The sun is by far the most important source of energy for all organisms on Earth.  Light is the medium through which an organism receives information about its environment.  It contains information that tells a plant when to grow, when to flower, and when to pro-duce fruit.  For radiant energy to have a biological effect, it must be absorbed by a photoreceptor.  Plants have photosystems to pro-cess energy and information.  The sun emits a continuous spectrum of radiant energy, but more than half is lost as a result of refrac-tion and difraction in the upper atmosphere, and by reflection off of clouds and particles suspended in the air.  Only radiation with wave lengths between 300 and 1000 nm, the so-called “biological window,” influence life processes.

The order Odonata is widely distributed on the American continent.  These organisms are found in association with bodies of water where they reproduce.  Information on the specific wealth in odonates of our country is insufficient; there are states in which very little is known about them.  The state of Michoacán is one of these.  The purpose of this study was to make a listing of the adult odo-nates present in Northeast Michoacán.  A series of collections were done in streams of three areas of that part of the state:  Area 1, Enandio; Area II, Los Azufres Park; Area III, Cerro Garnica Park.  The organisms were collected from December 1988 to April 1991 and deposited in the entomology collection of the Zoology Laboratory of one of the campuses of the National University (UNAM), ENEP-1.  Thirty-one species belonging to six families and 17 genera were identified.  The most representative species was hetaerina vulnerata;  the most abundant family was Calopterygidae, and the most diverse was Coenagrionidae.  The largest specific wealth was found in the warmest area (Anadio).  Also, 18 new records were found in the locations mentioned.

The mangrove system along the coast of Quintana Roo was observed and five types of mangrove were defined:  composit mangro-ve, dwarf mangrove, shoreline mangrove, fringe mangrove and island mangrove.  The ecological importance of mangroves as a ha-bitat was analyzed.  They are places where many species feed and where birds and crocodiles nest.  They are hydraulic regulators and have a role in preventing floods.  They filter pollutants coming from the continent, and they are a buffer zone for waves and tides on the coastline.  Furthermore, many families depend economically on these ecosystems.

Drought is worldwide problem, and the study of the mechanisms plants use to deal with drought has produced a large quantity of in-formation at different levels and approaches.  In spite of the complexity of the responses, if one or more characteristics is to be measured or considered when studying the physiological state of a plant under conditions of stress, it is necessary to have a holistic perspective in order to know what is happening, and thus make better use of the information to disign strategies to select plant popu-lations that are resistant.

The health of young Pinus hartwegii trees was compared in two national parks:  Ajusco and Zoquiapan.  Although both are located near Mexico City, Ajusco National Park receives the flow of polluted air after it passes through the big city.  The variables related to vigor in both locations were screened to detect those that are more explicative of the conditions of forest health:  crown color, needle retention, tree tip condition, needle damage, shape of trunk, and dwarf mistletoe infection.  In both locations, the trees were of the same diameter, but the Zoquiapan trees were younger and taller than those of the Ajusco Park.  The means for Zoquiapan were age 7.9 years and height 3.75 m, while for Ajusco they were age,10.3 years, and height 2.25 m.  The health of the Zoquiapan forest was better than that of the Ajusco forest, because the trees of the former had more natural green foliage, longer needles, sharper tips, less damaged needles, and better trunk shape.

Characteristics of pine pitch canker disease are described.  The causal agent was Fusarium subglutinans (Deuteronmycotina: Mo-niliales).  The fungus was found in northern and central regions of Mexico:  Federal District and states of Durango, Hidalgo, Jalisco, Mexico, Michoacán, Morelos, Nuevo León, Puebla, Tamaulipas, Tlaxcala, and Verzcruz.  The range of hosts includes 19 species of pine.  Trees of different ages were affected by the disease; a great variability in symptoms was observed, from shoot wilting, with no resin flow, to cankers in stems, with heavy resin flow.  Spropdochia were found in Pinus douglasiana and P. radiata.  Pathogenicity tests were done;  15 strains were inoculated in 12 species of pine.  Also, the spread and development of the infection in inoculated pine seedlings were registered.  The results showed significant differences in (p00.05%) in pathogenicity.  The fungus faster in P. cembroides, P. montezurnae, P. gregii, P. pseudostrobus and P. patula than in P. ayacahuite, P. Ieiophylla, P. douglasiana, P. mi-choacana, P. halepensis, and P. pringlei.  The isolated strains from P. pseudostrobus, P. arizonica, P. discolor, and P. leiophylla were more pathogenic than any other strain.  Finally, the characteristics of the fungus are presented.

A review of available methods of cone and seed insect control is presented. Specific control options are given for 12 genera conside-red the most important for Mexico. The importance of forest seed production is discussed as a key factor in successful reforestation, ecological restoration and forest production. Also, the possibility of adopting control measures against this insect group is conside-red. The discussion in presented in the economic and technological context in which the establishments devoted to forest seed pro-duction in Mexico are immersed.

This research was carried out in a plantation belonging to Fábricas de Papel Tuxtepec (FAPATUX) to determine the variations in re-sin content in wood from Pinus caribaea var. hondurensis under two conditions (tapped and untapped trees).  Three different stem heights and on four different logging dates (September, November, February and April).  Also studied was how stem height, stem diameter and bark width influence resin content. The results showed that resin content is similar at 0.30 m and 1.30 m tree height, but less than at 3.70 m, with 2.92, 2.318, and 1.515%, respectively.  Trees tapped at 0.30 m and 1.30 m had statistically higher con-tents compared with untapped trees, exhibiting an average content of 2.677% and 1,862%, respectively.  In contrast, at 3.70 m, the-re was no significant difference in resin content between tapped and untapped trees.  In September and November, resin content was statistically similar, but higher than those reported in February and April, which were also similar.  Stem height and bark width had very little influence on resin content.

Traditionally, stimulating of pine resin production has been done with chemical stimulants. Today, these stimulants are prepared in paste form with concentrations of 40-60% and are used in all of the countries that apply the Method of Bark Spiking Resination. Initial research in the use of biostimulants began in the former USSR and German People’s Republic and introduced in the production pro-cess. Later, Cuba joins in the new alternative to increase resin yields. The experience in Cuba is based on the use of growth regula-tors as biostimulants. The most important results with the species Pinus caribaea Morelet, Pinus tropicalis Morelet, and Pinus cu-bensis Griseb.

An elementary profit-cost analysis for an agroforestry system is presented involving only two crops where, as usual, the goal is to maximize the profit function. That is, the producer must decide how much of each resource is to be dedicated to each of the crops to have the maximum profit within the constraints of the resources available.This analysis was motivated by recent research (Duarte 1992, Rodríguez 1991) in which optimization of a system is obtained invol-ving only one crop, contrary to the objective of establishing an agroforest system. The study of the problem in a simple framework shows the necessity of including at least one constraint, relative to the risk that comes with the obtained profit, and then avoid mono-culture where the risk is very great compared with other alternatives. The measure of risk used was the multiplicative inverse of the profit-cost ratio, which also allows the inference of some additional conclusions, such as the importance of estimates of profits and benefits to determine rational solutions, the differential role of the resource land relative to that of capital, and finally the valuation of forest plantations.

The evaluation of site quality and the determination of appropriate densities are very important topics in the management of forest stands.  In this study, site quality was classified using the Schumacher model in its anamorphic version, and densities were determi-ned using the Reineke Stand Density Index (IDRR) and Crown Competition Factor (CCF) at the Sitio Permanente de Experimenta-ción Forestal “Cielito Azul” located in San Miguel de Cruces, Durango, Mexico. The most important results showed that 61.12% of the total area is represented, in equal percentages, with site qualities for 23 and 26 m, followed by the site quality for 29 m with 16.67%, and finally the site quality for 19.68m. The best site qualities (32, 35 and 41 m) were found in only 8.34% of the area. IDRR was 2685 trees with a 25.4 quatratic diameter reference. CCF varied from 6916 trees (10 cm d.b.h.) to 1282 trees (30 cm d.b.h.).

A volume estimation system for Pinus cooperi was developed, using taper functions. These equations describe the stem shape.  By integrating a taper function, a volume equation is generated. Data from 35 stem analyses were used. Regression techniques implemented in SAS were worked to fit nine volume functions and ten taper functions.  The best volume equation was log(v) = -0.821609 + 0.980899 log (D2H).  The best taper equation was: d2 = D2(1.044093 - 2.832906 +7.624771 2-10.415754 3-4.569118 4) Integration of this equation yields:   which can be applied to predict total merchantable volume inside the bark to any stem height limit and also to predict a bole segment volume.  Tree volume inside bark for the species may be predicted by    which finally results in V = 0.3762987 (D2H).