9:15 - 10:00 AMApproaches for determining

growing season length Bud break, leaf expansion, litterfall.

Estimation through heat-sum.Quantitative monitoring through sap

flux.

1) Bud break, leaf expansion (leaf phenology) affect the cycling of water and carbon in the environment.

2) In addition, leafing out is among the most sensitive

biological responses to climate change.

Therefore, leaf phenology records can help us understand plant responses to climate change. For example, across the world, many spring events are occurring earlier—and fall events are happening later—than they did in the past.

Bud break, leaf expansionWhy Monitor Leaf Phenology?

Bud break, leaf expansionWhy Monitor Leaf Phenology?

Despite their importance, broadly distributed phenological data are relatively rare.

With sufficient observations, we can document patterns of phenology for critical plant species across the state, and then use this information to build models to help us understand and adapt to changing landscapes and climates.

Bud break, leaf expansion, litterfall. Main objectives for this coming year:

Is the timing of spring tree phenology (green tip of leaf emerging from buds)

and leaf out (full leaf development) different between West and East North Carolina?

If so, what simple factors affect such differences?

1st assignment: Litterfall collection (useful for deciduous forests with

adequate spatial and temporal sampling schemes)

2nd assignment: Estimation of bud break and full leaf development

through heat-sum• What is the influence of temperature on bud break

and full leaf expansion?

• Definition: sum of number degrees of average temperature >5°C (41°F) for each day

• Example: Grapes begin to grow when the temperature reaches above 10°C (41°F). To reach maturity, a total amount of heat above this temperature is required. Successful growth in Southern France for grapes is about 800°.

2009

March April May June

Red

map

le (

kgh2

Otr

ee-1

day-

1 )

0

2

4

6

8

10

12

14 Red maple

mm

day

-10

10203040

Precipitation

3rd assignment: Sap flow as a proxy for bud break?

2009

March April May June

Red

map

le (

kgh2

Otr

ee-1

day-

1 )

0

2

4

6

8

10

12

14

Lobl

olly

pin

e (k

g h2O

tree

-1da

y-1 )

0

10

20

30

40

50Red maple L.Pine

mm

day

-10

10203040

Precipitation

3rd assignment: Sap flow as a proxy for bud break?

2009

March April May June

Red

map

le (

kgh2

Otr

ee-1

day-

1 )

0

2

4

6

8

10

12

14 Red maple

mm

day

-10

10203040

Precipitation

3rd assignment: Sap flow as a proxy for bud break?

Notion of vapor pressure deficit

• Vapor Pressure Deficit, or VPD, is the difference (deficit) between the amount of moisture in the air and how much moisture the air can hold when it is saturated (Wikipedia).

• = driving force for transpiration

2009

March April May June

Red

map

le (

kgh2

Otr

ee-1

day-

1 )

0

2

4

6

8

10

12

14 Red maple

VP

D (

kPa)

0.00.20.40.60.81.0

VPD

Normalizing sapflow by VPD

Red

ma

ple

(kg h

2Otr

ee-1

day-

1)

0

2

4

6

8

10

12

14 Sapflow

2009

March April May June

Red

ma

ple

(kg h

2O

kP

a -

1 tre

e-1

day-

1 )

0

10

20

30Sapflow/VPD

VP

D (

kPa)

0.00.20.40.60.81.0

VPD

Sapflow corrected Sapflow corrected for VPDfor VPD

conductanceconductance

50%50%

100%100%

15%15%

Bud break?

Endleaf expansion?

Litterfall and sapflow

September October November DecemberSeptember October November December

Cumulative litterCumulative litter