Fragmentation of habitats has been a collateral effect of agriculture and immoderate pruning that has had many adverse effects in plant populations, which remain as relics in those spots or virtual islands where they may become extinct.The biogeography theory of islands explains, from an ecological perspective, the number of species present in islands and similar habitats (surrounded by environments hostile to the species). According to this theory, the number of species present in an island is determined by the balance that is established between the rate of immigration and the rate of extinction, which is, in turn, defined by the island’s size and its distance from the continent. These fundaments have practical application in the design of Protected Areas and Biological Reserves.

The vegetation types of the Las Cañadas subregion and contiguous areas to the E-NW and W-SW of the Lacandona region (Chiapas, Mexico) are described and a map showing their distribution is presented. Some brief comments on the present and potential uses of forest resources are included. From the viewpoint of vegetation, this is one of the most diverse areas in the country.

The purpose of this work was determine and recognise the main tree communities and their floristic composition on the Sierra de Álvarez, San Luis Potosí. Through preliminary distances traveled and systematic sampling on field, information of floristic composition, species dominance and similarity index were obtained, which it made comparison among the determinated communities. These were nine oak forests which were clustered in four different kinds (humid, subhumid, on ravine, and dry), according to species dominance and environmental physical characteristics. Differences in dominant physiognomically species were found but also some resemblance in species composition, which coincided with data of similarity. These showed scarce smilarity between the Quercus grisea forest and the majority other oak forests analized, provided that showed grater similarities among themselves.

Crazy squash (Cucurbita foetidissima) is a wild plant which grows in places considered improductive. It supports high temperatures, it is very resistant to pests, and it has many possibilities as a source of food. The root, which grows rapidly in length and diameter, can be consumed by livestock and even humans. Its leaves and seeds have a high protein content, and the seeds are also rich in oil. These characteristics give it potential as a food, forage, or industrial crop in semiarid zones.

With the purpose of determining the magnitude and pattern of individual variation in a natural population of Pinus radiata var. cedrosensis, 17 morphological and anatomical variables of needles, cones, and seeds were studied in 32 Pinus radiata trees from Cedros Island, Baja California. Central trend and dispersion measures were obtained, and an analysis of variance was done for each of the variables. All of the variables studied had a highly significant variance (p<0.01), except for the number of needles per fascicle, which was constant (2 per fascicle). The greatest portion of total phenotypic variation occurred between trees. The number of stomatal rows had a relatively high value for the error source. According to the results, Pinus radiata var. cedrosensis showed a high degree of intraspecific variation even when the natural distribution pattern was restricted. 

Following the fundaments of chemistry of the analytical method of the Weende system, or proximal analysis, this study aimed to determine the nutritional content of the seeds of Pinus maximartinezii Rzdeowski. The analysis was done in the Nutrition Laboratory of the Department of Animal Science at the University of Chapingo. The results showed that the seeds are a high-protein food, containing 48.2% protein as lean matter, and a high-energy food, with 36.4% fat. This is comparable only with soybean paste. Also, because of its low moisture content, it is easy to store.

The biology of the peppertree psyllid (Calophya rubra Blanchard) is described. The studies were conducted in the field and laboratory in Chapingo, State of Mexico. Life cycles were followed in two time periods. The first was from September to October, 1997; at  that time, the life cycle required an average of 48 days to be completed. The second was from January to March, 1998; an average of 68 days was required to complete the cycle. The average oviposition was 50 eggs per female (range, 25-110). Measurements of  length and width of bodies of 523 exuvies and nymphs showed that five nymphal instars occur. Average length for nymphal instars N1 to N5 were, respectively, 0.23, 0.34, 0.50, 0.68, and 1.07 mm, while the average width for the same instars (N1 to N5) were, respectively, 0.17, 0.28, 0.40, 0.58, and 0.99 mm. Length and width measurements were analyzed with a χ2 test and principal component analysis. Both methods ratified the presence of five nymphal instars. Natural enemies of the psyllid were also studied. An outstanding new species of parasitoid, Tamarixia n. sp. (Hymenoptera: Eulophidae) was found. This is possibly an important regulator 

In this study, charts of five tree associations in the El Tecolote watershed, Durango, Mexico, were made. Two methods were used. The first was based on Landsat Thematic Mapper digital data and classified with a criterion of generalized squared distance (control classification). The second method used topographic information of aspect and topographic position in combination with Landsat TM data, using Bayes’ theorem (combined classification) through relationships of probability. The control classification had a mapping  accuracy of 65.6% and a combined classification of 82.42%. There were significant differences between the two methods employed.

This work was carried out to develop a quantified land suitability procedure using a geographical information system (GIS GRASS4.0) of zone 14 of the UTM covering the state of Guerrero, Mexico. This procedure was based on the main quality of land degradation risk by water erosion that terrain is exposed to because of the lack of plant cover. Risk of erosion was calculated using the Wischmeier Universal Soil Loss Equation, which considers rain erosivity, soil erodibility and relief effect factor, which includes  steepness and slope length. The evaluation indicates the feasibility of using forest zones under the criteria of conservation, restoration, and wood production reas defined in Mexican Forest Legislation. The digital cartographic units obtained represent provisional  classes of suitability for groups of vegetation and land use evaluated mainly on the basis of maximum risk of water erosion.

Sustainability is concerned with maintaining the productive capacity of a system for a foreseeable future. It is thus necessary to consider the construction of measurements that appropriately assess the sustainability of a given silvicultural strategy since these measurements are lacking. The approach used in this work does not assure the perpetuity of the production of a forest system, but  it guarantees detection beforehand of its possible degradation or destruction so that it can be maintained as a system that generated goods. The study is important considering that there is much uncertainty about the results that man-made decisions will have on the  use of a forest, inside and outside the system. The components involved in the measures were supported by ideas generally used in silviculture, economics and statistics. Basically, two alternatives, with a few modalities within each, are analyzed.

The effect of chemical modification on sorption and creep behavior of wood was studied. Small blocks of Sitka spruce (Picea stichensis Carr.) were chemically modified with a molar solution of n-butyl isocyanate (n-BuNCO) in the presence of refluxing pyridine and compared with blocks treated with a 25% solution of polyethylene glycol 3350 (PEG). Untreated control blocks were also used. Swelling, shrinkage and creep behavior of wood in the radial direction was measured on blocks with similar degrees of bulking and using a linear variable differential transducer. Anti-swelling and anti-creep efficiencies were also calculated with respect to untreated controls. Creep behavior was carried out at 20ºC and 90% relative humidity for 24 hours, applying 34% of the máximum crushing strength. Dimensional changes were made by changing the relative humidity from 30% to 90% and then from 90% to 30% at 20ºC for both conditions. The anti-swelling efficiency values were 67% and 53% for blocks treated with n-BuNCO and PEG, respectively. However, during a cycle of radial swelling and shrinkage, the change in dimensions was 41% for n-BuNCO-treated blocks and 31% higher for PEG-treated blocks than for the control blocks. The creep level of blocks treated with n-BuNCO was about 42.4% lower than that of untreated control blocks, while it was 69.3% higher for blocks treated with PEG.

This research was carried out to determine the efficiency of six anti-sapstain chemicals that are sold in Mexico to combat Cladosporium sp sapstain fungi. Pinus hartwegii was used as the wood substrata. Four of these products, Oxmotox™, Pentatox™, Fungitox™, and Biotox™, are made from sodium-pentachlorophenate. One of them is a mixture of boric acid and borax, and the sixth one, Busan 1009, is made of methylene (bis) tiocyanate. The minimum effective concentrations needed to prevent sapstaining for a four-week exposure of the chemicals was estimated to be 3.09% Osmotox, 3.98% Pentatox, 2.45% Fungitox, and 2.57% Biotox. For the borate mixture, the results were not positive, since a strong sapstain occurred, and the concentration required was 141.25%. In contrast, no sapstain occured with methylene (bis) tiocyanate, even with the smallest tested concentration; it is estimated that the concentration required is less than 0.25%.