[CANUFNET] FW: Tree Mortality Information Bulletin - Version 2

[Sheila Flint]

Thanks so much for sending the LANTA article. Excellent information and one that I can use when I receive all the phone calls for dead trees on my boulevard! It's sure tough being a tree on the prairies!

>>> "For Trees" <trees at fortrees.ca> 6/29/2010 7:13 PM >>>
Here is a LANTA bulletin that has been circulating relating to the topic of
winter kill on the prairies.

 

ForTreeslogocolourTC_logo_English

Gerard Fournier

Board Certified Master Arborist #PR-0130BT

Tree Canada Community Advisor-Southern Alberta

 

President

For Trees Company Ltd.

1-877-390-TREE (Alberta toll-free)

 <http://www.fortrees.ca/> http://www.fortrees.ca 

 

 

 

From: Cheryl - LANTA Administration [mailto:admin at landscape-alberta.com] 
Sent: June-29-10 10:34 AM
To: Cheryl - LANTA Administration
Subject: Tree Mortality Information Bulletin - Version 2

 

To: LANTA Members:

 

Below, and attached printable pdf, is an updated Tree Mortality Information
Bulletin. We have built upon the first Bulletin sent last week and now
included more details about plant dormancy, the effects of weather and
weather data from across Alberta during the time in question.  We hope you
can use this information when discussing the subject with your clients.
(Thanks to all members who provided feedback to the first bulletin - much
appreciated.) 

 

 

PLANT INFORMATION BULLETIN - HIGH MORTALITY IN URBAN TREES

 

Urban tree and shrub mortality rates in Alberta have spiked this year due to
a combination of weather events that occurred between September 2009 and May
2010.

 

What happened to cause such an increased loss of plants? The answer is not
an easy one to explain as there are many factors to take into consideration.
Plants are complex organisms and a basic understanding of their physiology
is needed before an explanation as to why so many "prairie hardy" plants did
not survive the 2010 spring season. 

 

The life of trees occurs in cycles. In early spring, as days begin to get
longer and the weather is warmer, the tree is pulling all of its energy
together for growth. As the weather continues to warm the tree begins to
grow rapidly, taking advantage of the long days and optimum sunlight. For
most trees, growth ceases by August. From this point until fall, the
objective of the tree is to prepare for winter. During fall, a tree stores
up food and energy reserves - everything that is needed for next spring's
growth. Between fall and spring is the period known as dormancy.  

 

What is dormancy? It is a period when the tree's physical life cycle is
temporarily stopped to help the tree minimize metabolic activity. Plants
prepare themselves for dormancy by going through a process termed "hardening
off," which is triggered in plants by the gradual decrease in day-time
temperatures and the length of daylight (photoperiod). Within the plant,
chlorophyll production slowly decreases, antifreeze proteins develop and
leaves prepare to drop (abscission). This is known as predictive dormancy
and occurs when an organism enters a dormant phase before the onset of
adverse conditions.  As you will read later, changing the environmental
conditions around the tree may alter the time of year when it goes into
dormancy.

 

When spring approaches, dormancy begins to come to an end and the
physiological process is reversed. Metabolic activity begins again triggered
by lengthening daylight and a gradual increase in temperature.   

 

It is the period between fall and the following spring that is of interest
in the examination of tree mortality, especially the period just before the
onset of dormancy and the period when dormancy is broken in spring.  

 

As mentioned above there are many factors that influence when a tree enters
the dormancy period, one of which is temperature. (Other factors may include
stress and too much water/fertilizer applied prior to leaf drop.) In an
average season the reduction in temperature during fall (September/October)
is gradual. If, however, temperatures are above or below 'average' this may
have an impact as to when and how well a tree enters its dormant period.   

 

Temperatures across Alberta in September 2009 were well-above average and
this would have had an influence on some plants not fully "hardening off"
before the cold weather arrived. In other words, the onset of dormancy would
have been retarded.  

 

For this bulletin, temperatures were reviewed in Grande Prairie, Edmonton,
Red Deer, Calgary and Lethbridge. The highest temperatures recorded for
September 2009 were: Grande Prairie 28C, Edmonton 33C, Red Deer 33C, Calgary
32C and Lethbridge 33C. The mean maximum temperature in these five locations
was 6.6C above the combined average of 13.6C.*

 

The above average warm weather continued into the first week of October 2009
and then in all locations plunged to well below 0C. The sub-zero
temperatures lasted for a week and were accompanied by strong winds -
combined this is called an advective freeze. The lowest temperatures
recorded during this period were: Grande Prairie -9C, Edmonton -10C, 

Red Deer -14C, Calgary -16C and Lethbridge -17C. The mean minimum
temperature in these five locations was -7.2C below the combined average of
+5C.*

 

The late onset of dormancy, caused by late fall warm weather and the sudden
and extreme drop in temperatures will have had an impact on the physiology
of some plants and may have caused extensive tissue damage. This is called
Consequential dormancy and occurs when organisms enter a dormant phase after
adverse conditions have arisen. This is what, in our opinion, we believe
happened in October 2009 - as indicated by leaves frozen in-situ on some
plants. The result of the tissue damage was not seen until this past spring,
when many plants failed to break dormancy as they normally would.  

 

A compounding factor in some tree & shrub mortality are adverse weather
conditions during late winter and early spring periods when plants are
coming out of dormancy. Plant growth in spring is stimulated by lengthening
daylight hours and slowly increasing temperatures. If temperatures rise too
quickly and too early in the dormancy cycle, some plants may begin cell
growth too soon. If temperatures drop below freezing after cell development
begins, tissue damage is therefore possible. 

 

Weather records indicate that this did happen in most locations this past
spring, although it is difficult to know whether this is when the cell
damage occurred or whether it was during the fall conditions noted above.
Regardless, when combined with all these environmental conditions, many
plants were unable to survive and leaf-out this spring. 

 

Another contributing cause of tree mortality is drought. Although 2010 has
so far been wet, successive dry years since 2001 have taken a significant
toll on a number of tree species throughout the province. Many
drought-stressed trees (ash in particular) have also been attacked by an
insect called the cottony psyllid (Psyllopsis discrepans) and this has
further contributed to some tree mortality. 

 

Why do some plants on the same street, even within the same species, have no
problem surviving extreme weather conditions while others don't? As a living
organism each one will react differently to environmental conditions - it
could be genetics, location, injury, stress or even how it was maintained
that contributes to how well it survives. Even plant scientists who conduct
research into plant hardiness find the answer to this question challenging.

 

Please contact your local garden centre, contractor or plant supplier for
more information.

 

* Weather data provided by Weather Underground

 

 

Landscape Alberta Nursery Trades Association (LANTA)

200, 10331-178 Street, Edmonton 

Alberta, T5S 1R5 Canada

Phone: 1-800-378-3198. 780-489-1991

Fax: 780-444-2152

 <http://www.landscape-alberta.com> www.landscape-alberta.com 

 

2010 Green Industry Show & Conference

Edmonton Expo Centre 

November 18th & 19th 2010

 <http://www.greenindustryshow.com> www.greenindustryshow.com 

 

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information. Please contact the sender immediately if you are not the 
intended recipient of this communication, and do not copy, distribute, 
or take action relying on it. Any communication received in error, or 
subsequent reply, should be deleted or destroyed.