Application of Remote Sensing Data for Locust Research and Management-A Review

Recently, locust outbreaks around the world have destroyed agricultural and natural vegetation and caused massive damage endangering food security. Unusual heavy rainfalls in habitats of the desert locust (Schistocerca gregaria) and lack of monitoring due to political conflicts or inaccessibility of those habitats lead to massive desert locust outbreaks and swarms migrating over the Arabian Peninsula, East Africa, India and Pakistan. At the same time, swarms of the Moroccan locust (Dociostaurus maroccanus) in some Central Asian countries and swarms of the Italian locust (Calliptamus italicus) in Russia and China destroyed crops despite developed and ongoing monitoring and control measurements. These recent events underline that the risk and damage caused by locust pests is as present as ever and affects 100 million of human lives despite technical progress in locust monitoring, prediction and control approaches. Remote sensing has become one of the most important data sources in locust management. Since the 1980s, remote sensing data and applications have accompanied many locust management activities and contributed to an improved and more effective control of locust outbreaks and plagues. Recently, open-access remote sensing data archives as well as progress in cloud computing provide unprecedented opportunity for remote sensing-based locust management and research. Additionally, unmanned aerial vehicle (UAV) systems bring up new prospects for a more effective and faster locust control. Nevertheless, the full capacity of available remote sensing applications and possibilities have not been exploited yet. This review paper provides a comprehensive and quantitative overview of international research articles focusing on remote sensing application for locust management and research. We reviewed 110 articles published over the last four decades, and categorized them into different aspects and main research topics to summarize achievements and gaps for further research and application development. The results reveal a strong focus on three species-the desert locust, the migratory locust (Locusta migratoria), and the Australian plague locust (Chortoicetes terminifera)-and corresponding regions of interest. There is still a lack of international studies for other pest species such as the Italian locust, the Moroccan locust, the Central American locust (Schistocerca piceifrons), the South American locust (Schistocerca cancellata), the brown locust (Locustana pardalina) and the red locust (Nomadacris septemfasciata). In terms of applied sensors, most studies utilized Advanced Very-High-Resolution Radiometer (AVHRR), Satellite Pour l'Observation de la Terre VEGETATION (SPOT-VGT), Moderate-Resolution Imaging Spectroradiometer (MODIS) as well as Landsat data focusing mainly on vegetation monitoring or land cover mapping. Application of geomorphological metrics as well as radar-based soil moisture data is comparably rare despite previous acknowledgement of their importance for locust outbreaks. Despite great advance and usage of available remote sensing resources, we identify several gaps and potential for future research to further improve the understanding and capacities of the use of remote sensing in supporting locust outbreak- research and management

Remote Sensing Applications to Support Locust Management and Research: Evaluating the Potential of Earth Observation for Locust Outbreaks in Different Regions

This dissertation focuses on satellite remote sensing applications for locust management and additional contributions to locust research. Specifically, the remote sensing-based characterization and interpretation of land surface cover and its dynamics are addressed with a special emphasis on the requirements of different locust species. At first, the aim of this dissertation is to provide a holistic overview of the existing applications using satellite data focusing on different locust species and thus, to present current and new opportunities. Furthermore, remote sensing and geospatial datasets are used in a model to categorize areas with ideal and less than ideal conditions for locust outbreaks. The benefit of up-to-date remote sensing data for preventive locust management is demonstrated using time-series-based Sentinel-2 land cover classification. Due to the diversity of the numerous locust species and their spatial distribution in different geographical locations, this research focuses mainly on two locust species, the Italian locust (Calliptamus italicus) and the Moroccan locust (Dociostaurus maroccanus), as well as on selected study areas within their extensive habitats, respectively. Both selected locust species caused numerous damages in Europe, the Caucasus, Central Asia and North Africa in the past. For both species, there is only a limited number of publications exploiting the capabilities of remote sensing methods. Therefore, this dissertation aims to explore the potential approaches of Earth observation datasets to support preventive locust management and research for both species.Die vorliegende Dissertation beschäftigt sich mit dem Einsatz der Satellitenfernerkundung im Bereich Heuschreckenmanagement und -forschung. Die fernerkundungsbasierte Charakterisierung und Interpretation der Landoberflächen-bedeckung und deren Dynamik stehen dabei - mit Fokus auf die Anforderungen der verschiedenen Heuschreckenarten - im Vordergrund. Ziel dieser Dissertation ist es zunächst, einen ganzheitlichen Überblick über vorhandene Anwendungen von Satellitendaten im Kontext Heuschreckenmanagement zu erarbeiten. Des Weiteren werden fernerkundungs- und geobasierten Datensätzen in einem Model verwendet, um Flächen mit idealen bzw. weniger idealen Bedingungen für Heuschreckenausbrüche zu kategorisieren. Der Vorteil von aktuellen Fernerkundungsdaten für präventives Heuschreckenmanagement wird anhand zeitreihenbasierten Sentinel-2 Landbedeckungsklassifikation demonstriert. Aufgrund der Vielfältigkeit der zahlreichen Heuschreckenarten und deren räumlicher Verteilung in verschiedenen geographischen Lagen, konzentriert sich diese Arbeit im Wesentlichen auf zwei Heuschreckenarten, die Italienische Schönschrecke (Calliptamus italicus) und die Marokkanische Wanderheuschrecke (Dociostaurus maroccanus), sowie auf ausgewählte Studiengebiete innerhalb deren weiträumigen Habitaten. Beide Heuschreckenarten verursachten zahlreiche Ausbrüche in der Vergangenheit mit Schäden in Europa, dem Kaukasus, Zentralasien und Nordafrika. Für beide Heuschreckenarten existieren nur wenige Forschungsarbeiten, die sich mit der Anwendung von Fern-erkundungsdaten auseinandersetzen. Vor diesem Hintergrund zielt diese Dissertation auf die Entwicklung von relevanten Methoden unter Einsatz von Fernerkundungsdaten für beide Heuschreckenarten ab, um präventives Heuschreckenmanagement und -forschung zu unterstützen.Данная диссертация раскрывает тему применения спутникового дистанционного зондирования для контроля саранчовых и проведения дополнительных исследований саранчи. В частности, особое внимание уделяется изучению потребностей различных видов саранчовых при описании характеристик земного покрова и его динамики на основе данных дистанционного зондирования. Первостепенная цель данной диссертации состоит в том, чтобы предоставить целостный обзор существующих приложений, использующих спутниковые данные, в разрезе различных видов саранчовых для того, чтобы раскрыть текущие и потенциальные возможности. Кроме того, дистанционное зондирование и наборы геопространственных данных используются для классификации территорий с идеальными и не идеальными условиями для нашествий саранчи. исследование сосредоточено в основном на двух видах саранчи, итальянского пруса (Calliptamus italicus) и марокканской саранче (Dociostaurus maroccanus), а также на определенных территориях, в пределах их обширногo местообитаний

Application of geospatial and remote sensing data to support locust management

Negative impacts on agricultural activities by different locust species are well documented and have always been one of the major threats to food security and livelihoods, especially for local communities. Locust management and control have led to less frequent and intense plagues and outbreaks worldwide. However, political insecurity and armed conflicts affect locust management, and can as well as changing climate, and land use management contribute to new outbreaks. In the context of the increasing world population and higher demand for agricultural production, locust pests will remain of high concern. Geospatial and remote sensing data have become an important source of information for different applications within locust research and management. However, there is still a gap between available information and actual practical usage. In this study, we demonstrate the importance of geospatial and remote sensing data and how this information can be prepared for a straightforward application for stakeholders. For this purpose, we use the h3-hexagonal hierarchical geospatial indexing system to simplify and structure spatial information into standardized hexagon units. The presented concept provides decision makers and ground teams with a simplified information database that contains area-wide information over time and space and can be used without detailed geospatial knowledge and background. The concept is designed for the use case of Italian locust management in the Pavlodar region (Kazakhstan) and based on actual practices. It can be extrapolated to any other study area or species of interest. Our results underline the importance of actual land management on locust presence. Up-to-date land management information can be derived from time-series analyses of remote sensing data. Furthermore, essential meteorological data are used to generate locust-specific climatic characteristics within the h3-system. Within this system, areal prioritizing for locust management can be achieved based on the included spatial information and experience from ongoing practices

Ajuste de un modelo para estimar el contenido de humedad del suelo utilizando TVDI en el Estado de Sinaloa, México

There are various direct and indirect methods used to estimate soil humidity. In remote perception or tele-detection, the TVDI, (Temperature-Vegetation Dryness Index), may be used, which uses terrestrial surface temperatures, and vegetation indexes as input standards. The proposal of this work is to present a quick manner of readjusting those figures where water bodies undergo some dry degree of the soil for the whole area of study. Four years were selected (2003, 2006, 2009 and 2012), the TVDI was estimated with input of MODIS products. An adjustment value was proposed based on the difference of the mean, and standard deviation of water bodies; this figure is applied to the resulting product, which lead to establish that water bodies show a humidity saturation of their soil. Adjustment values are different for each year of study. Humidity content is consistent to expected variability according to the various uses of soil and vegetation. Results agree with drought reports to the State of Sinaloa.Para la estimación del contenido de humedad en el suelo, existen diversos métodos entre los cuales son directos e indirectos. En percepción remota o teledetección, se puede utilizar el TVDI (Temperature-Vegetation Dryness Index), que utiliza de parámetros de entrada las temperaturas superficiales terrestres e índices de vegetación. La propuesta de este trabajo, es presentar una manera rápida de reajustar aquellos valores donde los cuerpos de agua presentan algún grado de sequedad en el suelo para toda un área de estudio. Se seleccionaron 4 años (20003, 2006, 2009 y 2012), se estimó el TVDI con insumos de productos MODIS. Se propuso un valor de ajuste basado en la diferencia de la media y desviación estándar de los cuerpos de agua, se aplica este valor en el producto generado dando como resultado que los cuerpos de agua presentan ahora si una saturación de humedad en sus suelos. Los valores de ajustes son diferentes para cada año de estudio. El contenido de humedad es consistente a la variabilidad esperada acorde a los diferentes usos de suelo y vegetación. Los resultados están acorde a los reportes de sequía reportadas para el Estado de Sinaloa.Â

How to Manage Migratory Pests and Potential Food Crises

Locusts are a threat to agriculture and livelihoods in many countries globally. The economic, social, and environmental consequences of these highly migratory pests are so substantial that they are treated as a national priority by many countries; several international commissions have been established to unite efforts. This Special Issue aims to shed light on some overarching questions: what have we learned from historical outbreaks; how serious is the threat; what research is ongoing and is needed to better manage these insects; how should the world respond to plagues today, especially in the context of climate change; are recommended preventive strategies really effective and what are the constraints to their application; and is there a possibility to make better use of biological alternatives to chemical pesticides

Improving slash-and-burn agriculture in Central Menabe, Madagascar

Slash-and-burn agriculture is considered as an important driver of deforestation in the tropics. In Madagascar, a biodiversity hotspot, this type of agriculture particularly threatens the tropical forest cover. On the south-western coast of the island, in Central Menabe, the dry tropical forest of Kirindy suffers from an annual deforestation of 2.6%. At such alarming rate, the forest will have entirely disappeared by 2050. The attention of past research programs and conservation actions were mainly on studying the forest or the general interactions between local populations and the forest, with little focus on the slash-and-burn agricultural system itself. Hence, understanding the cultivation practices and assessing alternatives to them is crucial to improve the current forest conservation initiatives. The present thesis answers to the need of an in-depth study of the agricultural practices in Central Menabe. The project aims to (1) analyze the practices of slash-and-burn cultivation in Kirindy forest, (2) explore alternative slash-and-burn practices which may be more sustainable for the forest, (3) determine the implementation perspectives of these alternatives. In a first stage, we have characterized soil productivity along repetitive slash-and-burn cultivation cycles and the farmerâs perception of their agricultural system. Then, we experimented a selective slash-and-burn agriculture (where trees are left intentionally within the cultivated fields), coupled with compost amendment. Finally, we have assessed the implementation potential of that technique through interviews and participating workshops with local farmers. Our findings highlighted that soil depletion due to plant uptake and erosion or leaching by heavy rains, as well as weed invasion were important problems of slash-and-burn cultivation in Central Menabe. Farmers perceive weeding as a work overload. Decrease in grain yield due to slash-and-burn agriculture reaches about 40% after three years of cultivation on the same field (from 4 to 2.5 t ha-1), and decreases up to 75% after a single cyclonic rainy season (from 4 to 1 t ha-1). Further, we demonstrated that combining compost and wood ashes (from the burnings) seems a promising solution to sustain cultivation on the fields. Compost, combined with wood ashes, multiplied corn yield by 5 compared to traditional slash-and-burn agriculture. Growth rates were accelerated and phenology stages of maize plants advanced. Furthermore, this combination also increased soil security by improving the remaining stock of nutrients after a rain simulation. On the other hand, a partial remaining tree cover (selective slash-and-burn agriculture) improved corn yields only when the soil was amended with ashes, not with compost, nor the combination of both. Implementing composting in the forest dwelling communities appears to be a challenging task. Several barriers were highlighted, among them the most important was the water constraints during a consequent period of time related to compost maintenance. Alternative slash-and-burn practices have not been much studied so far because the use of fire was always considered as destructive. Thus, our result will contribute to the development of new forest management strategies which would balance conservation of habitats and rural communities agricultural needs, while minimizing the impact on primary forest

A cricket Gene Index: a genomic resource for studying neurobiology, speciation, and molecular evolution

<p>Abstract</p> <p>Background</p> <p>As the developmental costs of genomic tools decline, genomic approaches to non-model systems are becoming more feasible. Many of these systems may lack advanced genetic tools but are extremely valuable models in other biological fields. Here we report the development of expressed sequence tags (EST's) in an orthopteroid insect, a model for the study of neurobiology, speciation, and evolution.</p> <p>Results</p> <p>We report the sequencing of 14,502 EST's from clones derived from a nerve cord cDNA library, and the subsequent construction of a Gene Index from these sequences, from the Hawaiian trigonidiine cricket <it>Laupala kohalensis</it>. The Gene Index contains 8607 unique sequences comprised of 2575 tentative consensus (TC) sequences and 6032 singletons. For each of the unique sequences, an attempt was made to assign a provisional annotation and to categorize its function using a Gene Ontology-based classification through a sequence-based comparison to known proteins. In addition, a set of unique 70 base pair oligomers that can be used for DNA microarrays was developed. All Gene Index information is posted at the DFCI Gene Indices web page</p> <p>Conclusion</p> <p>Orthopterans are models used to understand the neurophysiological basis of complex motor patterns such as flight and stridulation. The sequences presented in the cricket Gene Index will provide neurophysiologists with many genetic tools that have been largely absent in this field. The cricket Gene Index is one of only two gene indices to be developed in an evolutionary model system. Species within the genus <it>Laupala </it>have speciated recently, rapidly, and extensively. Therefore, the genes identified in the cricket Gene Index can be used to study the genomics of speciation. Furthermore, this gene index represents a significant EST resources for basal insects. As such, this resource is a valuable comparative tool for the understanding of invertebrate molecular evolution. The sequences presented here will provide much needed genomic resources for three distinct but overlapping fields of inquiry: neurobiology, speciation, and molecular evolution.</p

Spatio-temporal Analysis of Agriculture in the Vietnamese Mekong Delta using MODIS Imagery

New methodologies using MODIS time‒series imagery were developed for revealing spatio‒temporal changes of agricultural environments and land use patterns in the Vietnamese Mekong Delta. The following methodologies were proposed:a Wavelet based Filter for Crop Phenology (WFCP), a Wavelet‒based fi lter for evaluating the spatial distribution of Cropping Systems (WFCS), and a Wavelet‒based fi lter for detecting spatio‒temporal changes in Flood Inundation(WFFI). The WFCP algorithm involves smoothing the temporal profi le of the Enhanced Vegetation Index (EVI) using the wavelet transform approach. As a result of validation using the agricultural statistical data in Japan, it was shown that the WFCP was able to estimate rice growing stages, including transplanting date, heading date and harvesting date from the smoothed EVI data, with 9‒12 days accuracy(RMSE). The WFCS algorithm was developed for detecting rice‒cropping patterns in the Vietnamese Mekong delta based on WFCP. It was revealed that the spatial distribution of rice cropping seasons was characterized by both annual fl ood inundation around the upper region in the rainy season and salinity intrusion around the coastal region in the dry season. The WFFI algorithm was developed for estimating start and end dates of fl ood inundation by using time‒series Land Surface Water Index and EVI. Annual intensity of Mekong fl oods was evaluated from 2000 to 2004, at a regional scale. Applying a series of wavelet‒based methodologies to the MODIS data acquired from 2000 to 2006, it was confi rmed that the cropping season for the winter‒spring rice in the fl ood‒prone area fl uctuated depending on the annual change of fl ood scale. It was also confi rmed that the triple rice‒cropped area in the An Giang province expanded from 2000 to 2005, because the construction of a ring‒dike system and water‒resource infrastructure made it possible to sustain a third rice cropping season during the fl ood season. The proposed methodologies(WFCP, WFCS, WFFI) based on MODIS time‒series imagery made it clear that while the rice cropping in the Vietnamese Mekong Delta was quantitatively(annual fl ooding) and qualitatively(salinity intrusion) affected by water‒resource changes, there were some regions where the cultivation system was changed from double rice cropping to triple rice cropping because of the implementation of measures against fl ooding.日本の食料自給率 (2005年時の供給熱量ベース) は、40% と先進7カ国の中で最も低い。日本は、その食料海外依存度の高さから、世界的な食料価格の変動の影響を最も受け易い国と言える。近年の経済発展に伴う中国の大豆輸入量の増加や世界的なエネルギー政策の転換 (バイオエタノール政策) は、世界の穀物需給バランスを不安定にさせつつあり、世界的な問題となっている。さらに、地球温暖化による農業生産影響、増加し続ける世界人口、鈍化する穀物生産性を考えれば、世界の食料需給バランスが将来にわたって安定し続けると言うことはできないだろう。他方、食料増産・生産性向上を目的とした集約的農業の展開は、発展途上国の農業環境にさらなる負荷を与えるかもしれない。世界の食料生産と密接な関係にある日本は、自国の食料安全保障を議論する前提として、急速に変わり行く世界の農業生産現場やそれを取り巻く農業環境を客観的に理解し、世界の農業環境情報を独自の手法によって収集・整理する必要がある。そこで、筆者は、衛星リモートセンシング技術を活用することによって、地球規模の視点で、時間的・空間的な広がりを持って変わり行く農業生産活動とそれを取り巻く農業環境情報を把握・理解するための時系列衛星データ解析手法の確立を目指すこととした。本研究では、インドシナ半島南端に位置するベトナム・メコンデルタを調査対象領域とした。ベトナムは、タイに次ぐ世界第2位のコメ輸出国であり、その輸出米の9割近くが、ベトナム・メコンデルタで生産されたものである。筆者は、ベトナム・メコンデルタを世界の食料安全保障を考える上で重要な食料生産地帯の一つであると考え、本地域における農業環境及び土地利用パターンの時空間変化を明らかにするためのMODIS データを用いた新たな時系列解析手法の開発を行った。　本研究において提案する時系列解析手法は、次の三つである。1. Wavelet‒based Filter for Crop Phenology (WFCP) ,2. Wavelet‒based Filter for evaluating the spatial distribution of Cropping System (WFCS) , 3. Wavelet‒based Filterfor detecting spatio‒temporal changes in Flood Inundation (WFFI) . WFCP は、時系列植生指数 (EVI) を平滑化するためにウェーブレット変換手法を利用しており、日本の農業統計データを用いた検証結果から、水稲生育ステージ (田植日、出穂日、収獲日) を約9－12日 (RMSE) の精度で推定可能であることが示された。WFCP を基に改良されたWFCS は、水稲作付パターンの年次把握を可能にし、ベトナムメコンデルタにおける水稲作付時期の空間分布が、上流部において毎年雨期に発生する洪水と沿岸部において乾季に発生する塩水遡上によって特徴づけられていることを明らかにした。WFFI は、時系列水指数 (LSWI) と植生指数 (EVI) から、湛水期間、湛水開始日・湛水終息日を広域把握し、メコン川洪水強度の年次変化を地域スケールで評価することを可能にする。そして、ウェーブレット変換を利用した一連の手法を、2000～2006年までのMODIS 時系列画像に適用することによって、メコンデルタ上流部の洪水常襲地帯において、冬春米の作付時期が、年次変化する洪水規模に依存していることを明らかにした。また、An Giang 省において、堤防建設 (輪中) や水利施設の建設によって、洪水期における水稲三期作が可能になった地域が、2000～2005年にかけて拡大していることを明らかにした。本研究で提案したMODIS 時系列画像を利用した時系列解析手法 (WFCP、WFCS、WFFI) によって、ベトナムメコンデルタにおける水稲生産が水資源の量的 (洪水) ・質的 (塩水遡上) 変動影響を受ける一方、洪水対策の実施によって、栽培体系を二期作から三期作に変更している地域があることを明らかにした

The Impact of Deciduous Shrub Dominance on Phenology, Carbon Flux, and Arthropod Biomass in the Alaskan Arctic Tundra

Arctic air temperatures have increased at two to three times the global rate over the past century. As a result, abiotic and biotic responses to climate change are more rapid and pronounced in the Arctic compared to other biomes. One important change detected over the past several decades by satellite studies is a lengthening of the arctic growing season, which is due to earlier onsets and/or delayed ends to growing seasons. A handful of studies also suggest the peak green season (i.e. when the tundra is at maximum leaf-out and maximum carbon uptake potential) is starting earlier in the arctic tundra. The vast majority of studies detecting shifts in the growing season suggest this is due to increasing spring and fall air temperatures, which lead to earlier spring snowmelt and later fall snowfall. Less well understood is how indirect consequences of arctic warming, such as ongoing changes in plant community composition, may also be contributing to these satellite signals. For instance, there is mounting evidence that deciduous shrubs are expanding into previously non-shrub dominated tundra in several parts of the Arctic. Deciduous shrubs may alter tundra canopy phenology and contribute to the regional shifts in timing of phenological events being detected by satellites. Concurrently, in many areas where deciduous shrubs are expanding they are also becoming taller. As taller shrubs become increasingly dominant, arctic landscapes may retain more snow, which could lengthen spring snow cover duration, and offset advances in the start of the growing season that are expected as a result of earlier spring snowmelt. As a consequence, deeper snow and later snowmelt in taller shrub tundra could delay plant emergence, and shorten the period of annual carbon uptake. Thus greater dominance of taller stature deciduous shrubs in the Arctic may actually delay the onset of the growing season, which would suggest that increasing deciduous shrub dominance may not be contributing to satellite signals of an earlier start to the growing season. To contribute to satellite-detected shifts in the onset of the growing and peak seasons, tall deciduous shrubs would need to have accelerated leaf development to compensate for deeper snow packs and later spring snowmelt relative to surrounding tundra. Understanding the drivers of shifts in tundra phenology is important since longer (or shorter) growing and peak green seasons would increase (or decrease) productivity and the period of carbon uptake, which will have implications for landscape-level carbon exchange, and ultimately global carbon balances. Given the rate and magnitude of changes occurring in the face of acute arctic warming, there is a need to monitor, understand, and predict ecological responses over large spatial and temporal scales. However, compared to more southern environments, the arctic tundra is characterized by considerable heterogeneity in vegetation distribution, as well as a short and rapid growing season. In addition, the arctic tundra is relatively vast and inaccessible. These characteristics can make it difficult to monitor and study changes in the Arctic, and make it difficult to develop landscape-level models able to predict changes in ecosystem dynamics and tundra vegetation. The use of airborne and satellite sensors has at least partially fulfilled these needs to monitor, understand, and predict change in the Arctic. The normalized difference vegetation index (NDVI) acquired from these sensors, for instance, has become a widely adopted tool for detecting and quantifying spatial-temporal dynamics in tundra vegetation cover, productivity, and phenology. This suggests that remote sensing technology and vegetation indices may be similarly applied to characterizing patterns of primary and secondary consumers (e.g. arthropods), which would be enormously useful in a region as vast and remote as the Arctic. The research presented in this dissertation provides useful insight into the influence vegetation community composition, particularly increasing deciduous shrub dominance, has on phenology, carbon flux, and canopy arthropod biomass in the arctic foothills region of the Brooks Range, Alaska. Findings in Chapter one suggest that delayed snowmelt in areas dominated by taller shrubs may have a short-lived impact on the timing of leaf development, likely resulting in no difference in duration of peak photosynthetic period between tall and short- stature shrubs. Findings in Chapter two suggest that greater deciduous shrub dominance not only increases carbon uptake due to higher leaf area relative to surrounding tundra, but may also be causing an earlier onset of, and ultimately a net extension of, the period of maximum tundra greenness and further increasing peak season carbon sequestration. Findings in Chapter three suggest that measurements of the NDVI made from air and spaceborne sensors may be able to quantify spatial and temporal variation in canopy arthropod biomass at landscape to regional scales in the arctic tundra