The forest microclimate in a Nothofagus pumilio primary forest (BV) and the effect of a regeneration felling (RG) and an open field (SD) were studied during seven years. Three weather stations measured the global solar radiation (RSG), the air temperature (Ta), the soil temperature at 15 (TS15) and 30 (TS30) cm depth, the relative humidity (HRa) and the wind speed (V). The results showed that the trends in meteorological variables were similar to those found in forests with similar characteristics. Almost all meteorological variables recorded in BV showed statistical differences, compared to SD, with the exception of Ta, and during the leafless period with Tmina (minimum air temperature) TS15 and TS30. When CR was compared to BV the variables RSG, HRa, TS15, TS30 (only during leafless period) and V showed significant differences. The higher differences between BV and CR were that in CR the RSG was 4.4 and 3.5 times higher than in BV, for the fully-leaved and the leafless period; and V was 1.2 times higher in CR than in BV. These differences suggest that the microclimate in CR changed respect BV. Because the microclimate and the water balance in the stand affect the vegetation, the differences found between BV and CR are important, and provide a baseline of information to evaluate the effects of the regeneration felling, the most frequently implemented cut in these forests.

Canopy gaps modify the environmental conditions available for plant growth in forests. Small canopy gaps are frequent in Nothofagus betuloides forests of Tierra del Fuego. Our objective was to study whether the forest floor vascular and non-vascular plant species composition and diversity are influenced by the occurrence of small-scale disturbances due to changes in the below-canopy solar radiation transmittances and forest floor heterogeneity (cover of litter, bare soil and fallen woody debris classed in three decay stages) in a N. betuloides forest located in south western Tierra del Fuego (53° 59t’S, 69°58′W). The vegetation was sampled in and around 13 canopy gaps (47 m2 on average). Following a light gradient, 65 plots (2 × 2 m) were established. The cover of all plant species was recorded using Londo’s scale. Species richness and total cover were calculated for each of the following taxonomical groups: spermatophyta (monocotyledons, dicotyledons), pteridophyta, bryophyta, marchantiophyta, anthocerotophyta and lichens. There were 63 species found on the forest floor. Marchantiophyta was the most diverse group with the highest species richness (6.6 species per plot). The vegetation on the forest floor was very homogeneous in species composition, richness and species diversity. The ordination analysis (NMS) showed that the community composition was weakly influenced by the patterns of below-canopy solar radiation transmittances and substrate heterogeneity. MRPP analysis of the community composition did not reveal differences in plant species assemblages between positions along transects running from areas beneath closed canopy to the open centres of canopy gaps. The marchantiophyte Chiloscyphus magellanicus was the only species which can be considered to be an indicator species; it was more likely to occur in gap centres (more open conditions). We conclude that these small canopy gaps do not very much modify the forest floor communities and the communities can be considered relatively stable

Seedlings of co-occurring species vary in their response to resource availability and this has implications for the conservation and management of forests. Differential shade-tolerance is thought to influence seedling performance in mixed Nothofagus betuloides–Nothofagus pumilio forests of Patagonia. However, these species also vary in their soil nutrient requirements. To determine the effects of light and soil nutrient resources on small seedlings we examined responses to an experimental reduction in canopy tree root competition through root trenching and restricting soil nutrient depletion through the addition of fertilizer. To understand the effect of light these treatments were undertaken in small canopy gaps and nearby beneath undisturbed canopy with lower light levels. Seedling diameter growth was greater for N. pumilio and height growth was greater for N. betuloides. Overall, diameter and height growth were greater in canopy gaps than beneath undisturbed canopy. Such growths were also greater with fertilizer and root trenching treatments, even beneath undisturbed canopy. Seedling survival was lower under such treatments, potentially reflecting thinning facilitated by resource induced growth. Finally, above-ground biomass did not vary among species although the less shade tolerant N. pumilio had higher below-ground biomass and root to shoot biomass ratio than the more shade tolerant N. betuloides. Above- and below-ground biomass were higher in canopy gaps so that the root to shoot biomass ratio was similar to that beneath undisturbed canopy. Above-ground biomass was also higher with fertilizer and root trenching treatments and that lowered the root to shoot biomass ratio. Restricting soil nutrient depletion allowed seedlings of both species to focus their responses above-ground. Our results support a view that soil nutrient resources, as well as the more commonly studied light resources, are important to seedlings of Nothofagus species occurring on infertile soils.