A fenologia é definida como o estudo da ocorrência de eventos biológicos, a influência defatores bióticos e abióticos nestes eventos e a relação entre as fenofases (fases caracterizadas porestes eventos) entre as mesmas espécies ou espécies diferentes (LIETH, 1974; TALORA eMORELLATO, 2000).
A paisagem analisada a partir da abordagem geossistêmica se apresenta enquanto um complexo dinâmico, criado pela relação sociedade-natureza e pela combinação de aspectos físicos, biológicos e sociais (PIMENTEL, et. al, 2018). Analisar a paisagem em unidades significa dividir conjuntos hierárquicos, bióticos e abióticos, naturalmente semelhantes e que obrigatoriamente interagem dialeticamente entre si, tornando-a sistemática (BERTRAND, 2004; OLEGÁRIO et al., 2014).
O estudo do comportamento fenológico parte da premissa da ocorrência de ciclos simultâneos de vida de uma espécie em relação a influência de fatores bióticos e abióticos e da interrelação entre as fases caracterizadas por estes eventos, entre mesmas espécies ou diferentes (Lieth, 1974).
The Topographic Wetness Index (TWI) is related to the distribution of saturation zones of surface water and water in the soil. In view of this, the occurrence of events related to plant phenology in semi-arid regions is usually influenced not only by rainfall rates, but also by water availability for vegetation. Analogously, this study aimed to analyze the plant phenology from the phenological metrics and relate them to the TWI, associating them to the Desertification process in the Caatinga biome. The applied methodology consisted in generating the TWI in the QGIS and SAGA GIS softwares, with the acquisition of the Digital Terrain Model (DTM) and spatial resolution of 30 meters. Then, the phenological metrics were extracted through MODIS/Terra (MOD13Q1) images that contain the vegetation index (EVI) corresponding to the temporal period from 2001 to 2017, being clipped in ENVI software and processed in TIMESAT program with the application of Savitzky-Golay smoothing filter. As main results the TWI indicated low humidity values in the higher regions and less prone to water saturation in the study area, and the highest values are in the flat/smoothed areas of the Pole more prone to water saturation. The phenological metrics extracted indicated a better analysis of the seasonal behavior of vegetation, specifically drought events in the Jeremoabo Pole. In this regard, the crossing of data between TWI and Phenological Metrics through cross-tabulation, offered better behavioral detailing between both variables in the region, and the metrics showed direct relations to the climatic seasonality of the region.
O estudo fenológico fundamenta-se na ocorrência de ciclos simultâneos, de forma a gerar parâmetros que permitem a análise e interação destes ciclos – denominadas métricas fenológicas. Esses estudos, alternativamente, podem ser realizados sem a observação direta partir de dados de sensoriamento remoto e possibilitam indicar o estado ambiental, fatores, efeitos e comportamento da vegetação. Desse modo, objetiva-se nessa pesquisa analisar o comportamento das classes de uso e cobertura vegetal a partir das métricas fenológicas extraídas de séries temporais do sensor Moderate Resolution Imaging Spectroradiometer (Modis) no Polo de Desertificação de Jeremoabo, no estado da Bahia, no período de 2001-2017. Foram utilizadas séries temporais de índice de vegetação realçado (EVI) do sensor para extrair as métricas fenológicas de início, fim, amplitude e comprimento do período de crescimento vegetativo; taxas de aumento (rebrota) e diminuição (senescência) e integrais maior (produtividade total) e menor (produtividade sazonal). Posteriormente, realizaram-se as tabulações cruzadas entre as métricas fenológicas obtidas e as classes de uso e cobertura vegetal para área de estudo: agropecuária e formações savânica, campestre e florestal. Os resultados obtidos evidenciaram padrões distintos entre as classes naturais e antrópicas da região. Observou-se que apesar da diversidade e heterogeneidade entre as feições vegetacionais da área de estudo, estas obedecem a um padrão ao longo do ciclo fenológico, inerente a sazonalidade climática, em específico, a irregularidade pluviométrica característica do semiárido brasileiro. Palavras-chave: Caatinga; Métricas fenológicas; Índice de vegetação.Times series of remote sensing data in the study of phenological behavior in the Jeremoabo Desertification Pole- BaA B S T R A C TThe phenological study is based on the occurrence of simultaneous cycles, in order to generate parameters that allow the analysis and interaction of the cycles – the phenological metrics. The studies, alternatively, can be realized without direct observation from remote sensing data and make it possible to indicate the environmental state, factors, effects and behavior of the vegetation. Therefore, the objective of this research is to analyze the behavior of land use and land cover classes from the phenological metrics extracted from time series of the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor in the Jeremoabo Desertification Pole, in the state of Bahia, in the period from 2001-2017. Time series of Enhanced Vegetation Index (EVI) were used to extract the phenological metrics of start, end, amplitude and length of the vegetative growth period; rates of increase (regrowth) and decrease (senescence) and higher integral (totl productivity) and lower integral (seasonal productivity). Subsequently, cross-tabulations were made between the phenological metrics obtained and the use and vegetation cover classes for the study area: agriculture and savanna, grassland and forest formations. The results obtained evidenced distinct patterns between the natural and anthropic classes in the region. It was observed that despite the diversity and heterogeneity among the vegetation features of the study area, the follow a pattern throughout the phenological cycle, inherent to climatic seasonality in particular, the rainfall irregularity characteristic of the Brazilian semiarid region. Keywords: Caatinga; Phenology Metrics; Vegetation Index
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