Cerrado sensu stricto sobre neossolo quartzarênico : fitogeografia e conservação

Abstract

O bioma Cerrado apresenta paisagens heterogêneas, caracterizando-se por apresentar uma elevada diversidade beta. O Parque Nacional de Sete Cidades e a Chapada Grande Meridional, ambos no Estado do Piauí, apresentam uma elevada heterogeneidade espacial com diferentes fitofisionomias e tipos de solos. Neste trabalho, foram estudadas a vegetação lenhosa do cerrado sensu stricto sobre Neossolo Quartzarênico destas áreas e foram relacionadas as variações florísticas e estruturais do cerrado sobre solos arenosos, com as variações locais do meio físico, como características químicas e físicas do solo e a altitude. Em cada área, foram amostradas dez parcelas de 20 m x 50 m distribuídas nas manchas de cerrado sobre Neossolo. No PNSC foram encontradas 45 espécies e 40 gêneros em 21 famílias botânicas com densidade de 1017 indiv.ha-1 e área basal de 10,71 m2.ha-1, a diversidade pelo índice de diversidade de Shannon foi 3,07 nats.indiv-1 e equabilidade de Pielou de 0,80. Na Chapada Grande Meridional foram encontradas 48 espécies (duas subespécies) e 26 famílias botânicas, com densidade de 930 indiv.ha-1 e área basal de 12,84 m2.ha-1. A diversidade alfa (índice de Shannon H’=2,75 nats.ind-1 e equabilidade de Pielou J=0,70) foi baixa, devido à concentração de densidade em Qualea grandiflora (30,11%) e Parkia platycephala (12,37%). As espécies amostradas nesses cerrados representam uma mistura de espécies de ampla distribuição nas zonas de baixa altitude, espécies típicas dos cerrados marginais do Nordeste e espécies de ampla distribuição no bioma e que ocorrem na Caatinga. Nestes cerrados, os limites superiores de altura dos indivíduos foram maiores àqueles descritos na literatura para o cerrado s.s., indicando um padrão estrutural dos cerrados do Nordeste que possuem árvores mais altas do que os cerrados do Planalto Central, porém menor riqueza florística no estrato lenhoso. Em ambas as áreas, a diversidade beta entre as parcelas foi alta, especialmente na comparação da densidade de espécies entre as parcelas, indicando a alta heterogeneidade ambiental do cerrado e a complementaridade das manchas para a manutenção da diversidade. No PNSC, a variação da vegetação foi relacionada ao gradiente de fertilidade, salinidade, acidez e textura do solo e altitude, separando espécies que também ocorrem em formações florestais de espécies que ocorrem exclusivamente nas formações savânicas do Cerrado. No PNSC, os solos de algumas parcelas possuem caráter solódico, devido à alta quantidade de sódio, relacionada com áreas de maior altitude. Na Chapada Grande Meridional, o gradiente de fertilidade, altitude, textura e salinidade do solo influenciou na distribuição de algumas espécies. Foram investigadas as diferenças florísticas, estruturais e ambientais, baseado em amostragens quantitativas, entre oito áreas de cerrado s.s. sobre Neossolo Quartzarênico, para a determinação de padrões fitogeográficos e de conservação do cerrado sobre solos arenosos. Os dados analisados provêm de levantamentos realizados em áreas de cerrado s.s. no Piauí e no Brasil Central, todos sobre Neossolo, totalizando 80 parcelas de 20 m x 50 m. Foram realizadas análises multivariadas, com o método TWISNPAN e Análise de Correspondência Canônica (CCA). De um total de 198 espécies que ocorreram em todas as áreas amostradas, foram analisadas 94 que ocorreram em duas áreas ou mais. As diferentes composições florísticas e estruturais encontradas entre as áreas analisadas, mesmo considerando um tipo de solo, indicam a elevada heterogeneidade da vegetação do cerrado. Na CCA, as variáveis ambientais que tiveram maior correlação com as parcelas e espécies foram temperaturas média e mínima anuais, precipitação média anual, insolação e número de meses secos. Nas divisões obtidas pelo método TWINSPAN e na CCA, as áreas analisadas do Piauí encontraram-se fortemente separadas das demais áreas analisadas, sugerindo que estes cerrados formam um subgrupo distinto das demais áreas dos cerrados do Nordeste. A alta diversidade beta encontrada e a pouca quantidade de espécies amplamente distribuídas e protegidas, são importantes fatores a serem considerados para a criação de novas e extensas unidades de conservação no bioma Cerrado. _________________________________________________________________________________ ABSTRACT

The Cerrado biome presents a large spatial heterogeneity and is characterized as having elevated beta diversity. The Sete Cidades National Park (PNSC) and Chapada Grande Meridional, both located at the state of Piauí, show great landscape diversity with different physiognomies and soils types. In this study, we investigated the woody vegetation of the cerrado sensu stricto (savanna woodland physiognomy) that occur on Entisols (Quartzarenic Neosols) and the relationship between the floristic and structure variations regarding the soils characteristics and altitude. In each area, we sampled ten plots with 20 m x 50 m, distributed in patches of cerrado on Entisols. At PNSC 45 species and 40 genera were found distributed among 21 botanic families, with stem density of 1017 indiv.ha-1 and basal area of 10.71 m2.ha-1. The Shannon diversity index was 3,07 nats.indiv-1 and the evenness was 0,80. At Chapada Grande Meridional 48 species (two subspecies) and 26 botanic families were encountered, with a stem density of 930 indiv.ha-1 and basal area of 12.84 m2.ha-1. The alfa diversity (Shannon index of 2,75 nats.ind-1 and evenness of 0,70) was low, because of the high density of Qualea grandiflora (30,11%) and Parkia platycephala (12,37%). The species sampled are a mixture of species with widespread distributions within the biome, species typically from the cerrado of the Northeast and others species that occur in the Caatinga biome. In these cerrados, the superior limits of tree height were larger than what is usually described for cerrado s.s., indicating a structural pattern of the Northeast cerrados, that have higher tress than the cerrados founds at the Planalto Central. However the Northeast cerrados are poorer in species than the other cerrados. In both areas, the beta diversity between the plots was high, especially when considering the species density, indicating a high environmental heterogeneity of cerrado and the complementarities between the patches towards the maintenance of biodiversity. At PNSC, the variation of vegetation occurred along gradients of fertility, acidity, salinity, texture and altitude. Species that also occur in forest formations were separated from species that occur exclusively in savanna formations. At PNSC, some of the soils sampled in the plots have a solodic characteristic, because of the high amounts of sodium, related to areas with higher altitudes. At Chapada Grande Meridional, the gradient of fertility, texture and salinity influenced the distribution of some species. In this study, differences in the floristic composition, structure and environmental characteristics were also investigated, based in quantitative samplings, between eight areas of cerrado s.s. on Entisols, to determine phytogeographic and conservation patterns of cerrados encountered on this type of soil. The data analyzed were from samples conducted at cerrados from Piauí state and the region of central Brazil, witch were all located on Entisols, and totalized 80 plots of 20 m x 50 m. Multivariate analysis were conducted, with TWINSPAN classification and Canonical Corresponde The Cerrado biome presents a large spatial heterogeneity and is characterized as having elevated beta diversity. The Sete Cidades National Park (PNSC) and Chapada Grande Meridional, both located at the state of Piauí, show great landscape diversity with different physiognomies and soils types. In this study, we investigated the woody vegetation of the cerrado sensu stricto (savanna woodland physiognomy) that occur on Entisols (Quartzarenic Neosols) and the relationship between the floristic and structure variations regarding the soils characteristics and altitude. In each area, we sampled ten plots with 20 m x 50 m, distributed in patches of cerrado on Entisols. At PNSC 45 species and 40 genera were found distributed among 21 botanic families, with stem density of 1017 indiv.ha-1 and basal area of 10.71 m2.ha-1. The Shannon diversity index was 3,07 nats.indiv-1 and the evenness was 0,80. At Chapada Grande Meridional 48 species (two subspecies) and 26 botanic families were encountered, with a stem density of 930 indiv.ha-1 and basal area of 12.84 m2.ha-1. The alfa diversity (Shannon index of 2,75 nats.ind-1 and evenness of 0,70) was low, because of the high density of Qualea grandiflora (30,11%) and Parkia platycephala (12,37%). The species sampled are a mixture of species with widespread distributions within the biome, species typically from the cerrado of the Northeast and others species that occur in the Caatinga biome. In these cerrados, the superior limits of tree height were larger than what is usually described for cerrado s.s., indicating a structural pattern of the Northeast cerrados, that have higher tress than the cerrados founds at the Planalto Central. However the Northeast cerrados are poorer in species than the other cerrados. In both areas, the beta diversity between the plots was high, especially when considering the species density, indicating a high environmental heterogeneity of cerrado and the complementarities between the patches towards the maintenance of biodiversity. At PNSC, the variation of vegetation occurred along gradients of fertility, acidity, salinity, texture and altitude. Species that also occur in forest formations were separated from species that occur exclusively in savanna formations. At PNSC, some of the soils sampled in the plots have a solodic characteristic, because of the high amounts of sodium, related to areas with higher altitudes. At Chapada Grande Meridional, the gradient of fertility, texture and salinity influenced the distribution of some species. In this study, differences in the floristic composition, structure and environmental characteristics were also investigated, based in quantitative samplings, between eight areas of cerrado s.s. on Entisols, to determine phytogeographic and conservation patterns of cerrados encountered on this type of soil. The data analyzed were from samples conducted at cerrados from Piauí state and the region of central Brazil, witch were all located on Entisols, and totalized 80 plots of 20 m x 50 m. Multivariate analysis were conducted, with TWINSPAN classification and Canonical Corresponde Analysis (CCA). From a total of 198 species that occur in all areas, 94 species that occur in two or more areas were analyzed. The differences encountered among the floristic compositions and structures between the areas, even when considering a same type of soil, indicates a high heterogeneity of the cerrado vegetation. In the CCA, the environmental variables that have the best correlations between the plots and species were mean temperature, mean of the minimum temperature, mean annual precipitation, solar radiation and number of dry months. The divisions obtained from TWINSPAN and CCA, show that the areas from Piauí were strongly separated from the others areas, suggesting that these areas are a distinct subgroup from the other Northeast cerrado areas. The high beta diversity and the few widespread species and that are protected are important factors to be considered for the creation of new and extensive protected areas in the Cerrado biome.