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Neotropical ecosystems between treeline and snowline, called páramos, stretch along Andean ranges from Costa Rica to northern Peru.The páramo climate is characterized by regular night frosts occurring throughout the year. Páramo plants use two strategies to deal with freezing temperatures.They either avoid ice formation in the tissues or tolerate extracellular ice formation. We tested the microclimate hypothesis, which suggests that the freezing resistance of the páramo plants is determined by plant height, that is, that taller plants experience a milder microclimate and avoid freezing, whereas smaller plants are exposed to the more extreme thermal conditions near the ground and tolerate them.We measured the temperature at which ice formed inside the plants (the 'exotherm'), and compared it with the temperature at which 50% damage to the tissue occurred (Lt50); a significant difference between the exotherm and Lt50 would indicate freezing tolerance whereas the absence of a difference would indicate avoidance by supercooling.We analysed the freezing resistance of 38 common Ecuadorian páramo species. We found no correlation between plant height and freezing resistance mechanism or injury temperature and reject the microclimate hypothesis.Tolerant plants reach higher altitudes than avoidant plants, but their altitudinal ranges largely overlap and the Lt50 does not differ between them. These results suggest that there is no qualitative difference between the two strategies to survive the páramo frosts. Shrub leaves were injured at significantly lower temperatures than other life forms, such as herbs, which may reflect leaf anatomical differences among the plants.

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Pinus rotundata dominated peatbog (Žofinka Nature Reserve) in the Třeboň Basin, Czech Republic, was affected by "natural" disturbances: wind damage (1984), followed by a bark beetle attack, and fire (1994, 2000). Phytosociological relevés were used to document vegetation. Soil water chemistry was compared in three differently affected stands: (1) an undisturbed Pinus rotundata bog forest, (2) a windthrow -bark beetle affected stand and (3) a site burned by wildfire in 2000. The species composition of the windthrow -bark beetle affected sites and the undisturbed P. rotundata bog forest differed mainly in the shrub and tree layers. Burned sites were partly colonized by anemochorous species (e.g. Taraxacum sp. div.) that disappeared within two or three years after colonization. Bare peat was colonized by bryophytes (e.g. Marchantia polymorpha and Funaria hygrometrica) typical of the disturbed sites, and by Polytrichum sp. div. and Aulacomnium palustre. Most plant species characteristic of the P. rotundata bog forest occurred at the burned sites eight years after the fire, but in different abundances. The edificator of the former community-P. rotundata-was mostly absent. Compared with windthrow followed by the bark beetle attack, fire promoted rapid expansion of Molinia caerulea. Soil water in both the undisturbed P. rotundata bog forest and the windthrow -bark beetle affected sites had a similar composition: very low pH values, high P concentrations, low concentrations of cations (Ca 2+ , Mg 2+ and K + ) and inorganic nitrogen. The concentrations of soluble reactive phosphorus (SRP) and NH þ 4 À N were negatively correlated with the groundwater table. Total P, SRP and NH þ 4 À N concentrations in the soil water at the burned site were by one order of magnitude higher than those in the P. rotundata bog forest, while concentrations of K + , Mg 2+ and Ca 2+ were only about two times higher. High concentrations of P and N in the soil water found three years after the fire indicated a long-term elevated nutrient content in the soil water.

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