Rete Montagna Interna,onal Congress Eurac Conven,on Center -‐ Bolzano/Bozen -‐ IT November, 6th -‐ 8th 2014
How sensi)ve is riparian vegeta)on to river morphological changes? A case study in the Italian Alps DANIELA CAMPANA, FRANCESCO COMITI, FRANCESCO GIAMMARCHI, GIUSTINO TONON
Free University of Bozen-‐Bolzano, Faculty of Science and Technology, Bolzano, Italy
2014
How sensiJve is riparian vegetaJon to river morphological changes? A case study in the Italian Alps
Daniela Campana, Francesco ComiJ, Francesco Giammarchi, GiusJno Tonon Free University of Bozen-‐Bolzano, Faculty of Science and Technology, Bolzano, Italy
INTERNATIONAL CONFERENCE Eurac ConvenJon Center – November 6th – 8th 2014
OUTLINE
• Study area • Aims of the research • Methods • Climate and hydrological regime • Tree growth paVerns • RestoraJon effects on tree growth • Conclusions
STUDY AREA • With a iver length of about 50 knm and a Ahr R flows in the orth-‐east 2 is the most watershed o f 6 30 k m of the province of Bozen/ important tributary of Rienz River
Bolzano
• 25 km2 of glaciers responsible of the nivo-‐glacial regime
Study area
STUDY AREA Mühlen in Taufers
Past river degrada)on • Narrowing of riverbed • Incision (gravel mining) • Bed armouring
UMenheim
• DisconJnuity between channel and floodplain (inundated for Q>30 yr) • Poor connecJon of riparian vegetaJon (dominated by Alnus incana) to river dynamics
Gais Study area
STUDY AREA Mühlen in Taufers
Restora)on
• River restoraJon program since 2003 by the Department of Hydraulic works of the Autonomous Province of Bozen (restoraJon 14,9 km in length) UMenheim
ü Widening of the riverbed ü Removal of the bank protecJon ü Raise riverbed elevaJon Gais Study area
STUDY AREA Mühlen in Taufers (restored in 2004-‐2006) 2003
2008
Photos by Autonomous Province of Bolzano Study area
STUDY AREA Gais (restored in 2007-‐2011) 2004
2011
Photos by Autonomous Province of Bolzano
Study area
AIMS OF THE RESEARC Address the growth response of the riparian forest along the Ahr River to river morphological changes
Assess the linkage among environmental factors and riparian forest growth We expected an enhanced tree growth ader the river restoraJon works Aims
METHODS • Riparian forest mostly formed by Alnus incana, locally associated with Fraxinus excelsior and Picea abies • Trees about 20 m high, with 85% of coverage • 2 samplings (October 2011-‐ October 2012) • 37 Alnus incana and 6 Fraxinus excelsior Mühlen
Gais
Methods
• 2 cores sampled from each individual with a 5 mm increment borer
METHODS • Annual ring width (resoluJon of 1/100 mm) and age measured with a dendrochronograph RINNTECH LINTAB 6 • Cross-‐daJng among each single tree in order to remove errors due to the presence of false rings or missing rings • StandardizaJon through a negaJve exponenJal in order to remove the juvenile growth trend and a calculaJon of an adjusted Tree Ring Index (TRI) Methods
Rein in Taufers
METHODS • Temperature data at Mühlen in Taufers since 1992 • PrecipitaJon data at Mühlen in Taufers since 1972; at Rein in Taufers used for analyzing long-‐term tree growth (data since 1921)
Mühlen in Taufers
• Water discharge at St. Georgen since 1986 • ElevaJon of groundwater table since March 2002 at 3 piezometers near Gais
Gais
• Data analyzed for the whole year and for the growing season (April-‐ September)
St. Georgen Bruneck Methods
CLIMATE AND HYDROLOGICAL REGIM • Seasonal paVern of water discharge with highest values between May-‐September • Groundwater table level between -‐3,77 m and -‐2,53 m • Water table rose slightly in the years 2008-‐2012
• Simple regression shows a relaJonship between water discharge and groundwater table level (R2 = 0.62 for annual data and R2=0.37 for seasonal data) -‐2
Mean daily water table
70
-‐3
60 -‐4
50 40
-‐5
30
-‐6
20 -‐7
apr-‐12
lug-‐11
oV-‐10
gen-‐10
apr-‐09
lug-‐08
oV-‐07
apr-‐06
gen-‐07
lug-‐05
oV-‐04
gen-‐04
lug-‐02
apr-‐03
oV-‐01
gen-‐01
apr-‐00
oV-‐98
Hydrology
lug-‐99
gen-‐98
apr-‐97
oV-‐95
lug-‐96
gen-‐95
apr-‐94
lug-‐93
oV-‐92
gen-‐92
apr-‐91
lug-‐90
oV-‐89
apr-‐88
gen-‐89
lug-‐87
0
oV-‐86
10
-‐8
Water table (m below surface level)
Mean monthly water discharge
gen-‐86
Water discharge (m3/s)
80
CLIMATE AND HYDROLOGICAL REGIM
Hydrology
•
No relaJonship between temperature and water discharge
•
RelaJonship between precipitaJon and water discharge (R2=0.84 for annual data and R2=0.56 for seasonal data)
•
PrecipitaJon influence groundwater table level (R2=0.47 for annual data and R2=0.54 for seasonal data)
TREE GROWTH PATTERN • Forward stepwise analysis
1,6
Alnus
1,2 1,0 0,8
2010
2001
1998
1995
1992
1989
1986
1983
1980
1977
1974
1971
1968
1965
1962
1959
1956
1953
1950
1947
1941
1944
1938
0,4
2007
RR
0,6
2004
TREE RING INEX
1,4
1,6
Fraxinus
1,2 1,0 0,8
2010
2007
2001
1998
1995
1992
1989
1986
1983
1980
1977
1974
1971
1968
1965
1962
1959
1956
1953
1950
1947
1941
1944
0,4
2004
RR
0,6
1938
TREE RING INDEX
1,4
Tree growth
• Alnus: groundwater table level of the growing season (R2=0.51) • Fraxinus: mean annual water discharge (R2 = 0.61) • Absence of a relaJonship between precipitaJon and tree growth
RESTORATION EFFECTS ON TREE GROW
• Gravel mining in the 1970s with a decrease in average width • Minimum width in 2000 • Riverbed width and elevaJon increased ader restoraJon works
• Does riverbed raise corresponds to an increased groundwater table ?
Gais
Mühlen in Taufers
(Campana et al., 2014)
Restoration
RESTORATION EFFECTS ON TREE GROW
• Segmented linear regression • Break-‐point at year 2009 for groundwater table depth (whole year and growing season)
Annual values
Growing season values
Annual values
Growing season values
• Break-‐point at year 2007 for annual water discharge values and at year 2008 for growing season values Restoration
RESTORATION EFFECTS ON TREE GROW
Alnus
• Segmented linear regression • Break-‐point at year 2009 for Alnus Fraxinus
• Break-‐point at year 2009 for Fraxinus
Restoration
CONCLUSIONS
ü Water discharge and groundwater table depth influence riparian vegetaJon growth ü Water discharge and groundwater table depth respond to restoraJon changes ü Riparian vegetaJon respond to restoraJon works ü Fraxinus beVer responds to river morphological changes than Alnus ü Further monitoring is needed for a beVer understanding of tree growth trend Conclusions
THANK YOU FOR YOUR ATTENTION!
QUESTIONS ARE WELCOME
2014