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Talk Outline ♦ What is climate change? ♦ Cold hardiness and climate change ♦ Provenance and seedling variability ♦ Dormancy and global warming ♦ Heat tolerance ♦ Photosynthesis and respiration ♦ Heat stress avoidance and tolerance ♦ Trees for 2050 ♦ What to do to combat climate change?
What is Climate Change? ü Climate change or global warming
ü “Greenhouse” gases, such as CO2, naturally occur in atmosphere to some degree
ü Help trap radiation, warm air and land ü Since 1800’s, humans have caused larger
amounts of these gases to be released into atmosphere
ü Sources: burning of fossil fuels such as coal, oil, gasoline, natural gas
ü Clear cutting forests, particularly in tropics releases significant levels of CO2
What is Climate Change? ü Climate change/global warming
ü Causing general warming over the earth ü Climates over the planet impacted ü Subtle to drastic changes in temperature,
precipitation, occurrence of catastrophic storms (tornadoes, floods, hurricanes)
ü Can urban trees make a difference in combating or greatly reducing climate change?
Cold Hardiness ü Ability to survive the freezing of water in plant
tissues ü Hardiness can also involve heat, drought,
moisture, salt stress, etc. ü Cold hardiness zone maps is a measure of
average, annual, minimum winter temperatures ü Does not report temperature extremes, annual
rainfall, summer temperature extremes, night temperatures; rare events
ü Plants hardy to zone 5: Wisconsin vs. Nebraska vs. western Montana
Dormancy ♦ As plants go dormant, buds will not grow even
though all other conditions are favorable ♦ Condition of rest develops within each bud or
seed of temperate zone plants ♦ To overcome true dormancy, buds must be
exposed for 4-8 weeks to low temperatures (-4 to 10°C or 25-50°F), depending on the species, or else will not break bud
♦ Maximum dormancy occurs in early winter (December), gradually decreasing to late winter (March)
Dormancy ♦ Without adequate chilling, plants may not leaf
out or are very slow to leaf out, or may die ♦ Once chilling hour temperature requirements
met, plant no longer dormant, just quiescent ♦ Starts to grow once temperatures are
adequate for growth ♦ Disadvantage if growth starts too early in
spring and late hard frost occurs ♦ Particularly a problem in some exotic plants
as may be more temperature dependent vs. photoperiod dependent like many native plants
Heat Tolerance ◆ American Horticultural Society Heat Zone
Map ü Based on average, annual days above 86°F ü Lower the heat zone, the cooler the climate,
ex. Zone 2 vs. 5 ü Wisconsin has four heat zones:
§ 2: Northeast WI and near UP border § 3: North central WI and Door County § 4: Eastern, western and central WI § 5: Extreme southern and western WI
Heat Tolerance ◆ Heat zones important in southern and
western U.S. ◆ Important in northern U.S. in urban
areas, particularly with lots of concrete and buildings nearby and limited planting space ü Ex. Paper birch prefers heat zones 3 and
below
Heat Effects on Plants ◆ Main effect of high temperature stress is
increased water use ◆ Water availability often limited ◆ Leaves loose water via transpiration as
temperatures rise ◆ Stomates begin to close, cooling effect
stopped ◆ Fewer carbohydrates available for growth,
pigment generation, defense ◆ Poor heat tolerant plants burn up carbs
made during night
Projected changes in summer average
temperature and rainfall for two Midwestern states
(Hayhoe et al. 2010)
Photosynthesis and Respiration ◆ Each 10°C increase in temperature,
respiration doubles (Q10 Principle) ◆ High night temperatures crucial in
amount of heat stress versus day temperatures
◆ Some plants (peppers, tomatoes, tropical plants) need high temperatures for sugar production
Heat Stress ◆ Optimum temperatures for Ps below 86°F (30°C)
ü Above temperature compensation point, Ps cannot replace the CO2 used in respiration, but respiration rates climb
ü High night temperatures increase dark respiration ü Carbohydrate reserves decline (less stress tolerant,
less growth, reserves for defense, increase pest susceptibility)
ü Less anthocyanin production (leaf, flower, and fruit color)
ü Rapid increase in transpiration, eventual death ü Fruit looses its sweetness
Heat Stress ◆ Above temperature compensation point
ü Structure and stability of cell membranes is compromised (excessive fluidity of membrane lipids causing leakage of ions)
ü Toxicity (release of ammonia in cell) ü Biochemical lesions within cell ü Membrane disruption, denaturation of
proteins (breakdown) ü Uncoupling of the chloroplast energy
transfer mechanism
Symptoms of Heat Injury ◆ Scorching of leaves and fruit ◆ Sunscald on bark ◆ Leaf abscission ◆ Inhibits shoot growth (less
meristematic activity) ◆ Inhibits root growth: death of root
tips and whole roots ◆ Death
Treatments ◆ Six provenances: AL, FL, NC, NJ,
CN, and MA ◆ Five temperatures: 22/18, 26/22,
30/26, 34/30, 38/34ºC ◆ Photoperiod: 16 hr, 600 umol/m2/sec
Avoidance to Heat Stress ◆ Plants avoid excessive heating by
decreasing their solar radiation absorption
◆ Reflective leaf hairs and waxes ◆ Leaf rolling and vertical leaf orientation ◆ Production in some species of small,
highly dissected leaves (minimize the boundary layer thickness and maximize conductive and convective heat loss)
Avoidance to Heat Stress ◆ Insulation: thicker bark and cuticle ◆ Some plant parts (fruit) can
decrease respiration as temperature increases
◆ Decrease absorption of radiant energy: cuticle, reflective leaf surface, energy not transmitted
◆ Transpirational cooling (evaporative)
Tolerance to Heat Stress ◆ Gradual, cumulative exposure to
high temperatures preconditions plants (less in spring, more in summer)
◆ Starvation prevention: Ps changes to increasing temperatures, slowly acclimates
Tolerance to Heat Stress Synthesis of heat shock proteins
ü Improved thermal tolerance ü Act as protective agents (help prevent
enzyme inactivation and protein breakdown) ü Scavenge denatured proteins ü Decreases membrane breakdown by
increasing lipid saturation ü Produced in cell nucleus and/or chloroplast ü Once returned to normal growing
temperatures, heat shock protein synthesis stops
Human intervention ◆ Plant shade trees and vines to shade
and cool environment around sensitive plants
◆ Plant groundcovers or use mulch to help cool soil and reduce evaporation
◆ Prune lower branches to increase air circulation
◆ Use evaporative cooling: irrigation, sprinklers, rain does this too
Climate Change and Trees? ü Trees can affect climate change
ü Use and sequester atmospheric CO2 via photosynthesis
ü As trees get larger over time, ability to sequester and store more carbon in plant tissues (trunk wood and roots) increases dramatically compared to herbaceous, annual or grass species
ü However, global CO2 emissions far exceeds amount used and stored in trees in a year
Trees for 2050 ◆ Study of 50 tree species best suited for a
warming Midwestern climate (Bell 2013) (http://www.chicagobotanic.org/plantinfo/tree_alternatives) ü Projected 40 tree species likely to survive and
thrive in 2050 ü Projected 10 tree species will not grow well in
this area and will begin to decline under worse case model scenario
ü Shagbark hickory, basswood, littleleaf linden (GREENSPIRE®), Amur maackia, American hophornbeam, Katsuratree, Sargent cherry, Norway spruce, Serbian spruce, Black Hills spruce
Trees for 2050 ◆ Climate change modeling indicates some
trees at northern edge of hardiness will do a bit better in slightly warmer conditions in 2020, however ü By 2050, 10 out of 50 trees species will not do
well (20%) ü By 2080, 39 out of 50 tree species will not do
well (78%) ü Only 11 (22%) of the original 50 tree species
will do well by 2080 if current global warming and CO2 emissions climb at today’s rates
What to do to Combat Climate Change?
ü So what can we do to combat climate change? ü Reducing CO2 emissions critical globally ü Significantly reduce use of fossil fuels in energy
and agricultural systems ü Reduction of waste, garbage by recycling more ü Lowered birth rates especially in overpopulated
countries, uses more resources ü Stricter air quality standards globally ü Greatly reduce amount of deforestation and
burning of tropical rainforests
What to do to Combat Climate Change?
ü So what can we do to combat climate change? ü Use of carefully sited shade trees cool
environment in summer and dramatically reduce use of electricity for a/c and power plant emissions
ü Trees planted near buildings can reduce summer energy use by 70%
ü Evergreens and trees can slow harsh winter winds and reduce energy use for heating by 30%
ü Improving the soil by incorporating a dense layer of processed charcoal (biochar)
Average Life Expectancy of Street Trees
◆ Downtown: 7 years ◆ City Average: 32 years ◆ Best City Site: 60 years ◆ Rural Site: 150 years ◆ Must increase species
diversity: 20:10:5 rule ◆ Proper plant health care
over entire tree life ◆ Watering will become
essential for some species
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