Original paper

The forest vegetation of Ramal de Guaramacal in the Venezuelan Andes

Cuello A, Nidia L.; Cleef, Antoine M.

Abstract

Montane forest community composition of Ramal de Guaramacal, Venezuelan Andes, 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 m2) 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 45 forest plots. The TWINSPAN phytosociological classification, 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 erythroxyli-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 marginatii 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 upper forest (Upper Forest Line or UFL) apparently caused by the “top effect”.

Keywords

floristic compositionforest structurelower montane rain forestupper montane rain forestsubalpine rain forestphytosociological classificationaltitudinal zonationvenezuelaandes