Landscape Plants and Climate Change

Dr. Laura G. Jull Dept. of Horticulture, UW-Madison

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

Atmospheric CO2 Readings at Mauna Loa Observatory (1960-2016)

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 and 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

1990 U.S.D.A. Plant Hardiness Zones

2012 U.S.D.A. Plant Hardiness Zones

Dormancy and Global Warming

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

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)

Betula papyrifera: paper birch, canoe birch

Native Environment

Native Environment?

Cornus alternifolia: pagoda dogwood

Abies balsamea: balsam fir

Photosynthesis and Respiration

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

Sun (top) and shade (bottom) leaf anatomy

Photosynthesis

CO2

H2O

O2

Carbs

Plant Growth

Respiration

Storage

Defense

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

Native range of Atlantic

white-cedar

Northern versus southern provenances of AWC

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

MA, CN, NJ, NC, AL, FL provenances at

30/26°C

MA, CN, NJ, NC, AL, FL provenances at

34/30°C

Heat Stress Avoidance and

Tolerance

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

“Shading” of newly planted shrubs

Rooftop Garden in Wilmington, NC (near the

beach)

Assortment of plants are irrigated

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

Climatic Suitability of American Linden and ‘Autumn Gold’ ginkgo

from 2016-2080

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

Have a Great Day and Think Spring!