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

Germination and seedlingemergence of four endangered oak speciesGermination and emergence of the endangered cloud forest oak species Quercus germana, Q. insignis, Q. sartorii and Q. xalapensis were observed under different light conditions (sun vs. shade) in a secondary forest fragment (SFF) and in a greenhouse (GRE). Seed weight variability was evaluated for each species and its relationship to germination and emergence determined. After 60 days, a total of 62.17% of the acorns had germinated and 37.79% had emerged in both experiments. Germination was highest in Q. sartorii (71.83% ± 2.09%), followed by Q. germana (66.33% ± 2.06%), Q. insignis (60.83% ± 2.34%) and Q. xalapensis (53.50% ± 2.32%). In the GRE, Q. insignis germination was higher under sun (62.00% ± 4.73%) than shade (48.00% ± 5.12%), whereas its emergence was the lowest (37.66% ± 3.46%) compared to other species in both light environments. In the SFF, germination and emergence only differed among species; Q. xalapensis germination was lowest (47.00% ± 3.11%) and Q. sartorii emergence was highest (58.66% ± 3.35%), compared to the other species. Acorn weight did not influence germination or emergence in any species. The implications of this study are discussed, along with recommended propagation techniques for growing oaks for forest restoration in disturbed areas.

Due to the fact that tree size can significantly influence community structure, and thus diversity, structural diversity indices which incorporate DBH and total tree height can be more accurate estimators than the classic diversity indices. The structural diversity of a tropical humid forest (THF) and a tropical sub-humid forest (TSF), in Tabasco, Mexico, was compared using eight structural indexes that estimate community basal area sorted by DBH and tree height classes. The species, DBH and total tree height of trees > 10 cm DBH were determined. The structural indices were statistically compared between the two communities. The TSF presented 27 species, 211 trees and 129 palms ha-1, a mean DBH of 28.0 cm and 9 trees > 20 m height. The THF presented 66 species and 591 trees ha-1, a mean DBH of 21.2 cm and 36 trees > 20 m height. The structural indices of the THF (2.76 – 6.737) were significantly higher than those of the TSF (2.345 – 4.978). The Gini indices of the THF (0.61 and 0.494) indicated that trees were more heterogeneous in size (diameter and height) than those of the TSF (0.583 and 0.419). The structural indices therefore evaluate species diversity and community structural diversity in a more complete way, with the THF presenting higher structural diversity than TSF, which suggests the value of their use within tree vegetation studies.

Mexico is the country with the highest number of Quercus species worldwide (157). The oaks have great ecological importance and economic potential. However, their seeds and nursery propagation have been scarcely studied. The aim of this study was to investigate the effect of nut size and color, as well as shade, on germination of Quercus deserticola. The experiment was installed in a controlled environment chamber (25 °C/20 °C, with a photoperiod of 10 h of light). The experimental factors were nut size (small and large), color (light brown and dark brown), and shade (with and without 40% shade). The experimental design was completely randomized blocks, with the blocks nested into the shade factor. An analysis of variance with a mixed procedure and a Tukey means comparison were conducted, with the variables germinative capacity and germinative energy and a logistic model was constructed to estimate the probability of germination. There was a significant effect of seed size (p = 0.0067), seed color (p < 0.0001) and shade (p = 0.0078) on germinative capacity. The highest germinative capacity (100%) was for large seeds of dark brown color and under shade. The germinative energy (number of days to reach 70% of the germinative capacity) was affected by seed color (p < 0.0001) and by the interaction seed size*color (p = 0.0267). The highest germinative energy (11.5 days) was for large and dark brown colored seed.

An analysis of the mechanisms of discoloration in oak wood during plain vacuum drying allowed us to identify three mechanisms of discoloration. These include degradation of hemicelluloses, oxidation of tannins and release of volatile organic components. We studied the alterations to the material by measuring color changes, determining the antioxidant potential and analyzing the surface using infrared spectroscopy. Three vacuum drying conditions were applied (46 °C, 61 °C and 70 °C at pressure levels of 6 kPa - 10 kPa (60 mBar - 100 mBar). Despite the difficulty of studying and establishing the role of the extractives in changes in wood color during vacuum drying, we found relationships between the drying temperature, antioxidant potential and C=O peak intensities in the infrared spectra. By the oxidation and hydrolysis reactions, certain chemical compounds are modified. In addition, the presence of water and air accelerates the formation of organic acids (acetic acid). These acids catalyze the hydrolysis of hemicelluloses. The increase in color saturation and brightness can be related to the thermal degradation of extractives (mainly the ellagitannins).

Interactions of climate and natural resources with environmental and social deterioration are analyzed in this study of an arid region of northern Mexico known as Galeana Valley. The story of the social development of the region was constructed through face-to-face interviews. The perceptions of farmers regarding vulnerability to climate change, water use and the possibility of adaptation were also analyzed. The main problems in the region arising from the analysis are drought and the depletion of hydrological resources, for which the aquifers are the only source of supply. The importance of direct sources of information and interaction with local stakeholders for creating diagnostics, aligning assistance and agendas of rural development is discussed.

The proper management of forest stands requieres knowledge about number, arrangement, and characteristics of seedtrees after the application of a reproduction method. In order to determine the number of seed-trees best suited in the seed-trees repopulation method in a Pinus arizonica Engelm. natural stand in Chihuahua state, the effect of five degrees of canopy closure (64.5, 119.5, 204.0, 233.0 y 345.0 m2 ha-1) on seed germination, and survival and growth of seedlings was evaluated at 6, 12 , 18 and 34 months after the application of final cut. Seed germination of the species was better in canopies of 64.50 m2 ha-1; however, in this condition high mortality occurred, specially inmediately after seed germination. Greater seedling growth was observed between seedling ages 6 and 12 months under wide canopy openings.

Pentachlorophenol (PCP) and its salt, sodium pentachlorophenate (NaPCP) are very persistent halogenated hydrocarbons with a wide spectrum of toxicity and which are used primarily to protect timber from fungi, bacteria and insects. PCP and NaPCP are chemicals with a high acute toxicity to human beings increased substantially by impurities such as c h l o r o d i b e z o d i o x i n s a n d chlorodibenzofurans. PCP has long term adverse effects, is mutagenic, causes alterations in immunological and endocrine systems; it increases susceptibility to infections and reproductive dysfunction. There are several studies on the adverse effects of these substances on human and ecosystems health caused by its persistence, bioaccumulation potential and the toxicity of the impurities. These works are the technical basis of the severe restrictions or even total ban status of PCP and its derivatives and residues in several countries. In Mexico, PCP is authorized for forest, urban and industrial applications as a wood preserver. PCP must be purchased and used only by or with the surveillance of a certified technician. There is a significant lack of information among people about the environmental and health risks from the misuse and inadequate disposal of PCP, NaPCP and its residues. The aim of this work is to diffuse the available technical information on this subject and recommend the application of the national and international legislative regulations on PCP use.

Wood anatomy of Quercus glabrescens Benth. and Q. potosina Trel., belonging to Leucobalanus subgenus ( white oaks), as well as that of Q. eduardii Trel., Q. ghiesbreghtii M. Martens & Galeotti and Q. xalapensis Humb. & Bonpl., belonging to Erythrobalanus subgenus (red oaks) is described from material collected in the municipality of Huayacocotla, Ver. The results obtained show differences in wood color, porosity characteristics, multiseriate ray sizes and in the type and abundance of extractives.

This paper presents the results of a study of the macroscopics and microscopic characteristics of the wood of Persea americana var. guatemalensis Mill ( Hass ). Samples were collected from commercial plantations.The study was motivated mainly by the situation prevailing around Mexican avocado production, and because this wood is considered to be underused. This study is part of a larger study on the technological characteristics of the wood of this species. From the fiber morphological relationships, an analysis is made about its characteristics as raw material for pulp and paper production. General information is included on the geographical distribution, taxonomy and reports on other studies and uses of this forest resource.

With the information presented in this paper, obtained from the technical literature, it is proved that shrinkage of wood can be explained partially from the lignin content. Temperate hardwood species, both from México and the United States undergo a greater shrinkage percentage than tropical hardwoods and softwoods from both countries. The three-dimensional stiffness of lignin, greater than that of the other chemical constituents of the cell wall, along with its low higroscopicity, restricts the movements due to changes in moisture content. Regression analyses to determine the influence of specific gravity and lignin content were performed, concluding that both have a marked importance. Specific gravity shows to be the most important variable, although the influence of lignin is also significant. It is remarked that it is necessary to carry out experimental studies on the effect of these variables on dimensional changes, along with that of other important variables, such as extractives and ray volume.