Produção de serrapilheira e decomposição foliar em fragmentos florestais de diferentes fases sucessionais no Planalto Atlântico do estado de São Paulo, Brasil

Litterfall and litter decomposition are vital processes in tropical forests because they regulate nutrient cycling. Nutrient cycling can be altered by forest fragmentation. The Atlantic Forest is one of the most threatened biomes in the world due to human occupation over the last 500 years. This scenario has resulted in fragments of different size, age and regeneration phase. To investigate differences in litterfall and leaf decomposition between forest successional phases, we compared six forest fragments at three different successional phases and an area of mature forest on the Atlantic Plateau of Sao Paulo, Brazil. We sampled litter monthly from November 2008 to October 2009. We used litterbags to calculate leaf decomposition rate of an exotic species, Tipuana tipu (Fabaceae), over the same period litter sampling was performed. Litterfall was higher in the earliest successional area. This pattern may be related to the structural properties of the forest fragments, especially the higher abundance of pioneer species, which have higher productivity and are typical of early successional areas. However, we have not found significant differences in the decomposition rates between the studied areas, which may be caused by rapid stabilization of the decomposition environment (combined effect of microclimatic conditions and the decomposers activities). This result indicates that the leaf decomposition process have already been restored to levels observed in mature forests after a few decades of regeneration, although litterfall has not been entirely restored. This study emphasizes the importance of secondary forests for restoration of ecosystem processes on a regional scale.A produção e a decomposição de serrapilheira são processos vitais nas florestas tropicais, uma vez que determinam a ciclagem de nutrientes. O processo de ciclagem de nutrientes pode ser alterado pela fragmentação florestal. A Floresta Atlântica é um dos biomas mais ameaçados mundialmente devido à ocupação humana nos últimos 500 anos. Este cenário resultou em fragmentos de diferentes tamanhos, idades e estádios de regeneração. Para explorar as diferenças na produção de serrapilheira e na decomposição foliar de acordo com o estádio sucessional da floresta, comparamos seis fragmentos florestais em três diferentes estádios sucessionais e uma área de floresta primária no Planalto Atlântico de São Paulo, Brasil. Coletamos a serrapilheira mensalmente de novembro de 2008 a outubro de 2009. Utilizamos bolsas de confinamento de serrapilheira para calcular a taxa de decomposição foliar de uma espécie exótica, Tipuana tipu (Fabaceae), durante o mesmo período de coleta da serrapilheira. A deposição de serrapilheira foi maior na área de estádio sucessional mais inicial. Esse padrão pode estar relacionado com as características estruturais dos fragmentos florestais, especialmente com a maior abundância de espécies pioneiras, que possuem uma maior produtividade e são espécies típicas de fragmentos em estádios iniciais de sucessão. Por outro lado, não encontramos diferenças significativas nas taxas de decomposição entre as áreas estudadas, o que pode ocorrer devido à rápida estabilização do ambiente de decomposição (efeito combinado das condições microclimáticas e das atividades dos decompositores). Estes resultados indicam que o processo de decomposição foliar foi restabelecido aos níveis das florestas maduras após algumas décadas de regeneração, embora a produção de serrapilheira ainda não tenha sido totalmente restaurada. Este estudo destaca a importância das florestas secundárias em um cenário regional de restauração de processos ecossistêmicos.Institute of Biosciences at the University of So PauloInstitute of Biosciences at the University of So PauloFundacao de Amparo a Pesquisa do Estado de So Paulo (FAPESP) [2008/58357-3, 2006/56054-8]Fundacao de Amparo a Pesquisa do Estado de So Paulo (FAPESP)German Department of Education and Research (German BMBF) [01LB 0202]German Department of Education and Research (German BMBF)Forestry Institute of Sao PauloForestry Institute of Sao Paul

Local plant species delimitation in a highly diverse Amazonian forest: Do we all see the same species?

Question: How reliable is the process of delimiting plant species by morphotyping sterile specimens from a highly diverse Amazonian forest plot? Location: Biological Dynamics of Forest Fragments Project (BDFFP), Central Amazon, Manaus, Brazil. Methods: A taxonomic exercise was conducted during a Center for Tropical Forest Science (CTFS) Taxonomy Workshop held in Manaus in April 2011, using specimens collected in a 25-ha forest plot. The plant species from this plot had been previously delimited by morphotyping of ca. 80 000 sterile specimens, a process that resulted in the recognition of 115 cases (accounting for 38% of all trees) in which species delimitation was problematic. For the workshop, we selected a subsample of specimens for eight of these difficult cases (taxonomic groups/complexes) and asked 14 participants with different levels of botanical training to independently sort these specimens into morphospecies. We then compared the classifications made by all participants and explored correlations between botanical training and plant classification. Results: The classification of specimens into morphospecies was highly variable among participants, except for one taxonomic group/complex, for which the median pair-wise similarity was 95%. For the other seven taxonomic groups/complexes, median pair-wise similarity values ranged from 52% to 67%. Training did not increase the similarity in the definition of morphospecies except for two taxonomic groups/complexes, for which there was higher congruence between the classifications made by participants with a high level of botanical training than in comparisons that included less-experienced participants. The total number of morphospecies defined by participants was highly variable for all taxonomic groups/complexes, with the total number varying from 12 to 46 (a 383% difference). Conclusions: Local plant species delimitation by morphotyping sterile specimens is prone to large uncertainties, and botanical training may not reduce them. We argue that uncertainty in species delimitation should be explicitly considered in plant biodiversity inventories as diversity estimates may be strongly affected by such uncertainties. We recommend that species delimitation and identification be treated as separate processes and that difficulties be explicitly recorded, so as to permit error estimates and the refinement of taxonomic data. Poor taxonomic knowledge, lack of tools and high diversity limit our ability to recognize plant species in Amazon forest plot inventories. While the identification of species is a well-known problem, the delimitation of local species is considered unproblematic. We show that local species delimitation is also prone to large uncertainties, and that botanical experience may not reduce them. © 2012 International Association for Vegetation Science