Low temperature resistance in saplings and ramets of Polylepis sericea in theVenezuelan Andes

摘要

The frequent occurrence of all year-round below zero temperatures in tropical high mountains consti-tutes a most stressful climatic factor that plants have to confront. Polylepis forests are found well abovethe continuous forest line and are distributed throughout the Andean range. These trees requireparticular traits to overcome functional limitations imposed on them at such altitudes. Consideringseedling and sapling stages as filter phases in stressful environments, some functional aspects of theregeneration of Polylepis sericea, a species associated to rock outcrops in the Venezuelan Andes, werestudied. We characterized microclimatic conditions within a forest, in a forest gap and surrounding openparamo 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 surroundingparamo. Minimum temperatures close to the ground were 3.6 °C lower in the open paramo compared tothe forest understory. Maximum temperatures were 9.0 °C higher in the open paramo. Ice nucleation andinjury temperatures occurred between —6 and —8 °C for both ramets and saplings, an evidence of frostavoidance to low nighttime temperatures. In this particular forest, this resistance ability is determinantin their island-like distribution in very specific less severe temperature habitats.