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Artemisia tridentataSalix exigua
Lepidospartum sq.
Populus fremontii
Salix laevigataArundo do.
Floodplain scrub
Floodplain herb.Salix lucida
Salix ex.-Arundo
Baccharis pilularis
Populus balsamifera
Salix lasiolepis
Mixed willowforest
Artemisia californica
Mixed willow scrub
Salix exigua-Baccharis salicifolia
Introduced herbaceous
Baccharis salicifolia
Mixed riparian scrubHIGH RELATIVE ELEVATION
INLAND
NOTRECENTLYFLOODED
GAINING
COASTAL
LOSING
RECENTLYFLOODED
LOW RELATIVEELEVATION
The lower Santa Clara River and its floodplain have been significantly altered by flood control, land use practices, and invasion by Arundo donax that have disrupted natural processes and resulted in riparian habitat loss. Despite these alterations, the lower river presents a unique opportunity to conserve and restore remaining riparian functions and ecosystems. To this end, the California State Coastal Conservancy is establishing the Santa Clara River Parkway by acquiring and enhancing floodplain habitat and flood-prone property.
This poster presents a subset of the analytical tools, understanding of vegetation dynamics and physical process linkages, and Arundo donax (giant
reed) treatment and other strategies developed and used to assist with acquiring, managing, and
restoring Parkway lands.
BACKGROUND
For more information, please visit:www.santaclarariverparkway.org
0
10
20
30
40
50
1820 1830 1840 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Water Year
Prec
ipita
tion
(inch
es) Dry Years
Wet Years
a)
b)
0
10
20
30
40
50
1820 1830 1840 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Water Year
Prec
ipita
tion
(inch
es) Dry Years
Wet Years
0
10
20
30
40
50
1820 1830 1840 1850 1860 1870 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
Water Year
Prec
ipita
tion
(inch
es) Dry Years
Wet Years
a)
b)
a)
b)
0
25,000
50,000
75,000
100,000
125,000
150,000
175,000
200,000
Salix lasiolepis
Baccharis pilularis
Artemisia califo
rnica
Artemisia ca- Erio
gonum fasc
Mixed willo
w forest
Mixed willo
w scrub
Salix exigua - B
accharis salic
Mixed rip
arian scrub
Populus balsamifera
Mixed scrub
Non-native grasses a
nd forbs
Salix lucida
Eucalyptus s
pp.
Baccharis salicifolia
Salix exigua - A
rundo donax
Riverwash scrub
Riverwash herbaceous
Arundo donax
Mixed rip
arian forest
Salix laevigata
Floodplain wetland
Lepidospartum squamatum
Salix exigua
Artemisia tri
dentata
Populus fremontii
Tamarix spp.
Dist
ance
from
rive
r mou
th (f
eet)
Dis
tanc
e fr
om r
iver
mou
th (ft
)
� Treat arundo in the spring/summer following major floods to take advantage of the removed biomass. � Control arundo in an upstream to downstream direction and from tributaries. � Control arundo in and adjacent to fire-prone shrub lands. � In monospecific stands of arundo, or where it occurs with immature native vegetation, use more economical mowing techniques to remove biomass prior to treatment. �Use hand-removal techniques around mature native trees and patches of native vegetation to enhance ability of native vegetation to recruit naturally after treatment.
The vegetation dynamics-physical
process linkages described above, as well as recent research by Coffman et al. (2010) on
the ecology and impact of arundo on the lower Santa Clara River, provides guidelines for prioritizing arundo treatment projects:
Promote and implement sensible revegetation
The nature of flooding and vegetation reset along the lower river should determine the area where active planting is implemented, to avoid the loss of expensive active revegetation efforts. Where active planting is reasonable, the riparian dynamics analysis results can be used to inform select plan species that are most likely to be successful at a given site.
�Allow natural recruitment in the active floodplain.
�Focus active revegetation in areas not subject to frequent, resetting floods.
�Actively revegetate sites following arundo removal.
Differences between the coastal fog belt and the arid inland portions of the watershed are at least partly responsible for the correlation between distance from river mouth and plant species distributions, although arundo occurs throughout the watershed.
Riparian vegetation along the lower Santa Clara River is sub-ject to infrequent but dramatic resets during large flood events, particularly during El Niño-Southern Oscillation
(ENSO) events, which are characterized by relatively high rainfall and, as a result, high flood magnitudes.
(LEFT) Riparian vegetation conditions before (June 2002), immediately after (February 2005), and nine months following the 2005 high-flow event (September 2005). (RIGHT) Average time since last flood (± 1 SE) of vegetation alliances in the analysis area.
Time since last flood and relative elevation above the channel were two of the strongest correlates with vegetation alliance distribution. This sug-gests that the extent and distribution of riparian vegetation is closely linked to the dramatic scouring of vegetation during ENSO cycles, and the progression of seral stages thereafter. Arundo is more common on surfaces that have been flooded within the past 40 years.
Vegetation Distribution CorrelationsCanonical correspondence analyrsis (CCA) was used to identify the environ-mental variables most affecting the distribution of vegetation alliances (list-ed below). Univariate analysis was then used to examine differences in re-lationships based on the most important environmental variables identified through CCA. This analysis identified linkages between physical processes and the establishment and maintenance of riparian vegetation and assisted in predicting how riparian vegetation may establish and persist on restored floodplains within the study area.
Linking Vegetation Dynamics with Physical Processes to Develop Arundo Control and Riparian Restoration Strategies for a Semi-arid River and its FloodplainZooey Diggory1*, Bruce Orr1, Amy Merrill1, Gretchen Coffman2, William Sears1,3, and Peter Brand4
INFORMED ARUNDO
TREATMENT and
RESTORATION STRATEGIES
ANALYTIC AL TOOLS
Accurate and current mapping of riparian vegetation, including invasive species, was a crucial first step in river corridor manage-ment and restoration planning. This project followed the State of California standard vegetation classification system, mapping to the vegetation alliance level, and included focused percent-cover mapping for invasive arundo and tamarisk.
Changes in the extent of riparian veg-etation along the lower Santa Clara River were quantified by mapping highly vegetated, partially vegetated and scoured areas on overlays of aer-ial photographs taken soon after six major floods.
01,0002,0003,0004,0005,0006,0007,0008,0009,000
10,00011,00012,00013,00014,00015,000
1938 1969 1978 1992 1995 2005
Scoured Channel BedPartially Vegetated FloodplainHighly Vegetated Floodplain
0
10
20
30
40
50
60
70
80
0
20,000
40,000
60,000
80,000
100,000
120,000
140,000
160,000
180,000
Percent VegetatedFlood Magnitude (cfs)
Acre
sPe
rcen
t Veg
etat
ed
Flood Magnitude (cfs)
Year
01,0002,0003,0004,0005,0006,0007,0008,0009,000
10,00011,00012,00013,00014,00015,000
1938 1969 1978 1992 1995 2005
Scoured Channel BedPartially Vegetated FloodplainHighly Vegetated Floodplain
0
10
20
30
40
50
60
70
80
0
20,000
40,000
60,000
80,000
100,000
120,000
140,000
160,000
180,000
Percent VegetatedFlood Magnitude (cfs)
Acre
sPe
rcen
t Veg
etat
ed
Flood Magnitude (cfs)
Year
Year Flow (cfs) Flood Recurrence Interval
1938 120,000 14 year
1969 165,000 24 year
1978 102,200 11 year
1992 104,000 12 year
1995 110,000 13 year
2005 136,000 16 year
VegetationMapping
Climate Flood Dynamics
Arundo has invaded, and in many areas replaced, native riparian vegetation in the watershed. In addition to reducing riparian habitat quality and quantity, accumulated arundo biomass increases the susceptibil-ity of the lower Santa Clara River riparian corridor to fire, and post-fire conditions further promote arundo growth rates by elevating nutrient levels and eliminating competition from native species (Coffman et al. 2010).
Floodplain DevelopmentOur historical flood mapping demonstrates the dramatic effect of le-vees and development in constraining the floodplain and limiting ri-parian vegetation. In the lowest reaches of the river where levees are most extensive, the riparian corridor has been reduced by nearly 70% compared with conditions in 1938.
Plant communities differ between gaining and losing groundwater reaches, with species such as Salix (willow) and Populus (cottonwood) occurring more frequently in gaining reaches, and Artemisia tridentata (sagebrush) and Lepidospartum squamatum
(scalebroom) occurring more frequently in drier, losing reaches. Arundo is established and survives in both gaining and losing reaches.
VEGE TATION-PROCESS LINK AGES
Preventing development in the floodplain and increasing floodplain width and connectivity with the river will ameliorate some of the most significant impacts on the lower Santa Clara River and promote a greater extent of native riparian vegetation.
Increase and improve floodplain connectivity
Invasion by Arundo
Implement strategic actionsto control arundo
0
10
20
30
40
50
60
Floodplain wetland
Riverwash scrub
Mixed willo
w scrub
Salix exig
ua - Arundo donax
Salix laevig
ata
Mixed willo
w forest
Arundo donax
Salix lucida
Baccharis salicifolia
Populus fremontii
Salix lasiolepis
Populus balsamifera
Salix exig
ua
Artemisia
californica - E
riogonum fasc
Mixed rip
arian forest
Lepidospartum squamatum
Tamarix spp.
Mixed rip
arian scrub
Salix exig
ua - Baccharis salic
Non-native grasses a
nd forbs
Artemisia
californica
Artemisia
tridentata
Mixed scru
b
Baccharis pilularis
Eucalyptus
Alliance
Time s
ince
last
floo
d (yr
s with
SE
bars
)
(BELOW) Flood events with corresponding aerial photographs used to examine changes in the extent of riparian vegetation in the lower Santa Clara River.
Historical Changes inRiparian Vegetation Extent
Riparian corri-dor conditions at river mile 11 in 1938 and 2005.
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
Mixed s
crub
Populus
balsa
mifera
Salix l
asiol
epis
Populus
fremon
tii
Salix e
xigua -
Arundo
dona
x
Mixed r
iparian
scrub
Mixed w
illow sc
rub
Euca
lyptus
Salix l
aevig
ata
Bacchari
s pilu
laris
Riverw
ash s
crub
Salix l
ucida
Riverw
ash h
erbace
ous
Flood
plain
wetlan
d sup
erallia
nce
Mixed w
illow fo
rest
Salix e
xigua -
Bacch
aris s
alicif
olia
Arundo
dona
x
Bacchari
s salic
ifolia
Non-nati
ve gr
asse
s and f
orbs
Artemisi
a cali
fornic
a
Mixed r
iparian
fores
t
Salix e
xigua
Artemisi
a trid
entat
a
Lepido
spart
um sq
uamatum
% o
f plo
ts w
ithi
n ga
inin
g or
losi
ng re
ache
s
% occurring in losing reaches
% occurring in gaining reaches
Percentage of plots within each vegetation alliance that occurs in gaining (blue) versus losing (orange) reaches. Overall, 54% of the reaches (red line) in the 1,490 alliance vegetation plots were in gaining reaches.
Extent of the 1938 and 2005 floods.
Reach 6 enlarged
The extent and density (percent cover) of arundo infestations in the lower river.
Groundwater Availability
(BELOW) a) Distribution of mean annual precipitation based on data from the period 1900–1960; b) Precipitation records indicate peri-ods of cumulatively wetter (blue) and drier (orange) periods in the watershed.
Distribution of gaining and losing reaches in the lower Santa Clara River watershed.
Land cover types within the lower Santa Clara River watershed.
Example of the detailed vegeta-tion mapping used for the lower Santa Clara River.
The Santa Clara River watershed. (BELOW) Area of vegetated
and unvegetated floodplain affected by selected floods.
Average longitudinal position (± 1 SE) of vegetation alliances in the analysis area.
�Acquire land for conservation through purchase or easements.
�Remove or stop repairing unnecessary berms and levees.
�Replace bank-edge levees with setback levees.
1Stillwater Sciences, 2855 Telegraph Avenue, Suite 400, Berkeley, California 94705; 2Riparian Invasive Research Laboratory, Marine Science Institute, University of California, Santa Barbara, CA 93106-6150; 3San Francisco Public Utility Commission, 1145 Market Street, 4th Floor, San Francisco, California 94103; 4California Coastal Conservancy, 1330 Broadway, 11th Floor, Oakland, California 94612; *Send correspondance to [email protected]
Species distribution and vegetation reset Species distribution Species distribution and vegetation structure
Vegetation extent Native vegetation extent
The four physical variables most significantly correlated with vegetation types from the CCA.