Influência da resolução espacial de modelos digitais de terreno sobre estimativas de insolação anual em uma área de topografia acidentada na Serra do Cipó (MG)

A heterogeneidade temporal e espacial da insolação sobre a superfície terrestre determina a dinâmica de uma série de processos ecossistêmicos, como fotossíntese e ciclagem hidrológica. A obtenção de estimativas da insolação anual a partir de modelos digitais de terreno é uma alternativa eficiente ao monitoramento in situ. Atualmente, modelos de elevação com altíssima resolução espacial podem ser gerados a partir de imageamento por veículos aéreos não tripulados, com baixo custo, abrindo novas possibilidades para o estudo dos processos ambientais. O presente estudo avaliou como o uso de modelos digitais de terreno em diferentes resoluções espaciais pode influenciar a variação espacial das estimativas de insolação anual, em uma região de relevo acidentado. Esta metodologia é importante para se compreender a variação espacial dos processos ecossistêmicos em escala local, em áreas de topografia complexa.

Accuracy and limitations for spectroscopic prediction of leaf traits in seasonally dry tropical environments

Generalized assessments of the accuracy of spectroscopic estimates of ecologically important leaf traits such as leaf mass per area (LMA) and leaf dry matter content (LDMC) are still lacking for most ecosystems, and particularly for non-forested and/or seasonally dry tropical vegetation. Here, we tested the ability of using leaf reflectance spectra to estimate LMA and LDMC and classify plant growth forms within the cerrado and campo rupestre seasonally dry non-forest vegetation types of Southeastern Brazil, filling an existing gap in published assessments of leaf optical properties and plant traits in such environments. We measured leaf reflectance spectra from 1648 individual plants comprising grasses, herbs, shrubs, and trees, developed partial least squares regression (PLSR) models linking LMA and LDMC to leaf spectra (400–2500 nm), and identified the spectral regions with the greatest discriminatory power among growth forms using Bhattacharyya distances. We accurately predicted leaf functional traits and identified different growth forms. LMA was overall more accurately predicted (RMSE = 8.58%) than LDMC (RMSE = 9.75%). Our model including all sampled plants was not biased towards any particular growth form, but growth-form specific models yielded higher accuracies and showed that leaf traits from woody plants can be more accurately estimated than for grasses and forbs, independently of the trait measured. We observed a large range of LMA values (31.80–620.81 g/m2) rarely observed in tropical or temperate forests, and demonstrated that values above 300 g/m2 could not be accurately estimated. Our results suggest that spectroscopy may have an intrinsic saturation point, and/or that PLSR, the current approach of choice for estimating traits from plant spectra, is not able to model the entire range of LMA values. This finding has very important implications to our ability to use field, airborne, and orbital spectroscopic methods to derive generalizable functional information. We thus highlight the need for increasing spectroscopic sampling and research efforts in drier non-forested environments, where environmental pressures lead to leaf adaptations and allocation strategies that are very different from forested ecosystems. Our findings also confirm that leaf reflectance spectra can provide important information regarding differences in leaf metabolism, structure, and chemical composition. Such information enabled us to accurately discriminate plant growth forms in these environments regardless of lack of variation in leaf economic traits, encouraging further adoption of remote sensing methods by ecologists and allowing a more comprehensive assessment of plant functional diversity

Sunglint correction in airborne hyperspectral images over inland waters

This study assessed sunglint effects in airborne high spatial and high spectral resolution images acquired by the SpecTIR sensor under different view-illumination geometries over the Brazilian Ibitinga reservoir (Case II waters). These effects were corrected using the Goodman et al. (2008) and the Kutser et al. (2009) methods, and a variant that used the continuum removal technique to calculate the oxygen absorption band depth. The performance of each method to removing sunglint effects was evaluated by a quantitative analysis of pre- and post-sunglint correction reflectance values (residual reflectance images). Furthermore, the analysis was supported by inspection of the reflectance differences along transects placed over homogeneous masses of waters or over specific portions of the scenes affected and non-affected by sunglint. Results showed that the algorithm of Goodman et al. (2008) produced better results than the other two methods, as it approached to zero the amplitude of the reflectance values between homogenous water masses free and contaminated by sunglint. The Kutser et al. (2009) method had also good performance, except for the most contaminated sunglint portions of the scenes. When the continuum removal technique was incorporated to the Kutser et al. (2009) method, results varied with the scene and were more sensitive to atmospheric correction artifacts and instrumental signal-to-noise ratio

Linking plant phenology to conservation biology

Phenology has achieved a prominent position in current scenarios of global change research given its role inmonitoring and predicting the timing of recurrent life cycle events. However, the implications of phenology to environmental conservation and management remain poorly explored. Here,we present the first explicit appraisal of howphenology-amultidisciplinary science encompassing biometeorology, ecology, and evolutionary biology- can make a key contribution to contemporary conservation biology. We focus on shifts in plant phenology induced by global change, their impacts on species diversity and plant-animal interactions in the tropics, and how conservation efforts could be enhanced in relation to plant resource organization. We identify the effects of phenological changes and mismatches in the maintenance and conservation of mutualistic interactions, and examine how phenological research can contribute to evaluate, manage and mitigate the consequences of land-use change and other natural and anthropogenic disturbances, such as fire, exotic and invasive species. Wealso identify cutting-edge tools that can improve the spatial and temporal coverage of phenological monitoring, from satellites to drones and digital cameras. We highlight the role of historical information in recovering long-term phenological time series, and track climate-related shifts in tropical systems. Finally, we propose a set of measures to boost the contribution of phenology to conservation science.Weadvocate the inclusion of phenology into predictive models integrating evolutionary history to identify species groups that are either resilient or sensitive to future climate-change scenarios, and understand how phenological m ismatches can affect community dynamics, ecosystem services, and conservation over time

Análise comparativa de produtos geoespaciais para monitoramento de precipitação em uma região montanhosa tropical

A precipitação é um importante elemento do sistema climático, entretanto a análise de seus padrões no território brasileiro é muitas vezes dificultada pela baixa densidade espacial da rede de pluviômetros em solo. Produtos geoespaciais derivados de dados de sensoriamento remoto,combinados ou não com dados in situ, ajudam a solucionar esta limitação. Este estudo teve como objetivo analisar as correspondências entre os padrões de precipitação representados através dos produtos TRMM, CHIRPS, WorldClim e CHELSA, disponibilizados com resolução mensal, em uma área montanhosa tropical (Cadeia do Espinhaço Meridional, Brasil). Os produtos apresentaram boa correspondência entre os padrões macroclimáticos registrados, com o produto CHELSA apresentando maior diferença em relação aos demais. O produto CHIRPS apresenta-se como a melhor opção para análises nesta região, devido à sua resolução temporal e a incorporação de dados de diferentes fontes em sua formulação

Land Surface Phenology in the Tropics: The Role of Climate and Topography in a Snow-Free Mountain

Leaf phenology represents a major temporal component of ecosystem functioning, and understanding the drivers of seasonal variation in phenology is essential to understand plant responses to climate change. We assessed the patterns and drivers of land surface phenology, a proxy for leafing phenology, for the meridional Espinhaço Range, a South American tropical mountain comprising a mosaic of savannas, dry woodlands, montane vegetation and moist forests. We used a 14-year time series of MODIS/NDVI satellite images, acquired between 2001 and 2015, and extracted phenological indicators using the TIMESAT algorithm. We obtained precipitation data from the Tropical Rainfall Measuring Mission, land surface temperature from the MODIS MOD11A2 product, and cloud cover frequency from the MODIS MOD09GA product. We also calculated the topographic wetness index and simulated clear-sky radiation budgets based on the SRTM elevation model. The relationship between phenology and environmental drivers was assessed using general linear models. Temporal displacement in the start date of the annual growth season was more evident than variations in season length among vegetation types, indicating a possible temporal separation in the use of resources. Season length was inversely proportional to elevation, decreasing 1.58 days per 100 m. Green-up and senescence rates were faster where annual temperature amplitude was higher. We found that water and light availability, modulated by topography, are the most likely drivers of land surface phenology in the region, determining the start, end and length of the growing season. Temperature had an important role in determining the rates of leaf development and the strength of vegetation seasonality, suggesting that tropical vegetation is also sensitive to latitudinal temperature changes, regardless of the elevational gradient. Our work improves the current understanding of phenological strategies in the seasonal tropics and emphasizes the importance of topography in shaping light and water availability for leaf development in snow-free mountains

Shared-role of vegetation types, elevation and soil affecting plant diversity in an old-tropical mountain hotspot

Despite the exceptional species richness and endemism, the environmental drivers of plant diversity along old tropical mountains remain under-explored. The respective importance of vegetation types, elevation, slope, and soil to drive diversity across life-forms is poorly addressed. Here, we tested whether environmental variables drove local and regional plant diversity along an old tropical mountain according to the three main life-forms: graminoids, herbaceous and woody species. We sampled all Angiosperm species on 180 plots across five elevations, at the tropical old-mountain region of Serra do Cipo, South-eastern Brazil. We assessed soil, slope, and vegetation types, and calculated richness and beta-diversity, applying generalized least square models, linear mixed-models and partial Mantel tests to test for relationships. Richness of graminoids and herbaceous species increased with greater elevation and more nutrient-impoverished soils, while woody richness showed the inverse pattern. Beta-diversity was primarily driven by species turnover, correlated with elevation and soil and higher in less dominant vegetation types, with unique species. Despite the limited elevational range in these old mountains, it still played an important role in filtering woody species, while fostering graminoid and herbaceous species. Conservation and restoration actions need to foster the high regional diversity supported by the old mountain heterogeneous landscape and the diversity of life-forms, especially the dominant and highly diverse grassy component

Massive tree mortality from flood pulse disturbances in Amazonian floodplain forests: The collateral effects of hydropower production

Large dams built for hydroelectric power generation alter the hydrology of rivers, attenuating the flood pulse downstream of the dam and impacting riparian and floodplain ecosystems. The present work mapped black-water floodplain forests (igapó) downstream of the Balbina Reservoir, which was created between 1983 and 1987 by damming the Uatumã River in the Central Amazon basin. We apply remote sensing methods to detect tree mortality resulting from hydrological changes, based on analysis of 56 ALOS/PALSAR synthetic aperture radar images acquired at different flood levels between 2006 and 2011. Our application of object-based image analysis (OBIA) methods and the random forests supervised classification algorithm yielded an overall accuracy of 87.2%. A total of 9800 km2 of igapó forests were mapped along the entire river downstream of the dam, but forest mortality was only observed below the first 49 km downstream, after the Morena rapids, along an 80-km river stretch. In total, 12% of the floodplain forest died within this stretch. We also detected that 29% of the remaining living igapó forest may be presently undergoing mortality. Furthermore, this large loss does not include the entirety of lost igapó forests downstream of the dam; areas which are now above current maximum flooding heights are no longer floodable and do not show on our mapping but will likely transition over time to upland forest species composition and dynamics, also characteristic of igapó loss. Our results show that floodplain forests are extremely sensitive to long-term downstream hydrological changes and disturbances resulting from the disruption of the natural flood pulse. Brazilian hydropower regulations should require that Amazon dam operations ensure the simulation of the natural flood-pulse, despite losses in energy production, to preserve the integrity of floodplain forest ecosystems and to mitigate impacts for the riverine populations