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Flora, vegetation and ecology in the Venezuelan Andes: a case study of Ramalde Guaramacal

Cuello Alvarado, N.L.

Publication date2010

Link to publication

Citation for published version (APA):Cuello Alvarado, N. L. (2010). Flora, vegetation and ecology in the Venezuelan Andes: a casestudy of Ramal de Guaramacal. Universiteit van Amsterdam, Institute for Biodiversity andEcosystem Dynamics (IBED).

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Download date:29 May 2021

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SUMMARY

Ramal de Guaramacal is an outlier and lower elevation mountain range up to 3,130

m located at the northeastern end of the Venezuelan Andes.

In Chapter 2, montane forest community composition of Ramal de Guaramacal

was studied along the altitudinal gradient on both sides of the range with different

slope expositions. Thirty five 0.1 ha plots were surveyed, with variable intervals of

30 to 150 meters between 1350 m and 2890 m and nine plots of variable size (50

m2 to 400 m

2) were surveyed in dwarf forests located between 2800-3050 m. A

total of 388 morphospecies with dbh ≥ 2.5 cm, corresponding to 189 genera and 78

families of vascular plants, were recorded from a total of 44 forest plots. The

TWINSPAN phytosociological clustering, based on both floristic composition and

species relative abundance, revealed seven forest communities at association level,

grouped in three alliances and one montane forest order group. Three subandean

forest (LMRF) communities and four Andean - high Andean forest (UMRF-

SARF) communities are distinguished and described according to the Zürich-

Montpellier method. The Geonomo undatae-Posoquerion coriaceae alliance

contains two subandean forest communities (Simiro erythroxylonis-Quararibeetum

magnificae and Conchocarpo larensis-Coussareetum moritzianae); the Farameo

killipii - Prunion moritzianae alliance contains one subandean forest community

(Croizatio brevipetiolatae-Wettinietum praemorsae) and one Andean forest

community (Schefflero ferrugineae-Cybianthetum laurifolii) and the Ruilopezio

paltonioides-Cybianthion marginati alliance includes one Andean (Geissantho

andini-Miconietum jahnii) and two high Andean forest communities (Gaultherio

anastomosantis-Hesperomeletum obtusifoliae and the Libanothamnetum griffinii).

Altitudinal zonation, forest floristic diversity, composition and forest structure is

discussed between slopes and along the altitudinal gradient and compared, where

possible, to other montane forests. In LMRF, Rubiaceae, Lauraceae and

Melastomataceae are the most speciose of woody families. In UMRF, the

Lauraceae family is still the most diverse, followed by Melastomataceae and

Myrtaceae, while in SARF the Asteraceae and Ericaceae are the most species rich

families. The structure of the montane forests of Ramal de Guaramacal becomes

more compressed towards higher elevations. LMRF are dense and of medium

height, with canopies up to 25 m tall, while UMRF canopies can reach up to 18 m,

and those of SARF are only 6-8 (10) m tall. Basal area was slightly increased on

the North than on the South slopes and shows different patterns against altitude

between slopes. More diversity and density of palms, lianas and climbers is clearly

observed in LMRF, but richness of liana species is also important in SARF

(forests). Forest altitudinal zonation is variable between the North and South

slopes of Guaramacal, with the forest zones of UMRF on the windward South

slope, tending toward reaching lower elevations than on the opposite and drier

North slope. There is a low altitudinal limit of the uppermost forest (Upper Forest

Line or UFL) apparently caused by the “top effect”.

In Chapter 3 zonal páramo vegetation communities present on top of Ramal de

Guaramacal, were studied with the aim to provide a syntaxonomic scheme or

classification, based on analysis of the physiognomy, floristic composition,

ecological relations and spatial distribution of the different vegetation

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Summary

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communities. A total of 91 vascular species, 33 species of bryophytes and 11

species of lichens have been documented from fifty 10 m-line intercept transects,

each surveying 10 m of altititudinal interval on zonal páramo vegetation present

between 2800 and 3100 m altitude. The interpretation of the TWINSPAN

clustering allowed the recognition of five vegetation communities at association

level grouped into two alliances and one order. Three associations of lower

subpáramo or shrubby páramo and two of upper subpáramo or bunchgrass páramo

dominated by rosettes and tussocks have been documented. The alliance Hyperico

paramitanum-Hesperomeletion obtusifoliae groups the shrubby páramo

associations: Ruilopezio paltonioides-Neurolepidetum glomeratae and Disterigmo

acuminatum-Arcytophylletum nitidum, present on wind protected slopes, dwarf

forests edges or along streams. The alliance Hyperico cardonae-Xyridion

acutifoliae groups one widely distributed shrubby páramo association Cortaderio

hapalotrichae-Hypericetum juniperinum and two open grass páramo associations:

Puyo aristeguietae-Ruilopezietum lopez-palacii and Rhynchosporo gollmerii-

Ruilopezietum jabonensis, present on wind exposed slopes. Asteraceae and

Ericaceae are the most speciose of families, followed by Poaceae and Cyperaceae.

The most diverse genera are Ruilopezia (Asteraceae), Rhynchospora (Cyperaceae)

and Hypericum (Clusiaceae). Diversity of species and growth forms is greater

among the shrubby communities, decreasing in the bunch grass-rosette

communities. Canonical correspondence analysis (CCA) indicates that floristic

composition of zonal vegetation communities is mostly related to slope angle and

altitude than to other observed variables such as pH, soil depth and humus

thickness. The generic and species composition is that of a rain bamboo páramo.

In Chapter 4 the azonal páramo vegetation present at the top of Ramal de

Guaramacal was studied by means of observations, plant collections and surveys

consisting of a total of 71 small plots of between 0.25 to 6 m2. Azonal vegetation is

represented in the study area by habitats experiencing water stress (peat bogs and

aquatic vegetation). The azonal vegetation present in two peat bogs areas of

Páramo El Pumar (Laguna El Pumar y Laguna Seca), and in a small valley where

water collects in Páramo de Guaramacal, near the „Las Antenas‟ area between

~2900 and ~3000 m were analyzed. A total of 53 morphospecies, belonging to 30

species of vascular plants, 20 species of cryptogams and 3 undetermined species of

algae have been documented for the azonal vegetation. The interpretation of a

TWINSPAN clustering, based on affinities of floristic composition and species

cover, allowed the recognition of six azonal vegetation communities grouped into

three alliances and one order. The new alliance Sphagno recurvi-Paepalanthion

pilosi groups the new bunchgrass association Paepalantho pilosi-Agrostietum

basalis and the both new Sphagnum bog associations: Sphagno recurvi-Caricetum

bonplandii and Sphagno sparsi-Caricetum bonplandii. The new alliance Carici

bonplandii-Chusqueion angustifoliae contains a bamboo páramo („chuscal‟)

association Carici bonplandii-Chusqueetum angustifoliae growing close to the lake

shores, in periodically flooded areas, and characterized almost exclusively by

Chusquea angustifolia. The alliance Ditricho submersi-Isoëtion Cleef 1981 is

represented by the submerged aquatic community of Sphagnum cuspidatum and

the Isoëtetum karstenii Cleef 1981.

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Flora, vegetation and ecology in the Venezuelan Andes

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Chapter 5 presents the study of the phytogeographical patterns and affinities of the

low altitude and wet páramo vascular flora of Ramal de Guaramacal with emphasis

in to the analysis of the floristic connections of the Guaramacal páramo flora with

the neighboring dry páramos of the Sierra Nevada de Mérida and other páramo

floras of the northern Andes and Central America. A total of 251 vascular plant

taxa belonging to 150 genera and 69 families were recorded from the vegetation

formations existing in the study area. The most species rich families are Astera-

ceae, Poaceae, Ericaceae and Orchidaceae, followed by the ferns families Grammi-

tidaceae and Lycopodiacae. The most diverse genera are the ferns and fern ally

Elaphoglossum, Huperzia and Hymenophyllum. The analysis of phytogeographical

composition of páramo flora at genus level showed that 52.8% of the genera are

Tropical. The Temperate component is represented by 33.3% of the genera and the

Cosmopolitan component by 13.9%. The Neotropical montane element (38.9%) is

high in Guaramacal páramo, the Páramo endemic element (1.9%) and the Andean

alpine element (0.9% and represented by only one genus (Lachemilla)) are low

compared to other páramo areas. The vascular flora of Páramo de Guaramacal is

largely composed of (1) a group of Neotropical widespread species (31%), (2) a

group of Andean distributed species (49%), part of them confined to the northern

Andes and part widespread in the Andes from Colombia to Bolivia, and (3) a

group of Venezuelan endemics (20%). From an eight páramo flora comparative

dataset, the closest relationships among páramos is observed between the generic

páramo floras of the Colombian Cordillera Oriental of Sumapáz and Sierra Nevada

del Cocuy, which are both closely related to that of the Sierra Nevada de Mérida in

Venezuela. The generic páramo flora of Ramal de Guaramacal shows the closest

relationship to southern Ecuador páramo flora of Podocarpus National Park.

According to Detrended Correspondance Analysis and Principal Component

Analysis ordination results, most of the variations in páramo floras may represent a

response to differences in ambient humidity.

Chapter 6 presents the analysis of functional diversity of mountain forests of

Ramal de Guaramacal as a function of altitude. Decreasing functional diversity is

generally seen as indication of ecosystem degradation. This study aimed to

examine if functional diversity changed with altitude in undisturbed Andean

forests as reference information for studies of degraded Andean systems. We

studied the vascular plant composition of 44 small plots located between 1330 m

and 3060 m in a well-protected forest reserve. We linked each species to their

functional traits related to energy balance and fragmentation, by means of

literature and herbarium studies. Detrended correspondence analysis was used to

detect the principal variation in the trait information. Using fourthcorner analysis,

we randomized the species assemblages in our relevées using two permutation

models, to test if trait composition changed with elevation. Functional trait

diversity was calculated on the basis of species and individuals in the relevées,

using Shannon, Simpson (1-D) and Fisher's alpha indices. Applying the same

permutations models as in the fourthcorner analysis, we tested the relationship of

functional diversity with elevation. Results show that forests in the Ramal de

Guaramacal area became more diverse in the energy balance related traits at higher

elevations, pointing at more prominent levels of overdispersion higher up the

slopes. Leaf size contributed substantially to the altitudinal variation in these traits.

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Summary

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The diversity in fragmentation related traits showed an opposite altitudinal pattern.

Subalpine rain forests (SARF) diverged from the altitudinal trends in

fragmentation related traits, probably as a consequence of edge effects in the

SARF-páramo mosaic, created by wind. We conclude that functional diversity of

undisturbed Andean forests in the Guaramacal area changed with altitude. Global

temperature rises might thus affect the functionality of Andean forests, but not

necessarily in a harmful way.

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Flora, vegetation and ecology in the Venezuelan Andes