Little is known about the species of Quercus in Mexico, due to its wide distribution, high intraspecific morphological variability and its capacity to form hybrids, which makes taxonomy of the genus difficult. The objective of the present study was to contribute to knowledge on foliar morphological variation of Q. laeta, a widely distributed species in Los Mármoles National Park (PNM), the secondlargest natural protected area in the state of Hidalgo. Seventeen morphological characteristics were measured in 470 leaves collected from the lower halves of the canopies of 47 trees. All characteristics examined showed a normal distribution; a nested analysis of variance showed that the only significant morphological differences in Q. laeta leaves between sites were diameter of the midvein in the central and basal portion of the leaf and petiole diameter at the base of the leaf. At the level of individuals, morphological variation was significant in 94 % of the characteristics analyzed. Discriminant analysis showed that the characters that differed significantly among sites were maximum width of the leaf, distance between apical and basal sutures, distance between apical and basal lobules, leaf length, and petiole diameter. Some of the foliar morphological characteristics analyzed can be considered specific to Q. laeta.

Knowledge of plant elemental composition is useful to know their nutritional needs and the kind of litter created around them. Plants can to form silicon phytolites, which are useful in paleontology and archaeology. Plants were collected from central-occident of Mexico, its elemental composition were analyzed by Scanning Electron Microscope equipped with an Energy Dispersive X-ray microanalyzer SEM-EDS. Semi-parasitic plants (Photosynthetic plants than take nutriments from the host plant) accumulated high quantities of potassium and chloride ions to use as osmolites. Tillandsia recurvata, which is epiphyte, accumulates high quantities of Silicon, as well as, Cyperus sp., this one reported as Silicon accumulator. Tagetes micrantha that is used in Mexican food could contribute with mineral nutrients like potassium and magnesium.

A set of calculation procedures for estimating the three parameters of the Weibull 3P probability density function was generated, including the location parameter. The optimal parameters of the Weibull 3P probability density function for modeling the diameters at breast height in different times at different densities of Pinus taeda plantations calculated by the generated procedures were evaluated. Yearly, during eight years, six plots for each of the five plantation densities were measured. Weibull 3P parameters were estimated by four alternative methods: the maximum likelihood, the moments, the percentiles and the hybrid. The optimization procedures looked for minimizing not only the error index but also the Kolmogorov-Smirnov, Anderson-Darling, Kuiper, Cramer-Von Mises and Watson goodness-of-fit statistics. The main findings of this research were four. First, the parameter estimation method and the plantation age affect the location parameter value. Second, 45% of the calculated location parameter values were negative. In these cases, a highly significant linear relationship was found between location, scale and shape parameters. Then, the effect of a negative location parameter value was compensated by the other parameter values. Third, the percentiles and the maximum verisimilitude methods produced the smallest and largest location parameter values, respectively. Fourth, the percentiles and moments parameter estimation methods had the best adjustment accuracy. Anderson-Darling goodness-of-fit test was associated with the moments’ method and the rest of goodness-offit tests was associated with the percentiles method for better adjustment accuracy.

The present study took place on a mine jal from Pachuca, Hidalgo. Such jal had the physical and chemical characterization of mining waste, the contents of potentially toxic elements (cadmium, copper, manganese, nickel, plumb, and zinc) and the vegetation parameters. Nine sampling sites were defined in the jal. The physical and chemical characteristics and the content of potentially toxic elements were determined in compound samples. The method of squares was used in order to identify plant species and in plant tissue samples of each species, the content of potentially toxic elements was determined. The mining wastes showed a franc-sandy texture and with a pH moderately alkaline and a low content of organic matter. The Zn (45 mg·kg-1) and the Pb (14 mg·kg-1) were the elements with a higher concentration. Twenty-five species of plants were identified and from these, Haplopappus venetus was the dominant species. Solanum corymbosum showed the highest accumulation of Cu (6 mg·kg-1) Brickelia veronicifolia of Pb (5 mg·kg-1) and Zn (20 mg·kg-1), Atriplex suberecta of Cd (1 mg·kg-1), Cynodon dactylon of Mn (69 mg·kg-1) and Bouteloua curtipendula of Ni (4 mg·kg-1). It is recommended to use these species in the rehabilitation of mining jales.

Investigations about the submontane scrub ecosystem are insufficient and the richness and diversity of its natural resources are still poorly known. This study was conducted in seven areas of the Sierra Madre Oriental (SMO) with a history of selective removal of woody species, in order to assess the characterization of the vertical and horizontal submontane scrub ecosystem, and determine diversity αα. Sampling was carried out in 73 sites of 100 m2 in an altitudinal range of 600-800 m, in which all woody species were assessed by obtaining dasometric information height (h), diameter (d0.10m) and cover (NS, EO). The ecological parameters of abundance (Ar), dominance (Dr), frequency (Fr), importance value index (IVI) were determined, as well as, the Shannon (H’) and Margalef (Da) indices. A total 23 families distributed in 52 species and 42 genera were found, Fabaceae being represented with 15 species. The most representative species were Acacia rigidula, Acacia berlandieri and Bernardia myricaefolia. A diversity index H’= 3, 0, indicates that is submontane scrub is very diverse in relation to other types of ecosystems of northeastern Mexico.

The Corixidae family is analyzed at La Goleta reservoir, Estado de México and their relationships with some environmental parameters during May 2007 and April 2008, locating three littoral stations of sampling, taking in each one, original and five replica at intervals of one hour. Were determined: depth, transparency, temperature, oxygen, pH, conductivity, hardness and alkalinity. The corixids were captured with network of spoon. Were evaluated diversity, maximum diversity, evenness and dissimilarity. Four corixids species were registered in 2007: Trichocorixella mexicana, Graptocorixa abdominalis, Krizousacorixa femorata and Trichocorixa parvula, being the one last a new registry for the zone. In 2008 two species only were registered: T. mexicana and G. adominalis. The greater diversity values and maximum diversity appeared in 2007 (0.7108 and 1.9997, respectively); whereas evenness was smaller in this period (0.3354). The second period registered smaller values of diversity and maximum diversity (0.6025 and 0.9998, respectively) and evenness was greater (0.6026). The dissimilarity analysis showed differences in both periods due to the fluctuations in the abundance of this familiy. We concluded that the conditions in the reservoir have been modified remarkably making descend the diversity values and the abundance from these organisms.

One of the most controversial technologies is the genetic engineering or biotechnology. Those in favour of the genetic manipulation think that most of the serious problems affecting our society, from the cancer and AIDS to the genetic malformations, and from the hunger of the Third World to the contamination problems, they can be surpassed with this technology: the absolute possibility to design any alive being in agreement with the industry and consumerism needs. Within some years, practically all crops could genetically be manipulated and the geneticists and companies will be the owners of the genetic resource. The opposite opinion considers that the plants will be designed by computer according to the interests of the most powerful companies. The real impact on the ecosystems is unpredictable. The biotechnology seems to forget that plant species are fruit of a slow and prolonged interaction to each other and with a load of environmental factors. In nature, any individual change happens in relation to the set of the ecosystem; while the biotechnology implies an abrupt and dangerous interference in assumption “benefit” of a single species. A sample is constituted by the different classes of wheat existing in Ethiopia, country of which is native this cereal. In nature, the introduction of genetically manipulated species could cause the destruction of many varieties, in genetic erosion.

This study describes the design and field implementation of a silvopastoril system on a hillside using the Nezahualcóyotl method to establish the tree component made of: Swietenia macrophylla King (Big leaf mahogany, Brazilian mahogany), Tabebuia rosea (Bertol) DC. (Rosy trumpet tree), Cedrela odorata L. (Spanish cedar, Mexican cedar). The field was in the region of Huatusco, on this field five leveled mounds-trenches were done and on the top of the mounds tress were planted every 4 m, tress were previously grown for two months in a nursery. After four months on the field survival rate was not different (˜=0.05) among species and higher than 80 %. Animal component of the system was not field implemented it was described and planned only, this component was made of a Brachiaria brizantha pasture and stocker cattle. Pasture establishment was design to be done along with growing maize with a share-cropper. Main costs for the establishment of a silvopastoril system using the Nezahualcóyotrl method were identified and the estimated total was $ 44,347.00 for each 1/3 of a ha. It was concluded that the Nezahualcóyotl method is an option in the establishment of the tree component of a silvopastoril system on hillsides.

In this work the qualitative and quantitative results of the thermal pyrolysis of Eucalyptus Saligna Smith is presented, to different heights of the commercial wooden log. The wood was collected from Pinar del Río, Cuba. The need to use this wood like energy source in the region led to the research at laboratory scale. The used trees were 20 and 22 years old, from which 20 cm disks were cut at 25; 55 and 85 % height of the log, milled to chips and air dried. The chemical composition was determined and was carried out the previous analysis of the samples, as well as the thermal decomposition in micro scale. The study of products from the pyrolysis (coal and tar), it was made in a reactor of fixed channel. The caloric value of the biomass and its charcoal was determined. The influence of the height of the log in the product yields from the pyrolysis was studied. As significant differences was observed as for the chemical composition of the studied wood: cellulose, hemicelulose and lignine, being observed an apparent increase of the lignine percentage with the height of the tree. The previous analysis belongs together with the chemical composition of the studied biomass. A small decrease was observed in the yield of the coal and of the percentage of tars with the height of the tree, this belongs together with the variation of the chemical composition according to the height of the tree. The biggest yield of coal and caloric value was achieved at the lowest height of the tree. The contribution to gas goes increasing with the height.

This research set as objective to quantify carbon stocks in aerial biomass of temperate communities of northern Durango, Mexico. The carbon concentration of several biomass components of 25 trees were quantified in the laboratory. Dasometric data of inventoried trees, together with alometric equations to estimate biomass and carbon concentrations were employed to estimate carbon expansion factors using stand volume. The carbon expansion factors were modeled as a function of the dasometric features of trees at the stand scale and the normal probabilistic density function was fitted to obtain information on the skewness of this parameter. The results showed that the carbon expansion factors are dependent of the mean tree height and they distributed normally. This information is important for the development of environmental management plans of forest ecosystems and will allow the broader use of forest inventory data.