Influência do tempo, espaço, fogo e fertilização na comunidade herbáceo-arbustiva no Cerrado

Abstract

The herbaceo-shrubby layer is composed of species with different growth habits: herbs, graminoids, sub-shrubs, vines and palms, each habit can also have distinct phenological strategies and life cycles (anual or perennial). This layer is neglected in the majority of studies dealing with temporal and spatial dynamics in the Cerrado Biome, as there is a general lack of specialists on some families, what greatly hampers species identification. Also, there is a lack of standard methodological sampling procedures able to measure the phenological and morphological diversity in the group. However, in the last decades there have been a growing interest and effort to attain a better knowledge about this layer's composition and structure, as its richness grows progressively from forests to grasslands (where about 90% of the species belong to the herbaceo-shrubby layer). Another important point to consider is that, being composed by species with distinct life cycles and morphologies, the herbaceo-shrubby layer has a faster response to environmental perturbation, both in time and space, compared to the tree layer. This thesis aimed to evaluate the herbaceo-shrubby layer's temporal and spatial dynamics. Besides, it was possible to observe the effects of a wildfire in a palm swamp (Vereda) community and the effects of nutrients addition on a forest-savanna ecotone. The thesis is structured in three chapters: In the first one, the structure and composition of four palm swamps (Vereda) located in the Distrito Federal were assessed. These palm swamps were hit by a wildfire on September 2011 and its regeneration were monitored until 2013. Its composition and structure before and after the fire were compared. In a short time interval (from 3 to 4 months), the communities' richness was reduced in 15% and its plant cover, in 49%. However, a time interval of more than 1 year was sufficient for the community to recover its richness and soil cover levels. Before the wildfire, the palm swamps were floristically distinct, even if beloinging to the same phytophysiognomy, showing the diversity of the herbaceo-shrubby layer. The similarity between the palm swamps increased after the fire, when the fire resilient species reestablished themselves. Environmental and spatial variables accounted for only 26% of the temporal and spatial variation found in the palm swamp communities. In the second chapter, the structure and composition of the herbaceo-shrubby layer of a savanna-forest ecotone was accompained for three years and five months after the September 2011 wildfire, comparing the effects of different nutrient additions on the recovery of the herbaceo-shrubby layer and the process of soil revegetation. Nutrient additions accelerated the recovery of the soil cover but also reduced plant species richness in 50%. After two years and five months, the soil covering levels were almost the same as before the fire in the control plots and the plant diversity in these plots were higher than in the fertilized plots. Along the study, it became clear th...

Fitossociologia do estrato herbáceo-subarbustivo do Parque Estadual do Mirador, Maranhão, Brasil

“…O estrato herbáceo-subarbustivo apresenta diferentes estratégias de sobrevivência, tais como ciclos de vida anuais a perenes (algumas espécies são capazes de completar seu ciclo de vida em poucos meses, devido as adversidades do ambiente), artifícios fenológicos (TANNUS et al, 2006;FELFILI, 2007), e são dotadas de diversas formas de crescimento (ROWE;SPECK, 2005, EUGÊNIO, 2016. Meirelles et al (1999) (MATAVELI et al, 2017), uma vez que se encontra ameaçado pelo avanço da fronteira agrícola (FERNANDES et al, 2016).…”