Carbon, water and energy balances of an Eucalyptus grandis plantation in Brazil: effects of clearcut and stand age
Yann Nouvellon
1, 2, José Luiz Stape
4, 2, Guerric Le Maire
1, Jean-Marc Bonnefond
5, Humberto Rocha
3, Otavio Campoe
6, Jean-Pierre Bouillet
1, 2, Jean-Paul Laclau
1, 7Incident Shortwave e long-wave IR radiation
Reflected Shortwave radiation and outgoing
longwave IR radiation Net radiation LI7500 [CO2], [H20], 20hz 3D Sonic anemometer U, V, W, T (20Hz) Rainfall Diffuse PAR, Direct PAR,
Total PAR Wind speed, Tair, Air relative humidity
0 10 20 30 40 50 60 0 100 200 300 400 S e m i-h o u rl y F lu x (W m -2 )
Months since February 2008
F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D
2008 2009 Clear cut 2010 2011 2012
Latent heat flux Sensible heat flux
0 10 20 30 40 50 60 -30 -20 -10 0 10 2008 2009 2010 2011 2012 S e m i-h o u rl y F c ( m o l m -2 s -1 )
Months since February 2008
0 500 1000 1500 2000 0.05 0.1 0.15 0.2 0.25
Days since January,1, 2008
v ( m 3 m -3 ) 2008 2009 2010 2011 2012 2013 0.15 m 0.5 m 1 m 0 500 1000 1500 2000 0.05 0.1 0.15 0.2 0.25
Days since January,1, 2008
v ( m 3 m -3 ) 2008 2009 2010 2011 2012 2013 2 m 3 m 4 m 0 500 1000 1500 2000 0.1 0.15 0.2 0.25
Days since January,1, 2008
v ( m 3 m -3 ) 2008 2009 2010 2011 2012 2013 5 m 6 m 7 m 0 500 1000 1500 2000 0.1 0.15 0.2 0.25
Days since January,1, 2008
v ( m 3 m -3 ) 2008 2009 2010 2011 2012 2013 8 m 9 m 10 m 0 5 10 15 20 -35 -30 -25 -20 -15 -10 -5 0 5 10 Time (hours) F c ( m o l m -2 s -1 ) March 2008 2009 2010 2011 2012 0 5 10 15 20 -35 -30 -25 -20 -15 -10 -5 0 5 10 Time (hours) F c ( m o l m -2 s -1 ) August 2008 2009 2010 2011 2012
Introduction: Eucalypt grandis plantations in Brazil are among the most productive forests of the world, reaching mean annual increments
of about 50 m3/ha/yr over short (6 yr) rotations. These high productions are generally associated with high water-use, but little is known on the effects of management practices on their carbon (C), water and energy budgets. We investigated the effects of stand age and clear
cutting on the C and water balances through continuous eddy-covariance measurements of latent (LE), sensible heat (H), and CO2 fluxes over a 5 yrs period encompassing two successive rotations: 2 yrs before and 3 yrs after clear cutting and replanting.
The third year after clearcutting and replanting, AET was higher than rainfall, leading to soil water-depletion till 10 m deep (Figure 4). This rapid depletion of soil water was consistent with the fast
exploration of the soil by fine roots (root front at 6-7 m deep at age 1 yr; Figures 1 and 6) and the fast increase in LAI (reaching 5 at age 2.5 yr).
Carbon budget: Clearcutting turned the forest from a strong C sink (NEP of ~ -1 tC/ha/month) to a C source (NEP increased up to ~ 1.6 tC/ha/month during replanting, about 1 month after the clearcut), but the plantation rapidly turned back to a C sink (C neutrality (NEP = 0) reached 7 months after
clearcutting (Figure 7), and then monthly NEP was always negative) due the rapid increase in LAI.
The water balance of these eucalypt plantations is thus characterized by three successive phases: 1) the first 18 months of the rotation, AET<rainfall allowing water storage in deep soil layers and a recharge of the water table, 2) from age 1.5 to 3 yrs, AET>=rainfall, resulting in water depletion in soil layers down to a depth of 10 m, and 3) from age 3 yrs to the end of the rotation, AET=rainfall. Our results suggest that process based models should take into account soil water dynamics in very deep soil layers to make reliable predictions of the effects of forest disturbances on C and water fluxes in deep tropical soils.
0 200 400 600 800 1000 1200 1400 -20 -18 -16 -14 -12 -10 2009 2010 2011 2012
Days since January 1, 2009
W a te r ta b le d e p th (m)
Root depth
(m)
W ater tabl e depth (m)Plantation Clear cut
0 10 20 30 40 50 60 70 80 -20 -15 -10 -5 0 5 10 15 20 25 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
LAI
Tree
height
(m)
Water balance: very dynamic troughout a rotation
Phase 1:
AET<Rainfall Deep recharge
Phase 2:
AET>=Rainfall Phase 3: AET=Rainfall
Stand age (months)
August 2012
2008 Clearcut and replantation February 2010 June 2010
Clear cut Clear cut
Rotation 1
Rotation 2
1 y 2 y 3.5 y 6 y Tower 0 10 20 30 40 50 60 -200 -100 0 100 200 2008 2009 2010 2011 2012Months since January 2008
N
E
P
(
g
C
m
o
n
th
-1)
0 10 20 30 40 50 60 2 4 6 2008 2009 2010 2011 2012Months since January 2008
A
E
T
(
m
m
d
a
y
-1)
Cle ar cutNet C loss
Net C
sequestration
1050 1100 1150 1200 1250 1300 1350 1400 -0.5 0 0.5 1 1.5 2 Soil water 0-10 m (mm) D a y ti m e B o w e n r a ti o ( H /L E ) Results:For the last 2 yrs before clearcutting, LAI was ~3.5 and fine roots were found down to a depth of 16 m. No percolation was observed below 5 m, and the 5-10 m soil layer was water-depleted. Actual evapotranspiration (AET) was approximately equal to annual precipitation (1350
mm). H was very low, except during some dry events characterized by sharp increases in the bowen ratio (H/LE) (Figure 2). Clearcut resulted
in an increase in soil temperature and H, and a strong decrease in AET (Figure 3), allowing gravitational water to reach 6, 8 and 10 m depths about 1.5, 2.5, and 3.5 months after clearcutting, respectively, in this sandy soil (Figure 4). From the clearcut (Oct 2009) to the end of the first rainy season (May 2010), the water table had raised from -18.5 to -15 m (Figure 5).
1. UMR Eco&Sols, CIRAD, Montpellier, France. 2. ESALQ, USP, Piracicaba, Brazil.
3. IAG, USP, Sao Paulo, Brazil.
4. NCSU, Raleigh, NC, United States.
5. EPHYSE, INRA, Villenave d'Ormon, France. 6. IPEF, Piracicaba, Brazil.
7. UNESP, Botucatu, Brazil.
Figure 1: Fine root distribution for different stand ages (from Laclau et al., 2013, Frontiers in Plant Sciences)
Figure 2: Bowen ration (H/LE) versus SWC (0-10 m) for the last 2 years of the rotation
Figure 4: Soil water content for different soil layers (till 10 m deep)
10 m deep trenches during installation of CS616
Figure 5: Time course of water table depth after clearcutting
Figure 3: Latent, sensible and CO2 effluxes before and after clearcutting
Figure 6: Canopy and root dynamic and soil water budget over a rotation
Soil water recharge
Soil water depletion
Figure 7: a) Monthly AET and b) monthly NEP before and after clearcutting
