Interciencia ISSN: 0378-1844 [email protected] Asociación Interciencia Venezuela Azócar, Aura; Rada, Fermín; García-Núñez, Carlos Functional characteristics of the arborescent genus polylepis along a latitudinal gradient in the high andes Interciencia, vol. 32, núm. 10, octubre, 2007, pp. 663-668 Asociación Interciencia Caracas, Venezuela Available in: http://www.redalyc.org/articulo.oa?id=33901003 How to cite Complete issue Scientific Information System More information about this article Network of Scientific Journals from Latin America, the Caribbean, Spain and Portugal Journal's homepage in redalyc.org Non-profit academic project, developed under the open access initiative FUNCTIONAL CHARACTERISTICS OF THE ARBORESCENT GENUS Polylepis ALONG A LATITUDINAL GRADIENT IN THE HIGH ANDES Aura AZÓcar, FermÍN Rada and Carlos GarcÍA-NÚÑEZ SUMMARY Polylepis is a genus restricted to the Andean Mountain cea avoids the less harsh conditions of its habitat through os‑ Range, naturally occurring above the upper continuous forest motic adjustments and cell wall elasticity changes. Mean CO2 limit. The purpose of this work was to integrate and compare assimilation rates were higher in P. australis (9µmol·m‑2·s‑1) functional characteristics in terms of water and carbon rela‑ campared to P. sericea (5µmol·m‑2·s‑1) and P. tarapacana tions and low temperature resistance mechanisms in different (3·µmol·m‑2·s‑1). Mean night leaf respiration rates were similar Polylepis species along a latitudinal gradient. The studied for all species (1‑2·µmol·m‑2·s‑1). In terms of low temperature species were P. sericea in Venezuela, P. tarapacana in Bolivia resistance, P. sericea shows daily osmotic adjustments and a and P. australis in Argentina. Seasonal measurements of leaf moderate supercooling capacity (‑9ºC). The other two spe‑ water and osmotic potentials, stomatal conductance, CO2 as‑ cies rely on freezing tolerance in order to survive the more similation and respiration rates, and injury and freezing tem‑ extreme low temperature conditions. The functional attributes peratures were compared. There is a gradient, in terms of described in this study for the different species in a wide en‑ functional attributes, along the environmental range. P. tarapa- vironmental range may explain some aspects of their success cana is the most tolerant species to water stress, while P. seri- along the latitudinal and altitudinal gradients. limate is an impor- Thus, minimum absolute temperatures unhn (2006) reported 26 species, with tant factor for plant become an important variable in or- the highest diversity found in Peru (14 growth; it governs dis- der to establish the distribution limits species, 3 endemic) and Bolivia (13 tribution and sets limits for survival. of the major vegetation types (Wood- species, 4 endemic); only one species One important characteristic of high ward and Williams, 1987; Prentice et was recorded for Venezuela, 3 in Co- mountain environments is the low air al., 1992). In spite of this, the genus lombia (1 endemic), 7 in Ecuador (2 temperature, which limits plant growth Polylepis does not seem to respond endemic), 2 in Chile and 4 in Argen- and survival in these habitats (Sakai in their distribution to this regime of tina (1 endemic). and Larcher, 1987). On the other hand, low temperatures, since it presents a Regional forest distribu- tropical high mountain environments unique altitudinal distribution reaching tion seems to be related to areas where present large daily variations and much higher elevations than those of solar irradiance is controlled by the small seasonal changes in temperature, any other angiosperm tree in the world slope aspect (direction) and inclination and freezing temperatures occur al- (Liberman-Cruz, 1986). Additionally, (angle), and sun elevation influences lo- most every day of the year (Hedberg, it is an endemic genus in the Andean cal distribution (Braun, 1997). The ge- 1961; Azócar and Monasterio, 1980). Mountain Range, found from Vene- nus creates a natural treeline well above Temperature and frost occurrence vary zuela in the north to Central Argentina the timberline (continuous forest line), with latitude, altitude and topography. in the south. Kessler and Schmidt-Leb- in some cases forming forest patches KEY WORDS / Andean Mountain Range / Carbon Relations / Gas Exchange / Low Temperature Resistance / Photosynthesis / Water Relations / Received: 05/02/2005. Modified: 09/14/2007. Accepted 09/20/2007. Aura Azócar. Biologist, Universidad Central de Venezuela (UCV). Dr. in Ecology, University of Montpellier, France. Professor, Universidad de Los Andes (ULA), Venezuela. Dirección: Laboratorio de Ecofisiología, Instituto de Ciencias Ambientales y Ecológicas (ICAE), ULA, Mérida, Venezuela. e-mail: [email protected] Fermín Rada. Biologist, University of Maryland, USA. Dr. in Tropical Ecology, ULA, Vene- zuela. Professor, ULA, Venezuela. e-mail: [email protected] Carlos García-Núñez. Forestry Engineer and Dr. in Tropical Ecology, Professor, ULA, Venezue- la. e-mail: [email protected] OCT 2007, VOL. 32 Nº 10 0378-1844/07/10/663-06 $ 3.00/0 663 between 4000 and 5200masl. In gen- Table I eral, Polylepis forests are restricted to Environmental characteristics and coordinates steep slopes in mid to low topographic of the studY sites positions, although some species are Study site Species Coordinates Altitude Mean Mean also found on flat terrains. Polylepis (masl) annual annual dominates the upper strata of woodlands temperature precipitation and shrublands, together with other less (°C) (mm) abundant woody species of the genera Berberis, Gaultheria, Valeriana, among Piedras Blancas, P. sericea 9°N - 70°W 4200 3.7 800 others. These woody species occasion- Venezuela ally form dense stands that cover most Nevado Sajama, P. tarapacana 18°S - 68°W 4300 3.4 347 of the surface, often called forests, that Bolivia are usually intermingled with patches of tussock grasslands, ferns or rock out- Los Gigantes, P. australis 32° S - 66°W 2100 8.0 854 Argentina crops (Kessler, 2006). Despite their relatively small area cover, these forests represent unique ecological islands of biodiver- life form (Simpson, 1979), character- man-Cruz et al., 1997). The study site sity that are vanishing rapidly; Fjeldsa ized by twisted shapes, a thick, dense- is located at Nevado Sajama Nation- and Kessler (1996) indicate that only ly laminated and flaky bark with red- al Park, where P. tarapacana forms 2% of the original Polylepis forests re- dish color (Simpson, 1986), and small the world’s highest woody plant forest main in Perú and 10% in Bolivia, sug- green-gray leaves. The trees are 1-6m (Liberman-Cruz, 1986; Braun, 1997) gesting that human occupation in the in height and have crown diameters around the Sajama Volcano. Although Andean highlands has led to consider- of 3-5m. With respect to their distri- the study site is considered a semiarid able destruction of these forests. bution, the species occur in different tropical high mountain environment, its All species of the ge- ecological habitats associated with el- latitudinal position determines a marked nus are exposed to very harsh climatic evation and humidity. seasonal pattern in temperature and pre- conditions in both their altitudinal and Three species were com- cipitation regimes, with a cold dry sea- latitudinal distribution, indicating that pared a latitudinal distribution gradient: son during the austral winter (May-Oct) their survival depends on very special P. sericea Wedd, in Venezuela, P. tara‑ and a wet warmer season (Nov-Apr; adaptive characteristics that allow them pacana Philippi, in Bolivia and P. aus‑ Liberman-Cruz et al., 1997). Absolute to sustain freezing temperatures and a tralis Bitter, in Argentina. Table I shows maximum and minimum temperatures distinct water stress due to precipita- the environmental characteristics and registered at 4200m are 21 and -19ºC, tion regimes and drying winds. Nor- geographic coordinates for the different respectively (Liberman-Cruz, 1986). mally, these conditions would prevent study sites. P. australis is found tree growth; however, the presence of P. sericea, in the Ven- at the north extreme of Sierra Grande many Polylepis species above the tim- ezuelan Andes, may reach an altitude in Córdoba, Argentina, mainly associ- berline, forming forest islands along of 4600m (Arnal, 1983), well above ated with rock outcrops. This species broad temperature and water availability the treeline (3200masl) in this tropi- has to cope with altitude conditions in gradients, suggests a high diversity of cal area (Monasterio, 1980). Its dis- a temperate environment. Most (83%) functional attributes, which in turn play tribution is always associated to more rainfall occurs in the summer (Renison a fundamental role in their survival. favorable thermal conditions in areas et al., 2002). Absolute daily maximum In this work, some where large boulders accumulate to- and minimum temperatures of 27.1 and functional attributes of three Polylepis wards the base of glacial cirques (Wal- -12.8ºC were registered during this species along a wide latitudinal gra- ter and Medina, 1969; Azócar and study. dient are integrated and compared, in Monasterio 1980). This species has the order to establish functional responses widest latitudinal distribution, from Field and laboratory studies that help explain their wide geographi- Venezuela to northern Bolivia. Appar- cal distribution. Functional charac- ently, this species has spread through Mean air temperature teristics are compared