Dare We Celebrate? It's an Early Spring Again

Issue: 
March-April 2009

WHEN WE FIRST GET THAT BREAK from the cold in mid-January, all the doom and gloom forecasted by climate change specialists falls on deaf ears. As winter truly lets go and March blows into April, we still look forward to an early spring. It is hard to care about the potential price we ‘could’ pay for the unseasonal warmth. After all, it is SPRING and winter is over! But if the forecasts are right and we don’t start preparing for climate change impacts on our forests, we could be in for a catastrophe. Let’s examine one harbinger of spring that is relatively easy to observe and measure – bud break.

Technically, bud break is when buds open after winter dormancy revealing shoots of tender growth. The phenomena is controlled largely by temperature. Natural Resources Canada (NRCan) says, “The reaction is an intricately balanced release of growth regulators of varying types in buds (also in roots as a result of increasing daytime temperature). A winter cold is required to prepare the meristems, i.e. growing points, for this occurrence.

A study in Edmonton showed trembling aspen are blooming 26 days earlier then they did 100 years ago. In another study started as far back as the 1950s, lilacs were found to be leafing out and blooming on average eight days earlier.

On the other side of the coin, yellow birch is dying back in eastern Canada due to late spring frosts. Here in Ontario, according to an Ontario Forest Research Institute (OFRI) newsletter, “In the spring of 2007 in northeastern Ontario, huge areas of young conifers, both planted and natural, experienced needle and bud damage prior to bud break.” Species included black spruce, white spruce, balsam fir, jack pine, eastern white cedar and larch. Whole tree mortality was more common among small seedlings, especially those in clear cut areas. Trees that were damaged were generally under eight meters tall and 20 years old. Mature overstory trees were not affected.

Bring on the Heat
Complementing our national love of spring, the Edmonton study on early aspen development is generally considered wonderful news. “Biomass accretion” is determined by the length of the growing season. Earlier bud break means more growth potential in a single year. At a time when we need more big trees to reduce the effects of climate change, knowing our trees can grow faster is a bonus (and I’m sure the logging industry won’t complain either).

Another positive point to warmer winters and earlier springs was documented by Victor Lieffers, University of Alberta, in 2001. He defines crown shyness as the empty space between the crowns of trees in fully stocked conifer stands. This “space” is thought to be due to collisions of the crowns during wind. Lieffers states that the bending angle necessary to cause 50% twig breakage is decreased linearly with decreasing temperatures for both lodge pole pine and white spruce. He implies that with warmer winters and earlier springs, the tops of our mature evergreens will be in better shape.

Gambling With Different Species
A point that could be considered positive or negative depending on your perspective is that hardiness zones are shifting – but not uniformly. NRCan has maps on their website. Visit http://atlas.nrcan.gc.ca. The western provinces are seeing the greatest shifts but Ontario is also changing. How this will challenge our native species remains to be seen. It is, however, an opportunity to try varieties once considered too tender for Ontario. NRCan says, “The best advice is to select a range of provenances, i.e. intra-species biodiversity. Also, select a range of species where possible. The conditions you consider [early spring followed by late frost] are becoming common and are similar to those of New York State, Pennsylvania and other points south. As far as climate change goes (theoretically), the provenances in those areas should be best adapted to the challenge.”

Pengxin Lu, Ontario Forest Research Institute, did a cold hardiness study on white pine in 2003. His conclusion was that white pine seeds could potentially be transferred northward within a distance of 2 to 2.5 degrees latitude without increasing cold damage. One degree of latitude is equal to 69 miles or 111 km. Keeping in mind the Great Lakes are a huge heat sink and remembering Lu’s research was only with white pine, there is a lot of room to experiment with many species new to Ontario.

Another point from NRCan: “Nature tends to favour variation within a species. Horticulture and silviculture tend to favour uniformity – through mass propagation of one supposedly ‘superior’ individual.” It is an easy solution. Plant or purchase trees grown from seed. It may take a little longer then stem cutting, but up front costs are lower and your plants will have the same genetic variations and potential for survival as seen in nature. Get it right with identical genetics and you get an instant landscape. Get it wrong, the result is mass failure.

Impacts on Native Species
Parts of BC and Oregon have the potential to not experience a sufficient “chilling period.” It’s hard to sympathize. Ontario’s snow birds in Florida certainly aren’t upset to miss winter. But it is 180 degrees wrong for Canadian trees. Winter’s chill is better for some trees and a necessity for others. While it is OK in some areas to experiment with more southerly species, we can’t afford to lose our native species.

In a joint study between Oregon and the University of BC, Douglas fir seedlings exposed to five-degree temperatures for 13 weeks (compared to those exposed to 7 and 9º C) produced significantly faster bud break and had greater numbers of active buds and weight of new growth. In a second study, two year-old grafted Douglas firs were exposed to mean winter temperatures of 9 to 12º C. Most died.

David Weinstein is leading a Cornell University study to investigate another potential climate change scenario. He is trying to determine if pollinators and plants are changing in sync. The problem is that the temperature responses of plants are not the same as those of insects. As long as temperatures stayed fairly consistent year after year, small variations have not been affecting the synchrony because both pollinators and plants have evolved to respond to small annual changes. However, with temperatures increasing so rapidly, small differences have started to play a role.

Weinstein is requesting that average citizens collect data, in the same way information has been collected on birds and lakes in Ontario for years, ensuring there is a wide base for the study. As a sideline of interest, the Canadian studies represent some of the longest-term data collecting sites in the world. Visit http://www.naturewatch.ca/english/plantwatch for details.

Last year, in Cornell University’s first real season collecting bud break data, they had almost 150 people making nearly 500 observations. Visit the Project Budbreak website at http://budbreak.tc.cornell.edu/.

Weinstein is also collecting other historical data sets on the timing of plant bud break, flowering, etc. Two of which include a 20 year record from central New York and an 80 year record from Wisconsin. He hopes to soon make these available online.

Results from the bud break study aren’t expected to start coming in for five to ten years. Meanwhile, every farmer is well aware that our native and domestic bees are already in crisis causing numerous challenges – but we don’t know if the issues are accented by the arrival of earlier springs. Weinstein comments, “We don’t yet know which pollinators to focus on, but the large declines in bee pollinator populations that have been recorded are of great concern. It’s not hard to imagine that a change in timing of the availability of pollen could be playing a role in their population declines.” Five years is going to be a long time for the orchard business to wait for Weinstein’s results.

Weinstein adds, “We haven’t yet seen conclusive proof that pollinators have been affected, but Europeans have noted that oak trees are beginning to form leaves significantly before the insects emerge that typically feed on these leaves when they are young and tender. The result is that the insect populations are greatly diminished, which is a good thing for the oaks, but a bad thing for bird populations that have historically depended on the insects for food. They have seen at least one bird population greatly decreased because of the changing conditions.”

More common earlier springs were also documented by S.J. Colombo (OFRI) in 1998. He found evidence of increasing earlier dates of bud break over the course of this century at half the stations examined. Risk of frost damage at most stations in the 1980s was usually greater than in earlier periods. Weather data modeled for climate warming of 5º C predicts bud burst will occur two to four weeks sooner than was the case during 1961 to 1980. Colombo stated, “As the climate gradually warms, frost risk is expected to fluctuate upwards or downwards. A late frost after a warm spell is the same as an early frost in autumn.”

NRCan explains further: “In preparation for winter, plants essentially pump water out of their interior plant cells (as ice crystals in a cell will rupture the cell walls) or exhibit an increase in the dissolved ions in cell contents (just the way dissolved salt lowers the freezing point of water). Once the weather warms up, this adaptation is lost (water is moved back inside the cells so they can function). At this point, if a frost occurs, plants are unprotected. Experiments show that dogwood stems, if adapted for cold, can survive immersion in liquid nitrogen. If not adapted, simple frost will cause cellular disruption (frost bite).”

Mitigating Temperature Changes
Ontario Forest Research Institute research scientist Rongzhou Man and several colleagues looked at the cold hardiness patterns of the conifer species that experienced the bud and needle damage in 2007 (mentioned at the beginning of this article). “The level of damage varied by species, generally ranging from 70-100% for needle morality, 20-30% for bud mortality, and about 15% for whole tree mortality two years after the frost damage. If the trend in climate change continues, with trees starting growth earlier each year, the frequency and possibly of the severity of frost damage will likely increase. Widespread damage will affect the productivity and health of the trees and the forests they live in.” They recommend increasing the use of alternative management approaches including the increased use of shelterwood systems in these stands. The environmental conditions under tree canopies are less extreme, therefore providing protection from frost damage.

This is a great idea for the boreal forest but it isn’t a viable solution for much of the urban forest. NRCan reports that the species at greatest risk are those in hardiness zones 6 and 7 – especially plants with early bud break and early flowering like magnolia, forsythia cultivators, pear and pecan hickories. “What climate change will do is select those individuals in a species that are the most adapted to variation – to early and late frosts.”

In an article published in Tree Physiology 2007, Xavier Morin tries to explain the problem. “Freezing events may cause stress or injury to plants… from the cell to the whole organism… Tree species subjected to low temperatures, as can occur at high elevations in the tropics, have developed mechanisms to cope with such stresses.” These mechanisms are in two classes. The first is avoidance of intracellular ice formation and the second is tolerance of extra cellular formation and the resulting cell dehydration.

The results showed that variation in cold hardiness in European oaks was related directly to variations in the concentration of soluble carbohydrates and that the relationship was driven by temperature. “Although cold hardiness varied significantly among species at all dates, it varied among populations only during the early and late hardening periods… A warmer climate usually leads to delayed leaf senescence and earlier bud burst so that in fall and spring, southern populations should exhibit lower cold hardiness then northern populations.”

Tom Noland, OFRI, agrees with this in principle but adds: “Research is needed to examine the cold hardiness of boreal tree species with variation of temperatures in winter, especially warm episodes. The buildup of carbohydrates, particularly soluble sugars, in tree tissues has been suggested as a winter antifreeze for trees. Research done at OFRI by Chris Glerum and Young Tae Kim shows a buildup of certain soluble sugars in tree seedlings as they become dormant and harden off in the fall. The seasonal profile of soluble sugars (especially sucrose) in trees usually shows a peak in concentration during the winter, which is associated with frost hardiness. The real culprit in most of these spring thaw/frost cycles causing damage to trees is the thaw causing them to physiologically activate and lose their frost hardiness by activating metabolism (of many biochemical processes). This starts the process of breaking down the accumulated sucrose in the tissues making them more susceptible to freezing damage. However, sugar concentration is just one of many factors determining frost hardiness in trees.”

Rongzhou Man said, “Trees always go through the seasonal cycle with the highest carbohydrate levels in the fall at the end of the growing season and the lowest levels in late spring and early summer at the beginning of growing season. In winter, starch is converted to sugar and other soluble carbohydrates to increase cold hardiness. However, the change in starch and soluble carbohydrates does not explain all the seasonal variations of plant cold hardiness. In addition, there is no reason why carbohydrate level in the winter of 2007 was lower than normal.” (Referring to the boreal forest die back in 2007.)

The direct cause of the tree die back in 2007 was found to be simply “earlier-than-normal loss of cold hardiness in warm spring, followed by a severe late spring frost with night temperatures down to -8 and –9º C.”

The winter die back of yellow birch in eastern Canada is likely due to these same problems. NRCan says cold hardiness of the birch is decreased because the xylem is breaking down during mid-winter thaws. This makes it difficult for water to pass from the root to the branches. It isn’t a new problem. It is just occurring more often in native species once considered hardy – not just in tender introduced species.

Bottom line is that spring is coming earlier. The rules we lived by in the past aren’t changing, but our climate is. We have to look at each species with a new appreciation for its bud break and the length of winter chill. Some trees are going to be just fine, others will need a shelterbelt or extra mulch, while some will simply not survive. Determining the difference is the professional arborist’s new job and it will be done one experiment at a time. The experts don’t have all the answers – yet.

SIDEBAR #1

Sweet Rewards: A Million Dollar Industry

Maple syrup is more then a sweet spring treat. Ontario’s maple syrup industry is valued at 11.2 million dollars annually. Canada produces 85% of the world’s production and the total has doubled in the last two decades.

Sugar maple trees in most of Ontario are in good shape for the 2009 tapping season due to sufficient moisture levels in the summer of 2008. Localized gypsy moth and drought in Essex and Kent are the exception.

Sap started flowing in early March in the southwest, along Lake Ontario and in Prince Edward County. Taps are predicted to continue to run for five to six weeks on average. This is an improvement to the threatened start to the flow in February as early flow is often low in sugar concentration making the industry less profitable.

Sugar maple is vulnerable to acid rain, fire and flood. Agriculture Canada says “There could be changes to the composition and geographical distribution of maple sugar bushes.” Predicted changes are potentially due to extreme weather events and climate change. Producers are encouraged to plant conifers as a wind break around woodlots. There is also the potential for planting maple further north.

Raise a glass of syrup and toast 2009 – or pour it on your pancakes. Looks like this year will produce an excellent vintage.

SIDEBAR #2

Reducing Your Carbon Footprint One Step at a Time: Report Your Success Stories

Canadians Meet the Challenge of One Million Acts of Green!
In the November/December 2008 issue of the Ontario Arborist, we reported on the One Million Acts of Green (OMAoG) initiative by CBC and Cisco. In early February of this year, it was announced that OMAoG reached its goal of 1,000,000 acts of green registered online at www.onemillionactsofgreen.com.

Participants from coast-to-coast and from all walks of life clearly embraced the program, pushing the campaign to its ultimate milestone in less than four months. Elementary and high schools, universities, municipalities, businesses and even local coffee shops demonstrated their commitment, challenged each other to ‘go green’ and collectively achieved the goal.

With the support and enthusiasm of Canadians nationwide, One Million Acts of Green is still going strong to see how high Canadians can go!

Keep logging your green acts, challenge co-workers, friends and family. With participants from over 50 countries, challenge your friends from abroad to meet Canada’s stellar results.

We welcome articles, short submissions and photographs of what you are doing personally or professionally to reduce your carbon footstep. Contact Ontario Arborist editor Joy Black at 519-371-6818, joy@npc-solutions.com

Our mission is to enhance and promote the care and benefit of trees for present and future generations in Ontario through education, research and awareness.