RESUMOA condição de aridez associada à pressão antrópica resulta em áreas de degradação extrema, conhecidas como núcleos de desertificação. No núcleo do Seridó a antropização é caracterizada por queimadas, cultivo do algodão no passado, pastoreio e exploração de lenha, que alteraram a composição florística e a estrutura da vegetação potencial. Com este estudo se objetivou identificar níveis de degradação na caatinga arbóreo-arbustiva do Seridó, por meio de técnicas multivariadas que envolveram variáveis do ambiente físico, da florística, fitofisionomia e diversidade da vegetação. O inventário florístico e fitossociológico foi realizado em 16 fragmentos, pelo método Ponto-Quadrante, com a inclusão de plantas com diâmetros no nível do solo 1 cm e altura > 1 m, totalizando 3472 indivíduos, que foram identificados em 15 famílias, 24 gêneros e 31 espécies. As famílias Euphorbiaceae, Mimosaceae, Apocynaceae e Caesalpinaceae apresentaram maiores VI, assim como as espécies Croton hemiargyreus, Aspidosperma pyrifolium, Mimosa hostilis, Caesalpinia pyramidalis e Jatropha mollissima. Os resultados mostraram que a degradação dos fragmentos está associada às condições ambientais mais favoráveis, o que indica causa antró-pica da degradação.Palavras-chave: florística, fitossociologia, biodiversidade, análise multivariada Analysis of degradation of 'Caatinga' in the desertification nucleus of Seridó -Brazil ABSTRACTThe anthropic pressure on the Brazilian semi-arid biome of 'caatinga' leads to extreme degradation areas known as desertification nucleus. In the desertification nucleus of Seridó the anthropisms are characterized by burning of 'caatinga' vegetation, cotton crop in the past, pasture and native vegetation exploitation, which altered the floristic composition and the structure of the potential vegetation. The objective of this study was to identify the degree of degradation of 'caatinga' vegetation of Seridó by means of multivariate techniques involving the environmental, phytofisionomy, diversity of vegetation. The floristic and phytossociologic inventory were carried out in 16, by square -point method with the inclusion of plants with stem diameter at ground level > 1 cm and height > 1 m, totalizing 3472 plants, which were identified in 15 families and 31 species. The Euphorbiaceae, Mimosaceae, Apocynaceae and Caesalpinaceae family and Croton hemiargyreus, Aspidosperma pyrifolium, Mimosa hostilis, Caesalpinia pyramidalis, Jatropha mollissima species occurred higher VI. The results showed that degradation of 'caatinga' is associated with more favorable environmental conditions, that evidence antropic causes of degradation.

A utilização de dados espectrais, na estimativa de parâmetros estruturais da vegetação, constitui-se num dos mais importantes papéis do sensoriamento remoto dos ecossistemas naturais. Neste trabalho foram aplicadas transformações espectrais, como os índices de vegetação e a fração de vegetação obtida pelo modelo de análise de misturas em dados do sensor TM/LANDSAT, com o objetivo de se estimar parâmetros estruturais da Floresta Nacional do Araripe, no Ceará. As imagens foram calibradas para radiância, ao nível do solo, e antes do processamento foram removidos seus "outliers". Tanto a fração de vegetação verde quanto os índices de vegetação e as respostas de bandas individuais, apresentaram correlação positiva e significativa com as estimativas da altura média da parcela, da área basal à altura do peito e da área basal na base. Os valores de coeficientes de correlação variaram entre 0,33 e 0,60. Os melhores relacionamentos foram obtidos com o índice de vegetação da razão simples e com o índice estrutural da vegetação para os quais foram estabelecidas as equações de regressão.

Phytomass is a critical information for economic and environmental activities like the establishment of policies for timber resources, forest management, studies of plant nutrient cycling, CO 2 sink, among other. The phytomass of a Caatinga area was obtained by an empirical method using normalized difference vegetation index (NDVI) of Landsat images, the plant area index (PAI) and the phytomass inventory. At a first stage, linear, logarithmic and non-linear models were developed and tested. Bush and tree specimens were considered in the study, so that most of the individuals that contribute to the spectral answer detected by satellite images were included. At a second stage, the orbital parameter NDVI was used to map the PAI, which was used to map the phytomass, based on the relationship of this phytomass as a function of PAI. The residues between measurements and estimates based on NDVI varied from 0 to 84%, while the residues of total dry weight of phytomass per ha obtained by mapping and by dendrometrical equations varied from 5 to 104%, with a large trend of 166 and 448% in open Caatinga areas, due to the contribution of the herbaceous stratum to NDVI.

This study investigated the relationship between leaf production, litterfall, water balance, Leaf Area Index (LAI), and Normalized Difference Vegetation Index (NDVI) in semideciduous forests. The goal was to model this phenomenon to obtain the estimates of this component as an additional compartment of the ecosystem carbon sink. The tests were conducted in eight semideciduous forest fragments. Twenty-four permanent plots were monitored monthly and LAI measurements and weighing of litterfall deposited in nets were conducted for a period of thirteen months. In this period, Landsat 5 and IRS satellite images were obtained and processed for generation of NDVI. The water balance was calculated for each day. The relationship among the variables “leaf dry weight,” “LAI,” “NDVI,” and “water balance” was verified and a regression model was built and evaluated. The deciduous phenomenon can be explained by hydric balance, and LAI and NDVI are ancillary variables. The tendency of the variables in the period of 13 months was explained by quadratic functions. The varied behavior among the monitoring sites helped to know differences in the deposition of leaves. This study showed that only the leaf component of the litterfall of a semideciduous forest in tropical climate can capture 4 to 8 Mg·ha−1·yr−1of CO2and this amount can be estimated using climate, biophysics, and vegetation index variables.