trees in our gardens - university of maryland€¦ · stressed plants more susceptible to insect...

Effects of climate change?

Trees in Our Gardens

Phil NormandyBrookside Gardens

• Is it real and documentable?

• A long-term or a short-term trend?

• What are the results, if it is real?

• Who are the experts?

These answers are not only not clear, they are hotly debated.But something is definitely different.

Temperature extremes result in more cold damage and heat stress

Rainfall extremes means more floods, longer droughts

Stressed plants more susceptible to insect and disease attack

More violent storms (?) means more severe damage

Lots of other aspects to this debate, but….

Response to more extreme/variable weather based or climate of origin regardless of continent

Native species not inherently better as regards climate change

If hotter climate, southerly trees move north, northern species retreat▪ Examples: southern oak species; white birches and

white pines

Reverse is true with colder winters, cooler summers Lilacs loving Georgia?

In the short term species don’t migrate as they did in the Ice Ages, but they perform differently. The marginal edge shifts.

Trees marginally adapted now will do better or worse depending on temperature shifts

In a warmer world: Trees happier in colder climates will likely become more

unhappy and stressed White birches, lindens

Trees from warmer regions will likely do better Southern magnolia in Philadelphia!

Existing trees: Maintain health to reduce effects of environmental stress

Water deeply during prolonged drought, but allow to dry between deep waterings

Eliminate turf over wide root area, mulch to 2”. Grass is competitive

Monitor closely for pests and diseases and treat if severeDon’t overprunePlant fast-growing species nearby to give light shade?

Give up on poor performers and replant wisely: you don’t have forever!

New trees: Know your own site conditions thoroughly: light, heat, wind

direction, soil conditions including texture and water retention. Local conditions can make large climate shifts better or worse for plants.

Note what’s done better recently, and worse.

Focus on species from warmer or more severe climates: the south, Great Plains, Central Asia, etc. Or species with a very large natural distribution over several zones (e.g., white oak)

Research is key.

Small trees to consider

Phil NormandyBrookside Gardens

• Wide natural range--N. America

• Takes more heat if shaded

• Native• As temperatures

rise, will need more water and part shade, good soil.

• Watch for borers

• Native• As temperatures rise, will need

more water and part shade, good soil…site carefully for success

• Native• Sun or shade• Can survive canker

diseases

• Thrives on heat, drought, extremes, poor soil

• Some treelike• Appreciates warmer

winters

Pretty tough. Will appreciate more severe winters.

Select most disease-free cultivars

Alternatives: Redbud Serviceberry Fringetree Okame cherry

• Among most heat-tolerant of cherries

• Fast

• Among most drought and urban-tolerant species

• Screen or accent• Shears well

Wide native range in N. AmericaTolerates some drought and flooding.Part shade, more water in climate extremes

• Drought/heat tolerant• Screening• Wildlife• Wide native range

• Tolerates sun or shade• Good hemlock replacement• Screen• Pest-free• Not native

• Smaller-growing clone formerly a bit tender

• Any S. magnolia likely to enjoy warmer climates

Shade/large trees to consider

Somewhat smaller stature and leaves but much more heat tolerant

• Extremely tolerant of heat, heavy soil, drought, and flooding

• Fast growth• Site over lawn not structures

• Wide natural distribution

• Very tolerant of heat, dry soils and flooding

• Fast-growing

• Tolerates standing water or dry soils

• No pests• Deciduous = winter light for

garden• Moderate growth rate; not fast

• Extremely soil and drought tolerant

• Highly resistant to Dutch elm disease

• Not native and some can seed

RESISTANT TO DUTCH ELM DISEASE

Larger evergreens to consider

• Heat-tolerant; somewhat shade-tolerant

• Large screen or specimen

• Replacement for Colorado blue or Norway spruces

• Narrow for a spruce

How will these do if temperatures rise?

Questionable…

Fuggedaboudit! Pest-prone anyway.

Consider instead: ‘Green Giant’

arborvitae Cryptomeria

Fuggedaboudit! Also brittle.

Consider instead:

‘Green Giant’ arborvitae

Serbian spruce Cryptomeria

Consider instead:

River birch (Betula nigra)which thrives on heat

Already struggling in DC areaConsider instead: One of the faster oaks

• Not sure how it will do with more heat and drought. Not drought-tolerant. Siting will be key.

• Baldcypress slower but more adaptable

Consider instead: Shumard oak Red oak Swamp white oak

Short life expectancy for an oak; gets shorter with more heat. Has more pests as well.