The ecogeographical differentiation of Amazonian inundation forests

20 Pages·2008·4.5 MB·English

--Hant
Systematics
P1. Syst. Evol. 162, 285-304
and
Evolution
© by Springer-Verlag 1989
The ecogeographical differentiation
of Amazonian inundation forests
K. KUBITZKI
Received August 31, 1987
Key words: Amazon region, biogeography, biotic diversity, choroldgy, ecogeography, refuge
hypothesis; tropical rivers, inundation forests, flood resistance; neotropical flora.
Abstract: Due to the considerable annual fluctuations of water level of the Amazonian
rivers, their river banks are fringed with periodically flooded forests of vast extension. The
biota of these communities are adapted to annual inundations that can last for more than
half a year. Water chemistry is most important for the floristic differentiation of these
flooded forests. White water rivers, which carry a rich load of suspended material originating
from the erosion of the Andes, have a floristic composition related to that of the non-
inundatable Amazonian forest. Clear water and black water rivers, which originate in the
Amazon Basin or its adjacent crystalline shields, are nutrient-poor and more or less acidic;
their flora is related to that of peculiar woodland and savannah vegetation on oligotrophic
white sand. The distribution patterns of floodplain species of nutrient-poor waters point
to a centre of diversity in the Upper Rio Negro region, and another one in the Guayana
lowland. These coincide with diversity centres for species of non-flooded habitats. Hence
it seems unlikely that species diversity is directly influenced by pluviosity. The flooded
forests have developed biotic interactions with the fish fauna of the Amazon Basin, which
are vital for their continued existence. It is assumed that the origin of these habitats, their
biota and their interactions dates back long into the Tertiary.
There is hardly another region on earth that is influenced by water as strongly as
Amazonia. Although the Amazon is not the Earth's longest river, it is by far the
mightiest, and its discharge is 4-5 times that of the Congo, the only river that
comes near to the Amazon. Its river banks and those of all its major and smaller
affluents are bordered by forests subject to periodical inundation. GouRou (1950)
and PIRES (1973) made the estimate that 2% of the whole area of Brazilian Amazonia
are covered by periodically flooded forests. If this estimate is applied to the whole
of Amazonia, we have to count with an inundatable area of more than 120 000 km 2.
3/4
Of this area, more than would be represented by vfirzea, which borders white
water rivers, while a smaller fraction would be covered by i gap 6, which fills the
floodplain of nutrient-poor clear and black water rivers.
Two factors are decisive for the existence and vast extension of periodically
flooded forests in Amazonia. First, the unequal annual distribution of precipita-
tions. In most parts of Amazonia, the rainy season is interrupted by a drier period
286 K. KUBITZKI'
,--, Rio Hadeiro at Porto VeLho (1968-1972)
a---t, Rio Amazonas atHonaus (1968 -1970)
m
/
\
I0 '~ . . . . Rio Negro at Borcelos (1968-1972)
/ • k
> / x
~s
/
L
~u
ii~ o A,
°7" \
/ \ y..\& a
0-,
; . ; . ; J A s o N o
Fig. 1. Amplitude and timing of water level fluctuations of Amazonian rivers. (After JUNK
1984)
of several month's duration, which, however, is not synchronous in all parts of the
Hylaea and is more or less absent in its northwestern part. Second, the Amazon
Basin is a low-lying plain, as is evident from the fact that Iquitos at a distance of
3600 km from the mouth of the Amazon lies only 100 m above sea level. Therefore,
the annual rise of the water level of the network of Amazonian rivers leads to
inundations of enormous extension, in contrast, for instance, to the Orinoco, which
never borders beyond its deeply incised bed. The amount of annual change in water
level is highest in Central Amazonia; at the mouth of Rio Jurufi the amplitude is
20 m; downstream the Amazon it decreases, reaching about 6 m at the mouth of
the Rio Tapajoz (Fig. 1), and is so small in the region of the estuary that it is
superimposed by the rise of the tide (SIoLI 1984).
Conditions for life in the seasonally flooded habitats are quite extreme. The
length of the annual period of flooding can amount up to 10months, and trees
can be covered by water up to 15 m deep. Often, trees keep their entire foliage in
the flooded stage, and after falling dry immediately seem to start with photosyn-
thesis. Another stress factor is the poorness of oxygen in the water and the rhi-
zosphere of flooded trees, which requires modifications of the respiratory pathway,
preventing the accumulation of toxic end products of anaerobic respiration, such
as ethanol. It is likely that this metabolic capacity is decisive in controlling the
floristic composition of temporarily flooded forests.
Since the dry period of flooded forests can be very short, regeneration must
imply special mechanisms of seedling establishment, apart from vegetative prop-
agation (Fig. 2), although we do not know anything about this. The ecophysiological
adaptations of periodically inundated forests have barely been touched upon (GEss-
NER 1968, SCHOLANDER • OLIVEIRA 1968, KEEL & PRANCE 1979).
The trees of the inundated forests have scarcely striking physiognomic traits,
despite the heavy stress exerted upon them through the fluctuations of the water
level. Morphologically differentiated respiratory roots, such as occurring in the
mangrove, are clearly absent and would not be of any use during inundations
lasting for months. In Amazonia such roots are only found in swamp forests subject
Amazonian inundation forests 287
Fig. 2. Couepia paraensis, showing vegetative propagation. Rio Nhamund/t, Par/t, Brazil.
(Phot. K. KUBITZKL 1 Oct. 1984)
Fig. 3. Eschweilera coriacea in clear water igap6 along the Rio Arapiuns, affl. to the Rio
Tapajoz, Brazil. (Phot. H. SIoLI, 14 Nov. 1952)
288 K. KUBITZKI:
to diurnal or other frequent changes of water level; Symphonia globulifera is a
foremost example. A remarkable trait is that the crowns of the trees often look
just as cut away on their lower surface, as has been illustrated by GESSNER (1968).
This is certainly due to the effect of the high flood, which prevents the growth of
those branches that are submerged for the longest time. Being far from universal,
this can be observed in Simaba orinocensis, Eschweilera coriacea (Fig. 3), and several
members of the Combretaceae, such as Buchenavia ochroprumna.
A most characteristic adaptation of the trees of the inundated forests is the
frequent occurrence of spongy aerenchymatous tissue in their diaspores, imparting
buoyancy, as has been pointed out by DVCKE (1949). The fruit production of the
flooded forests has also great importance for the sustenance of the fish populations
which, in turn, contribute towards the dissemination of their diaspores (GOULDING
1980).
The floristic composition of the periodically inundated forests was described by
pioneers such as SPRUCE (1908), HUBER (1910), and DUCKE (1913). Further con-
tributions are due to DUCKE 8~ BLACK (1953), RODRIGUES( 1961), TAKEUCHI( 1962),
HUECK (1966), KEEL ~ PRANCE (1979), PRANCE (1979), WORBES (1983), JUNK
(1984), and ADIs (1984). A first attempt towards an ecophysiological study of the
inundated forests has been made by GESSNER (1968).
In view of the peculiar stress situation to which the floodplain forests are exposed,
problems of ecologic, floristic, and evolutionary nature emerge. Here I want to
deal with the differentiation of the flora of periodically inundated forests in de-
pendence on water chemistry,, and with the relationship of their elements to those
of non-inundatable forests on terra firme. This implies the question of the age and
origin of the flora of these forests.
Floristic differentiation according to water chemistry
The three main river types of Amazonia - white water, clear water, and black water
rivers- are known since the time of A. R. WALLACEa nd have carefully been studied
and characterized by limnologists, such as H. SioLi and collaborators. However,
the terminology and delimitation of Amazonian forest types subject to inundation
is still controversial. Local people do not differentiate according to water quality;
for them, all flooded forests is vfirzea, or, when it has more water, igap6 (lit. "the
place where the water stands") (J. M. PIRES, pers. comm.). In the usage of biologists,
the vfirzea comprises the alluvial floodplain including the forest growing on it,
which originates from the annual flood of white-water rivers that are rich in sus-
pended matter. The vfirzea fringes the Amazon itself, the Rio Madeira, Rio Purus
and other white-water rivers rich in sediment load. Igap6, in contrast, is defined
to comprise inundated river banks together with their vegetation that have origi-
nated by vertical erosion (SIoLI 1954). In my usage, in which I follow PRANCE
(1979), the river banks not only of black water rivers, but of clear water rivers as
well are called by name igap6, even when their rivers have some insignificant
sedimentation due to their sediment load stemming from the nutrient:poor Tertiary
fresh water sediments of Central Amazonia. Due to their poverty in nutrients and
relative low pH the conditions for life in clear water are much more alike to those
in black water than in white water.
Amazonian inundation forests 289
The floristic differentiation between vfirzea and igap6 has often been emphasized,
and characteristic elements are listed in Tables 1 and 2. Such a differentiation is
also apparent with respect to the mycoflora, as has been discovered by SI~ER
(1984).
Biomass and local species diversity of the vfirzea are higher than of the igap6.
However, the flora of the former is much more uniform than that of the latter
which has much regional differentiation, so that in total the flora of the igap6 is
richer than that of the vfirzea. There is hardly an independent flora of clear-water
igapds, although their flora may appear impoverished in comparison with that of
black water regions, at least that of the Rio Negro basin. There is also no significant
difference in the fish fauna between black and clear water (GouI~DING 1980).
Despite the rather clear separation of the floras of vfirzea and igap6, there are
some tree species in common to them; DucKE (1913) mentioned Campsiandra
laurifolia, Macrolobium acaciaefolium, and Symmeriapaniculata for both river types;
PRANCE (1979) listed Virola elongata, Caryocar microcarpum, and Allantoma lineata
as common elements. In fact, the list could be considerably extended: Caraipa
densifo lia, Pachira aquatica and P. insignis, Swartzia polyphylla, Vataireag uianensis,
and Licaria arrneniaca are species that occur in all river types, the two last-mentioned
also on terra firme. One has also to consider that the water quality of a river
can change during the course of the year. This occurs regularly in the side branches
of the Amazon river where, depending on the water level, either the white water
of the main river, or the nutrient-poor water of an affluent may be dominant.
Several rivers are known that are turbid in the rainy season but transparent in the
dry one; the Rio Tocantins is the largest of them.
Altogether, the floristic differentiation between the domains of nutrient-poor
and nutrient-rich water is clear although the reasons for this might be difficult to
define, since the ecological optimum of a species under the influence of competition
may be quite different from its physiological optimum. The species listed in Tables
1 and 2 have a high indicator value for trophic conditions, and in those places
where nutrient-poor rivers cross bars of Palaeozoic limestone, vfirzea species are
present. This can be observed in the lower course of the Rio Trombetas/Rio Cuminfi
de Oeste. A similar phenomenon is produced by the influx of white water of the
Rio Branco into the lower Rio Negro.
Ecological relationships of tree species of flooded forests
The flora of Amazonian flooded forests represents no independent floristic stratum,
but has close ties to the flora of non-flooded habitats. There is an especially close
relationship between vfirzea and terra firme forest on latosol. In the vfirzea one
can find wide-spread forest species of the neotropics, such as Guazuma ulmifolia,
or species of even wider tropical distribution, such as Spondia, lutea, which in
Amazonia have developed flood-resistant ecotypes. The differentiation of vfirzea
species proper is exemplified by the moraceous genus Maquira, in which one species
(M. coriacea) is bound to the vfirzea, while another (M. calophylla) occurs there
facultatively; the remaining species are restricted to terra firme (BERG 1972). In
the western part of the Hylaea, the differentiation between vfirzea and terra firme
fades away, and vfirzea species such a Ceiba pentandra or Pseudobombax munguba
occur also in the non-inundated forest. This is because the soil of the terra firme
290 K. Ktm~a-zKI: Amazonian inundation forests
Fig. 4 Fig. 5
Fig. 4. Qualea retusa, wide-spread in Amazonia on upper sandy river banks, tolerating
short-termed inundation. (Orig.).- Fig. 5. Oeotea pauciflora, occurring on higher, peri-
odically inundated river banks, on savannahs, and in terra firme forest. Its sister species,
O. cernua, occurs equally in periodically flooded and non-flooded habitats. (After pers.
comm. by J. ROHWER)
Fig. 6 Fig. 7
Fig. 6. Panopsis rubescens vat. rubescens, a tree of sandy river banks wide-spread in Guayana
and Amazonia. The fruits are indehiscent, not wettable, and buoyant. (Partly based on
SI~EUMER 1954 and STEYERMARK 1982).--Fig. 7. Cynometra spruceana [-= C. martiana
(HAYNE) BAILL.], a species of sandy and rocky river banks on black water and clear water
rivers of Amazonia and western Guayana with buoyant husks. (After DWYER 1958, updated)
BO°
r
~0o 7.° E0° t0° ~W 10° T0° ~0' ~0o
Fig. 8 Fig. 9
Fig. 8. Swartzia polyphylla, one of the most frequent riverine species of Amazonia and
Guayana, occurring preferably in periodically inundated floodplains of clear water rivers,
but of black water and white water too. The most closely related species occur partly in
flooded forests (S. schomburgkii BENTH.), partly in never flooded forests (S. parvifolia
SCHERY, S. remiger A~sH.). The husk is buoyant. (After COWAN 1968, updated).- Fig. 9.
Simaba orinocensis (incl. S. multiflora A, Juss.) is a typical species of periodically flooded
riverine forests of Amazonia and Guayana, preferably in nutrient-poor water. The fruit,
which is preferred by fish, has a sour taste, as is often the case with fish-dispersed fi'uits.
(After CAVALCANTE 1983, and THOMAS 1984, updated)
7o. ~0o ~oo ~oo I B~ t 5~° 50~
806 70° S0° 50o ~0" ~0o V0° 6"° S0°
Fig. 10 Fig. 11
Fig. 10. Ramatuella argentea, R. virens (incl. R. maguirei EXELL & STACE and R. latifolia
MAGUIRE) and R. crispialata [incl. R. obtusa (MAGUIRE) STACE ~ EXELL] are restricted
to the floodplains and savannahs of the Upper Rio Negro and Upper Orinoco region.
(After EXEL & STATE 1963, and pers. comm. by C. A. Sa'ACE 1976).-Fig. 11. Glandonia
williamsii, G. macrocarpa, and G. prancei occur on periodically flooded savannahs and
ploodplains, the fruit keeps afloat. (After ANDERSON 1981)
292 K. KUBITZKI:
70" SO* SO" ~0"
Fig. 12 Fig. 13
Fig. 12. Burdachia prismatocarpa is restricted to black water and clear water rivers of
Amazonia and Guayana. The same is true of the other species of the same genus (Fig. 13)
and the three species of the related genus Glandonia (Fig. 11). The fruit is buoyant. (After
ANDERSON 1981).- Fig. 13. Burdachia sphaerocarpa, a species of periodically flooded river
banks on nutrient-poor rivers of Amazonia and Guayana. (After ANDERSON 1981, updated)
Fig. 14 Fig. 15
Fig. 14. Buchenavia reticulata, from the Upper Orinoco Basin and western Amazonia, and
B. ochroprumna from central and eastern Amazonia occur in floodplains of nutrient-poor
waters. The differentiation of the whole genus may have occurred in such habitats. (After
EXELL & Sa'ACE 1963, and pers. comm. by C. A. STACE 1976, updated).- Fig. 15. Buchenavia
suaveolens (incl. B. pterocarpa EX~LL & STACk), a floodplain species of the Upper Rio
Negro and Upper Orinoco region. (After EX~LL & STACE 1963, and pers. comm. by C. A.
STATE 1976)
Amazonian inundation forests 293
e0° s0*
Fig. 16 Fig. 17
Fig. 16. Macrolobium angustifolium, a frequent tree species of floodplains of white water,
clear water and black water rivers in Amazonia and Guayana. Its closest relative, M.
bifolium, occurs in periodically inundated floodplains and savannahs mainly of the Guayana
lowland. (After COWAN 1953, updated).- Fig. 17. Macrolobium multijugum, a floodplain
tree of nutrient-poor waters of Amazonia and Guayana; the closest relatives, M. molle and
M. discolor, are in the Upper Rio Negro and Upper Orinoco region. (After COWAN 1953,
updated)
70v 6~m $0~ ~0a ~0 m 70~ 6~ S0~
~. 60° s0° ~0o 80o 70° s~ o ~°
Fig. 18 Fig. 19
Fig. 18. Henriquezia verticillata is distributed in the Rio Negro Basin, H. nitida in the Upper
Rio Negro/Rio Orinoco region; all species occur in periodically flooded habitats, H. jenmanii
also in tidal forests. (After ROGEkS 1984).- Fig. 19. Of the 11 known species of Elizabetha
only E. princeps occurs in periodically flooded forests of the Rio Negro Basin and Guayana,
while its closest relative, E. paraensis, is distributed in eastern Amazonia, where it occurs
on terra firme. (After COWAN 1976)
294 K. KUBITZKI :
70° ~ 5D D 40 ~ BO° 7~ D 6Q a so o ~oo
?~ 60 ~ 5~D ~0 o 80 ° 70 o 6~ • ~o ~g*
Fig. 20 Fig. 21
Fig. 20. Exellodendron coriaceum is a species of periodically inundated river banks and
savannahs of Guayana and eastern Amazonia. (After PRANCE 1972, updated).- Fig. 21.
Byrsonima leucophlebia occurs on sandy river banks and savannahs of Amazonia and
Guayana. (After ANDERSON 1981, updated)
Fig. 22 Fig. 23
Fig. 22. Leopoldinia piassaba is a species of black water igap6 of the Upper and Middle
Rio Negro region. (Orig.).- Fig. 23. Schistostemon oblongifolium is a tree with buoyant
fruits of periodically inundated floodplains of the Upper Orinoco and Rio Negro Basin.
(After CUATRECASAS 1961)