Temperate forests are naturally heterogeneous because of slopes with different aspects. Mexican forests are under constant anthropogenic perturbations. Therefore, the availability of safe microsites for seed germination is crucial for forest regeneration. Secondary vegetation removal is practiced in some forests of central Mexico as part of management. The objective of this work is to evaluate the effects of secondary vegetation removal and of slope orientation on some environmental variables and on shrub germination in an Abies religiosa forest. We carried out an experiment with 24 microsites differently orientated (South/North), and with/without secondary vegetation (Undisturbed and Perturbed): US, UN (undisturbed microsites, south and north facing) and PS, PN (perturbed microsites, south and north facing). The environmental variables measured in the microsites were light (through the Global Site Factor and the R/FR ratio), soil temperature and moisture. These data were analyzed with generalized linear models and variation coefficients. These statistical methods were also applied for germination analysis of Senecio angulifolius and Ageratina glabrata. Soil nitrogen and pH were also measured and analyzed with ANOVA; a canonical correspondence analysis (CCA) was carried out with the environmental and germination data.
Results/Conclusions
Values of GSF and R/FR showed the highest values in undisturbed and south facing microsites (US), because they receive the highest solar radiation and because were bigger than in perturbed (P) microsites. GSF values differed significantly due to the effect of disturbance (Z=-4.28, p=1.86e-05***) and slope orientation (0.007**) as well as the R/FR ratios (Z=-2.80, p=0.005**; Z=-2.090, p=0.001**), the widest VC value for this variable was found in the PS microsites [VC = 1.02], because of slope orientation and because of the absence of secondary vegetation. Slightly higher values of nitrogen and lower pH values were found in P microsites. Soil temperature was the highest in PS and PN however, no significant differences were found in these three variables. Soil moisture was significantly higher in undisturbed microsites (Z=-6.98, p=2.91e-12 ***) than in perturbed ones because secondary vegetation has a protective effect avoiding soil moisture loss. Germination percentages of both species were the highest in US (A. glabrata Z= -2.24, p=0.024; S. angulifolius Z=-1.356, p=0.0021**), because secondary species have high light and high soil moisture requirements which are fulfilled in south facing microsites where there is presence of secondary vegetation, this is why we don’t suggest its removal.