Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

In Mexico there are tree species, specifically, the group of conifers, which allow to analyze and reconstruct the climatic variations of the past of one or more geographical regions. The objective of this study was to determine the dendrochronological response potential of Abies guatemalensis Rehder. to climatic variability in Ixtlán de Juárez, Oaxaca. Earlywood, latewood and total ring chronologies of 206 years (1810-2015) were developed. The seasonal correlation analysis revealed a direct relationship between the residual RWI chronology with the winter-spring precipitation (r = 0.67, p < 0.01) and an indirect relationship with the maximum spring temperature (r = -0.42, p < 0.01) of the current year of growth. Using a linear regression model, the accumulated precipitation from February to April was reconstructed over the last 136 years (1880-2015), which explained 44% of the variability of the local meteorological records of the calibration period (1952-2010). The driest periods occurred in the 1880´s, 1900´s, 1940´s, 1970´s, 1980´s, 1990´s and 2000´s. The spectral analysis of the reconstruction showed quasi-cyclic periodicity of 2.2 years and 3.8 years, indicating an association with El Niño-Southern Oscillation. The sensitivity of the species to climatic variations reflected in the thickness of its growth rings, suggests that A. guatemalensis has potential for hydroclimatic reconstructions, which will allow to extend in time the instrumental records for broader analyses of fluctuations in the climate and its trends in this region of the country.

At the global scale, forest fires are a source of significant emissions of gases and particles to the atmosphere that disperse over a large area and can be transported over great distances at the continental scale. Among these emissions, there are greenhouse gases, which are released in large quantities into the atmosphere after a forest fire. In this work, an attempt has been made to estimate greenhouse gas (GHG) emissions from large forest fires in recent years in Catalonia, Spain. These estimates are based on the characterization and quantification of the biomass that makes up the pre-existing forest fuels in the burned areas, the assessment of fire severity and consumption rates, and the application of published emission factors. The results obtained indicate that percentages between 44,4% and 70,3% of pre-fire biomass were consumed, corresponding respectively to total equivalent carbon emissions between 15 013 t and 387 335 t. A Lagrangian model (Hybrid Single Particle Lagrangian Integrated Trajectory) was used in order to determine the dispersion ranges and trajectories of the smoke plumes. The smoke plumes from the fires reached large distances, mainly affecting the Mediterranean region and North of Africa.

According to future climate projections, many species will see their ranges reduced, mainly those that live in cold forests. The aim of the present study was to model the current distribution and climate change scenarios of the Pinus hartwegii Lindl subalpine forest for 2041-2060 in the Transverse Neovolcanic Belt. Pinus hartwegii Lindl records were obtained from the Global Biodiversity Information Facility (GBIF) and field. The 19 WorldClim bioclimatic variables for the present and future were downloaded from the CRNMCM5 and HADGEM2_ES Global Circulation Models with two radioactive forcings of 4.5 (CO2 constant pathways) and 8.5 (CO2 high pathways). The spatial autocorrelation of the variables was eliminated. The environmental variables and presence records were uploaded to the MaxEnt program, where 75% of the data was used to train the models and 25% to validate them. The parameters of the best model were transferred to generate future models. The models presented an excellent statistical fit (training and validation tests > 0.9) for both periods. The determining variables of both periods analyzed were mean annual temperature (BIO1) and altitude (DEM). Climate change scenarios predict an increase in average annual temperature between 0.7 °C and 2.1 °C and reductions between 11.7% and 26.9% in the subalpine niche of Pinus hartwegii Lindl. Nevado de Toluca and Pico de Orizaba are the most susceptible sites to climate change. On the other hand, Izta-Popo Park would present a 37.4% niche increase.

The scarce knowledge about the growth and development of the species of arid and semiarid zones in Mexico, has generated an over-use. Among the most important economically in Coahuila is the candelilla, of which the technical information available for decision-making in management is limited. Therefore, the objectives were: a) to group six municipalities based on the individual production of biomass evaluated in 10 natural populations of Euphorbia antisyphilitica Zucc. and, b) adjust allometric models to estimate the biomass of E. antisyphilitica in different growing conditions in the center and south of Coahuila. With an analysis of variance and the minimum significant difference, the municipalities were grouped; for each group, models were adjusted, using the ordinary least squares method. Three biomass production groups were obtained per individual (GI, GII and GIII). The models to estimate the total green biomass (kilogram per individual) for each group, resulted with an R2Ajus higher than 0.86, in the first two groups, and for GIII it was 0.64, the RMSE (root mean square error) was lower than 0.425 and the parameters of the models were significant (p < 0.05), in the four cases. In addition, the four selected models presented normality, homogeneity of variances and the nonexistence of collinearity between variables. The selected models are statistically reliable to estimate the biomass by individuals of each group considered in this study, so they can be a useful tool in the development of management plans for the use of candelilla.

Worldwide, most tree cover loss studies are focused on quantifying it by means of remote sensing techniques. These studies frequently omit land use and vegetation classes, thus, the information of loss occurring for each of the land use vegetation types that exists in a region is limited. In order to identify which plant communities have been most affected by the tree cover loss process in the period 2000 - 2016 within the Usumacinta basin, in this study, two sources of information were analyzed simultaneously, namely: the series II of land use and vegetation of the National Institute of Statistics and Geography of Mexico (Inegi) and the results from the evaluation of change in tree cover at the global scale made by Hansen et al. (2013). The results indicate that of the 347 317.68 ha of tree cover lost between 2000 and 2016 in the basin, 62% corresponds to three categories: the tropical rain forest (26%), one of the most biodiverse vegetation types in the country, secondary vegetation derived from tropical rain forest (19.1%) and the cultivated grassland (17%), a class strongly affected by anthropogenic activities. Most of the rain forest loss was concentrated on the medium part of the basin, while most of the grassland loss was located in the lower region. Conversely, the vegetation classes with less tree cover loss were also the least represented on the surface in the basin. The results derived from this work will serve to identify the most threatened systems and guide conservation actions in the region.

In Mexico, the deforested area is high and the percentages of plant survival in reforestation programs are low. One of the key factors to increase plant survival is a good seedling quality. For the plant production in forest nurseries of Mexico, two groups of substrates are basically used: one mostly with soil (in traditional nurseries) and other with an important proportion of peat moss (technified nurseries). The first alters the natural areas already disturbed and the second is expensive. This work aims to evaluate the seedling quality of Pinus greggii Engelm. ex Parl. produced in different sawdust-based growing media, with fertilization and inoculation with an ectomycorrhizal fungus. The plants were grown in a greenhouse and evaluated after 10 months. The seedling quality was evaluated through the use of indicators, and morphological and physiological indices. Also, the physical and chemical properties of the growing media used in the present study were analyzed. In general, the seedlings were graded as medium to high quality. The treatments that obtained good grades with the highest number of quality indicators corresponded mostly to those inoculated. The best treatment corresponded to one with 80% sawdust and 20% pine bark growing media, with 8 g of controlled-release fertilizer and 75 ppm of nitrogen. It is possible to produce quality Pinus greggii seedlings with growing media based on sawdust, fertilized and inoculated with mycorrhizae fungus.

This work aimed to evaluate if the current procedure to harvest forest floor litter is sustainable. For this purpose, the litter production in an oak forest under forest floor removal, at three condition levels, was evaluated: without forest floor removal (C1), with recent forest floor removal in the last two years (C2), and with forest floor removal occurred in a previous time longer than two years (C3). The mass of nutrients (N, P, K, Ca, Mg and S) was also measured in the biomass that returned to the forest floor through the litter fall. Litter traps of 0.5 m2 area were used and the litter bulk density and forest floor depth were measured. Litter production was higher in sites C2 and C3 [(9.36 ± 0.64; 10.04 ± 1.92) Mg ha-1 year-1, respectively], compared to the control site C1 [(6.74 ± 0.45) Mg ha-1 year-1). The mass of nutrients that returns to the forest floor was 40% higher in sites with forest floor removal. The results suggest that the removal of forest floor has a stimulating effect on litter production. However, even when there may be a process of stimulation in litter production, this result should be cautiously considered as the data showed that the time period for recurrent removals of forest floor, in a sustainable way, is about 14 years. This is, a span at least two and a half times greater than that used currently in oak forests. A sustainable scheme implies that the time between two removal dates is equal to the time required to form the organic layer retired.

Oak forests are important from an environmental point of view, since they have a significant function as a carbon storage. This study is based on a destructive sampling of 165 oak trees with the objective of developing allometric equations to estimate aboveground biomass of six oak species (Quercus rugosa, Q. obtusata, Q. sideroxyla, Q. coccolobifolia, Q. laurina y Q. candicans). Allometric equations as additive system were generated to estimate biomass by structural components (stem, branches and foliage), the of additivity property guaranteed total biomass estimations as well as a generalized model. To improve the predictive capacity of the equations, models that include variables of diameter at breast height, total height and wood density were fitted. The highest percentage of biomass was concentrated in tree stem with 60.6%, while in the branches and foliage a concentration of 36.1 and 3.28%, respectively. The developed equations explained more than 95% of the total tree biomass, and compared with equations developed in other regions for the same genus, showed lower percentual bias. Such equations could be used for the region, as well as in forests with similar structural and growth features to those oak communities in forests from Santa Rosa and Guanajuato mountain ranges.

Litterfall and its decomposition represents the main nutrient input in forest soils whereby organic matter is cycled, thus influencing the circulation of nutrients in ecosystems. Therefore, the aim of this study was to determine litterfall nutrient-input and deposition via fallen leaves. Litterfall was collected at three sites: 1) a pine-oak forest, 2) an ecotone in a transition zone between a pine-oak forest and a piedmont shrubland, and 3) a thorn scrub in the Tamaulipan thorn-scrub vegetation community. At each site, an experimental plot was selected to allocate ten litter canisters to collect litterfall. Total litterfall deposition was highest at the ecotone, followed by the thorn scrub and the pine-oak forest (hereupon, the pine-oak forest will be referred to as “pine forest” for simplicity) (706.0 g m-2 year-1, 495.6 g m-2 year-1, and 483.0 g m-2 year-1, respectively). Leaf litter abundance was greater than that of twigs, reproductive structures, or miscellaneous components (385.3 g m-2 year-1, 84.6 g m-2 year-1, 55.7 g m-2 year-1, and 35.8 g m-2 year-1, respectively). Total deposition of nutrients (mg m-2 year-1)varied as follows: Ca, from 3.7 (pine forest) to 13.5(thorn scrub); K, from 1.0 (pine forest) to 3.8 (ecotone); Mg, from 0.5 (pine forest) to 1.3 (ecotone); N, from 2.7 (pine forest) to 8.3 (ecotone); P, from 0.1 (pine forest) to 0.3 (ecotone); Cu, from 1.0 (pine forest) to 2.9 (ecotone); Fe, from 35.2 (pine forest) to 89.3 (ecotone); Mn, from 27.7 (pine forest) to 71.8 (ecotone), and Zn from 7.3 (thorn scrub) to 7.8 (ecotone). Litterfall and nutrient input was more abundant during the months of winter than at any other time of the year.

The physical and chemical characteristics of the substrates are important to obtain a nursery plant with adequate morphological characteristics. Three substrates of current use in forest nurseries were characterized: S1: moss peat, vermiculite and perlite; S2: composted bark, peat moss and sawdust and S3: pine sawdust, moss peat and composted bark, all in 3: 1: 1 vol proportion, to which 8 g L-1 of Osmocote® fertilizer of 8 - 9 months of release was added. They were used to produce Pinus greggii var. australis Donahue & Lopez. The porosity, pH, electrical conductivity and carbon/nitrogen ratio were evaluated before and after plant production, while granulometry, retention curves and water release only before production. The initial and final ranges of total porosity, aeration and water retention were 77% - 83%; 19% - 27% and 54% - 63%, respectively. In all substrates the aeration porosity decreased, and the water retention increased at the end. The readily available water varied from 19% to 30%, higher in S3. According to the granulometry, the largest proportion of particles was from 0.26 mm - 0.75 mm in diameter. The initial (4.8-5.3) and final (6.3-6.7) pH values are in the acid range. The initial EC was 0.9 dS - 1.7 dS, lower than the end one of 1.7 dS - 2.4 dS. The C/N ratio was different for the three substrates; S1 presented the lowest value (159), S2 with 537 and S3 the largest (613). The alternative substrates evaluated have suitable characteristics to be used in the production of forest plant and to replace the use of peat moss.