Low temperature resistance in saplings and ramets of Polylepis sericea in the Venezuelan Andes

Abstract

The frequent occurrence of all year-round below zero temperatures in tropical high mountains constitutes a most stressful climatic factor that plants have to confront. Polylepis forests are found well above the continuous forest line and are distributed throughout the Andean range. These trees require particular traits to overcome functional limitations imposed on them at such altitudes. Considering seedling and sapling stages as filter phases in stressful environments, some functional aspects of the regeneration of Polylepis sericea, a species associated to rock outcrops in the Venezuelan Andes, were studied. We characterized microclimatic conditions within a forest, in a forest gap and surrounding open pa´ramo and determined low temperature resistance mechanisms in seedlings, saplings and ramets. Conditions in the forest understory were more stable compared to the forest gaps and open surrounding pa´ramo. Minimum temperatures close to the ground were 3.6 C lower in the open pa´ramo compared to the forest understory. Maximum temperatures were 9.0 C higher in the open pa´ramo. Ice nucleation and injury temperatures occurred between 6 and 8 C for both ramets and saplings, an evidence of frost avoidance to low nighttime temperatures. In this particular forest, this resistance ability is determinant in their island-like distribution in very specific less severe temperature habitats.