Water and Carbon Cycles in Heterogeneous Water and Carbon Cycles in Heterogeneous Landscapes: Landscapes:

An Ecosystem PerspectiveAn Ecosystem Perspective

Chapter 4

How water and carbon cycles connect the organizational levels of How water and carbon cycles connect the organizational levels of organisms, ecosystem, and landscape, and what we know of the organisms, ecosystem, and landscape, and what we know of the

mechanisms of their operation. mechanisms of their operation.

1. Obstacles that one faces trying to connect these different levels and the ways to tackle them;

2. Current research questions and approaches;

• Ecosystem vs landscape

• Ecosystem ecology vs landscape ecology

• Lack of ecosystem studies at landscape level

• Extremely difficulty to measure an ecosystem process (e.g., water and carbon fluxes)

• Sound experimental design is extremely difficult to develop

• Challenge in scaling (up and down)

BackgroundBackground

Spatial display of growing season ecosystem Spatial display of growing season ecosystem evapotranspiration from eight ecosystems evapotranspiration from eight ecosystems

Region, Biome

LandscapeEcosystem

CommunityOrganism

(Canopy)

Organ (Leaf)Tissue

AggregateOrganizational level

Region, Biome

LandscapeEcosystem

CommunityOrganism

(Canopy)

Organ (Leaf)Tissue

AggregateOrganizational level

Change of organization / hierarchical level

Organizational levels above and below Organizational levels above and below ecosystem. We differentiate between change in ecosystem. We differentiate between change in

organizational level (shown with arrows) and organizational level (shown with arrows) and simple aggregation. simple aggregation.

Major Major waterwater fluxes in a forested watershed fluxes in a forested watershed

Cover Area (ha) Area contribution ET (mm) ET contribution

MRP 1796 0.15 271 0.16

MHW 4688 0.40 251 0.40

YRP 283 0.02 270 0.03

PB 1876 0.16 265 0.17

YHW 3058 0.26 239 0.25

SummarySum

11702Sum1.00

Mean253

Sum1.00

Water Fluxes: Growing season Water Fluxes: Growing season evapotranspiration for five ecosystems and evapotranspiration for five ecosystems and their relative contributions at a landscape their relative contributions at a landscape

scale in northern Wisconsin. scale in northern Wisconsin.

Ecosystem transpiration flux saturates with Ecosystem transpiration flux saturates with increasing vapor pressure deficit increasing vapor pressure deficit

))(a

cw

aapn

r

rr

VPDcR

E

E is evapotranspiration, is the slope of the saturation vapor pressure-temperature curve, Rn is canopy net radiation, cp is the specific heat capacity of air, a is the density of air, VPD is vapor pressure deficit from canopy to air, ra is the bulk vegetation aerodynamic resistance, w is the density of water, is the latent heat of evaporation, is the psychrometric constant, and rc is canopy resistance. Aerodynamic resistance, ra, is affected by canopy properties and the flow of air through and above the canopy, while rc = (GSL)-1, where GS is canopy average stomatal conductance and L is canopy leaf area.

Evapotranspiration (E) – Monteith Model (1965)Evapotranspiration (E) – Monteith Model (1965)

VPDmGG lnSrefS

where -m is the logarithmic sensitivity of the GS response to VPD. GSref is defined as maximum GS at VPD=1 kPa. This model is preferred over the Ball-Berry stomatal conductance model (Ball et al., 1987) because of its use of relative humidity as the driving factor instead of VPD.

Stomata Conductance (GStomata Conductance (Gss) – Jarvis Model (1976)) – Jarvis Model (1976)

Topography (A) and ecosystem types (B) of a Topography (A) and ecosystem types (B) of a section of CNNF section of CNNF

Seasonal dynamics of simulated and measured Seasonal dynamics of simulated and measured ecosystem evapotranspiration and volumetric ecosystem evapotranspiration and volumetric

soil moisture soil moisture

Major Major CarbonCarbon fluxes in a forest fluxes in a forest

Global carbon cycle

Atmospheric carbon pools can be reduced by:

1) Reduce carbon emission from fossil fuel combustion.

2) Increase carbon storage by:

• Increasing ecosystem productivity, and

• Decreasing plant decomposition

Terrestrial ecosystem carbon cycle

units: Pg/yr (1x 1015 g)

- 3

1500

900

480

720

140

80

Pools

Fluxes

Atmosphere

39

25

13

2 24

31

74 43

31

+2

0-2 X

Forests cover a wide geographical area and contain 80% of all aboveground terrestrial carbon (Waring and Running, 1998)

http://www.globalforestwatch.org

Large Carbon Storage

Fast

Slow

Small Carbon Storage

Fast

Fast

The ability for terrestrial ecosystems to The ability for terrestrial ecosystems to store carbon depends on the rate at which store carbon depends on the rate at which carbon dioxide is absorbed through carbon dioxide is absorbed through photosynthesis and released by photosynthesis and released by decompositiondecomposition

Units: Tons C ha-1 yr-1

In the United States, major carbon sinks are in the east part of the

continent (Myneni et al., 2001).

Units: Tons C ha-1 yr-130N

50N

40N

120W 110W100W 90W 80W 70W

Why focus on timber Why focus on timber harvesting?harvesting?

Timber harvesting is a major agent of ecosystem disturbance worldwide.

Timber harvesting affects microclimate, carbon pool sizes, decomposition, and ecosystem

respiration.

Decomposition and Decomposition and RespirationRespiration

They are the primary mechanisms that recycles carbon bound in plant tissue or in organisms back to the atmosphere.

These two processes determine the capacity of an ecosystem pool to hold carbon.

Swiss-Cheese MosaicPine Barrens

The Checker-board landscapeThe Checker-board landscape

Spatial Mosaics of Managed Landscapes in N. WISpatial Mosaics of Managed Landscapes in N. WI

An accurate assessment of the An accurate assessment of the contribution of terrestrial ecosystems to contribution of terrestrial ecosystems to the global carbon budget should consider the global carbon budget should consider the diversity of site conditions and the diversity of site conditions and developmental stages developmental stages within the landscape mosaic.within the landscape mosaic.

Landscapes are composed of a variety of ecosystems differing in type, age, size, shape, and spatial arrangement. A key question is:

Are managed landscapes a C sink or source?

The cumulative C fluxes of a landscape are determined by the land mosaic; that is, the

various ages and types of ecosystems present, as well as their size and shape.

HypothesisHypothesis

0 20 40 60 80 100

0

2

4

-2

Ne t

Ec o

sys t

em P

rod u

ctiv

ity (

Mg.

h a- 1

)

t3

t4

t1

t2

0 20 40 60 80 100

0

3

6

9

12

5

1

34

2

Pro

port

ion

o f th

e La

n ds c

a pe

(10 0

ha )

Successional Age (year)

Cumulative NEP (Mg)

-71.3

-23.7

294.7

133.790.4

0

200

400

-200

Scaling

(a)

(b)

(c)

Changes in NEP with age (a) and the age structure of a hypothetical landscape (b) together determine the cumulative NEP of the landscape (c)

Chen et al. 2004.

CWD

Atmosphere

Soil

Roots

Non-photo-tissue

Photo-tissue

Autotrophic respiration

Leaf respiration

Stem respiration

Soil surface CO2 efflux

Leaf litter

Root & mycorrhizal respiration

Heterotrophic soil respiration

Leaf litter respiration

Photorespiration

CWD respiration

Leaf net photosynthesis

Gross primary productionNet primary production

Modified from Gifford 2003

Heterotrophic respiration

Leaf gross photosynthesis Net ecosystem exchange

Respiration: forest ecosystem carbon fluxes

J-Rover: The Mobile Flux CartJ-Rover: The Mobile Flux Cart

Net ecosystem exchange of carbon (NEE) as a Net ecosystem exchange of carbon (NEE) as a function of ambient photosynthetically active function of ambient photosynthetically active

radiation (PAR) radiation (PAR)

Growing season cumulative NEE, ER, and GEP in Growing season cumulative NEE, ER, and GEP in stands of different ages stands of different ages

1:625,000

Landscape-level variation in gross ecosystem Landscape-level variation in gross ecosystem productivity, ecosystem respiration and net productivity, ecosystem respiration and net

ecosystem exchange of carbon ecosystem exchange of carbon