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Effects of monodominant patches on the organization and structure of plant communities in subtropical coastal dune vegetation

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Polliana Zocche-de-Souza
Total Authors: 1
Document type: Doctoral Thesis
Institution: Universidade Estadual de Campinas, Instituto de Biologia
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Some plant species change biotic and abiotic conditions in levels capable of interfering on the organization and structure of the community. The hypotheses that the importance of positive interspecific interactions increases whilst conditions become more stressful are being questioned because of the increasing evidences of negative interspecific interactions in these conditions. Loss of richness and diversity caused by monodominant species shows the need of questioning the role of interspecific interactions in environments with stressful conditions. In this thesis, we observed how monodominant patches act on different plant community parameters, which mechanisms work as environmental and biological filter and provide their dominance. We used patches of the shrub species Dalbergia ecastaphyllum (L.) Taub. (Fabaceae) as study system. These patches occur in predominantly herbaceous restingas in dunes of subtropical coastal plains. We asked whether the shrub cover interferes with and modifies vegetation (Chapter 1). We evaluated the differences between patches and adjacent open areas monitoring richness and others species' cover for four years. We found out the shrub is expanding; modifying the species composition, community structure, and the majority of relationships with others species are negative. The reduction of cover and richness in the patch areas is dependent of the shrub cover percentage and occupation type. Richness reduction in patches did not lead to losses in total richness in foredune. We asked whether mechanisms as allelopathic effects on green and senescent leaves of Dalbergia are present, and whether shade affects germination and seedling growth (Chapter 2). We evaluated these effects by germination experiments and seedling growth monitoring in laboratory using aqueous extracts of green and senescent leaves of Dalbergia maintaining the same amount of light reduction measured under its canopy in the field. Extract of green leaves inhibited the seed germination. Extract of senescent leaves inhibited, delayed, or decreased seed germination. Shading alone did not affect germination, but mitigated the allelopathic effects on germination. Dalbergia can act on restinga community organization causing instant negative effect, which decreases after senescence. We investigated in the field whether Dalbergia litter layer prevents seedlings emergence on patch areas (Chapter 3). We monitored seedlings emergence in patch areas with and without litter. The litter layer reduced the number of emerged and survived seedlings, their survival time, and seedlings richness were lower in areas with litter. The dynamics of Dalbergia patch in coastal plains has a relevant role in community modeling and structure in foredunes. Different mechanisms of a monodominant shrub species work as filters restricting germination, growth, emergency and occurrence of species in patch areas. Such information will be useful for restoration methods of impacted coastal dunes based on interspecific interactions and aiming natural plant regeneration more efficiently (AU)

FAPESP's process: 11/00103-9 - Can the Dalbergia ecastaphyllum affects the seed rain, germination and seedling growth in Restinga?
Grantee:Polliana Zocche de Souza
Support type: Scholarships in Brazil - Doctorate