Trees for the Bay

Potomac Watershed RoundtableOctober 7, 2011

Jim McGloneUrban Forest Conservationist

TREES AND STORMWATER

Stormwater

Stormwater

Deciduous forest intercepts 13% of rain annuallyEvergreen 21%

Leaf Area Index

• Measure of square meters of leaf area over a square meter of ground – m2/m2

• For a healthy, vertically diverse forest LAI is 6-7• Most urban/suburban forests are missing shrub

layer and have an LAI of 4-5• 148,260 gallons of stormwater per acre per year

are intercepted• 49,420 gallons of stormwater management lost

per acre to deer browse

RIPARIAN BUFFERS

Buffer Benefits

• Biological energy• Shade – Cooling– Dissolved oxygen

• Infiltrate upland storm flows• Filter pollutants from uplands• In-stream habitat– Cover– Pools

Buffer Benefits

• Biological energy• Shade – Cooling– Dissolved oxygen

• Infiltrate upland storm flows• Filter pollutants from uplands• In-stream habitat– Cover– Pools

TREES, AIR AND WATER

Air Pollution to Water Pollution

• Deposition of air pollutants – N, Hg, SOx, NOx, etc. - on land, then rain washes air deposited pollutants into surface waters

• Rain drops intercept and wash pollutants out of air

• Air pollutants directly deposited into water• Reducing air pollution can help reduce water

pollution

Direct Absorption

SOx, NOx, Ozone

Air Pollution Damage to Trees

Shade and Energy

• Summer – Deciduous trees on the south and west of buildings can reduce cooling costs by >10%, and allow winter warming.

• Winter – trees on north can break winter winds and reduce heating costs by >5%

Transpiration and Heat Island

Transpiration can reduce heat island effect and ambient temperatures. This means lower cooling costs

This Landscape Uses no Lawn Mowers

TREES AND STREAMS

Sediment Load

Sediment Quantity × Sediment Size ~ Stream Velocity × Discharge

Buffer Benefits

• Biological energy• Shade – Cooling– Dissolved oxygen

• Infiltrate upland storm flows• Filter pollutants from uplands• In-stream habitat– Cover– Pools

Biological Energy

Nutrient Processing

Bacterial Activity that requires biological energy

Nutrient Processing

Effects of Sedimentation

Leaf Matter that Provides Biological Energy for Microbes

Lose Benthic Invertebrate Habitat

Chesapeake Bay

• Increased discharge is directly responsible for sediment loading - #1 bay pollutant

• Increased discharge lowers in-stream nutrient processing, but is not only contributor to nutrient loading - #2 bay pollutant

Some Tree Benefits• Health

– Fitness– Asthma– Psychological– Healing

• Stress Reduction– Reduced domestic conflict– Less school aggression

• Improved attention– Direct Attention Fatigue– Reduced HDAD

• Aesthetic• Bio-affinity• Spiritual

• Economic– Shopping– Energy reduction– Property values– New business– Absenteeism– Job satisfaction

• Crime reduction• Traffic

– Clear zone– Calming – Asphalt

• Environmental services– Stormwater– Air quality– Carbon– Habitat

Engineered Stormwater Management Can’t do This

http://www.sierraclub.org/sprawl/community/transformations/index.asp