Ecological and ecophysiological patterns in a pre-altiplano shrubland of the Andean Cordillera in northern Chile

We report on community structural, ecophysiological, phenological, and morphological measurements made on woody plant species in the high elevation pre-altiplano zone on the western slopes of the Andean Cordillera of northern Chile. Notwithstanding extreme conditions of low rainfall, high atmospheric vapour demand and diurnal temperature fluctuation, a diversity of habitats (associated with drainage and slope aspect), appreciable local plant species richness (28 woody perennial plant species in a small area), and an array of adaptive morphological ecophysiological and phenological traits are present among woody species in these shrublands. Family diversity was low with four families accounted for 82% of the species. A range of gas exchange and watering use efficiency strategies was present ranging from highly efficient CAM species with a carbon isotope discrimination (delta) of 3.7-7.5 per thousand through C3 species with varying stomatal and gas exchange characteristics with a delta of 14.4 to 19.8 per thousand. Drought-deciduous small-leaved amphistomatic species from arid slopes generally had high stomatal conductance and high carbon assimilation rates during the rainy season. These drought deciduous species were largely leafless and, with one exception had low water potentials, during the dry season. Wash and less xeric site species commonly had broader evergreen to semi-evergreen leaves, higher dry season water potentials, and relatively consistent and moderate rates of gas exchange throughout the year. For all species, intrinsic water use efficiency (as estimated from the inverse of c(i):c(a) ratio) correlated positively with mean leaf width (broader leaves had a lower higher intrinsic WUE) and dry season water potential. The charismatic high altitude tree, Polylepis rugulosa (Roaceae), had a population structure that suggests highly episodic establishment of seedlings, likely in sequences of wet years. Little of the area of these significant shrublands is currently protected. It would be desirable to add areas of pre-altiplano shrublands to adjacent national parks to ensure the persistence of these important communities.