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

Tropical montane cloud forests (TMCF) are under severe threat from deforestation, fragmentation and degradation. Several tree species are harvested and commercialized by local communities through unplanned selective logging. Lack of information regarding the growth rates of the most economically valuable timber species hampers the design of effective sustainable management schemes for TMCF. The objective of this study was to determine the diameter growth rates and evaluate the influence of tree size, crown class and neighbouring tree basal area on the growth of common and valuable TMCF timber species. Annual diameter growth was measured during two years in 60 trees (10 to 45 cm in diameter at breast height; dbh) each of Alnus acuminata, Liquidambar styraciflua and Quercus xalapensis, located in two unmanaged secondary TMCF sites in Veracruz, Mexico. High diameter growth rates (centimeter per year [cm yr-1]; mean ± SE) were recorded in the three species; the highest was recorded in A. acuminata (1.62 cm yr-1 ± 0.08 cm yr-1), followed by Q. xalapensis (0.91 cm yr-1 ± 0.07 cm yr-1) and L. styraciflua (0.71 cm yr-1 ± 0.08 cm yr-1). Diameter growth rate was inversely related to the basal area of the neighbouring trees, indicating a negative effect of competition in the three species. Dominant trees had higher growth rates than supressed trees in the three species. The high growth rates recorded in forests with no previous management and the negative effect of basal area of neighbouring trees support the potential for silvicultural management in secondary TMCF.

Silvicultural practices tend to simplify the composition and structural complexity of the forest. The purpose of this study was to assess the changes in forest structure, tree diversity and demographic dynamics of mixed-wood stands harvested by group selection (GS) and seed tree (ST) regeneration methods in the Sierra Juárez of Oaxaca, Mexico. In addition, an unharvested forest was included in the evaluation as a reference site (RF). Data for this study (base area, diameter, height, survival and recruitment) come from 29 permanent sampling plots of 1000 m2 established in the 2007-2012 period. The results revealed that the GS and ST demonstrated rapid growth, despite the high density of the operating areas. In both sites, a similar silvicultural criterion was applied, and this may have been the reason these sites showed no differences in forest structure, annual timber volume increment and species diversity or species richness. However, the GS forest showed features similar to ST, on a wider tree diameter distribution and a higher diversity index for tree species than the RF site. The results generated contribute to the understanding of the ecological processes of the pine-oak ecosystems and to implement the best silvicultural system. Development of intensive forest management that incorporates characteristics of mature forests are recommended as the best practice in terms of forest productivity and ecosystem conservation, in the Sierra Juárez of Oaxaca.

The objective of this study was to determine the effect of different tree covers on the productivity and quality of the pasture and on specific microclimatic variables in an Acacia caven-based silvopastoral system. A trial that included four tree-cover treatments (0%, 30% - 40%, 50% - 60% and over 70%) was established in an experimental set-up with complete randomized blocks and three repetitions. In addition to the productivity and quality of the pasture, probes were used for the continuous measurement of soil temperature and moisture at 15 cm depth, ambient temperature and relative humidity. The period of analysis included two prairie growth seasons. Three models were considered for the statistical analyzes: i) tree cover on pasture productivity; ii) tree cover on microclimatic variables; and iii) the prairie productivity, considering the microclimatic variables as covariables. The results indicate that in the second growing season, the highest productivity was achieved with the tree-less treatment (0% cover). No effect of tree cover on the quality of the prairie was detected, nor on the microclimatic variables in either period. The microclimatic variables that best explained the development of the prairie were the minimum relative humidity and the ambient temperature. After two growing seasons, it is not possible to determine which treatment generates the best conditions for the productivity of the pasture, so it is necessary to continue with the measurements.

Selecting where to establish forest plantations is crucial to maximize its probability of success. Multi-criteria decision analysis for land suitability accomplishes this purpose by matching ecological requirements of chosen species for planting against soil productive potential and climate conditions. This study describes a model developed under both a hierarchical analytical process framework and a multi-objective land allocation approach, in a GIS environment, to select optimal sites for establishing six pine species (Pinus engelmannii, P. leiophylla, P. arizonica, P. cembroides, P.chihuahuana and P. durangensis) for commercial purposes in Northern Mexico. The model considers climatic, edaphological and topographical criteria and subcriteria that affect the location of suitable areas to establish commercial forest plantations. Sub-criteria values were standardized, weighted and ordered by pairwise matrices considering their importance regarding to planting such tree species. Initially, the model quantified the suitability of the land to establish forest plantations. Then, such suitability results were optimized through a multiobjective procedure to identify the best species to plant in the area under four decision scenarios: harvesting age, wood quality, survival, and susceptibility to both pests and diseases. The results indicate that the municipality of Durango has the greatest number of optimal areas to establish forest plantations with the species analyzed.

The basic density of wood from 59 tree species was determined in order to estimate the weight of woody biomass from the volume of wood measured in forest inventories. Published information about wood properties of some of these species is scarce. The 59 species considered belong to the families Anacardiaceae, Burseraceae, Meliaceae, Rutaceae, Sapindaceae and Simaroubaceae, all of which are included in the order Sapindales. The basic density was determined in samples obtained in forest inventories performed in the last two decades in various regions of Brazil. Most of the species analyzed (68%) had light or semi-heavy wood (basic density between 0,51 and 0,80), although the density varied widely between species, ranging from 0,38 for Simarouba amara to 1,25 for Schinopsis lorentzii. A literature search revealed data on the basic density of the wood of three quarters of the species under study. According to this data, the wood considered in the present study is 21% more dense than wood from the same species growing in other regions. This study provides new information on wood of tree species about which very little was previously known. The analyzed Brazilian tree species in the order Sapindales were found to be important because of the high basic density of their wood. These trees thus contribute efficiently to biomass accumulation and to the corresponding carbon fixation.

The present research studies the slenderness`s answer to fractionated mineral fertilizer application in Pinus caribaea var caribaea Morelet y Golfari plantations on sandy loam soil. The fertilizer formula used was NPK (8-10-10). Seven treatments were established, differenced by fertilizer doses and application regime, alternate and continuous, and an additional witness treatment, without fertilizer. Measures of total height and normal diameter were taken, and the slenderness index was calculated for the 288 analyzed trees at 6 years, 15 years and 35 years of age. At 6 years of age, slenderness mean values were significantly higher with a single doses application of 300 g tree-1 of (NPK); at 35 years of age, the mean was statistically lower than 80 in those treatments with fertilizer doses of 600 g tree-1, 800 g tree-1 or 1000 g tree-1 respectively in alternate regime. These reached the lowest slenderness values. A linear relation between slenderness and diameter at 1,30 m was found in treatments with fertilization and a logarithmic one in the treatment without fertilization. A direct relationship between the proportion of trees with slenderness lower to 80 and the standing trees was found. Individuals with slenderness between 70 and 90 achieved higher wood volume.

The water transport in terrestrial vascular plants is passive and is determined by the transpiration or loss of water through the leaves. The cohesion-tension theory is the most accepted to explain this process, which is complemented by the Ohm's law analogy, which analyzes the flow of water as a catenary process. Resistance to water stress and cavitation is strongly associated with the anatomical characteristics of the xylem, the intervessel pits, and their membranes, the latter being altered depending on the chemical properties of the aqueous solution that flows through them. Based on these premises, this review addresses the phenomenon of ascent of water in terrestrial vascular plants and analyzes the concepts, theories, and methods most used in the study of hydraulic architecture. In addition, it points out the differences in xylem structure and water transport between dicots and monocots.

Oreomunnea mexicana(Stand.) J.F. Leroy is a relict species, threatened and a key species for cloud ecosystem functionof the Sierra Juárez, Oaxaca, the most extensive and best conserved in Mexico. This study includes a diagnostic on two critical stages of the process of population regeneration of O. mexicana. To this end, it analyzed the: 1) production, dispersion, viability and germination of seeds, 2) effect of predation on the growth and survival of the seedlings, and 3) effect of environmental variables (soil, canopy structure and solar radiation) on the regeneration of the species. The study was made from 2014 to 2015 in the cloud forest of Santiago Comaltepec, Oaxaca, Mexico, in two locations (San Bernardo and El Orquidiario). Differences in seed production were found between years and between locations, as well as low seed viability and a high percentage of seed parasitism. The establishment and growth of the seedlings are subject to find suitable microhabitats, since seedlings have specific illumination and soil requirements. The high edaphic specificity faced by the species could be a key factor for its fragmented and discontinuous distribution in Sierra Juárez. Further population regeneration studies are recommended to increase knowledge of the species and thereby achieve its conservation.

Although precise species-specific aboveground tree biomass equations are needed in the Dominican Republic to quantify potential carbon storage in the context of climate change and sustainable forest management, there has been a lack of available information concerning total aboveground biomass and/or carbon content for naturally occurring Pinus occidentalis trees. The objectives of the study were to develop species-specific allometric biomass models for P. occidentalis, as well as to assess variation in carbon concentration among stem plus bark, branches and foliage by means of chemical analyses. Predictor variables included diameter at breast height (DBH) and total tree height (H), alone and in combination. Model fitting methods employing linear and nonlinear regression techniques were used and evaluated based on goodness-of-fit criteria. Two competing biomass models produced similar goodness-of-fit statistics: model 4, fitted by the Weighted Non-linear Least Squares technique, , and model 6, fitted by modeling the variance component and applying the Maximum Likelihood method, . Average carbon concentration (%) was highest in foliage tissue (49.8%), followed by branches (46.37%) and, lastly, stem plus bark (45.95%). On average, each individual tree is storing 175 kg of total aboveground carbon. To our knowledge, this is the first account reporting carbon fraction for this tropical species. Calculated wood carbon fractions from the study can be easily incorporated into forest C accounting, and may reduce errors in forest C valuations, which nowadays are performed using global estimates published elsewhere.

The estimation and mapping of aboveground biomass over large areas can be done using the remote sensing tools. The objective of this study was to estimate the aboveground biomass of two types of tropical forest: semi-evergreen (SETF) and semi-deciduous tropical forest (SDTF) in the Yucatan Peninsula, Mexico, using metrics obtained from LiDAR (Light Detection and Ranging) data. Data from 365 plots of the National Forest and Soils Inventory of Mexico were used to calibrate aboveground biomass models using multiple linear regression and Random Forest. These models were used for mapping aboveground biomass along LiDAR strips. The transformed regression model explained the variance by 62% (RMSE = 41.44 Mg ha-1 for SETF & 36.60 Mg ha-1 for SDTF) for both types of vegetation. The models of Random Forest explained the variance by 57% (RMSE = 40.73 Mg ha-1) for SETF and only 52% (RMSE = 35.10 Mg ha-1) by SDTF. The mismatch between the field data and LiDAR data, as well as the error in the precision of the coordinates of the inventory plots, were recognized as factors that influenced on the results. Despite the above, the estimates obtained could serve as a basis to estimate the complete biomass inventory in the study area by incorporating spectral data derived from a remote sensor that covers the entire area.