• Energy Research

Estimating forest structural attributes using multispectral remote sensing is challenging because of the saturation of multispectral indices at high canopy cover. The objective of this study was to assess the utility of hyperspectral data in estimating and mapping forest structural parameters including mean diameter-at-breast height (DBH), mean tree height and tree density of a closed canopy beech forest (Fagus sylvatica L.). Airborne HyMap images and data on forest structural attributes were collected from the Majella National Park, Italy in July 2004. The predictive performances of vegetation indices (VI) derived from all possible two-band combinations (VI(i,j) = (Ri - Rj)/(Ri + Rj), where Ri and Rj = reflectance in any two bands) were evaluated using calibration (n = 33) and test (n = 20) data sets. The potential of partial least squares (PLS) regression, a multivariate technique involving several bands was also assessed. New VIs based on the contrast between reflectance in the red-edge shoulder (756-820 nm) and the water absorption feature centred at 1200 nm (1172-1320 nm) were found to show higher correlations with the forest structural parameters than standard VIs derived from NIR and visible reflectance (i.e. the normalised difference vegetation index, NDVI). PLS regression showed a slight improvement in estimating the beech forest structural attributes (prediction errors of 27.6%, 32.6% and 46.4% for mean DBH, height and tree density, respectively) compared to VIs using linear regression models (prediction errors of 27.8%, 35.8% and 48.3% for mean DBH, height and tree density, respectively). Mean DBH was the best predicted variable among the stand parameters (calibration R2 = 0.62 for an exponential model fit and standard error of prediction = 5.12 cm, i.e. 25% of the mean). The predicted map of mean DBH revealed high heterogeneity in the beech forest structure in the study area. The spatial variability of mean DBH occurs at less than 450 m. The DBH map could be useful to forest management in many ways, e.g. thinning of coppice to promote diameter growth, to assess the effects of management on forest structure or to detect changes in the forest structure caused by anthropogenic and natural factors

Many migrating herbivores rely on plant biomass to fuel their life cycles and have adapted to following changes in plant quality through time. The green wave hypothesis predicts that herbivorous waterfowl will follow the wave of food availability and quality during their spring migration. However, testing this hypothesis is hampered by the large geographical range these birds cover. The satellite-derived normalized difference vegetation index (NDVI) time series is an ideal proxy indicator for the development of plant biomass and quality across a broad spatial area. A derived index, the green wave index (GWI), has been successfully used to link altitudinal and latitudinal migration of mammals to spatio-temporal variations in food quality and quantity. To date, this index has not been used to test the green wave hypothesis for individual avian herbivores. Here, we use the satellite-derived GWI to examine the green wave hypothesis with respect to GPS-tracked individual barnacle geese from three flyway populations (Russian n = 12, Svalbard n = 8, and Greenland n = 7). Data were collected over three years (2008-2010). Our results showed that the Russian and Svalbard barnacle geese followed the middle stage of the green wave (GWI 40-60%), while the Greenland geese followed an earlier stage (GWI 20-40%). Despite these differences among geese populations, the phase of vegetation greenness encountered by the GPS-tracked geese was close to the 50% GWI (i.e. the assumed date of peak nitrogen concentration), thereby implying that barnacle geese track high quality food during their spring migration. To our knowledge, this is the first time that the migration of individual avian herbivores has been successfully studied with respect to vegetation phenology using the satellite-derived GWI. Our results offer further support for the green wave hypothesis applying to long-distance migrants on a larger scale.

Cette étude étudie le comportement d'éloignement des éléphants par rapport à la dynamique de la végétation induite par les précipitations. Les données sur les mouvements ont été acquises pour cinq troupeaux de célibataires et cinq troupeaux familiaux de femelles pendant trois ans dans l'aire protégée de Marsabit au Kenya et les changements dans la végétation ont été cartographiés à l'aide de la série temporelle de l'indice de végétation à différence normalisée MODIS (NDVI). Dans la zone d'étude, des altitudes de 650 à 1100 m.a.s.l connaissent deux périodes de croissance par an, tandis que des périodes de croissance supérieures à 1100 m.a.s.l. durent un an ou plus. Nous constatons que les éléphants réagissent rapidement aux changements dans la disponibilité du fourrage et de l'eau, effectuant des migrations en réponse à des événements pluviométriques importants et mineurs. La migration en altitude des éléphants individuels correspondait étroitement aux modèles de verdissement et de sénescence de la végétation dans leur domaine vital. Les éléphants occupaient des altitudes plus basses lorsque l'activité de la végétation était élevée, alors qu'ils se retiraient dans la forêt à feuilles persistantes à des altitudes plus élevées tandis que la végétation sénescait. Les domaines vitaux des éléphants ont diminué en taille et se chevauchaient moins avec l'augmentation de l'altitude. Une hypothèse récente selon laquelle les migrations des ongulés dans les savanes résultent de précipitations saisonnières compensatrices et de gradients de fertilité est démontrée et étendue aux migrations à plus courte distance. En d'autres termes, le compromis entre la mauvaise qualité du fourrage et l'accessibilité dans la forêt avec ses sources d'eau toute l'année, d'une part, et le fourrage de meilleure qualité dans la garrigue de basse altitude avec sa disponibilité saisonnière en eau, d'autre part, entraîne les migrations relativement courtes (les deux principaux corridors sont de 20 et 90 km) des éléphants. En outre, une compétition intra-spécifique accrue semble influencer l'utilisation de l'habitat des animaux pendant la saison sèche, ce qui indique que l'empiètement humain sur la forêt affecte la population d'éléphants. Este estudio investiga el comportamiento de los elefantes en relación con la dinámica de la vegetación impulsada por las precipitaciones. Los datos de movimiento se adquirieron para cinco solteros y cinco rebaños familiares femeninos durante tres años en el área protegida Marsabit en Kenia y los cambios en la vegetación se mapearon utilizando la serie de tiempo del índice de vegetación de diferencia normalizada MODIS (NDVI). En el área de estudio, las elevaciones de 650 a 1100 msnm experimentan dos períodos de crecimiento por año, mientras que los períodos de crecimiento superiores a 1100 msnm duran un año o más. Encontramos que los elefantes responden rápidamente a los cambios en la disponibilidad de forraje y agua, haciendo migraciones en respuesta a eventos de lluvia grandes y pequeños. La migración en altura de los elefantes individuales coincidió estrechamente con los patrones de reverdecimiento y senescencia de la vegetación en su área de distribución. Los elefantes ocupaban elevaciones más bajas cuando la actividad de la vegetación era alta, mientras que se retiraban al bosque de hoja perenne en elevaciones más altas mientras la vegetación se senescía. Los rangos de hogar de los elefantes disminuyeron de tamaño y se superpusieron menos con el aumento de la elevación. Se demuestra una hipótesis reciente de que las migraciones de ungulados en las sabanas son el resultado de la compensación de las precipitaciones estacionales y los gradientes de fertilidad, y se extiende a las migraciones de distancias más cortas. En otras palabras, el equilibrio entre la mala calidad del forraje y la accesibilidad en el bosque con sus fuentes de agua durante todo el año, por un lado, y el forraje de mayor calidad en los matorrales de baja altitud con su disponibilidad estacional de agua, por otro lado, impulsa las migraciones relativamente cortas (los dos corredores principales son de 20 y 90 km) de los elefantes. Además, el aumento de la competencia intraespecífica parece influir en el uso del hábitat de los animales durante la estación seca, lo que indica que la invasión humana del bosque está afectando a la población de elefantes. This study investigates the ranging behavior of elephants in relation to precipitation-driven dynamics of vegetation. Movement data were acquired for five bachelors and five female family herds during three years in the Marsabit protected area in Kenya and changes in vegetation were mapped using MODIS normalized difference vegetation index time series (NDVI). In the study area, elevations of 650 to 1100 m.a.s.l experience two growth periods per year, while above 1100 m.a.s.l. growth periods last a year or longer.We find that elephants respond quickly to changes in forage and water availability, making migrations in response to both large and small rainfall events. The elevational migration of individual elephants closely matched the patterns of greening and senescing of vegetation in their home range. Elephants occupied lower elevations when vegetation activity was high, whereas they retreated to the evergreen forest at higher elevations while vegetation senesced. Elephant home ranges decreased in size, and overlapped less with increasing elevation.A recent hypothesis that ungulate migrations in savannas result from countervailing seasonally driven rainfall and fertility gradients is demonstrated, and extended to shorter-distance migrations. In other words, the trade-off between the poor forage quality and accessibility in the forest with its year-round water sources on the one hand and the higher quality forage in the low-elevation scrubland with its seasonal availability of water on the other hand, drives the relatively short migrations (the two main corridors are 20 and 90 km) of the elephants. In addition, increased intra-specific competition appears to influence the animals' habitat use during the dry season indicating that the human encroachment on the forest is affecting the elephant population. تبحث هذه الدراسة في سلوك تحديد المدى للفيلة فيما يتعلق بديناميكيات الغطاء النباتي التي يحركها هطول الأمطار. تم الحصول على بيانات الحركة لخمسة عزاب وخمس قطعان عائلية من الإناث خلال ثلاث سنوات في منطقة مارسابيت المحمية في كينيا وتم تعيين التغييرات في الغطاء النباتي باستخدام السلسلة الزمنية لمؤشر الاختلاف الطبيعي للغطاء النباتي (NDVI). في منطقة الدراسة، تشهد الارتفاعات من 650 إلى 1100 ميللي ثانية في السنة فترتين للنمو، بينما تستمر فترات النمو التي تزيد عن 1100 ميللي ثانية في السنة أو أكثر. نجد أن الفيلة تستجيب بسرعة للتغيرات في العلف وتوافر المياه، مما يؤدي إلى هجرات استجابة لكل من أحداث هطول الأمطار الكبيرة والصغيرة. تتطابق الهجرة الارتفاعية للفيلة الفردية بشكل وثيق مع أنماط تخضير وشيخوخة النباتات في نطاقها الأصلي. احتلت الفيلة ارتفاعات منخفضة عندما كان النشاط النباتي مرتفعًا، في حين تراجعت إلى الغابة دائمة الخضرة على ارتفاعات أعلى بينما كان الغطاء النباتي يشيخ. انخفضت نطاقات منازل الأفيال من حيث الحجم، وتداخلت بشكل أقل مع زيادة الارتفاع. تظهر الفرضية الحديثة القائلة بأن هجرات ذوات الحوافر في السافانا ناتجة عن موازنة هطول الأمطار وتدرجات الخصوبة المدفوعة موسمياً، وتمتد إلى هجرات لمسافات أقصر. وبعبارة أخرى، فإن المفاضلة بين جودة الأعلاف الرديئة وإمكانية الوصول إليها في الغابة مع مصادر المياه على مدار السنة من ناحية والأعلاف عالية الجودة في الأراضي المنخفضة الارتفاع مع توافرها الموسمي للمياه من ناحية أخرى، تدفع الهجرات القصيرة نسبيًا (الممران الرئيسيان هما 20 و 90 كم) للفيلة. بالإضافة إلى ذلك، يبدو أن المنافسة المتزايدة بين الأنواع تؤثر على استخدام موائل الحيوانات خلال موسم الجفاف مما يشير إلى أن التعدي البشري على الغابة يؤثر على عدد الأفيال.

A seamless vegetation type map of India (scale 1: 50,000) prepared using medium-resolution IRS LISS-III images is presented. The map was created using an on-screen visual interpretation technique and has an accuracy of 90%, as assessed using 15,565 ground control points. India has hitherto been using potential vegetation/forest type map prepared by Champion and Seth in 1968. We characterized and mapped further the vegetation type distribution in the country in terms of occurrence and distribution, area occupancy, percentage of protected area (PA) covered by each vegetation type, range of elevation, mean annual temperature and precipitation over the past 100 years. A remote sensing-amenable hierarchical classification scheme that accommodates natural and semi-natural systems was conceptualized, and the natural vegetation was classified into forests, scrub/shrub lands and grasslands on the basis of extent of vegetation cover. We discuss the distribution and potential utility of the vegetation type map in a broad range of ecological, climatic and conservation applications from global, national and local perspectives. We used 15,565 ground control points to assess the accuracy of products available globally (i.e., GlobCover, Holdridge’s life zone map and potential natural vegetation (PNV) maps). Hence we recommend that the map prepared herein be used widely. This vegetation type map is the most comprehensive one developed for India so far. It was prepared using 23.5 m seasonal satellite remote sensing data, field samples and information relating to the biogeography, climate and soil. The digital map is now available through a web portal (http://bis.iirs.gov.in).

Biodiversity loss and variation in species responses to climate and land use change have been found across broad taxonomic groups. However, whether species from the same taxonomic group with distinct geographical ranges will respond differently is poorly understood. The aim of this study is to predict the potential impacts of future climate and land use change on the distribution of narrow- and wide-ranging Rhododendron species, and estimate their relative contribution in China. We applied the presence-only ecological niche model MaxEnt to predict the distribution of 10 narrow-ranging and 10 wide-ranging Rhododendron species for the year 2070, using three general circulation models and three scenarios of climate and land use change. We measured the predicted distribution change of each species using change ratio, distance and direction of core range shifts, and niche overlap using Schoener's D. We found that the distribution areas of six narrow-ranging species would decrease, of which one species would go extinct. The remaining four narrow-ranging species would experience range expansion. Distribution of all the wide-ranging Rhododendron species would decrease. All Rhododendrons will shift to the northwest. We conclude that Rhododendron species generally will be negatively affected by the climatic and land use change expected in 2070 from the three scenarios evaluated in this study, but some narrow-ranging species may be positively influenced. Narrow-ranging Rhododendron species are more vulnerable compared to wide-ranging Rhododendron species. This study demonstrated that the effects of climate and land use change on alpine and subalpine plant species is species-specific, thereby strengthening our understanding of the impacts of climate and land use change on plant distribution.

In mapping the forest¿woodland¿savannah mosaic of Budongo Forest Reserve, Uganda, four classification methods were compared, i.e. Maximum Likelihood classifier (MLC), Spectral Angle Mapper (SAM), Maximum Likelihood combined with an Expert System (MaxExpert) and Spectral Angle Mapper combined with an Expert System (SAMExpert). The combination of conventional classifiers with an Expert System proved to be an effective approach for forest mapping. This was also the first time that the SAMExpert had been used in the mapping of tropical forests. SAMExpert not only maps with high accuracy, but is also fast and easy to use, making it attractive for use in less developed countries. Another advantage is that it can be executed on a standard PC set up for image processing. Combining the conventional classifiers (MLC and SAM) with the Expert System significantly improved the classification accuracy. The highest overall accuracy (94.6%) was obtained with SAMExpert. The MaxExpert approach yielded a map with an accuracy of 85.2%, which was also significantly higher than that obtained using the conventional MLC approach. The SAMExpert classifier accurately mapped individual classes. Of the four classes of woodland mapped, the Open Woodland (with Terminalia) and Wooded Grassland classes were more accurately mapped using SAMExpert. The Open Woodland had been previously identified by ecologists, but had never been mapped.