Zonal vegetation

--- an outline in altitudinal sequence from the west side and from the east side of the Cocuy massif ---

Text by prof. dr. A.M. Cleef, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam.

Montane forests and páramos make up the natural vegetation cover of the Sierra Nevada del Cocuy. The Upper Forest Line (UFL) is near to 3700 m on the dry west slope and at about 3200-3400 m on the wet east slope (Cleef 1981). The high crest line of this mountain range prevents the wet climate of the east slope to penetrate the dry slopes and valleys of the west side.

The west side of the Sierra Nevada del Cocuy daily experiences the ascent of dry warm air masses from the Chicamocha valley. In the uppermost reaches of the Cocuy Range the influence of the trade winds charged with humidity is limited by the high barrier of the crest zone.

The deep Chicamocha valley near Capitanejo contains dry forest and open xerophytic vegetation (Albesiano et al. 2003). Upslope of the río Nevado almost all natural forests have been cleared during the last centuries, except for some Quercus humboldtii patches roughly between Panqueba and Chita. It is unknown how far the oak forests extended upslope in the past, but supposedly up to 3200 m at least. Palynological studies could provide conclusive evidence. The landscape around the small town of El Cocuy (2800 m) is open with agricultural fields and a lot of erosion is evident (Etter & Villa 2000).

Remnants of the high Andean forest with local dominance of Polylepis quadrijuga are still present and, where not cleared, consist completely of an open Gynoxys paramuna dwarf forest, mostly grazed and with trees and shrub of Ageratina theaefolia, Berberis sp., Diplostephium rhomboidale, Hesperomeles obtusifolia, Myrsine dependens, Pentacalia vaccinioides and species of Solanaceae.

Above the UFL at 3700 m a shrubby subpáramo of Pentacalia vaccinioides and Diplostephium alveolatum with Espeletiopsis jimenez-quesadae is found along with low shrubs of Arcytophyllum nitidum  at 3700 m. A Calamagrostis effusa bunchgrass páramo extends up to 4300 m and is more open in the upper part. Espeletiopsis colombiana is found here, but most impressive are the large stem rosettes of Espeletia lopezii on humid and wet ground.

Espeletia lopezii avoids dry zonal habitats at lower altitude, but old stem rosettes of this species can be spotted in the uppermost grass páramo covering high ridges over 4300 m (and up to 4800-4900 m), which were free of ice in the past. 

The border between the bunchgrass páramo and the superpáramo is at around 4300-4350 m, mostly on terminal moraines, and is marked by low shrub of Loricaria complanata and locally by shrubs and treelets of Pentacalia vaccinioides. Conspicuous whitish ringlike low cushions of Paepalanthus lodiculoides var. floccosus are regularly spotted on these moraines. Most rare is the presence at this border of  a tussock grassland of Stipa hans-meyeri at about 4400 m. Morrainic block fields close to the grasspáramo superpáramo border contain shrubs and treelets of Diplostephium rhomboidale, Lachemilla polylepis, Loricaria complanata, Pentacalia vaccinioides and Valeriana arborea among others.

On the bare morrainic landscape plant growth is limited to pioneer species covering up to 20% maximally, mostly only 5% or less. This dry type of superpáramo goes up to almost 4900 m, which at present is more or less the lower limit of snow and ice. The uppermost reaches are almost devoid of plant cover, exept for rock crevices.

Draba litamo, an emblematic and common species of the superpáramo here, seems to have also medical properties (Uribe 1948).

The east side of the Sierra Nevada del Cocuy belongs to the Boyacá Department in the North and to that of Arauca in the South, with the municipalities of Güicán and Tame respectively.

The very wet humid montane forests down to the Llanos along the Casanare river valley both have been surveyed by the late Thomas van der Hammen and Roberto Jaramillo with Maria Teresa Murillo in 1967 (van der Hammen et al. 1981, and further elaborated by Grabandt 1980 and Keizer et al. 2008).

The uppermost lower montane or subandean rain forests between 2100 and 2550 m are most diverse and attain locally over 40 m in height. They consist of Weinmannia cf. pinnata with cyatheaceous tree ferns and tree species of Acalypha, Billia, Brunellia, Cecropia, Eugenia, Freziera, Guarea, Hedyosmum, Myrsine, Ocotea, Piper, Psychotria, Sapium, Saurauia and Ternstroemia among others.

From 2550 m up to the UFL at about 3200 m dense, epiphyte loaden wet upper montane or Andean rain forests are found consisting of with Weinmannia rollottii and Hedyosmum sp. They are largely unexplored.

Common tree species belong to Brunellia, Clethra, Clusia, Drimys, Freziera, Geissanthus, Hedyosmum, Miconia, Myrsine, Ocotea, Oreopanax, Piper, Schefflera, Ternstroemia and Weinmannia cf. pinnata. Geonoma weberbaueri, a characteristic entire-leaved understory palm extends up to close near the UFL in the reach of the subalpine  rain forest or high Andean forest.

In the headwaters of Quebrada Los Osos, affluent to río Casanare, some additional observations were made in 1977 by Thomas van der Hammen and Antoine M. Cleef. Trunks of trees of 12 m in height of the wet subalpine forest were heavily covered by epiphytes, mainly liverwort species of Plagiochila, Riccardia cf. fucoides and Herbertus pensilis. Species of Frullania (Hepat.) and Usnea (Lich.) are most common on the branches. Tall bamboos of Chusquea (Neurolepis) and Chusquea angustifolia are locally dominant and cyatheaceous tree ferns are mostly replaced by arboreal species of Blechnum. In the UFL dispersed gentianaceous treelets of Symbolanthus tricolor and a 4 m tall Epidendrum orchid species appear. Other common shrubby species include the treelet Bucquetia cf. vernicosa, and B. glutinosa, Symplocos theiformis, Aragoa aff. lycopodioides (A. hammenii?), Diplostephium cf. huertasii (most northern distribution site), Clethra fimbriata, Plutarchia cf. coronaria, Ageratina tinifolia, Ribes sp., Muehlenbeckia tamnifolia, among others.

A wet shrubby subpáramo dominated by bamboos (Chusquea tessellata mainly) grows well developed on moraines together with high-stemmed Espeletia curialensis and/or Espeletia lopezii. Because of the overall presence of large boulders the shrub páramo is rather open. Boulders and big stones have a ground cover of almost 50%. Common are some shrub species shared with the Venezuelan Andes such as Miconia mesmeana, Ilex  truxillensis var. bullatissima, and Bejaria tachirensis. Branched rosettes of espeletioid Libanothamnus tamanus inhabit as shrubby patches larger morrainic boulders between 3000 and 3300 m.

In the bamboo páramo at higher altitude are gradually less shrubs and dwarf shrubs. Hypericum magniflorum occurs at 3300 m and the moraines are covered by low Chusquea bamboos, Disterigma empetrifolium and Rhacocarpus purpurascens, associated with Oreobolus goeppingeri and Arcytophyllum muticum. In terrain depressions only Chusquea bamboo cover (up to 50 cm) is dominant.

Occasionally, in protected sites (or where larger boulders abound) small shrubby forest patches can be found with Gynoxys paramuna, Saracha quitensis. Miconia latifolia, M. salicifolia, Vaccinium floribundum and Ribes sp. From about 3450 m Espeletia lopezii appears in level areas together with the last tall stem rosettes of Espeletia curialensis on the drier slopes up to 3600 m). Espeletia cleefii is present in the zonal bamboo páramo of the valley slopes and continues from about 3550 m upslope into the lowermost superpáramo reaching almost 4300 m.

 Towering above the valley bottom is the zonal high bamboo-covered steep valley slopes that go up into the superpáramo. From about 3900 m the páramo becomes gradually drier and the highest part of the moraines are not covered by bamboos but only by Calamagrostis effusa grass bunches and dark-greenish ringlike cushions of Oreobolus goeppingeri. Bamboos mostly collect in humid depressions between moraines. Also the composition of the shrubby pockets changes with higher altitude. Larger morainic boulders at 3950 m now harbour e.g. Siphocampylus ferrugineus, Gynoxys paramuna, Pentacalia guicanensis, Diplostephium juajibioyi and Senecio cocuyensis, probably present here because of the pioneer habitat, similar to the superpáramo.

From 4000 m upwards cushion bogs appear on the valley bottom consisting of Plantago rigida, Breutelia sp. and low shrub of Pentacalia flosfragans. Flat areas, with active coarse-sandy sedimentation from the superpáramo contain low shrub of Loricaria complanata and Pentacalia flosfragans with rosettes of Oritrophium peruvianum growing dispersed over the level valley bottom. Low shrub of Loricaria complanata mixes up with bamboos on the valley floor near the transition to the superpáramo.

On the zonal stony valley slopes Chusquea tessellata bamboos disappear from the grassland around 4150 m remaining bluish bunches of Calamagrostis effusa with stem rosettes of Espeletia cleefii.

At about 4300 m is the lower border with the humid superpáramo. Here, species richness is greater than in the dry western side of the Cocuy Range. Poa grasses are rather abundant also with some endemic Senecio species (S. adglacialis, S. cocuyanus, S. pascuiandinus, S. supremus). Stem rosettes of Espeletia cleefii penetrate into the lower superpáramo near Patio Bolos and stands can be found as far to the north as the Quebrada Blanca valley directly north of Laguna La Plaza. They have been found only in the southeastern slopes of the Cocuy Range. Towards the north mainly Espeletia lopezii stemrosettes are prominent. The humid lower superpáramo is most rich in vascular species, bryophytes and lichens, especially in the first vertical 50-100 m. Characteristic are the big rosettes of Valeriana plantaginea. Mostly yellowish flowering Draba species, Lachemilla tanacetifolia, Myrosmodes subnivalis are common in rock crevices and on lithosoils. Further low shrubs of Pentacalia guicanensis, P. vaccinioides, and the herbs Senecio canescens with nodding capitula, Senecio cocuyanus, Senecio niveoaureus spectacularly yellowish flowering and Senecio cf. formosus. In between morainic boulders (up to 1 m) rosettes up to 1 m of Draba hammenii can be found associated with Poa pauciflora and Senecio niveoaureus. Dwarf shrubs of Diplostephium colombianum and Lachemilla polylepis with reddish stems are also common in crevices between ice-polished rock surfaces. Between larger morrainic boulders grow trees of Gynoxys paramuna, Diplostephium rhomboidale,Pentacalia andicola, Valeriana arborea. Low shrub of Loricaria complanata is also present and extends over the stony slopes.

Frost heaving is acting more strongly on the steep gravelly slopes in the humid lower superpáramo. Especially rosette plants with massive taproots or impressive rhizomes survive the daily movements of the substrate. Even special communities adapted to this unsafe daily moving ground have been identified. They consist of vascular species such as Agrostis breviculmis, Arenaria venezuelana, Calandrinia acaulis, Castilleja paramicola, Hypochaeris sessiliflora, Oritrophium limnophilum, Senecio cf. formosus and acrocarpous moss species of Grimmia and Bryum and the lichen Thamnolia vermicularis.

Site conditions locally allow for the establishment of isolated high Andean forest patches in the uppermost upper grasspáramo on both sides of the Cocuy Massif. Extensive stands, or better the remnants, are still present on the western slopes of Valle Lagunillas and on the Ritacuba moraines. The Valle de Cojines on the east side of the Cocuy Massif harbours a large, and mostly intact, patch of dwarf forest consisting mainly of Pentacalia andicola and Gynoxys paramuna with associated trees and shrubs of Diplostephium rhomboidale, Myrsine dependens, Pentacalia flosfragrans, and Sericotheca argentea.

As a rule, the upper superpáramo vegetation is poor in plant cover and species. Only on humid rocky cliffs and ledges mosses and lichens are most commonly associated with Draba and Senecio species. On dry ice-polished ledges occasionally old woody 'treelets' of Vaccinium floribundum var. ramosissimum 

has been observed pressed against the rocky surface, which may heat up considerably during day time.

The snow-line today is at about 4900 m, but 40 years ago it was around 4750 m. That implies that the terrain around the Cocuy Massif today is much better accessible for roundwalks. A massive colonization by mosses, such as by Polytrichum juniperinum, has taken place in the morainic areas, which became free of ice and snow during the last 10-15 years. Colonization by herbaceous vascular species starts mostly close to boulders, where substrate is most stable and the warmth of the boulders during night is important for the establishment and growth of pioneering vascular species, such as Senecio cocuyana, S. cf. formosus, Valeriana plantaginea, Hypochaeris sessiliflorus, Castilleja paramicola, Agrostis breviculmis, Draba spp. (D. arauquensis, D. barclayana, D. boyacana, D. litamo and D. ritacuvana) The most prominent pioneers are the whitish-leaved patches of Senecio niveoaureus and the conspicuous tussocks of Cortaderia cf. colombiana