Impact of water availability on Cork oak growth: results of a

Lobo do Vale R., Kurz-Besson C., Rodrigues L., Almeida P., Herd A., Chaves M.M., Pereira J.S. (in Press) Impact of water
availability on Cork oak growth: results of a field rainfall manipulation experiment. In “Present and Future of Cork Oak in
Portugal” (2012). Oliveira MM, Matos JA, Saibo NJ, Gil L (Eds.), Soc. Portuguesa de Fisiologia Vegetal, Oeiras, Portugal.
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Impact of water availability on Cork oak growth:
results of a field rainfall manipulation experiment
Raquel Lobo do Vale 1, Cathy Béatrice Kurz Besson 2, Pedro Almeida 1,
Alastair Herd 1, Maria Manuela Chaves 1, João Santos Pereira 1
1. Instituto Superior de Agronomia, Tapada da Ajuda, 1349-017 Lisboa, Portugal
2. Instituto Dom Luiz, Centro de Geofísica da Universidade de Lisboa Faculdade de Ciências,
Campo Grande, 1749-016 Lisboa, Portugal
Cork oak trees cover about 716000 ha and 13.4% of the Portuguese territory area [1]. They are mostly cultivated as
savannah-type agro-forestry systems distributed mostly over the driest region of Portugal. In spite of the slight expansion
(+12%) of Cork oak area in the country over the last 40 years, mean tree density showed a drop of 23% over the last decade
[1], with higher tree density stands decreasing in profit to stands with low ones. Under the same decade (1998-2011)
including the extreme drought of 2005 [2], Cork oak mortality had a four fold increase [1], and fire occurrence duplicated,
showing an increasing of tree vulnerability and signs of decline of the species in Portugal.
Though an increase in the trend of annual precipitation was found for Portugal over the last centuries [3], climate
model simulations predict an increase in drought severity and a significant reduction of spring precipitation within the end
st
of the 21 century [4]. To better understand and quantify the impact of precipitation changes on Cork oak growth and
carbon balance, water availability was experimentally manipulated from 2003 to 2005 in a Montado area from south
Portugal. Rainfall income was manipulated according to 3 treatments: Dry, Wet and Ambient with 80, 120 and 100% of the
total annual precipitation, respectively (Fig. 1). Twenty-seven trees (3 trees*3 treatments*3 replicates) were selected.
Carbon gain was examined measuring carbon assimilation and stomatal conductance (A and gs, LiCor 6400), tree height and
diameter at breast height (DBH), leaf area index (LAI, Hemiview), specific leaf area (SLA) and leaf area density (LAD) while
carbon loss was evaluated measuring litterfall, on a monthly basis during 3 years.
Despite the significant treatment effects found in soil moisture at different depths mostly during the summer
periods, no significant instantaneous effect of the treatments could be detected on gas exchange parameters (A, gs), except
in July 2005 (one week after the last 13mm irrigation). While trunk diameter increment was 59% higher in trees from the
DRY area in 2003, the difference dropped to 4% in 2004, and to -10% in 2005, as compared to AMB trees. The last 13mm
irrigation pulse applied to the WET area had a highly significant positive effect on Cork oak physiological variables, with a
231% increase in A, 342% in gs, and 33% increase in DBH (Fig. 2). A higher increase in height and LAI and a lower decrease
of SLA were found in WET trees as well. Leaf surface area adjustment in response to water stress could be observed
through a significant decrease of LAI (-11%), LAD (-50%) and SLA -16%) in trees from the DRY area (Fig. 2), that can be
interpreted as a mechanism involved in the eco-hydrological equilibrium: optimizing biomass increase and reducing water
stress [5].
The highest amount of litterfall was observed in the DRY areas. In 2005, there was an increase (+12%) of leaf
litterfall in the WET areas probably linked to the increase in LAI and higher growth in this treatment. However, there was no
significant difference in the total litterfall amount between 2004 and 2005, suggesting that the extreme reduction of
precipitation observed in 2005 did not affect the total production of dead aboveground biomass. Nevertheless, the peak of
litterfall occurred later in 2005, mainly between May and October, while it covered the period from February to September
in 2004.
Aknowledgement: EVK2-CT-2002-00158 (MIND), Pest-OE/CTE/LA0019/2011 - IDL
Key-words: Transpiration, water status, precipitation availability
Lobo do Vale R., Kurz-Besson C., Rodrigues L., Almeida P., Herd A., Chaves M.M., Pereira J.S. (in Press) Impact of water
availability on Cork oak growth: results of a field rainfall manipulation experiment. In “Present and Future of Cork Oak in
Portugal” (2012). Oliveira MM, Matos JA, Saibo NJ, Gil L (Eds.), Soc. Portuguesa de Fisiologia Vegetal, Oeiras, Portugal.
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References
400
200
2005
Year
Figure 1. Annual precipitation or water income
amount per treatment, as compared to the 30-yr
average (1951-1980) (horizontal line). Treatments
are indicated as Wet (W), Dry (D) and Ambient(A).
2.5
2.0
1.5
DBH inc. (m)
3.0
1.0
75
70
65
60
2003
0.35
2004
2005
-2
2004
2
2003
LAD (m .m )
0
3.5
SLA (cm2.g-1)
W
A
D
4.0
***
600
LAI (m2.m-2)
Precipitation (mm)
Normal 1951-1980
6.0
5.8
5.6
5.4
5.2
5.0
4.8
4.6
4.4
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
**
800
Height (m)
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Gradiva, Lisbon.
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340.
0.30
W
D
A
0.25
0.20
0.15
*
P<0.05
0.10
0.05
2003
2004
2005
Year
Figure 2. Cork oak growth parameters measured between 2003
and 2005 in Herdade da Mitra, Évora, Portugal.