This  study describes  the  vegetation  found  in the  Lacandona tropical  forest.   The typical associations of the  Lacandona forest  are evergreen rain forest, semi-evergreen rain forest, deciduous  lowland rain forest, pine-oak forest, riparian vegetation. ·and succession communities (acahuales).   The indigenous management methods are described, including wildlife hunting, collection of "camedora" or xhate"  palm, handcrafts and logging of fine tropical woods for household use.  The current state of local wildlife and the number of endangered species are also described, based on the existing forest inventory and wildlife studies.  Lastly, the study concludes that shifting agriculture, extensive cattle-raising, and human settlements have all affected the conservation and sustainable development of the Lacandona tropical forest.

Odonate nayades are aquatic insects that have important functions in the bodies of water where they inhabit.  There is scarce knowledge of the physical and chemical characteristics of their habitat.  Determining these characteristics is precisely the objective of this study.  Nayades were collected from streams located in northwestern Michoacán, Mexico.  The species found are reported together with the physical and chemical characteristics of the collection sites.   The results indicate that Lauragaster  diadema  and  Oplonaeschna armata  are the  species that are the most tolerant within the parameters  studied, and thus they are the species  that are found in greatest abundance in this area.

With the main objective of analyzing the external morphological variability of oaks, information is presented with an emphasis on Mexican species.  The most common morphological characteristics used in describing and typifying the species is discussed to high­ light their variability.   Some of the species are mentioned as examples.  This has had much influence in the taxonomic complexity of the genus and the large number of synonyms of many of the known species.  Also included is a list of species of Quercus by subgenus and series.  The list includes the most exact number of those existing in Mexico.  The conclusions discuss the importance of external morphological variability of Mexican oaks in causing confusion and lack of understanding, as well as the perspectives for re­ search in the topic in relation to ecology and plant geography of Quercus in the this country.

This paper is a contribution to the technological knowledge of Quercus insignis wood, in terms of its anatomy, quality indexes of pa­ per pulp, basic density, shrinkage, welling, Janka hardness, static bending stress, perpendicular compression, shear and toughness of Quercus insignis wood.  The results indicate that the wood of Quercus insignis can be classified as heavy, very shrinkable, hard, and highly elastic, with good impact absorption.  Based on the anatomic, physical and mechanical characteristics. it is suggested that the wood  be  used for floors, packing boxes, pallets, tool handles and railroad ties. Its fibers are considered short and semirigid for paper pulp.

A provenance/progeny test of Pinus greggii Engelm. was established in Patoltecoya, Puebla, in August 1994, to evaluate the level of its intraspecific  variation  in growth  and adaptive traits.   In this field test, five half-sib families of 12 provenances were included in a split-plot experimental design with five replications.Thirty-three months after planting, a significant variation (p≤0.001) was found both between and within provenances in height and diameter growth, as well as in number and average length of growth cycles. Southern provenances (Zimapán and Molango, Hidalgo, and El Madroño, Querétaro) had larger diameters and were taller than the northern provenances (Las Placetas, Nuevo León, Los Lirios, Coahuila, and San Juan, Coahuila). Differences in height between southern and northern provenances were due to differences in both number and average length of growth cycles. Family-mean heritability values were relatively high {h2>=.50) for all growth traits evaluated, except number of growth cycles, which  had a heritability of 0.35. individual-tree heritability for number of growth   cycles was  also  much lower  (h²=0.15)  than for the other traits (h2>0.30).   When inter- and  intra-population  variation  for  number  and length of stem growth  units for one of the growth  cycles  in 1997 was  evaluated  in a sample of populations and families, significant  differences were found for both components at the population level, but not at the family level.  Path analysis showed, however, that the number of  growth units has greater influence on length of  growth cycles than the average length of growth  units.  Therefore, number of growth units may be used in a breeding program.

This study was done to assess cultural practices done to increase seedling quality of Pinus cembroides Zucc. grown in a greenhouse at Montecillo, Mexico, and this species' affinity with a group of mycorrhizal fungi (rhizospheric soil), collected from a natural forest of pinion.   Six treatments were  applied  as a result of the interaction between two essential variables:  mycorrhiza (inoculated and no inoculated seedlings) and aerial  pruning (O,  25 and 50%), in greenhouse-grown  seedlings  in containers (156 cm   inoculation was carried out four  months after germination with  a mixture composed  of substrate  and rhizospheric soil.  During transplanting, dry rhizospheric soil was p!aced in contact with the root system.  Five samplings were done, one per month, to evaluate morphological and physiological  variables.   In addition, variables such as quality index and transpiration efficiency were obtained.   Data were analyzed with  ANOVA (P≤0.0001) and a test of means.   The results of the six different treatments obtained from the mycorrhiza-pruning interaction showed that  inoculated, 25%  pruned  seedlings  of Pinus  cembroides  Zucc.  produced  plants with  higher  quality  in terms  of morphology and physiology.   Three species of mycorrhizal fungi were obtained from the inoculum collection site: Clitocybe, Inocybe and Leucopaxillus.

Because there are no studies that analyze the dynamics of land use in the rural areas of Mexico, this research created a methodol­ogy to determine the trends and forecasts in land use and population growth.  Two communities located m the Texcoco River Basin were used as case studies. The variables analyzed were urban land use, agricultural  land use, land used for grazing  livestock and forest land.  Aerial photographs with a scale of 1:20000 taken in 1970, 1983, 1989, and 1995 were used.  This data was used in con­ junction with interviews with farmers.  The main land uses were found to have changed in scale over time. Influenced by population growth and introduction of new technology.

Performance was analyzed over time of a relationship of areas in eight species of secondary vegetation in three permanent silviculture research sites, in which the slash-and-burn system was used, located in the experimental station "lng. Eduardo Sangri Serrano," Escarcega, Campeche, Mexico.  Nine different ages were included in the study, as well as the inverse relationship between area  (A_r) of the cylinder's surface formed by the diameter and the height of the  crown and the smallest area (A_m) possible from the  cylinder that has the same volume as that estimated with the original variables of the crown.  That is, the behavior of A_mlA_r1, is studied and is referred to as efficiency.The performance of the relationship as a function of time was examined using Schumacher’s empirical model of growth.  Solving far age in the model and with the mean values of the measurements of the relationship of the species studied, for a minimum acceptable efficiency (EMA) of 0.97, the ages at which this value is reached for each species were calculated.  These ages coincide with the reduction of the mean annual increase in diameter.

Some forest  management procedures  currently used in Mexico are focused on forest cultivation or silviculture.  Since many forests are still old growth, large timber volumes have to be removed in order for the forest mass to be renewed.   In the first cut, large volumes are available.  However, for successive cuttings small volumes of timer are available compared to previous cuttings.  This situation is not opportunely foreseen because management programs do not make projections of the future state of the forest. This paper emphasizes the need to consider mainly growth as a tool to achieve more efficient forest management.

Little research has been done in Mexico on the dynamics of land use in rural areas.   Because of this we have developed a work methodology, which enables us to study changes and tendencies in land use and population growth.  Aerial photographs with a scale of 1:20000 taken in 1970, 1983, 1989, and 1995 were used to study land use in two communities in the Texcoco River Basin.  The variables analyzed were urban land use, agricultural land use, land used for livestock and land used for forestry.   This information was complemented by interviews with farmers.  The main land uses were found to have changed over time.  These uses also changed in scale.  The changes were determined by population growth, the quality of social services and the introduction of new technology.