Too wet for aquatic plants? Floristic composition and phytodiversity in the wetlands along the base of the Bolivian Andes

2004·15.8 MB·English

by  Nur Ritter

RHODORA,
Vol. 106, No. 925, 1-32, 2004
pp.
TOO WET
FOR AQUATIC PLANTS?
AND
COMPOSITION PHYTODIVERSITY THE
FLORISTIC
IN
WETLANDS ALONG
THE BASE OF THE BOLIVIAN ANDES
NUR
RlTTER
P.
California State University, Stanislaus.
Endangered Species Recovery Program,
CA
1900 N. Gateway Ave., Fresno, 93727
[email protected]
e-mail:
An
abstract. investigation of the vascular plant flora o( the wetlands in the
Chapare, an extremely high-precipitation region along the base of the Bolivian
Andes, was undertaken from 1994 to 1996. One hundred lifty-one species in 52
families and 107 genera were identified as occurring in the region's wetlands. In
contrast to the terrestrial flora of the Chapare and of other regions in the Andean
forelands. Chapare wetlands were found to be characteristically species-poor (5-^49
species). Nevertheless, the Chapare wetland flora contained a number of rare or
noteworthy species, and represented the southern distributional limit for a number of
taxa. The diversity of Chapare ''wetland species" species considered to be
(i.e.,
strongly associated with Neotropical wetlands) was low relative to other South
American lowland regions when considered terms of number of species and
in total
A
from species-area curves. regional trend toward fewer wetland species with
increased precipitation was apparent; however, data supporting this relationship were
inconclusive. Despite low (S0rensen's Index) between study
floristic similarities
sites, the majority of the Chapare study sites were closely situated in an ordination by
(DCA)
Detrended Correspondence Analysis of the floras of 46 wetlands distributed
throughout Bolivia. At the regional scale, floristic similarities with other regions
As
considered in this study were relatively low. might be expected, an ordination of
the regional data indicated that the Chapare wetland flora was most strongly
associated with the other lowland Bolivian regions, while the most geographically
distant regions were also the furthest removed ordination space.
in
Key Words:
Neotropics, Bolivia. Chapare, wetlands, aquatic plants, phytodiversity
The region along the base of the Cordillera Oriental (Eastern Range) of
Andes Cochabamba
the Bolivian the Department of colloquially
in
is
Andean
referred to as the Chapare. At times, the slopes are also included
in the delineation of the Chapare Guyot and Watson 1994; Solomon
(e.g.,
name
1989), but the most often used solely in reference to the lowlands,
is
a usage that also applied here. The Chapare (Figure occupies the
is 1)
transition between the Andes and the extensive floodplain that extends
northwards through the Department of Beni and eastwards to the
The
Brazilian Shield. largest part of this floodplain, the Beni basin,
is
m
characteristically quite level and occupies elevations between 150-250
1
Rhodora
106
2 [Vol.
b
a.
.
-
r
/
s
i
.
.
I
hapare
*Puerto Villarroe
(
1
Rk> Chimore
-
a
TOlaTooan e
ChmvztQ
- -
f
*
.
Vaile de Sajta
. H
Scafe(km)
."
"
r n 20 I)
K t
\
-\ ZZZ3
l
c.
Figure Study locations, South America, with approximate centers
1. site a. oi'
Geographic (OGUs): Lowland Amazonian
extra-Bolivian Operational Units A. Peru;
Central Amazonia; C. Brazilian portion of the Gran Pantanal de Mato Grosso; D.
IS.
Rio Parana Delta. Bolivia occupies the shaded portion the center of the continent.
in
OGUs:
Bolivia, with approximate delineation of the Bolivian White-water
b.
I.
—
Too Wet
2004] Ritter For Aquatic Plants?
3
(Killeen et al. 1993; Plafker 1964). Topography in the Chapare is more
low
variable, with creating a dissected Although Chapare
hills relief. the
region includes territory from three provinces (Chapare, Tiraque, and
name
Carrasco) the colloquial for the region quite functional, circum-
is
scribing an area characterized by high high temperatures, low
rainfall,
elevations, and (previously) extensive tracts of rainforest. Although the
precise geographic limits are not clearly defined, the Chapare has an area
of approximately 3000 (Henkel 1995) 4000 kirT (determined from
to
maps
using the "cut and weigh method," Lind 1985).
cf.
The Chapare
situated in an "inside corner" of the Andes, formed by
is
a change from an approximately southwest to northeast orientation of the
mountains to a more eastern bearing. This region and the adjacent Andean
Maximum
amount mean
slopes receive the highest of Bolivia.
rainfall in
annual precipitation in the Chapare reaches an estimated 4900 mm/yr,
mm
maximum
6900
with a hydrologic year of (Morris
1983).
et
al.
even lower Andean above
Rainfall is greater in the slopes just the
Chapare, where mean annual precipitation estimated to reach 6000
is
(Moraes and Beck 7000 mm/yr (Guyot and Watson
1992)
to 1994).
away
Rainfall decreases northwards from the mountains and eastwards
toward the City of Santa Cruz (Morris 1983). Thus, the approx-
et al. in
km
70 between two most Chapare
imately the disjunct study sites (see
Materials and Methods) mean annual precipitation ranged from about
mm mm
>
2500 4500
to (estimated from isohyets presented in Morris et
1983). Despite abundant precipitation, the region experiences
al. still
few months low many
a of rainfall (roughly, June to August), such that of
Mean
the area's small ponds and roadside ditches dry out completely.
C
monthly temperatures range from 20 38 (Henkel with mean
to 995), a
1
annual temperature of 21.8° (Maldonado et al. 1996) to 25°C (Killeen et
1993). Temperatures the region always remain above 0°C.
al. in
The
slopes of the Cordillera Oriental are precipitous, with the transition
between montane peaks (> 4500 m) and the lowlands occurring over
30-40 km, The above Chapare
a short distance (ca. linea recta). slopes the
are characterized by deposits of sedimentary rocks that consist primarily of
m
may
shales and be greater than 200 thickness (Morris 1983).
in et
al.
<
Floodplain; Chiquitania; Bolivian portion of the Gran Pantanal de Mato
II. III.
Grosso; IV. Chapare; V. Andean Piedmont, Location of the Chapare (Bolivia)
c.
study sites: a. Mariposa Wetland; b. Ivirgarsama Marsh; c. Senda F Wetland; d. Villa
Tunari Pond; Sinahota Pond; Valle de Sajta Curichi; Puerto Villarroel Laguna.
e. g.
f.
Rhodora
4
Vol. 106
I
These substrata and their derived soils are unstable and tend to erode
when
rapidly stripped of vegetation (Morris 1983); rates of erosion
et al.
are extremely variable, ranging from an estimated 000-20, 000 t/krrr/yr
1
(Guyot and Watson 1994). At the base of the mountains, the shales are
overlain by deposited alluvial materials. These deposits are generally
from
arrayed sequentially coarse materials at the foothills to liner-grained
away
sediments from mountains (Morris
the 1983).
et
al.
The Andean Chapare
rivers draining the steep slopes arrive the with
at
great force and are extremely dynamic upon reaching the easily crodible
soils. Erosion and sedimentation occur rapidly (Morris 1983), with
et al.
lateral channel migrations a constant feature o( the Chapare's rivers.
Salo (1986) analyzed channel dynamics Peruvian Amazonia by
et al. in
comparing photographs from 1962-63 with 1976 Landsat
aerial a
They
(satellite) image. estimated that for their area of study in lowland
Peru the mean lateral erosion rate meander bends during this period
ol'
was 12 m/yr (Salo et 1986). seems reasonable that channel migra-
al.
It
Chapare
tion the rivers could be o( a similar magnitude.
in
The
rivers of the Bcni basin are characteristically very turbid (Guyot
and Watson corresponding white-water
1994), to rivers (sensu Sioli
On
brown
1975). the floodplain, the rivers are an opaque from their large
load of suspended line particles; however, river water in the Chapare
is
generally much more transparent. This phenomenon presumably occurs
Andean
because the rivers and streams that drain the slopes are generally
clear and only carry large amounts of sediments when the vegetative
cover, which protects the weathered substratum, subjected land-
to
is
and
slides other large-scale disturbances Sioli 1984).
(cf.
Historically, the Chapare's terrestrial vegetation was dominated by
tall
forest, characterized by high diversity (Killecn et 1993). However,
al.
during the 1960s and '70s the government advanced colonization of the
region, constructing roads to and within the Chapare and apportion-
new
ing 202,000 ha of land for colonists (Henkel 1995). Lossina has
been extensive and large portions of the region have been cleared for
80%
agriculture, with approximately of the land dedicated to the culti-
20%
vation of coca (Erythroxylum coca) and the remaining to other crops.
Consequently, Chapare's remaining
the greatest part the forested
of"
secondary
habitats are forest.
There have been few limnological investigations of the Chapare's
and
aquatic habitats, references to the aquatic flora are nearly nonexistent.
Limnological studies were undertaken by Barra (1990), Cadima
et
al.
Maldonado Of
and
(1990), et al. (1996). these, the sole reference to the
who
vascular was from Maldonado macrophytes
flora et al., listed the
—
Too Wet
2004] Ritter For Aquatic Plants? 5
Table Study of the Chapare region (Bolivia), with elevation, approximate
sites
1.
area, number of species encountered, approximate location, and dates visited.
Study Site Elev. Area
Name
(m) Spp. Location Dates Visited
(ha)
Mariposa Wetland 220 49 17°01'S, 65°02'W 1/27/94; 3/5/95;
1.5
I
6/8/95; 11/1/96
Ivirgarsama Marsh 200 0.7 44 17°01'S, 64°50'W 2/23-24/96; 5/10/96;
10/27/96
65°08'W
Senda F Wetland 200
0.2 19 16°52'S, 6/1/94; 1/94;
1/1
1
3/4/95
65°26'W
Pond 300
Villa Tunari 0.3 17°01'S, 1/12/94; 3/5/95;
1 1 1
6/8/95
65°I8'W
Pond 240
Sinahota 0.15 9 17°00'S, 1/12/94; 6/8/95
1
64°43'W
ValledeSajta 220 0.2 6 17°07'S, 3/20/95
Curichi
200 64°48'W
Puerto Vi larroel 30.0 5 16°49'S, 3/19/95; 1/1/96
I 1
Laeuna
encountered in a series of lakes on the Rio Ichilo fioodplain. Additional
who
information conies from Jimenez (1984), listed various wetland
species in his account of the flora of the Department of Cochabamba.
In the present study, undertook a botanical survey of the wetlands of
I
the Chapare as a portion of a larger study of the wetlands of Bolivia (Ritter
My
2000). specific objectives were as follows: to prepare a provisional
1)
checklist of the vascular plant species associated with Chapare wetland
noteworthy from
habitats; 2) to identify rare or species these habitats; 3)
estimate the range of site-level vascular plant species richness; 4) to
to
compare Chapare wetland lowland regions
species richness the flora to
in
Bolivia and other South American countries; and 5) to examine floristic
in
among To
Chapare wetland and these regions. these
similarities the flora
ends, the flora of the Chapare wetlands listed and noteworthy species
is
Comparisons and
are discussed. of species richness floristic similarity are
made
made between study At the regional level, comparisons are
sites.
Amazonia
among
Chapare wetland and seven lowland regions
the flora in
and extra-Amazonian South America.
AND
MATERIALS MRTIIODS
were
Study Within Chapare, seven wetland systems
the
sites.
Although
established as study sites (Table Figure field research
).
1 ; 1
was
was concentrated on these systems, additional botanical collecting
undertaken variety of wetland types small marshes, streams.
in a (e.g.,
Rhodora
6
[Vol. 106
oxbow
rivers, lakes, strand lakes, and inundated roadside ditches). Brief
descriptions of the study sites follow.
Mariposa Wetland.
1.
The Mariposa Wetland was located alongside the highway from the
km
Chapare to Santa Cruz, approximately 1.5 east o( the community of
Mariposa. The system consisted of two small (< 0.3 ha) ponds fringed
with of marshy The ponds occupied shallow depressions
a strip habitat.
m
when
(ca. 2 deep) that were created for an adjacent highway was
fill
excavated from The marsh was between ponds and
the situated the
site.
the highway and was essentially a wide 50 m) section of the "borrow
(ca.
canals" that typically flanked the highway and other roads the region.
in
many
Although these canals extend for kilometers, investigations of the
m
Mariposa "system" were limited an approximately 200 long section
to
A
of marsh, centered on the two ponds. small, seasonal stream delineated
the western edge of the study Total study area was approximately
site. site
0.8 ha.
many
In contrast to similar small bodies o( water in the Chapare. the
ponds
contained water throughout the year, suggesting they received
that
some
subsurface water inflow. During the dry season, standing water
disappeared from most areas of the marsh; soil conditions varied from
fairly dry to saturated during this period. Although this system un-
doubtedly received substantial inputs o( runoff from adjacent uplands
during the rainy season, there were no large rivers near the Thus, the
site.
system did not appear to receive the periodic influxes of water-borne
many
sediment were
that characteristic of of the Chapare's aquatic
habitats.
Ivirgarsama Marsh.
2.
The Marsh was
Ivirgarsama located alongside the unpaved road that
connected highway Cruz town
the to Santa with the of Puerto Villarroel.
The was composed
system pond
of a small 0.2 ha) shallow with an
(ca.
adjoining (ca. 0.5 ha) marshy area in the area between the pond and the
road. Smaller sections of marsh also occurred along the other edges of
A
the pond. narrow stream flowed through the system, entering the pond
at one end and discharging through the marsh at the far end of the system.
As
with Mariposa Wetland, marsh was widening
the the essentially a
of a typical roadside borrow canal, however the pond the Ivirgar-
at
sama Marsh appeared to be of natural origin. The Ivirgarsama Marsh was
among
unique the Chapare study sites because of the well-developed
floating mats of vegetation present along the edges of the pond.
—
Too Wet
2004] Ritter For Aquatic Plants? 7
Senda F Wetland.
3.
The Senda F Wetland was located between the town of Chimore and
The was unpaved
the Rfo Chapare. system situated adjacent to an road
A
and was contiguous with the borrow canals that flanked the road.
number
small stream flowed into the southeast corner of the marsh, and a
of small, fairly deep pools were present. Hence, habitat heterogeneity
was much higher than was typical for the region's roadside canals. The
m
maximum
surveyed was approximately 80 long with width of
area a
Water
about \5 in on either side of the road. levels at the site fluctuated
seasonally and standing water was absent from parts of the marsh during
of
the driest portions the year.
Tunari Pond.
Villa
4.
The Villa Tunari Pond was a small pond located alongside the
km
town
Cochabamba-Santa Cruz highway, approximately 4 east of the
of Villa Tunari. As was situated near to the start of the ascent of the
it
Range) Andes, system occupied
Cordillera Oriental (Eastern of the the
m) Chapare During
a slightly higher elevation (300 than the other sites.
the dry season, the pond's surface covered an area of about 0.3 ha;
during the rainy season, large portions of the upland areas adjacent to the
pond became shallowly inundated and the limits of the "system" were
Maximum depth during the rainy season was on the order of
indistinct.
2.0-2.5 m; water levels dropped significantly during the dry season.
Although the basin was never observed to be entirely without standing
seems might occur during dry
water, likely that this years.
it
Sinahota Pond.
5.
The Sinahota Pond was another small (approximately 0. 5 ha) seasonal
1
pond situated alongside the Cochabamba-Santa Cruz highway, approx-
Maximum
km
town depth during
imately 2 west of the of Sinahota. the
rainy season was about 2.0 m; during the dry season the system dried out
The was
completely. basin steep-sided and, contrast to the Villa
fairly in
Tunari Pond, inundation did not appear to extend to the surrounding areas
during typical high water stages.
Valle de Sajta Curichi.
6.
In the Bolivian lowlands, a "curichi' is a system that occupies a section
'
dry-down
of a former river channel, and which normally does not
The
completely during the dry season (Beck 984). Valle de Sajta Curichi
1
m)
consisted of two small ponds separated by a narrow (10 strip of land.
—
most
The ponds originally comprised a section of a river channel likely
Rhodora
8 106
[Vol.
—
the nearby Rib Zabala and developed into their present form after being
stranded due channel migration. The ponds appeared be connected
to to
by a subterranean passage and the system was said to contain water year-
round.
Puerto Laguna.
Villarroel
7.
The Puerto Villarroel Laguna, a large curichi, was the largest and
deepest of the Chapare study sites. Despite being located in a region
kw
characterized by white-water/ the system's water was stained dark
'
Maximum
from organic acids. depth was difficult to determine, but
appeared to be at least 4 m. The lake's area as estimated using the cut and
weigh method (Lind 1985) on a scale topographical map, was
1: 1()(),()()()
found occupy 70 however, during was
to ha; visits to the site the area
As
visually estimated at about 15 ha. a compromise, 30 ha. was selected
as a rough approximation of the system's size.
Vegetation sampling. Sampling focused on compiling comprehen-
As were
sive site floras. noted, the study sites fairly limited in size
was
(Table possible survey each Fieldwork
I); it to site in its entirety.
was conducted from June 1994 November
intermittently to 1996. Sites
received multiple visits (Table whenever possible in order to view the
1)
systems under different hydrologic conditions and thus to maximize the
number
of species encountered. Preferably, fieldwork was scheduled so
that sites were visited during both the wet and dry seasons, but due to
was
various constraints this not always possible.
Voucher specimens were made of species observed each
all at site
and, with one exception, were deposited the Herbario Forestal
in
New
(bolv; Cochabamba) and the University o( Hampshire's Hodgdon
When
Herbarium were
(niia). available, duplicates deposited the
at
Herbario Nacional de Bolivia (lpb; La Paz), the herbarium of the Museo
"Noel Kempff Mercado^
de Historia Natural (usz; Santa Cruz), and the
A
Missouri Botanical Garden herbarium (mo). checklist, including
life-
form and species abundances each presented an Appendix.
at site, is as
A
Floristic comparisons. regional checklist of wetland species was
compiled from the study and augmented by data from general
sites
collecting in the Chapare, from the literature, and from exsiccatae listed in
TROPICOS.
Garden
the Missouri Botanical database, Published sources
used augment were Maldonado which was
to the checklist (1996),
et
al.
incorporated and Jimenez which was reviewed
in its entirety, 1984), for
(
species collected from the Chapare.
—
Too Wet
For Aquatic
2004] Ritter Plants':? 9
Table 2. Operational Geographic Units (OGUs) utilized in this study, with
number
estimated total area, of wetland species, and Holistic similarity (S0rensen's
OGU
OGUs
Index) between the and the Chapare. Detailed descriptions of the and an
account of the sources used in compiling the floras are given in Ritter (2000).
Approximate Area No. of
Floristic
OGU
2
(km
Species Similarity
)
Chapare 4000
13
1
Andean Piedmont 5000 244
33.6
White-water Floodplain 325,000 464
31.5
Chiquitanfa 90,000 541 28.4
1
Gran Pantanal (Bolivia and 40,000 451 23.4
1
Brazil)
Amazonia
Central (Brazil) 70,700 429 32.8
Lowland Amazonian
Peru 533.100 255 28.8
Rio Parana Delta (Argentina) 23,700 297
10.7
Floristic relationships were analyzed two scales: among study
at 1)
among
sites and, 2) regions (mesoregional scale sensu McLaughlin
made among
1994). Regional comparisons were the flora of the
OGUs
Chapare and
the following (Operational Geographical Unit,
cf.
Amazonia Lowland Amazonian
Crovello 1981): Central (Brazil), Peru,
the Rio Parana Delta region (Argentina), the Gran Pantanal de
Mato
Grosso and and
(Bolivia Brazil), three additional areas of
lowland Bolivia (the White- water Floodplain, Chiquitanfa, and Andean
OGU,
Piedmont regions). For each estimated wetland
total area, total
species, and calculated floristic similarities are presented in Table 2.
It
number
should be noted that the total of wetland species included for
Chapare comparisons number
the in regional less than the of species
is
listed in the Appendix, as species lacking complete identifications and
species not considered be strongly associated with wetlands were
to
excluded from regional comparisons. Salient characteristics of
floristic
OGUs
the are presented where warranted; detailed descriptions, and an
OGU
account of the sources used to compile floras are given in Ritter
(2000).
Ascription of wetland species. If order undertake regional-
In to
scale comparisons, a checklist of wetland species (Ritter, unpubl.
A
OGU.
was
database) used determine species presence each
to in
complete account of the sources used compiling the checklist and
in
a discussion of the criteria used in the ascription of species presented
is
in Ritter (2000).
Rhodora
10 Vol. 106
I
OGUs
Data among
analysis. Degrees of similarity were
florist ic
analyzed using S0rensen\s Index (Magurran 1988):
=
+
2j-
b
S
(a
OGU
number number
where
a the total of species in b the total of
is I,
OGU OGU
number
species and the of species present both
in 2, in
j 1
OGU
and
2.
As
with most similarity indices, S0rensen's Index gives equal weight to
However,
species calculating Holistic similarity. shared rare or
all in
OGUs
uncommon
species a pair of can also serve as valid indicators of
in
Connor
floristic similarity (Simberloff and 1979). In order to assess the
relative contribution these species to overall Holistic similarity, the
ol'
OGUs.
frequencies of "species classes" species present
(e.g., in all
OGUs,
species restricted to 2 etc.) were graphed. This analysis was not
among OGUs; was
conducted comparisons
rather restricted solely to
all
it
OGUs.
between the Chapare Mora and the other Because
floristic
similarities (Sorensen's Index) between the Rib Parana Delta region and
OGU
OGUs
other were uniformly low, was excluded from
this this
all
analysis.
OGUs
among
In order to express floristic relationships all simulta-
OGUs
neously, data were organized binary matrix of versus species
into a
(recorded as presence-absence values) and were ordinaled using
Dctrended Correspondence Analysis (DCA; and Gauch
Hill 1980).
PC-ORD (MjM
Ordinations were conducted using the software package,
Software, Gleneden Beach, OR).
R [-SUITS
One
Vegetation description. hundred fifty-one species, 52
in
families and 107 genera, were identified as being associated with Chapare
The
wetlands (Appendix). Poaceae (14 genera, 25 spp.) and Cyperaceae
were Panicum
(8 genera, 7 spp.) the best-represented families: (Poaceae,
1
9 spp.) and Ludwigia (Onagraceae, 7 spp.) were the best-represented
eenera.
The number
Biodiversity. o( species encountered the individual
at
sites varied widely (5-49 spp.; Table and was not consistently
1),
correlated with area. For example, the largest site (the Puerto Villarroel
Laguna, 30 ha) possessed the fewest species and the second largest
(5),
Mariposa Wetland, number
site (the .5 ha) the greatest of species (49). In
1
order to compare richness in the Chapare sites with wetlands from other