scholarly journals Overwhelming presence of non-food vegetation undermines the reliability of NDVI as a surrogate of forage abundance for a large herbivore in a tropical forest habitat

2018 ◽  
Author(s):  
Hansraj Gautam ◽  
Evangeline Arulmalar ◽  
Mihir R Kulkami ◽  
TNC Vidya
Keyword(s):  
Tropical Forest ◽  
Vegetation Index ◽  
Species Abundance ◽  
Negative Relationship ◽  
Ground Level ◽  
Food Abundance ◽  
Total Abundance ◽  
Large Herbivore ◽  
Forage Availability ◽  
Food Species

AbstractThe use of remotely-sensed vegetation indices has increased in wildlife studies but field-based support for their utility as a measure of forage availability largely comes from open-canopy habitats. In this paper, we assessed whether the popular vegetation index, NDVI, actually represents forage availability for Asian elephants in a southern Indian tropical forest. We found that the number of food species was a small percentage of all plant species, and the abundance of food species compared to total species abundance varied across different vegetation categories. NDVI was not a good measure of food abundance in any vegetation category partly because of a) small to moderate proportional abundances of food species relative to the total abundance of all species in that category (herb and shrub categories), b) abundant overstorey vegetation resulting in low correlations between NDVI and food abundance despite a high proportional abundance of food species and a concordance between total abundance and food species abundance (graminoid category), and c) the relevant variables measured and important as food at the ground level (count and GBH) not being related to primary productivity (trees and recruits). NDVI had a negative relationship with the total abundance of graminoids, which represent a bulk of elephant and other herbivore diet, because of the presence of other vegetation types and canopy cover that positively explained NDVI. We also found that spatially interpolated total graminoid abundance modelled from field data outperformed NDVI in predicting total graminoid abundance, although interpolation models of food graminoid species abundance were not satisfactory. Our results reject the utility of NDVI as a surrogate of elephant forage abundance in tropical forests with multistorey vegetation, a finding that has implications for studies of other herbivores in such habitats.

scholarly journals Use of Unmanned Aerial Vehicles (UAVs) Imagery in Phenotyping of Bambara Groundnut

2020 ◽  
Vol 12 (6) ◽  
pp. 12
Author(s):  
Tengku Adhwa Syaherah Tengku Mohd Suhairi ◽  
Siti Sarah Mohd Sinin ◽  
Eranga M. Wimalasiri ◽  
Nur Marahaini Mohd Nizar ◽  
Anil Shekar Tharmandran ◽  
...  
Keyword(s):  
Vegetation Index ◽  
Ground Level ◽  
Bambara Groundnut ◽  
Growth Stages ◽  
Remotely Sensed Data ◽  
Nutrition Security ◽  
Lack Of Information ◽  
Normalised Difference Vegetation Index ◽  
Underutilised Crops ◽  
Crop Parameters

In this experiment, proximal measurements and Unmanned Aerial Vehicle (UAV) imagery was used to determine growth stages for bambara groundnut (Vigna subterranea (L.) Verdc.). The crop is a high potential crop due to its ability to yield in marginal environments, but neglected and underutilised due to lack of information on its growth in different environments. This study evaluated the correlation between Normalised Difference Vegetation Index (NDVI) derived from the ground as well as airborne sensors to test the ability of remotely sensed data to identify growth stages. NDVI and chlorophyll content of bambara groundnut leaves were measured at ground level at 18, 32, 46 and 88 days after planting (DAP) comprising vegetative, flowering, pod formation and maturity growth stages. The UAV imagery for the experimental plots was acquired with 0.2m resolution at maturity. The result showed a significant (p < 0.05) linear relationship between proximal NDVI and chlorophylls content at all growth stages ofgrowth. The R2 varied from 0.57 in the vegetative stage to 0.78 in the flowering stage. Furthermore, NDVI derived from proximal measurements and UAV data showed a significant (p < 0.05) correlation. The observed high correlation between proximal sensors, UAV data and crop parameters suggest that remote sensing technologies can be used for rapid phenotyping to hasten the development of models to assess the performance of underutilised crops for food and nutrition security.

scholarly journals Effect of disturbance on plant species abundance and density distribution in tropical forest of Sunsari district, Eastern Nepal

2016 ◽  
Vol 6 (1) ◽  
pp. 1-12
Author(s):  
Tilak Prasad Gautam ◽  
Tej Narayan Mandal
Keyword(s):  
Carbon Sequestration ◽  
Species Composition ◽  
Tropical Forest ◽  
Tropical Forests ◽  
Tree Species ◽  
Forest Disturbance ◽  
Species Abundance ◽  
Forest Degradation ◽  
Tree Density ◽  
Shrub Species

The disappearance of global tropical forests due to deforestation and forest degradation has reduced the biodiversity and carbon sequestration capacity. In these contexts, present study was carried out to understand the species composition and density in the undisturbed and disturbed stands of moist tropical forest located in Sunsari district of eastern Nepal. Study revealed that the forest disturbance has reduced the number of tree species by 33% and tree density by 50%. In contrary, both number and density of herb and shrub species have increased with forest disturbance.

scholarly journals Assessing Correlation of High-Resolution NDVI with Fertilizer Application Level and Yield of Rice and Wheat Crops using Small UAVs

2019 ◽  
Vol 11 (2) ◽  
pp. 112 ◽  
Author(s):  
Senlin Guan ◽  
Koichiro Fukami ◽  
Hitoshi Matsunaka ◽  
Midori Okami ◽  
Ryo Tanaka ◽  
...  
Keyword(s):  
High Resolution ◽  
Vegetation Index ◽  
Normalized Difference Vegetation Index ◽  
Ground Level ◽  
Fertilizer Application ◽  
Alignment Algorithm ◽  
Distribution Maps ◽  
Ripening Stages ◽  
Highly Correlated ◽  
Multispectral Sensing

The aim of this study was to use small unmanned aerial vehicles (UAVs) for determining high-resolution normalized difference vegetation index (NDVI) values. Subsequently, these results were used to assess their correlations with fertilizer application levels and the yields of rice and wheat crops. For multispectral sensing, we flew two types of small UAVs (DJI Phantom 4 and DJI Phantom 4 Pro)—each equipped with a compact multispectral sensor (Parrot Sequoia). The information collected was composed of numerous RGB orthomosaic images as well as reflectance maps with spatial resolution greater than a ground sampling distance of 10.5 cm. From 223 UAV flight campaigns over 120 fields with a total area coverage of 77.48 ha, we determined that the highest efficiency for the UAV-based remote sensing measurement was approximately 19.8 ha per 10 min while flying 100 m above ground level. During image processing, we developed and used a batch image alignment algorithm—a program written in Python language–to calculate the NDVI values in experimental plots or fields in a batch of NDVI index maps. The color NDVI distribution maps of wide rice fields identified differences in stages of ripening and lodging-injury areas, which accorded with practical crop growth status from aboveground observation. For direct-seeded rice, variation in the grain yield was most closely related to that in the NDVI at the early reproductive and late ripening stages. For wheat, the NDVI values were highly correlated with the yield ( R 2 = 0.601–0.809) from the middle reproductive to the early ripening stages. Furthermore, using the NDVI values, it was possible to differentiate the levels of fertilizer application for both rice and wheat. These results indicate that the small UAV-derived NDVI values are effective for predicting yield and detecting fertilizer application levels during rice and wheat production.

Population decline in semi-migratory caribou (Rangifer tarandus): intrinsic or extrinsic drivers?

2013 ◽  
Vol 91 (11) ◽  
pp. 820-828 ◽  
Author(s):  
Guillaume Bastille-Rousseau ◽  
James A. Schaefer ◽  
Shane P. Mahoney ◽  
Dennis L. Murray
Keyword(s):  
Density Dependence ◽  
Rangifer Tarandus ◽  
Vegetation Index ◽  
Normalized Difference Vegetation Index ◽  
Population Decline ◽  
Negative Relationship ◽  
Population Limitation ◽  
Continental Scale ◽  
Delayed Density Dependence ◽  
Winter Severity

Many populations of caribou (Rangifer tarandus (L., 1758)) across North America, including Newfoundland, are in a state of decline. This phenomenon may reflect continental-scale changes in either the extrinsic or the intrinsic factors affecting caribou abundance. We hypothesized that caribou decline reflected marked resource limitation and predicted that fluctuations should correspond to time-delayed density dependence associated with a decline in range quality and decadal trends in winter severity. By conducting time-series analysis using 12 populations and evaluating correlations between caribou abundance and trends in (i) vegetation available at calving (normalized difference vegetation index, NDVI), (ii) winter weather severity (index of North Atlantic Oscillation, NAO), and (iii) caribou morphometrics, we observed strong evidence of density dependence in population dynamics (i.e., a negative relationship between caribou population size and caribou morphometrics). Caribou population trajectories were time-delayed relative to winter severity, but not relative to calving-ground greenness. These island-wide correlations could not be traced to dispersal between herds, which appears rare at least for adult females. Our results suggest that trends in winter severity may synchronize broad-scale changes in caribou abundance that are driven by time-delayed density dependence, although it remains possible that calving-ground deterioration also may contribute to population limitation in Newfoundland. Our findings provide the basis for additional research into density dependence and caribou population decline.

Factors influencing the pattern of fire severities in a large wildfire under extreme meteorological conditions in the Mediterranean basin

2009 ◽  
Vol 18 (7) ◽  
pp. 755 ◽  
Author(s):  
Imma Oliveras ◽  
Marc Gracia ◽  
Gerard Moré ◽  
Javier Retana
Keyword(s):  
Vegetation Index ◽  
Normalized Difference Vegetation Index ◽  
Fire Severity ◽  
Fire Behavior ◽  
Negative Relationship ◽  
Canopy Cover ◽  
Mediterranean Ecosystems ◽  
Meteorological Conditions ◽  
Landsat Images ◽  
The Difference

In Mediterranean ecosystems, large fires frequently burn under extreme meteorological conditions, but they are usually characterized by a spatial heterogeneity of burn severities. The way in which such mixed-severity fires are a result of fuels, topography and weather remains poorly understood. We computed fire severity of a large wildfire that occurred in Catalonia, Spain, as the difference between the post- and pre-fire Normalized Difference Vegetation Index (NDVI) values obtained through Landsat images. Fuel and topographic variables were derived from remote sensing, and fire behavior variables were obtained from an exhaustive reconstruction of the fire. Results showed that fire severity had a negative relationship with percentage of canopy cover, i.e. green surviving plots were mainly those with more forested conditions. Of the topographic variables, only aspect had a significant effect on fire severity, with higher values in southern than in northern slopes. Fire severity was higher in head than in flank and back fires. The interaction of these two variables was significant, with differences between southern and northern aspects being small for head fires, but increasing in flank and back fires. The role of these variables in determining the pattern of fire severities is of primary importance for interpreting the current landscapes and for establishing effective fire prevention and extinction policies.

scholarly journals Drone Surveys Revealed Bottom-Up, And Not Top-Down, Effects On The Marsh Deer Local Abundance

2021 ◽  
Author(s):  
Ismael Verrastro Brack ◽  
Andreas Kindel ◽  
Douglas Oliveira Berto ◽  
José Luis Passos Cordeiro ◽  
Igor Pfeifer Coelho ◽  
...  
Keyword(s):  
Mixture Models ◽  
Negative Relationship ◽  
Dry Season ◽  
Relative Influence ◽  
Top Down ◽  
Large Herbivore ◽  
Large Herbivores ◽  
Bottom Up ◽  
Vegetation Greenness ◽  
Local Abundance

Abstract Context: Spatial variation in large herbivore populations can be highly affected by the availability of resources (bottom-up) but modulated by the presence of predators (top-down). Studying the relative influence of these forces has been a major topic of interest in ecological and conservation research, while it has also been challenging to sample large herbivores. Objective: i) Explore the use of spatiotemporally replicated drone-based counts analysed with N-mixture models to estimate abundance of large herbivores. ii) Evaluate the relative influence of bottom-up (forage and water) and top-down (jaguars) processes on the local abundance of the threatened marsh deer.Methods: We conducted spatiotemporally replicated drone flights in the dry season of Pantanal wetland (Brazil) and imagery was reviewed by either one or two observers. We fitted counts using N-mixture models (for single and double observer protocols) and modelled local abundance in relation to vegetation greenness, distance to water bodies, and jaguar density.Results: We found a positive relationship of marsh deer local abundance with vegetation greenness, a negative relationship with distance to water, but no relation with jaguar density. Individuals were concentrated in the lower and wetter region, even though it is the area expected to be more lethal from jaguar predation.Conclusions: Bottom-up processes are shaping the distribution of marsh deer in the dry season; the benefits of accessing high-quality areas outweigh predation risk from jaguars. Spatiotemporally replicated drone-based counts may serve as an accessible and cost-effective protocol for large herbivores abundance estimation and monitoring while accounting for imperfect detection.

scholarly journals Grazing Effects on Day Butterflies in a Mediterranean Woodland Ecosystem in Northern Israel

2020 ◽  
Author(s):  
Gad Ish Am ◽  
Talia Oron
Keyword(s):  
Endangered Species ◽  
Nature Reserve ◽  
Species Abundance ◽  
Similarity Index ◽  
Cattle Grazing ◽  
Grazing Management ◽  
Butterfly Species ◽  
Total Abundance ◽  
Species Similarity ◽  
Mediterranean Woodland

Abstract The effects of cattle grazing on biodiversity in Mediterranean woodlands are yet unknown. To assess these effects on diurnal butterflies, we conducted daytime surveys in the Mt. Meron nature reserve (northern Israel) in two habitats over two different years. In each habitat we chose one site that was grazed by cattle and, as a control, a similar but ungrazed site. Belt transects (5m wide), divided for 100m replications, were surveyed five times on ridges in 2015 (11 replications, 538 butterflies, 25 species), and nine times in valleys in 2016 (12 replications, 3,944 butterflies, 38 species). In both habitats, species similarity index between sites was high. Richness was higher in the ridge control and evenness was higher in the valley grazed site. In both habitats total abundance was ca. twofold higher in the control, and the abundance of woody affiliated butterflies was threefold higher in the control, probably due to overgrazing, which affects butterflies’ breeding niches. For batha polyphagous and oligophagous butterfly species, abundance was similar between the sites, and for a few of those, associated with increaser plants, it was even higher in the grazed sites. However, the batha monophagous species were significantly more abundant in the control. Monophagous and endangered species were found to be more sensitive to cattle grazing. We conclude that the current cattle grazing management in Mt. Meron reserve affects butterfly populations negatively. Therefore, we recommend more regulated grazing and early-season deferment precautions, along with designation of no-grazing areas in reserves.

scholarly journals Australian mosquito assemblages vary between ground and sub-canopy habitats

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Boni F. Sebayang ◽  
Tanya L. Russell ◽  
Kyran M. Staunton ◽  
Michael Townsend ◽  
Christopher Paton ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Mosquito Species ◽  
Species Abundance ◽  
Latin Square ◽  
Ground Level ◽  
Larval Habitat ◽  
Resting Behaviour ◽  
Trap Height ◽  
Host Blood ◽  
And Control

Abstract Background The surveillance and control of mosquito-borne diseases is dependent upon understanding the bionomics and distribution of the vectors. Most studies of mosquito assemblages describe species abundance, richness and composition close to the ground defined often by only one sampling method. In this study, we assessed Australian mosquito species near the ground and in the sub-canopy using two traps baited with a variety of lures. Methods Mosquitoes were sampled using a 4 × 4 Latin square design at the Cattana Wetlands, Australia from February to April 2020, using passive box traps with octenol and carbon dioxide and three variations of a sticky net trap (unbaited, and baited with octenol or octenol and carbon dioxide). The traps were deployed at two different heights: ground level (≤ 1 m above the ground) and sub-canopy level (6 m above the ground). Results In total, 27 mosquito species were identified across the ground and sub-canopy levels from the different traps. The abundance of mosquitoes at the ground level was twofold greater than at the sub-canopy level. While the species richness at ground and sub-canopy levels was not significantly different, species abundance varied by the collection height. Conclusions The composition of mosquito population assemblages was correlated with the trap types and heights at which they were deployed. Coquillettidia species, which prefer feeding on birds, were mainly found in the sub-canopy whereas Anopheles farauti, Aedes vigilax and Mansonia uniformis, which have a preference for feeding on large mammals, were predominantly found near the ground. In addition to trap height, environmental factors and mosquito bionomic characteristics (e.g. larval habitat, resting behaviour and host blood preferences) may explain the vertical distribution of mosquitoes. This information is useful to better understand how vectors may acquire and transmit pathogens to hosts living at different heights. Graphical abstract

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