Niall P Hanan

Niall P Hanan
New Mexico State University | NMSU · Department of Plant and Environmental Sciences

PhD

About

183
Publications
42,126
Reads
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Introduction
Niall P Hanan is a faculty member in the Department of Plant and Environmental Sciences, New Mexico State University and contributes to research at the Jornada Long-term Ecological Research (LTER) site. Niall does research in temperate and tropical grasslands and savannas, focusing on ecosystem processes, ecological and biogeochemical interactions. Website: https://savannalab.nmsu.edu)
Additional affiliations
January 2011 - July 2014
South Dakota State University
Position
  • Professor (Full)
July 1998 - December 2010
Colorado State University
Position
  • Senior Researcher

Publications

Publications (183)
Article
L’élevage contribue environ à 15% du produit intérieur brut de l’ensemble des pays sahéliens de l’Afrique de l’ouest. Au Mali, il est la deuxième activité socioéconomique après l’agriculture. Il est pratiqué de façon extensive avec des mobilités saisonnières des troupeaux à la recherche du disponible fourrager, dans le contexte du changement climat...
Conference Paper
Full-text available
La présente étude contribue à l'amélioration de la connaissance sur la cohabitation des strates ligneuse et herbacée des formations savanicoles en fonction des perturbations anthropiques au Mali. Pour ce faire, un dispositif expérimental a été installé suivant le gradient bioclimatique qui abrite les savanes au Mali. Il s'agit du Sahélien-sud, du S...
Article
An analysis of carbon stored in the plants and soil of an African savannah suggests that atmospheric carbon dioxide concentrations — and thus global warming — might be less affected by frequent fires than we thought. Analysis of carbon above and below ground after long-term burning.
Article
Full-text available
Background: Termites are important ecosystem engineers in the tropics and sub-tropics, so understanding their diversity, particularly their functional diversity, across biogeographical scales is important for understanding where they alter theenvironment and deliver ecological services. Feeding groups combine phylogeneticand dietary information abo...
Article
Full-text available
Drylands are a critical part of the earth system in terms of total area, socioeconomic and ecological importance. However, while drylands are known for their contribution to inter-annual atmospheric CO2 variability, they are sometimes overlooked in discussions of global carbon stocks. Here, in preparation for the November 2021 UN Climate Change Con...
Article
Full-text available
Non‐forest ecosystems, dominated by shrubs, grasses and herbaceous plants, provide ecosystem services including carbon sequestration and forage for grazing, and are highly sensitive to climatic changes. Yet these ecosystems are poorly represented in remotely sensed biomass products and are undersampled by in situ monitoring. Current global change t...
Article
Full-text available
The ecological and environmental science communities have embraced machine learning (ML) for empirical modeling and prediction. However, going beyond prediction to draw insights into underlying functional relationships between response variables and environmental “drivers” is less straightforward. Deriving ecological insights from fitted ML models...
Article
Full-text available
Africa’s ecosystems have an important role in global carbon dynamics, yet consensus is lacking regarding the amount of carbon stored in woody vegetation and the potential impacts to carbon storage in response to changes in climate, land use and other Anthropocene risks. In this study, we explore the socioenvironmental conditions that have shaped th...
Article
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Ecosystems across the United States are changing in complex and surprising ways. Ongoing demand for critical ecosystem services requires an understanding of the populations and communities in these ecosystems in the future. This paper represents a synthesis effort of the U.S. National Science Foundation‐funded Long‐Term Ecological Research (LTER) n...
Article
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The global community faces fundamental challenges related to natural resource management, particularly in low and middle income countries. Increasing populations and changing climate exacerbate the challenges of food security, water, and environmental management and sustainability faced by rural communities, cities, and governments alike. Sound env...
Article
Full-text available
An analysis of satellite images has pinpointed individual tree canopies over a large area of West Africa. The data suggest that it will soon be possible, with certain limitations, to map the location and size of every tree worldwide. Individual tree canopies pinpointed over a large area of West Africa.
Preprint
Full-text available
Non-forest ecosystems, dominated by shrubs, grasses and herbaceous plants, provide ecosystem services including carbon sequestration and forage for grazing, yet are highly sensitive to climatic changes. Yet these ecosystems are poorly represented in remotely-sensed biomass products and are undersampled by in-situ monitoring. Current global change t...
Article
Full-text available
Vegetation buffers local diurnal land surface temperatures, however, this effect has found limited applications for remote vegetation characterization. In this work, we parameterize diurnal temperature variations as the thermal decay rate derived by using satellite daytime and nighttime land surface temperatures and modeled using Newton’s law of co...
Data
The WAVeTrends dataset is a 0.05 degree (5.55 km) vegetation change product, spanning the West African Sudano-Sahel region. It provides pixel-wise information on concurrent woody and herbaceous vegetation trends over a 32-year period (1982-2013). Change in woody vegetation was derived using long-term rain use efficiency (RUE) sensitivity, i.e., the...
Article
Full-text available
The West African Sahel Cropland map (WASC30) is a new 30-m cropland extent product for the nominal year of 2015. We used the computing resources provided by Google Earth Engine (GEE) to fit and apply Random Forest models for cropland detection in each of 189 grid cells (composed of 100 km 2 , hence a total of~1.9 × 10 6 km 2) across five countries...
Article
Full-text available
Black-tailed prairie dogs (Cynomys ludovicianus) have been described as a keystone species and are important for grassland conservation, yet many concerns exist over the impact of prairie dogs on plant biomass production and consequently livestock production. The ability to map plant communities in pastures colonized by prairie dogs can provide lan...
Article
Full-text available
Savanna woody plants can store significant amounts of carbon while also providing numerous other ecological and socio-economic benefits. However, they are significantly under-represented in widely used tree cover datasets, due to mapping challenges presented by their complex landscapes, and the underestimation of woody plants by methods that exclud...
Poster
Full-text available
Large bare termite mounds are common in tropical drylands and impact the landscape by altering vegetation productivity, surface albedo, and water redistribution processes. Termite mounds have previously been mapped at local scales using LiDAR and field-based work. However, little is known about their distribution over larger geographic scales. Usin...
Article
Full-text available
The use of high resolution imagery in remote sensing has the potential to improve understanding of patch level variability in plant structure and community composition that may be lost at coarser scales. Random forest (RF) is a machine learning technique that has gained considerable traction in remote sensing applications due to its ability to prod...
Article
Full-text available
Globally, the spatial distribution of vegetation is governed primarily by climatological factors (rainfall and temperature, seasonality, and inter-annual variability). The local distribution of vegetation, however, depends on local edaphic conditions (soils and topography) and disturbances (fire, herbivory, and anthropogenic activities). Abrupt spa...
Article
Full-text available
We assess 32 years of vegetation change in the West African Sudano-Sahelian region following the drought events of the 1970s and 1980s. Change in decadal mean rain use efficiency is used to diagnose trends in woody vegetation that is expected to respond more slowly to post-drought rainfall gains, while change in the slope of the productivity–rainfa...
Article
In southern Africa, termite diversity is especially well documented, with over 50 genera known to occur in the region. More specifically in Kruger National park, there are 28 genera that have been documented (Coaton, 1962; Davies et al., 2013). In this study, we characterised termite diversity (genus richness and functional diversity) along a singl...
Article
Full-text available
The original version of this Data Descriptor incorrectly referenced the “United Nations (UN) Food and Agriculture Organization (FAO) soilGrids250m system”. This has been corrected to “SoilGrids predictions” throughout the text in both the HTML and PDF versions.
Article
Full-text available
The cover of woody perennial plants (trees and shrubs) in arid ecosystems is at least partially constrained by water availability. However, the extent to which maximum canopy cover is limited by rainfall and the degree to which soil water holding capacity and topography impacts maximum shrub cover are not well understood. Similar to other deserts i...
Conference Paper
Full-text available
Remote sensing is the only pragmatic method for long term global vegetation monitoring. Different remotely sensed parameters have been identified to quantify vegetation states and several are operationally used for monitoring vegetation. Small-scale field studies have noted that thermal response to changing diurnal conditions is a useful indicator...
Article
Full-text available
Herbivores alter plant biodiversity (species richness) in many of the world’s ecosystems, but the magnitude and the direction of herbivore effects on biodiversity vary widely within and among ecosystems. One current theory predicts that herbivores enhance plant biodiversity at high productivity but have the opposite effect at low productivity. Yet,...
Article
Full-text available
Accurate estimates of cultivated area and crop yield are critical to our understanding of agricultural production and food security, particularly for semi-arid regions like the Sahel of West Africa, where crop production is mainly rain-fed and food security is closely correlated with the inter-annual variations in rainfall. Several global and regio...
Article
Full-text available
The Earth is a complex system comprising many interacting spatial and temporal scales. We developed a transdisciplinary data-model integration (TDMI) approach to understand, predict, and manage for these complex dynamics that focuses on spatiotemporal modeling and cross-scale interactions. Our approach employs human-centered machine-learning strate...
Article
Full-text available
Hydrologic soil groups (HSGs) are a fundamental component of the USDA curve-number (CN) method for estimation of rainfall runoff; yet these data are not readily available in a format or spatial-resolution suitable for regional-and global-scale modeling applications. We developed a globally consistent, gridded dataset defining HSGs from soil texture...
Article
Full-text available
Aim Past analyses of satellite‐based fire activity in tropical savannas support the intermediate fire–productivity hypothesis (IFP), which posits a close correlation with estimates of total net primary productivity in drier savannas and declines towards the extremes. However, these analyses ignore the distinct roles played by herbaceous and woody v...
Article
Full-text available
Aim The aims of this study were to (1) estimate current rates of woody encroachment across African savannas; (2) identify relationships between change in woody cover and potential drivers, including water constraints, fire frequency and livestock density. The found relationships led us to pursue a third goal: (3) use temporal dynamics in woody cove...
Article
Full-text available
Article available via Nature's Sharedit service using the following link: https://rdcu.be/LGq4
Article
Full-text available
Savannas are widespread global biomes covering ~20% of terrestrial ecosystems on all continents except Antarctica. These ecosystems play a critical role in regulating terrestrial carbon cycle, ecosystem productivity, and the hydrological cycle and contribute to human livelihoods and biodiversity conservation. Despite the importance of savannas in e...
Conference Paper
Full-text available
Globally, the spatial distribution of vegetation is driven primarily by climatological factors, interacting locally with disturbances including fire, herbivory and other anthropogenic activities. Depending on the nature of feedbacks, disturbances may trigger alternate states under otherwise similar climatic and edaphic conditions. Previous studies...
Conference Paper
Full-text available
The West African Savanna-Sahel (WASS) region features a delicate balance of woody and herbaceous vegetation systems that play an important role in the cycling of carbon, water and energy, while supporting agro-pastoralist livelihoods (food for grazing animals, browse and fuelwood). Quantifying the temporal trends separately for these two types of v...
Article
Full-text available
Bastin et al. (Reports, 12 May 2017, p. 635) infer forest as more globally extensive than previously estimated using tree cover data. However, their forest definition does not reflect ecosystem function or biotic composition. These structural and climatic definitions inflate forest estimates across the tropics and undermine conservation goals, lead...
Article
The shortgrass steppe (SGS) occupies the southwestern part of the Great Plains. Half of the land is cultivated, but significant areas remain under natural vegetation. Despite previous studies of the SGS carbon cycle, not all aspects have been completely addressed, including gross productivity, ecosystem respiration, and ecophysiological parameters....
Article
Full-text available
Vegetation structure in water-limited systems is to a large degree controlled by ecohydrological processes, including mean annual precipitation (MAP) modulated by the characteristics of precipitation and geomorphology that collectively determine how rainfall is distributed vertically into soils or horizontally in the landscape. We anticipate that w...
Article
Full-text available
Vegetation structure in water-limited systems is to a large degree controlled by ecohydrological processes, including mean annual precipitation (MAP) modulated by the characteristics of precipitation and geomorphology that collectively determine how rainfall is distributed vertically into soils or horizontally in the landscape. We anticipate that w...
Article
The majority of research on savanna vegetation dynamics has focused on the coexistence of woody and herbaceous vegetation. Interactions among woody plants in savannas are relatively poorly understood. We present data from a 10-year longitudinal study of spatially explicit growth patterns of woody vegetation in an East African savanna following excl...
Conference Paper
Full-text available
La présente étude est une contribution à l'amélioration de la connaissance sur la dynamique des formations savanicoles sous l'influence des perturbations anthropiques et du climat. Pour ce faire, un dispositif expérimental a été implanté dans les bioclimats où sont rencontrées les savanes au Mali. Il s'agit du Sahélien-sud, du Soudanien-nord, du So...
Article
Land surface phenology (LSP) in the Sahara Desert is poorly understood due to the difficulty in detecting subtle variations in vegetation greenness. This study examined the spatial and temporal patterns of LSP and its responses to rainfall seasonality in the Sahara Desert. We first generated daily two-band Enhanced Vegetation Index (EVI2) from half...
Article
In 2014, the USAID project ‘Grazing lands, livestock and climate resilient mitigation in Sub-Saharan Africa’ held two workshops, hosted by the Colorado State University, which brought together experts from around the world. Two reports resulted from these workshops, one an assessment of the state of the science, and the other an inventory of relate...
Article
Full-text available
In the Great Plains, grassland carbon dynamics differ across broad gradients of precipitation and temperature, yet finer-scale variation in these variables may also affect grassland processes. Despite the importance of grasslands, there is little information on how fine-scale relationships compare between them regionally. We compared grassland C ex...
Technical Report
Full-text available
This report is a detailed review, synthesis, and analysis of the current “state of the science” concerning the potential for carbon sequestration in grazing lands through improved land management practices in Sub-Saharan Africa (SSA). It aims to provide an up-to-date assessment of the science of C sequestration from improved land management, includ...
Article
Full-text available
Theory and empirical evidence for the impacts of fire and herbivory in savannahs is well established - they are top-down disturbances that maintain savannahs in disequilibrium states away from potential tree cover. In African savannahs, the demand for fuelwood is extremely high, so tree harvest likely also has an impact, both directly and indirectl...
Article
Full-text available
Over many decades our understanding of the impacts of intermittent drought in water-limited environments like the West African Sahel has been influenced by a narrative of overgrazing and human-induced desertification. The desertification narrative has persisted in both scientific and popular conception, such that recent regional-scale recovery ("re...
Article
Full-text available
Staver & Hansen (2015, Global Ecology and Biogeography, doi: 10.1111/geb.12285) comment on our recent paper (Hanan et al., Global Ecology and Biogeography, 2014, 23, 259–263) in which we argue that classification and regression tree methods used with remote sensing data to predict tree cover may bias inference of bifurcations in savanna vegetation...
Article
Full-text available
Contemporary theory on the maintenance and stability of the savanna biome has focused extensively on how climate and disturbances interact to affect tree growth and demography. In particular, the role of fire in reducing tree cover from climatic maxima is now well appreciated, and in certain cases, herbivory also strongly affects tree cover. Howeve...
Article
Full-text available
An understanding of rainfall characteristics at multiple spatiotemporal scales is of great importance for hydrological, biogeochemical and land surface modeling studies. In the present study, patterns of rainfall are analyzed over the African continent based on 3-hourly 0.25° Tropical Rainfall Measuring Mission (TRMM) estimates between 1998 and 201...
Article
Full-text available
Savannas cover 60% of the African continent and play an important role in the global carbon (C) emissions from fire and land use. To better characterize the biophysical controls over soil respiration in these settings, half-hourly observations of volumetric soil-water content, temperature, and the concentration of carbon dioxide (CO2) at different...
Article
Full-text available
Accurately measuring evapotranspiration (ET) is essential if we are to derive reasonable estimates of production and water use for semi-arid savannas. Estimates of ET are also important in defining the health of an ecosystem and the quantity of water used by the vegetation when preparing a catchment-scale water balance. We derived ET0 from an autom...
Article
Full-text available
Staver & Hansen (2015, Global Ecology and Biogeography, doi: 10.1111/geb .12285) comment on our recent paper (Hanan et al., Global Ecology and Bioge-ography, 2014, 23, 259–263) in which we argue that classification and regression tree methods used with remote sensing data to predict tree cover may bias inference of bifurcations in savanna vegetatio...
Preprint
Full-text available
Theory and empirical evidence for the impacts of fire and herbivory in savannas is well established – they are top-down disturbances that maintain savannas in disequilibrium states away from potential tree cover. In African savannas the demand for fuelwood is extremely high, so tree harvest likely also has an impact, both directly and indirectly, o...
Preprint
Theory and empirical evidence for the impacts of fire and herbivory in savannas is well established – they are top-down disturbances that maintain savannas in disequilibrium states away from potential tree cover. In African savannas the demand for fuelwood is extremely high, so tree harvest likely also has an impact, both directly and indirectly, o...
Article
Full-text available
Ecologists have long sought to understand the factors controlling the structure of savanna vegetation. Using data from 2154 sites in savannas across Africa, Australia, and South America, we found that increasing moisture availability drives increases in fire and tree basal area, whereas fire reduces tree basal area. However, among continents, the m...
Article
Full-text available
1. The stress-gradient hypothesis (SGH) predicts an increasing importance of facilitative mechanisms relative to competition along gradients of increasing environmental stress. Although developed across a variety of ecosystems, the SGH's relevance to the dynamic tree—grass systems of global savannas remains unclear. Here, we present a meta-analysis...
Article
Full-text available
Water is a precious resource since the lives and livelihoods of human societies depend on their ability to access this resource. This is particularly true in arid and semiarid regions like the Sahel where permanent surface waters are rare and hydrological solutions (e.g., accessing deep aquifers) are often not feasible. This work is devoted to the...