Respuesta del crecimiento de Pinus oocarpa Schiede a variables climáticas en el noroeste de Lagunas de Montebello, Chiapas, México

Dendrochronological studies are used to reconstruct some climatic variables; in México these studies have focused on central and northern temperate forests where trees present well defined annual rings. Few studies have been carried out in the southern part of the country where annual ring growth is not easily identified and thus makes cross-dating problematic. We analyzed the dendrochronological potential of Pinus oocarpa Schiede for reconstructing climatic variables in the northwest portion of Lagunas de Montebello, Chiapas. We used a selective sampling approach and collected 65 increment cores from 34 trees. While our samples showed a high frequency of false rings (8 to 60 %), we were able to date 30 samples from 22 trees (46 %) using standard dendrochronological techniques and developed total chronologies for total ring width, earlywood, and latewood for a period of 91 years (1925-2015). We found a significant influence of mean precipitation and mean maximum and minimum temperature over the annual ring growth of P. oocarpa in the period 1961-2004. Our results show that winter-spring precipitation (January-May) was the most important for the species’ annual ring growth. However, we found the highest correlation between spring (March-May) precipitation and the earlywood chronology (r = 0.719, P < 0.05). The earlywood chronology also showed potential for reconstructing minimum temperatures (March to May) (r = 0.732, P < 0.05), while the latewood chronology had the potential for reconstructing the maximum temperature (September to January) (r = 0.714, P < 0.05). These results showed that P. oocarpa can be used to reconstruct climatic variables in the Mexican tropics. We recommend that new areas with older trees should be explored in order to increase the depth of chronologies and reconstruct climate records several centuries into the past.

Effects of selection cuts on winter habitat use of snowshoe hare (Lepus americanus) in northern temperate forests

Selection cutting is used in northern temperate forests where regeneration dynamics are driven by gap formation. By creating openings in the canopy, selection cutting modifies shrub cover, an important criterion in winter habitat selection by snowshoe hare (Lepus americanus Erxleben, 1777), a key species in North American forests. The objective of this study was to determine the effects of selection cuts on snowshoe hare habitat and to evaluate the restoration of habitat quality over time. Occurrence indices for snowshoe hare (fecal pellets and tracks) were modelled according to habitat quality parameters for 22 hardwood stands that were subjected to selection cutting between 1993 and 2007 and 30 untreated stands (15 hardwood and 15 mixedwood) in Abitibi-Témiscamingue, Quebec. Model selection based on the Akaike second-order information criterion (AICc) identified lateral cover as the only habitat structure parameter having a positive effect on snowshoe hare abundance in the study sites. Indicators of snowshoe hare presence were highest in untreated mixedwood stands but more abundant in selection cuts than in untreated hardwood stands. The use of selection cuts by snowshoe hare increased with time since logging was performed. We conclude that selection cutting exerted a positive effect on the use of hardwood stands by snowshoe hare.