Effect of human disturbance on the structure and regeneration of forests in the Nevado de Toluca National Park, Mexico

Sample plots were established in the principal forest types in the the Nevado de Toluca National Park, Mexico including those domi- nated by Pinus hartwegii, Abies religiosa, Quercus laurina and Alnus jorullensis. The vertical structure was defined by three strata in the coniferous forests and two strata in the broadleaved forests. Timber harvesting in Abies religiosa and Quercus laurina forests and fires generated by humans in Pinus hartwegii forests impeded the recruitment of saplings. Mature trees were also heavily impacted by logging in Pinus hartwegii forests. On the contrary, Alnusjorullensis forests were increas- ing due to the disturbance of Pinus and Quercus forests, as well aban- doned crop lands within the park. A combination of logging, uncon- trolled fire, and grazing appears to be compromising the recruitment of important tree species in this national park. These factors, together with human settlements, have also increased the proportion of early succes- sional species. Changes in forest structure from human disturbance indicate a need to control these activities if conservation goals are not to be compromised.

Dinamic of Bacteria Desnitrificants and Nitrificants in the Rizospheric of Wheat with Slow Release of Fertilizer,Irrigated with Waste or Well Water

The study of the paper about the rhizosphere in the transformation of nitrogen compounds can generate knowledge of the microbial and biochemical atmosphere of the rhizosphere of wheat, for the understanding of the dynamics of the N in agricultural zones, with the purpose of optimizing the fertilizer use and increasing the productivity of the cultures. Therefore, the objective of the present work was to know the effect the rhizosphere in the dynamics of the bacterial populations that take part in the cycle of the N in wheat nourished with slow release fertilizer and one commercial, irrigated with waste water or well. Analyses in the soil took place vertisol used in the experiment with the rhizospheric and non rhizospheric fraction. The slow release fertilizer used has a matrix enriched with N and P and is in the process of being patented (it explains in materials and methods). Each fertilizer was evaluated and the combination of the slow release fertilizer with organic fertilizer. The technique of the number most probable was used (MNP) to carry out the quantification of the nitrificants and denitrificants bacteria to the 55, 67 and 97 days after sowing (Dds). The results obtained for the MNP of denitrificants bacteria and Nitrosomonas indicate that the effect average of the types of water, soil and fertilizers, as well as their interaction to each other was not significant (p > 0.05). The effect of the fertilizing type and soil (rhizospheric and non rhizospheric) in the MNP of Nitrobacter was significant (p < 0.05). The tendencies show that the non rhizospheric soil is more favorable for the development of denitrificants bacteria and Nitrobacter, whereas the MNP of Nitrosomonas was greater in rhizospheric soil.

Chihuahuan沙漠南缘沙漠化进展评价——以San Luis Potosi高原为例（英文）

The aim of this study is to establish if the San Luis Potosi Plateau(SLPP), which is part of the southern edge of the Chihuahuan Desert, is generating desertification processes, indicating a progression of the desert toward the central part of Mexico. Therefore, we analyzed the temporal evolution of four environmental indicators of desertification: Normalized Difference Vegetation Index(NDVI), Normalized Difference Water Index(NDWI), Iron Oxides Index(IO) and Surface Temperature(ST). Landsat TM images are used to cover a period from 1990 to 2011. A new equation of total balance is proposed to generate an image of the overall evolution of each factor which is applied to get a probability map of desertification. The evolution of NDVI, NDWI and IO shows a behavior almost stable over the time. In contrast, the ST shows a slight increase. The outcomes of this study confirm periods of vegetation re-greening and 8.80% of the SLPP has the highest probability to develop desertification. The most affected area is the portion west of the region, and the east and south are the least affected areas. The results suggest a slight advance of the desert, although most of the area doesn't have the necessary conditions to develop desertification.