The equatorial dry forest of northern Peru
The dry forest of northern Peru forms a narrow band flanking a 100-km stretch of the western Andes foothills, bordered to the west by coastal desert. The area is under ever-increasing pressure from agricultural encroachment from the lowlands, including large-scale sugar cane and rice plantations , free-ranging cattle, and from subsistence maize cultivation in the uplands. There are also threats from extractive mining development. The climate is extreme, with temperatures in low elevations averaging 30o C and highs reaching above 40 o C, and average precipitation of only 50 mm. This region is also among the areas most sensitive to and impacted by the El Nino-Southern Oscillation (ENSO). During El Nino events, the normally arid climate is replaced by a humid tropical climate and rainfall can exceed 1000 mm in a year.
Our study site is approximately 60 km north of the city of Chiclayo in the department of Lambayeque and encompasses approximately 100 km2 of mountainous terrain that emerges out of a flat coastal outwash plain, approximately 30 km inland from the Pacific coast, and rises into successively higher mountains to the east. Elevation in the study area ranges from 200 m at the mountain base to >1200 meters at the top. This discreet mountain range comprises 3 connected peaks: Cerro de Venado, Calabosa, and Motopillo, from which steep-sided valleys radiate outwards in all directions, dropping 150 – 500 m/km to the surrounding plain. Steep valleys contain boulder-strewn, dry narrow stream beds; a few hold small spring-fed pockets of water throughout the year, typically located fairly high, near the head of the valleys. Vegetative associations are characteristic of the Pacific Tropical Desert, including the Arid Tropical Desert and the Super-Arid Pre-Mountainous Desert. Typical vegetation associated with this region includes algarrobo (Prosopis spp.), hualtaco (Loxopterigium huasango), palo santo (Bursera graveolens), pasallo (Eriotheca ruizii), overo (Cordia lutea), sapote (Capparis scabrida), and five varieties of cactus (Cactacaea). Above 600 m, forests of pasallo and palo santo dominate. Lower elevations are dominated by overo and sapote, which reliably produces crops of fruit every year, with staggered ripening from December – March, moving up the elevational gradient.
Vegetative conditions change remarkably little however and this area can go years with very little precipitation. Trees and shrubs are mostly leafless and ground vegetation is minimal. However, every 6 or more years precipitation is high, transforming the normally open habitat into a jungle of vines and foliage. Rank growth of dormant ground vegetation and vines, including numerous varieties of wild tomato (Solanum spp), obscures trails and sign, and blankets trees and shrubs, severely hindering visibility and travel for observers, if not also for bears. Gradual drying of the habitat through winter returns the vegetative cover to its more typical state.