A preliminary simulation model created to explain the dynamics and relative composition of ecological tree groups is described. The simulations indicated differences in structure and composition between a managed and a non-managed forest. Management aimed to favor prototypes 1 and 2 were coherent, but was unfavorable for Prototype 3, which was absent. In some intermediate stages management of prototype 2 and 3 showed greater structural similarity to tropical forests with little perturbation. The search for sustained incorporation and higher rates of survival of prototype 2 again promoted the differences that were unfavorable for prototype 3.

This work consists on the analysis of germinatión and evaluatión of pregerminative treatments (scarification and depth seeding methods)on seeds of Pinus arizonica and Pinus durangensis collected from the northwest region of the Méxican State of Durango. On the Pinus arizonica, the seeds submerged in oxygenated water at 3 % for 12 hours, to, cause the greater germination of seeds. (96.7 %), meantime of the Pinus durangensis the greater germinataion (85.5 %) of obtain without scarification the seeds. For both species, seeds submerged in boiling water of 30 seconds presented the least germination rate. For both species, the greatest germination rate was obtained at depths of 1.0 and 1.5 cm, with a germination rate of 97 and 89 % in Pinus arizonica and Pinus durangensis, respectively. So the lowest germination rate was obtained at a depth of 3.0 cm.

Two independent trials were established to increase germination capacity of Gmelina arborea seeds. In the first trial, the effect of seed size (small, medium, and large) and two periods of seed imbibition (1 and 6 days) on seed germination were evaluated. In the second trial, several pre-germination treatments (imbibition in different water solutions during a 12-hours period, were also evaluated. In both trials, seeds were placed in a germination chamber at 30 °C during a 30-day period. Analysis of variance showed that the imbibition period did not affect (P<0.05) the rate and percentage of seed germination; however, seed size had a significant effect (P<0.05) on these variables. Large seeds had higher rate and percentage of seed germination than the two other seed sizes. In the second trial, pre-germination treatments did not affect the rate and percentage of seed germination, but they had a significant effect on the rate and total amount of seedlings emerged. Pre-germination treatments also affected the number of plants per seed, the time required to start germination (T10), and germination vigor (T50). Use of a solution with 3 % hidrogen peroxide accelerated seed germination and increased germination vigor of seed.

Propagation of superior genotypes of Eucalyptus pellita is a promising alternative for afforestation and breeding programs. This paper describes the technology for the clonal propagation of selected trees of E. pellita to obtain seedlings of high quality for planting directly in the field or for establishing seed orchards. Young shoots from selected trees were cut as uninodal stumps and disinfected in a sodium hypochloride solution. Survival of aseptically established node segments was 38.3 %. The segments were transferred to culture media containing auxins and cytokinins. Eight treatments were designed to study the effect of the hormones and their interaction. An average of 25.4 small stems per cultured bud was obtained every 30 days during the first three subcultures. The multiplication rate increased with the number of subcultures, and large masses of buds were observed. For root induction, the liquid media tested were supplemented with IBA and IAA. The treatment in which both auxins were combined at 2 mg⋅L-1 provided 85 % rooted explants with a good connection between the vascular system of the stem and the root. The acclimatization step developed under controlled conditions in a nursery with 80 % survival at 20 days.

Under greenhouse and laboratory conditions, the symptoms of the canker caused by the fungus Cytospora were studied. The hosts Populus deltoids and Salix babylonica were used. Both rooted cuttings and small pieces of branches (rods) of both hosts were inoculated with fungi obtained from cultures. Under greenhouse conditions, the rooted cuttings showed the following symptoms and signs. On Day 7, an ellipsoidal lesion was evident; the bark was sunken, wrinkly, soft and watery, and the color changed from green to dark brown. Fourteen days later, black pycnidia measuring between 0.5 and 1.5 mm in diameter appeared on the bark. On Day 21, conidia exuded from pycnidia, and long, slender orange threads formed by the conidia protruded. The conidia were hyaline, 1-celled and allantoid, 1 to 1.5 ìm wide and 3.5 to 5 ìm long. Small rods kept in the laboratory (temperature 28±1 °C in complete darkness) showed symptoms and signs very similar to those observed in the rooted cuttings; only small variations were detected in the time it took for signs of the disease to appear. Pycnidia and conidia threndhills were evident 10 and 14 days after inoculation, respectively. The fungus Cytospora chrysosperma Pers. ex. Fr. (sexual state Valsa sordida Nit.) was identified as the causal agent of the disease.

This paper analizes the recent problematic related with rats, mice, gophers, squirrels, lagomorphs and birds in Mexican agroecosystems. This situation was evaluated by a survery done by the Secretaría de Agricultura, Ganadería y Desarrollo Rural (SAGAR) in the different States of Mexico. The rodents are the major (59.3 %) vertebrate pests that affect the Mexican agroecosystems. Corn, sorghum, rice, bean and sugar cane are the crops most damaged by vertebrate pest. Likewise, it analizes the different methods used to control these populations.

Dragonflies (Anizoptera) and damselflies (Zigoptera) belong to the order of odonatos. In their juvenile stage, well-known as naiad, they are found in aquatic environments, while in their mature state they live completely in the air, with preying feeding habits. They are considered natural controllers because they do not have a preference for their prey. As naiads they consume minnows or other aquatic larva and insects, and in the mature stage they eat any flying insect.

A study was conducted to analyze diet of Cooper’s hawk (Accipiter cooperii) to determine the occurrence of Mearns quail (Cyrtonyx montezumae) in hawk diets in the northwestern region of the State of Mexico and to study some morphological characteristics of Cooper’s. The study area was defined as published in the hunting proclamation 1997 for Region II which encompasses 249,000 ha, 73 % forest land and 27 % grassland. Eighteen Cooper’s hawks were presumably residents according to their morphological characteristics. Nesting activity was observed from February to mid March, while breeding behavior and hatching were from March to May. Territory was defended in a surrounding area of 4.5 km2. Four nests were found within forest land areas (38 to 50 % of the habitat). Four hawk pellets were collected and analyzed, showing prey differences between pellets. Mearns quail was found in only one of the four pellets analyzed. Cooper´s diet was based on several small birds: Zenaida macrorura, Sturnella neglecta, Piranga ludiviciana, Toxoma ocellatum, Toxoma curvirostre, Turdus rufopalliatus, Scardafella inca, Colombina passerina, Zenaida asiática, Aechmolophus mexicanus, Mimus ployglottos and Cyrtonyx montezumae. This study suggests that there is a small Cooper’s hawk resident population in the region, and that Mearns quail in not the main prey as suggested previously.

NOTA CIENTIFICA

Over 150 years of occupancy by northern Europeans has markedly changed vegetative conditions in the Southwest. Less fire due to grazing and fire suppression triggered a shift to forests with very high tree densities, which in turn contributed to destructive forest tires. Options to deal with these changes include prescribed fire, thinning and timber harvest to mimic natural disturbances and conditions. However, there are barriers to implementing these activities on a scale large enough to have a significant benefit.

NOTA CIENTIFICA

This work analyzes transverse (pith-bark) and longitudinal (base-crown) variation in tracheid length, basic density, moisture content, volumetric and lineal shrinkage of wood from Abies religiosa (H.B.K.) Schl. Et Cham and Pinus ayacahuite var. veitchii Shaw trees. Cross-sections of the trunks were cut every 1.30 m from the base up and each of the sections was cut into blocks of five growth rings in north-south and east-west directions. The results were analyzed with the Schumacher growth model and a linear regression model. Transversally, the two species showed similar results for tracheid length and shrinkage, with pith increasing toward the bark. Longitudinally, no definite tendency was found. Basic density and moisture content did not show defined behavior in either direction or species.