Christian WEHENKEL 1* , José Javier CORRAL-RIVAS 2 , José Ciro HERNÁNDEZ-DÍAZ 1 1 Instituto de Silvicultura e Industria de la Madera, Universidad Juárez del Estado de Durango, Km 5.5 Carretera Mazatlán, 34120 Durango, México 2 Facultad de Ciencias Forestales, Universidad Juárez del Estado de Durango, Río Papaloapan y Blvd. Durango s/n, Col. Valle del Sur, 34120 Durango, México e-mails: wehenkel@ujed.mx ( * corresponding author), jcorral@ujed.mx, jciroh@ujed.mx GENETIC DIVERSITY IN RELATION TO SECONDARY SUCCESSION OF FOREST TREE COMMUNITIES POLISH JOURNAL OF ECOLOGY (Pol. J. Ecol.) 59 1 45–54 2011 Regular research paper ABSTRACT: Forest succession is a funda- mental ecological process, which has significant implications for the biological, biophysical, and biogeochemical processes in an ecosystem. Ge- netic diversity is not only a product of the num- ber 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 environ- mental 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 (Ger- many). Each of the eight stands was subdivided into six plots in a grid of 40  40 m to detect as much as possible tree species and genetic variants within the forest tree community and succession- specific structures. To define secondary succes- sion, 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 suc- cession 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 statis- tically significant in several relationships. The transspecific genotype diversities were often sig- nificantly greater in the earlier successional stages than in the later stages. Selection effects during replacement of light and nitrogen demanding spe- cies 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 con- clude 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. KEY WORDS: climax tree species, covaria- tion, permutation test, secondary succession, di- versity 1. INTRODUCTION Forest succession is a fundamental eco- logical process, which has significant im- plications for sustainable natural resource management as well as for the biological, biophysical, and biogeochemical processes in an ecosystem (S o n g et al. 2002). It is mostly defined as a directional non-seasonal cu- mulative change in the types of forest (spe- cies composition) that occupy a given area over time. Colonization, establishment, and