behind broken stubs to allow the proper development of new tissue to close over wounds. Stressed trees need to access energy stored in their limbs in order to recover, sprout, produce new leaves, and defend itself against organisms that cause decay. It is better to leave the tree looking unbalanced and misshapen than to remove large portions of the live canopy at this time. Shaping can be done later as part of the restoration process.

II. Allow Time for Recovery

Natural disasters can often strips the leaves from a tree, this is especially common from wind damage during hurricanes. This interrupts the tree’s ability to photosynthesize and store energy. In response to the damage, the tree sends out epicormic shoots, typically referred to as sprouts, found mostly along the top and at the tips of branches. To produce the sprouts, the tree uses energy (starch) stored in the living wood, which temporarily weakens the tree. Allowing sprouts to grow will rebuild the starch reserves and other energy-storing compounds, increasing strength of the tree over time.

Allowing time is vital. Sometimes it can be a year or two before its first pruning. The different factors that affect recovery include: tree age, tree size, tree species, tree health, and extent of damage and all should be taken into consideration.

tree-branch-sprouts

Sprouts form after damage is done to the branch of this tree.

III. Restoration Pruning Program: Sprout Management

It is time to begin sprout management once you’ve determined that a tree is worth restoring, its canopy cleaned, and the appropriate length of time has passed for recovery. The essence of sprout management is training the sprouts so it is easiest for them to grow strong branches and build structure back into the tree.

First Pruning Visit

This  typically doesn’t happen until two or more years after the storm. Dead portions of branches that did not sprout and any other dead branches and stubs in the canopy should first be removed. The goal for the first pruning visit is to reduce some sprouts, remove some, and leave some.

The most vigorous sprouts often develop side branches, and these are the ones that should be left. Leave all lower side branches on developing sprouts that will remain in order to encourage strength. Remove sprouts located near the selected sprouts to allow space for growth. Ideally, the selected sprouts should be spaced approximately 12 inches or more apart.

Second and third pruning visits

In terms of timing allow about a year between pruning visits. Continuing sprout management by keeping the most vigorous sprouts and reducing or removing competing sprouts is vital. Large and severely damaged trees may need more pruning visits, while young or moderately damaged trees may only need a second visit to complete sprout management.

Later pruning visits

These visits typically occur four or more years after the storm and include mainly structural pruning. The priority here is to reduce limbs that are larger than half the diameter of the main trunk. As explored in other posts, trees fail in storms at areas in the canopy where there are structural weaknesses like codominant stems, bark inclusions, and unbalanced and overextended canopies.

750px-steve_lubiana_pruning_at_granton_vineyard_tasmania_2010

Pruning done the first time on this tree.

IV. Restoration of Palms

Hardwood trees and palms generally have similar reparation plans, however there are enough different that it warrants its own step. As with hardwood trees, the priority when restoring palms is to eliminate hazards and minimize removal of live tissue. Irrigation two to three times per week can also help palms recover if rainfall is lacking.

Step 1. Remove dead fronds that could fall and hit a target.

Step 2. Remove fronds that are smothering the bud.

Step 3. Leave bent green fronds attached to palm until new fronds emerge.

Step 4. Leave fronds that are yellowing or have brown tips.

For more information check out this resource.

V. Start a Tree Management Program

This one is easy! Just check our previous posts and start your UFMP (which you most likely already have).

This marks the end of our Urban Forestry Management Plan series. In the following weeks I’ll be posting some lighter-hearted posts like which cities have awesome urban forests or how tree shaping works.