Abstract
Bryophytes play an important role in the process of ecological succession: conditioning the environment favourably for the emergence of subsequent groups. The objective of this study was to investigate the distribution of bryophyte communities in a cronossequence in the Caxiuanã National Forest, Pará, Brazil. To this end, biological material was collected in forest remnants with different successional stages based on regeneration age: Stage I (0 - 10 years), Stage II (10 - 25), Stage III (> 25) and Stage IV (primary forests). Density, richness and composition of species were compared between successional stages and the occurrence of possible indicator-species was investigated. The identified taxa were also classified by guilds of tolerance to solar radiation and colonized substrate. Composition of species was the variable that most contributed to understanding the distribution of bryophyte communities throughout successional stages, with eight species identified as potential indicators of some successional stages. Generalist species predominated in all stages. The richness of sun tolerants, in turn, decreased with the progress of succession, while shade tolerants increased. The land use history and land cover can influence the availability and quality of substrates and consequently their colonization by bryophytes in the different stages.
Highlights
Anthropological disturbances in tropical forests, no matter the extent, cause changes in the dynamics of the established communities (Chazdon 2008, Machado et al 2017)
The plots were distributed in areas with different successional stages according to the classification proposed by Chazdon (2008) with adjustments to primary forests, which were classified here as Stage IV (Table I)
Even if the Stage II had more species than stages III and IV, and the later two were equivalent in number of species, there was no significant difference. Both density and richness throughout the stages studied are not in line with the hypothesis that there is an intermediate period of the ecological succession process in which these parameters are higher than in mature forest (Peet 1995) and support the results found by Holz & Gradstein (2005), which indicated that Species richness of cryptogamic epiphytes in secondary and primary forests of the Cordillera de Talamanca, Costa Rica were nearly the same, showing that primary forests are not necessarily more diverse than secondary forests
Summary
Anthropological disturbances in tropical forests, no matter the extent, cause changes in the dynamics of the established communities (Chazdon 2008, Machado et al 2017). After the deterioration and abandonment of disturbed areas, the process of spontaneous regeneration starts to reestablish the dynamic equilibrium of a mature forest (Chazdon 2012). The dynamics of secondary succession in tropical rainforests follows a progression of stages in which there is a gradual increase of taxonomic richness as well as structural and functional complexity of the forest (Chazdon 2012, Salomão et al 2012). The author considered a set of parameters such as seed germination, species recruitment and ecological groups. In this classification, the first successional stage is characterized by the dominance of species tolerant to high solar incidence such as herbaceous plants, shrubs and woody lianas; after 10 years, the considerable
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