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Effect of climate and physiography on the distribution of trees and shrubs species in northwest Mexico

Martínez-Antúnez P., Wehenkel C., Hernández-Díaz J. C., González-Elizondo M., Corral-Rivas J., Pinedo-Álvarez A.

Polish Journal of Ecology

2013

Vol. 61, nr 2

283--295

In order to understand the environmental variables that may impact more on the distribution of species of trees and shrubs, a correlation analysis applying the Covariation (C) of Gregorius was conducted among 14 variables of climate and physiography, and the number of individuals of 72 species, which were found in 1804 sampling plots (covering about 123,317 km2) of the National Forests and Soils Inventory (INFyS) developed by the National Forest Commission in Mexico (CONAFOR). Among the studied species there are several of the genera Quercus, Pinus and Junniperus, which are mainly distributed in the Sierra Madre Occidental, where they stand out for their abundance. The results show that the density of 88% of the studied species have a significant correlation (P <0.025) with at least five of the 14 variables analyzed. Seven of the variables showed significant correlation (P <0.025) with at least 74% of the studied species: ‘Julian date of last spring frost’ with an average value of covariation (C) equal to 0.71, ‘average duration of the frost-free period’ with average value of C = 0.71’, degree days above 5°C’ with covariation of 0.69, ‘altitude above sea level’ with C = 0.66; ‘mean temperature in the coldest month’, ‘mean temperature in the warmest month’ and ‘mean annual temperature’, with average values of C = 0.65 for each of these last three variables. The ‘geographic orientation of the ground’ was the least correlated with the density of the species, since only 10% of them showed significant correlation with this variable.

Genetic diversity in relation to secondary succession of forest tree communities

Wehenkel C., Corral-Rivas J., Hernandez-Diaz J.

Polish Journal of Ecology

2011

Vol. 59, nr 1

45-54

Forest succession is a fundamental ecological process, which has significant implications for the biological, biophysical, and biogeochemical processes in an ecosystem. Genetic diversity is not only a product of the number of species present in a given area, but also of successional change from colonization of gaps by pioneer species to mature climax forest. Genetic diversity should be higher in earlier successional stages than in later stages because high environmental predictability in later successional stages favours low genetic diversity. In the present study the relationship between secondary succession and genetic diversity was explored in eight stands of characteristic tree communities in the Thuringian forest area (Germany). Each of the eight stands was subdivided into six plots in a grid of 40 x 40 m to detect as much as possible tree species and genetic variants within the forest tree community and successionspecific structures. To define secondary succession, the mean Ellenberg indicator values for light and nitrogen in the herb layer, weighted for coverage, as well as the percentage of climax tree species in naturally regenerated stands were used. All species and genotype diversities based on the investigated tree species were calculated by the so-called Hill numbers. The results showed that the Gregorius's Covariation (C) of secondary succession with the transspecific genotype diversity as well as the transspecific genotype diversity per species for the enzyme systems AAT, HEK, PGI, MDH, IDH as well as the AFLP trait was statistically significant in several relationships. The transspecific genotype diversities were often significantly greater in the earlier successional stages than in the later stages. Selection effects during replacement of light and nitrogen demanding species and plant communities by more economical and competitive species such as Abies alba Mill. and Fagus sylvatica L. probably dominated in the study. Based on the results of the study, we conclude that genetic diversity may be an essential attribute of stages of secondary succession that should be further explored because of its relation to adaptability and ecological stability.