Climate change threats to southeastern coastal plain forests: an ecosystem services perspective

Climate change threats to southeastern coastal plain forests: an ecosystem services perspective

Steven Brantley Joseph W. Jones Ecological Research Center

Outline • Ecosystem services from

southeastern forests • Definitions • Contemporary regional

issues • Climate change mitigation • Water scarcity

• History • Past and current trends in

SE coastal plan land use • Future

• “Savannification” of southeastern forests

Definitions • What are ecosystem services?

• Benefits people obtain from ecosystems

• Goods, services, and natural assets

• Vital to human health and livelihood

• Often lack a formal market • “Free” benefits to society • Public goods • Often overlooked in decision

making

Definitions • Categories and examples of

ecosystem services • Provisioning: Food, water,

fuel, fiber • Regulating: climate control

and feedbacks, watershed services

• Supporting services: Soil formation, nutrient cycling

• Cultural services: recreation, cultural heritage

• Further reading: U.N. Millennium Ecosystem Assessment

Threats to forest ecosystem services

from climate change

• Direct threats • Physical effects on

trees/stands • Increases in stress • Increases in disturbance

• Indirect threats • Policies to mitigate climate

change • Fire suppression • Biofuel production






• “Savannification” of southeastern forests?

Contemporary regional issues: Carbon sequestration

• The capture and storage of atmospheric CO2

• Important climate change mitigation strategy

• Ecosystem C sequestration: potential generally based on the “best available science”.

• C science v. C accounting

Forest C sequestration in the southeastern U.S.

• Southeast has been the strongest C sink in the U.S. during the past century (Coulston et al. 2014)

• Climate • Warm, wet climate ideal for high

NEP (Novick et al. 2015) • Changes in land use practices

• Afforestation of abandoned agricultural land

• Young forests • Fire suppression • Increase in short-rotation

pulpwood production

What effect of climate change?

• Carbon sequestration rates expected to decline

• Increased water stress for trees

• Increased atmospheric demands

• Increased frequency and severity of droughts

• Lower NEP • Increased tree mortality

McDowell et al. 2015

What effect of climate change? • Carbon sequestration rates expected to decline

• Lower vigor and higher mortality (McDowell et al. 2015) • Tall conifers particularly vulnerable (Bennett et al. 2015) • Shifts from mesic to xeric stand characteristics?

• Lower stand density (and NEP)? • Shorter trees (increased root-shoot ratio)? • “Savannification” (Hansen et al. 2001, Ingram et al. 2013,

others) • Interactions between climate change and other factors

• Forest aging causes a slow down in C sequestration • Land use change; especially reversion back to agriculture.

Contemporary regional issues: Water scarcity

Contemporary regional issues: Water scarcity

• Growing regional population

• Increased Municipal withdrawals

• Growing world population • Increased Agricultural

withdrawals • Increased

Evapotranspiration • Increased PET from climate

warming • Land use intensification

Forests and water supply • Improve Water Quality

• Filter nutrients and pollutants

• Reduce sedimentation • Regulate timing and

magnitude of streamflow

• Mitigate Flooding • Stabilize baseflow

• Forested lands supply some or all surface water for ~50 million people in the southeast.

Water yield

From Brooks 2015, Science

R = P – ET

Yield =R/Area

Declining water yield in the southeast

P. Caldwell, unpublished data

What effect of climate change? • Higher atmospheric demand for water

• Potential Evapotranspiration (PET)

• Increased frequency and severity of droughts • Negative effects on municipal withdrawals, agriculture,

stream biota, and ecosystem services from estuaries

• Other, more complex and interacting effects • Ex. CO2 -- plant feedbacks






• “Savannification” of southeastern forests?

Longleaf Pine

Land use change

LLP

Old field

Pulpwood

Short rotation pulpwood

Row crops Mixed Pine-

Hardwood

Land use intensification: Agriculture

Land use intensification: Agriculture

Land use intensification: Forestry

Land use conversion and C sequestration

LLP

Old field

Pulpwood



Hardwood

C loss

C gain

Land use conversion and water yield

LLP

Old field

Pulpwood



Hardwood

Lower yield

Higher yield

Future of forests in the southeast • Ecosystem services perspective

• Maintain C pools and maximize C sequestration* • Improve water yield while maintaining water quality

and flood mitigation benefits of forest cover

Where does longleaf pine fit in?

• Longleaf pine is highly resilient • Lower susceptibility to insect-induced mortality • Drought tolerant • Reduced risk of catastrophic fires

• Longleaf pine is one of the most conservative land cover types in terms of absolute water use (ET)

• Frequent fire reduces ET • Supports and maintains ecosystems with low basal/leaf area which

equals lower transpiration and reduced interception loss • Selects for species that tend to be more conservative in terms of

water use

Savannification

Cons • Lower basal area • Less productive • More frequent fires • Less canopy diversity

Pros • Lower basal area • Less water use • Lower fire severity • More understory

diversity • Better wildlife habitat • More resilient

• Drought • Storms

Points for Discussion

• Changes in land use have resulted in a very strong C sink in the southeastern U.S.

• Sink is slowing down as forests age.

• Climate change may make this sink even weaker.

• Climate change mitigation strategies that focus primarily on high NEP have tradeoffs.

• Streamflow has declined throughout the southeast • Climate change has caused 10.2 mm/decade increase in PET.

• Land use intensification has caused 50mm/decade change in actual ET.

• Can forest management play a role in mitigating water scarcity?

Acknowledgements

• Will Flatley • Paula Fornwalt • Kamal Gandhi • Jim Vose • Larry Band • David Wear • Peter Caldwell • Chelcy Miniat • Steve Jack • Stribling Stuber • Steve Golladay • Other Jones Center staff