Granville, Jean-Jacques de

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Monocotyledons and pteridophytes indicators of environmental 
cogstraints in the tropical vegetation 
JEAN-JACQUES DE GRANVILLE 
I 
RESUMÉ 
GRANVILLE, J.-J. DE (1984). Monocotylédones et ptéridophytes, indicateurs du niveau de con. 
trainte dans la vigétation tropicale. Candollea 39: 265-269. En anglais, résumé français. 
La proportion demonocotylidonespar rapport au total des angiospermes dans hne végktation tropi- 
cale homogène est faible lorsque les conditions écologiques sont optimales. Elles augmentent 
lorsqu’apparaissent de puissants facteurs limitants. La répartition des monocotylédones dans la 
forêt montre qu’elles occupent des biotopes marginaux: Bpiphytes et herbes du sous-bois. L’étude 
de la dynamique de la végétation permet de mettre en évidence les échanges qui existent entre ces 
deux ensembles. La proportion de monocotylBdones exprime donc le niveau de contrainte du milieu 
et leur répartition dans les différents ensembles structuraux d’un site forestier indique son âge 
approximatif. 
j 
ABSTRACT 
GRANVILLE, J.-J. DE (1984). Monocotyledons and pteridophytes indicators of environmental 
constraints in the tropical vegetation. Candoilea 39: 265-269. In English, French abstract. 
vegetation is small when the ecological conditions are optimal. It increases when there appears strong 
ecological limiting factors. The distribution of monocotyledons in the forest reflects its occupation 
of marginal biotopes: epiphytes and understory herbs. The study of the dynamics of the vegetation 
allows to put in evidence the exchanges which exist between these two layers. The proportion of 
monocotyledons hence expresses the level of environmental constraints and their distribution in dif- 
ferent structural entities of a forest-site reflects its approximative age. 
I , 
1 
The proportion of monocotyledons in relation to the total angiosperms in a homogenous tropical 
The simple qualitative and quantitative analysis of the tropical lowlands vegetal cover plainly 
provès that the repartition of the monocotyledons is not hazardous: on one hand it varies steadily 
from one formation to another and, on the other hand, inside the very forest formations, 
monocotyledons are not uniformly distributed. 
Monocotyledon repartition among the big vegetal formations 
1. A neotropical example: French Guiana 
I The percentage of monocotyledons figured with reference to the total amount of terrestrial 
angiosperms in the various plant formations has been obtained from data established in French 
Guiana (GRANVILLE, 1976, 1978; HOOCK, 1971) and completed by the ones established by 
LINDEMAN (1953) in Suriname (Fig. 1A). 
l On solid ground forest, according to cases, the proportion of monocotyledons is quite small 
:andvaries between the0070 to 13% brackets, whileonmarshes, it varies from 12% (“marsh forest:‘) 
to 31% (“swamp wood“). These low lying boggy grounds, called “pinotières“ in French Guiana, 
I are striking by their abundance of large leaves monocotyledons: Cyclanthaceae, Marantaceae, 
I Musaceae, Rapateaceae, Zingiberaceae. The most characteristic palms are Euterpe oleracea and, 
on the coastal zone, Mauritia flexuosa. The proportion of monocotyledons increases with the in- 
crease of water content in the soil together with the degradation of ecological conditions: on sub- 
coastal herbaceous swamps, it varies from 25% (“Eleocharis mutata swamps“) to 63% 
J 
I CODEN: CNDLAR , 
ISSN: 0373-2967 ; 
39(1) 265 (1984) 
o CONSERVATOIRE ET JARDIN 
BOTANIQUES DE GENÈVE 1984 
266 CANDOLLEA 39, 1984 
(“‘Lagenocarpus guianensis swamps“). Alismataceae, Araceae (Montrichardia arborescens), 
Cyperaceae, Gramineae, Lemnaceae, Pontederiaceae, Typhaceae, Xyridaceae are, here, 
predominant. 
On the contrary, when one leaves the optimal ecological conditions that prevail in the hard 
ground forest on deep soil, to reach progressively’dryer formations, by lack of water or ground, 
the percentage of monocotyledons also progress: the “savanna forest“, on more or less podzolised 
soil, counts 16% of terrestrial monocotyledons and the outcrop scrub forest, on thin soil, 32% 
(Bromeliaceae, Cyperaceae, Gramineae, Marantaceae). On the coastal dry savannas, where 
Cyperaceae, Eriocaulaceae, Gramineae, Xyridaceae predominate, monocotyledons are abundant: 
35 to 40% (“savanes hautes“ on ferrallitic soils) and 45 to 60% (“savanes basses“ on podzolised 
soils). On the “savanes-roches“ of rocky outcrops, the average ratio of monocotyledons is 57% 
but a keener analysis made in Tumuc-Humac area, shows that it may reach 100% on the succulent 
facet (orchid tufs on bare rock) while it is only of 41% on the Ischaemum guianense facet (con- 
tinuous grass cover on thin soil). 
To come last, the epiphytic communities of the forest canopy are in strong majority composed 
of monocotyledons (Araceae, Bromeliaceae, Orchidaceae): 86% for tropical America in its whole, 
according to MADISON (1977). 
2. A paleotropical example: Ivory Coast 
A similar calculation carried out for Ivory Coast from ADJANOHOUN (1964) as well as 
GUILLAUMET’s data (1967) give very comparable results to these of French Guiana (Fig. IB). 
In the dense rain forest on solid ground, the proportion of monocotyledons varies from 12% 
(deep and rich soil on metamorphic rocks) to 18% (thin soil on granite). In the marsh or swamp 
forests where palms genus Raphia dominate with Commelinaceae and Marantaceae, it varies from 
27% (low lying raphia and Gilbertiodendron splendidum lands) to 44% (raphia low lands). Her- 
baceous swamps count more than 40% monocotyledons, mainly Cyperaceae, Gramineae, Maran- 
taceae (Thalia geniculata): Thalia geniculata ponds (41 Yo), Lotidetia phragmitoides association 
(480/0), Vetiveria nigritana association (50%1), Isoetes nigritana and Ophioglosstrm gomezianum 
association (53%). 
As well as in French Guiana, formations showing a more or less xeric facies, present a more 
important score of monocotyledons than the solid ground forest on deep soil: 21% in the sub- 
coastal forest on pseudopodzols, 29% on the dry savannas with predominance of Cyperaceae and 
Gramineae (Brachiaria brachylopha association), 42 to 50% in the herbaceous outcrop formations 
(Afrotrilepis pilosa association). 
Lastly, according to MADISON (1977), for the whole tropical Africa, the canopy counts 94% 
of epiphytic monocotyledons (mainly orchids). 
Repartition of monocotyledons in the Guianese forest 
Figure 2 schematizes the monocotyledon repartition in the principal formations in French 
Guiana and emphasizes their relative ecology with the forest dynamics. 
The sole layer, rich in herbaceous monocotyledons, of the low formations (savannas, marshes, 
outcrops) divides itself at the forest level (Fig. 2B) to give an upper set with heliophile herbs 
(epiphytes) in the canopy and a lower set constituted by heliophile terrestrial species (shade tolerant 
seedlings) or subsciaphile ones (understory plants). The richness in monocotyledons of each of 
these sets is not constant and varies with the dynamics of the forest. As a matter of fact, we know 
that the forest is not uniform in space but is constituted of a mosaic of sylvigenetic phases of dif- 
ferent ages (HALLE, OLDEMAN & TOMLINSON, 1978). During a young sylvigenetic phase, 
the understory is rich in terrestrial monocotyledons and the canopy poor in epiphytes (Fig. 2C1). 
In an old phase, the contrary happens: canopy is rich in monocotyledons (Bromeliaceae, Cyclan- 
thaceae, Orchidaceae) and the understory quite impoverished in monocotyledons, only counts 
seedlings checked in their growth and awaiting a casual clearing (Fig. 2c3). 
A A .  FRENCH GUIANA 
canopa (epiphytes) 
"savanes-roches" (outcrops) 
"savanes basses" 
Ilsavanes hautes" 
odtcrop scrub forest 
Ilsavanna f o r e s t "  
evergreen rain forest on solid ground 
marsh forest and swamp forest 
"dry" savannas J 
herbaceous swamps 
MOldO C CT Y LE DON S 1 
A 5. I V 2 R Y  COAST 
canopy (epiphytes) 
outcrop herbaceous formations 
dry  savannas 
forest on pseudopodzol 
evergreen rain forest on solid ground 
marsh forest and swamp forest 
herbaceous swamps, w e t  savannas 
$ MONOCOTYLEDONS I 
(I? 
(1) Terrestrial plants only 
Fig. 1. - Proportion of monocotyledons among the main plant formations in French Guiana (tropical America) and Ivory 
Coast (tropical Africa). 
"SAVANE-ROCHE" 
OUTCROP 
S C R U B  F O R E S T  
+ + + + + +  "D9Y" SAVANNA 
+ A + + + + + +  
+ + + + + + e + +  
(understory rich in 
acaulescent palms 
SOLID fROUND F O R E S T  
es between the 
and the s o i l  
Fig. 2. - Distribution and dynamics of the monocotyledons in the guianese vegetation. 
u W
W 
- 
m e
J.-J. DE GRANVILLE: INDICATORS OF CONSTRAINTS IN TROPICAL VEGETATION 269 
As the sylvigenetic phase goes, the interchanges of monocotyledons between the ground level 
and the canopy are shown by the growing of the big palms and the scandent vines (Fig. 2C2), 
mainly Araceae and Cyclanthaceae, and, in the other way, by the fall of epiphytes out of the open 
places ("Chablis", Fig. X 4 ) .  
Conclusion 
In French Guiana as well as in Ivory Coast, monocotyledons prefer marginal biotopes. From 
what we have observed, it is the same for pteridophytes. The proportion of monocotyledons, com- 
pared to the total of angiosperms (or monocotyledons + pteridophytes compared to the total of 
vascular plants) increases proportionaly with the hostile character of the environment. A high pro- 
portion of monocotyledons, therefore, reveals reality of important limitative factors or a recent 
perturbation ofthe station (human intervention, pasturage, fires, casual clearing in forest, to give 
examples). On one side, monocotyledons are colonizing plants in the open formations, and on 
the other side they have an important impact on the sylvigenesis. 
The reasons of  this peculiar ecology, implying a great adaptative facility, seem to be due to 
the lack of cambium and secundary growing that constitute their essential characteristics. These 
striking histological features of both monocotyledons and pteridophytes involve the impossibility 
of reiteration and important ramification, hence a display of growing ways and different architec- 
tural models than these of dicotyledons. The adaptability of monocotyledons is a definite advan- 
tage for the exploration and the colonization of the medium, either horizontal (creeping herbs) 
or vertical (scandent vines, growth in height without increase of the crown among the tall palms, 
well adapted to fill up gaps in the canopy after a tree fall). The highly specialized structures 
(epiphytes, hydrophytes) are also striking advantages for the exploitation of special biotopes. 
Applications of this type of researches, in order to enhance the value of natural ecosystems 
are possible: appreciation of the ecological bondage of the environment, roughly figured after the 
monocotyledon ratio, planification of monocotyledon agro-ecosystems in the best conditions. 
In fact, the geographic limits for the application of the above theory, valid for French Guiana 
and Ivory Coast, are not known yet. It remains, very likely, true for the lowland tropical vegetation 
in general, but its extension to the mountains, as well as to temperate or cold countries, has to 
be studied. 
REFERENCES 
ADJANOHOUN, E. (1964). Végétation dessavaneset desrodiersdécouvertsen Côte-d'Ivoire. Mem. ORSTOM no 7, Paris. 
GRANVILLE, J.-J. DE (1976). Un transect a travers la savane Sarcelle (Mana, Guyane française). Cali. ORSTOM, sér. Biol. 
GRANVILLE, J.-J. DE (1978). Recherches sur la flore et la v6gétation guyanaises. Thesis, U.S.T.L., Montpellier. 
GUILLAUMET, J.-L. (1967). Recherches sur la végétation et la flore de ¡a région du Bas Cavally (Côte-d'Ivoire). Mkm. 
NALLE, F., R. A. A. OLDEMAN & P. B. TOMLINSON (1978). Tropical trees and forests. An architectural analysis. 
HOOCK, J. (1971). Les savanes guyanaises: Kourou. Essai de pliytoécologie numérique. Mém. ORSTOM no 44, Paris. 
LINDEMAN, J. C. (1953). The vegetation of the coastal region of Suriname. Kemink en Zoon N. V., Utrecht. 
MADISON, M. (1977). Vascular epiphytes: their systematic occurrence and salient features. Selb.vana 2: 1-13. 
XI(1): 3-21. 
ORSTOM no 20, Paris. 
Springer Verlag, Berlin, Heidelberg & New York. 
Adresse de l'auteur: ORSTOM, Centre de Cayenne, B. P. 165, Cayenne, Guyane. 


Monocotyledons and Pteridophytes indicators of environmental constraints in the tropical vegetation

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