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Marion Pfeifer
  • Ridley Building 2, School of Biology, Newcastle University, marion.pfeifer@newcastle.ac.uk.

    TropHum research group: https://blogs.ncl.ac.uk/marionpfeifer/

    Projects:
    Global LAI project: https://globallai.wordpress.com/
    BIOFRAG project: https://biofrag.wordpress.com/

Marion Pfeifer

We present a model-based investigation of the effect of discrete-return lidar system and survey characteristics on the signal recorded over young forest environments. A Monte Carlo ray tracing (MCRT) model of canopy scattering was used to... more
We present a model-based investigation of the effect of discrete-return lidar system and survey characteristics on the signal recorded over young forest environments. A Monte Carlo ray tracing (MCRT) model of canopy scattering was used to examine the sensitivity of model estimates of lidar-derived canopy height, hlidar to signal triggering method, canopy structure, footprint size, sampling density and scanning angle, for broadleaf and conifer canopies of varying density. Detailed 3D models of Scots pine (Pinus sylvestris) and Downy birch (Betula pubescens) were used to simulate lidar response, with minimal assumptions about canopy structure. Use of such models allowed the impact of lidar parameters on canopy height retrieval to be tested under a range of conditions typically not possible in practice. Retrieved hlidar was generally found to be an underestimate of ‘true’ canopy height, hcanopy, but with exceptions. Choice of signal triggering method caused hlidar to underestimate hcanopy by not, vert, similar 4% for birch and not, vert, similar 7% for pine (up to 66% in extreme cases). Variations in canopy structure resulted on average in underestimation of hcanopy by 13% for birch and between 29 and 48% for pine depending on age, but with over-estimates in some cases of up to 10%. Increasing footprint diameter from 0.1 to 1 m increased retrieved hlidar from significant underestimates of hcanopy to values indistinguishable from hcanopy. Increased sampling density led to slightly increased values of hlidar to close to hcanopy, but not significantly. Increasing scan angle increased hlidar by up to 8% for birch, and 19% for pine at a scan angle of 30°. The impact of scan angle was greater for conifers as a result of large variation in crown height. Results showed that interactions between physically modelled (hypothetical) within canopy returns are similar to findings made in other studies using actual lidar systems, and that these modelled returns can depend strongly on the type of canopy and the lidar acquisition characteristics, as well as interactions between these properties. Physical models of laser pulse/canopy interactions may provide additional information on pulse interactions within the canopy, but require validation and testing before they are applied to actual survey planning and logistics.
Forest edges influence more than half of the world’s forests and contribute to worldwide declines in biodiversity and ecosystem functions. However, predicting these declines is challenging in heterogeneous fragmented landscapes. Here we... more
Forest edges influence more than half of the world’s forests and contribute to worldwide declines in biodiversity and ecosystem functions. However, predicting these declines is challenging in heterogeneous fragmented landscapes. Here we assembled a global dataset on species responses to fragmentation and developed a statistical approach for quantifying edge impacts in heterogeneous landscapes to quantify edge-determined changes in abundance of 1,673 vertebrate species. We show that the abundances of 85% of species are affected, either positively or negatively, by forest edges. Species that live in the centre of the forest (forest core), that were more likely to be listed as threatened by the International Union for Conservation of Nature (IUCN), reached peak abundances only at sites farther than 200–400 m from sharp high-contrast forest edges. Smaller-bodied amphibians, larger reptiles and medium-sized non-volant mammals experienced a larger reduction in suitable habitat than other forest-core species. Our results highlight the pervasive ability of forest edges to restructure ecological communities on a global scale.
Tropical montane forests are amongst the most threatened ecosystems by climate change. However, little is known about climatic changes already observed in these montane areas in Africa, or the adaptation strategies used by pastoralist... more
Tropical montane forests are amongst the most threatened ecosystems by climate change. However, little is known about climatic changes already observed in these montane areas in Africa, or the adaptation strategies used by pastoralist communities. This article, focused on three mountains in northern Kenya, aims to fill these knowledge gaps. Focus-group discussions with village elders were organized in 10 villages on each mountain (n = 30). Villages covered different pastoralist ethnic groups. Historical data on rainfall, temperature and fog were gathered from Marsabit Meteorological station. All participants reported changes in the amount and distribution of rainfall, fog, temperature and wind for the past 20–30 years; regardless of the mountain or ethnicity. They particularly highlighted the reduction in fog. Meteorological evidence on rainfall, temperature and fog agreed with local perceptions; particularly important was a 60% reduction in hours of fog per year since 1981. Starting farming and shifting to camel herding were the adaptive strategies most commonly mentioned. Some adaptive strategies were only mentioned in one mountain or by one ethnic group (e.g. starting the cultivation of khat). We highlight the potential use of local communities' perceptions to complement climatic records in data-deficient areas, such as many tropical mountains, and emphasize the need for more research focused on the adaptation strategies used by pastoralists.
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Background: Canopy structure, defined by leaf area index (LAI), fractional vegetation cover (FCover) and fraction of absorbed photosynthetically active radiation (fAPAR), regulates a wide range of forest functions and ecosystem services.... more
Background: Canopy structure, defined by leaf area index (LAI), fractional vegetation cover (FCover) and fraction of absorbed photosynthetically active radiation (fAPAR), regulates a wide range of forest functions and ecosystem services. Spatially consistent field-measurements of canopy structure are however lacking, particularly for the tropics. Methods: Here, we introduce the Global LAI database: a global dataset of field-based canopy structure measurements spanning tropical forests in four continents (Africa, Asia, Australia and the Americas). We use these measurements to test for climate dependencies within and across continents, and to test for the potential of anthropogenic disturbance and forest protection to modulate those dependences.
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A B S T R A C T Changes in structure and functioning of tree communities in response to forest fragmentation may alter tropical forest's capacity to store carbon and regulate climate. However, evidence for indirect effects of forest... more
A B S T R A C T Changes in structure and functioning of tree communities in response to forest fragmentation may alter tropical forest's capacity to store carbon and regulate climate. However, evidence for indirect effects of forest fragmentation on above – and belowground carbon pools through changes in forest biodiversity is scarce. Here we focus on understanding the relative importance of taxonomic and functional diversity and tree cover to explain above-and below-ground carbon stocks in coastal dune forest fragments. We surveyed tree species composition and structure in six coastal forest patches varying in size from 215 to 13350 ha, in Kwa-Zulu Natal, South Africa. For each fragment, we estimated carbon stocks of two pools, aboveground biomass (AGC) and soil organic carbon (SOC). We used structural equation models to test if and to what extent the effects of forest fragmentation on AGC and SOC were mediated by tree cover and taxonomic and functional diversity. Our results showed that forest fragmentation directly reduced AGC, but increased SOC. In contrast, forest fragmentation indirectly, through decreasing functional diversity, increased AGC, but decreased SOC. Small patches therefore had few tree species that were functional similar and had high AGC, but low SOC, which led to a negative relationship between species richness and AGC. Tree cover was not affected by fragmentation, and had a direct positive effect on AGC but not on SOC. Our results suggest that forest fragmentation simultaneously affect multiple processes which directly and indirectly affects carbon stocks of different pools. Fragmentation may trigger a process of biotic homogenization, in which a few species are positively related with carbon storage above-, but not below-ground.
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Understanding cultural preferences toward different ecosystem services is of great importance for conservation and development planning. While cultural preferences toward plant species have been long studied in the field of plant... more
Understanding cultural preferences toward different ecosystem services is of great importance for conservation and development planning. While cultural preferences toward plant species have been long studied in the field of plant utilisation, the effects of ethnicity on ecosystem services identification and valuation has received little attention. We assessed the effects of ethnicity toward different ecosystem services at three similar forest islands in northern Kenya inhabited by Samburu and Boran pastoralists. Twelve focus groups were organised in each mountain, to evaluate the ecosystem services provided by the forest, and assess which plant species are most important for provisioning different ecosystem services. While water was always identified as the most important ecosystem service, the second most important differed; and some were only mentioned by one ethnic group or in one location. Preferred plant species for food, fodder, medicine resources, poles and firewood followed the same pattern. Our results showed that ethnicity and location affect ecosystem services' identification and importance ranking. This should be taken into account by decision-makers, e.g. as restricted access and regulated extraction is likely to affect people differently. Conservation and development projects would be more effective if they were initiated with an understanding of how people already use and value their forests.
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Land use change is a major threat to biodiversity. One mechanism by which land use change influences biodiversity and ecological processes is through changes in the local climate. Here, the relationships between leaf area index and five... more
Land use change is a major threat to biodiversity. One mechanism by which land use change influences biodiversity and ecological processes is through changes in the local climate. Here, the relationships between leaf area index and five climate variables – air temperature, relative humidity, vapour pressure deficit, specific humidity and soil temperature – are investigated across a range of land use types in Borneo, including primary tropical forest, logged forest and oil palm plantation. Strong correlations with the leaf area index are found for the mean daily maximum air and soil temperatures, the mean daily maximum vapour pressure deficit and the mean daily minimum relative humidity. Air beneath canopies with high leaf area index is cooler and has higher relative humidity during the day. Forest microclimate is also found to be less variable for sites with higher leaf area indices. Primary forest is found to be up to 2.5 °C cooler than logged forest and up to 6.5 °C cooler than oil palm plantations. Our results indicate that leaf area index is a useful parameter for predicting the effects of vegetation upon microclimate, which could be used to make small scale climate predictions based on remotely sensed data.
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Habitat fragmentation studies have produced complex results that are challenging to synthesize. Inconsistencies among studies may result from variation in the choice of landscape metrics and response variables, which is often compounded... more
Habitat fragmentation studies have produced complex results that are challenging to synthesize. Inconsistencies among studies may result from variation in the choice of landscape metrics and response variables, which is often compounded by a lack of key statistical or methodological information. Collating primary datasets on biodiversity responses to fragmentation in a consistent and flexible database permits simple data retrieval for subsequent analyses. We present a relational database that links such field data to taxonomic nomenclature, spatial and temporal plot attributes, and environmental characteristics. Field assessments include measurements of the response(s) (e.g., presence, abundance, ground cover) of one or more species linked to plots in fragments within a partially forested landscape. The database currently holds 9830 unique species recorded in plots of 58 unique landscapes in six of eight realms: mammals 315, birds 1286, herptiles 460, insects 4521, spiders 204, other arthropods 85, gastropods 70, annelids 8, platyhelminthes 4, Onychophora 2, vascular plants 2112, nonvascular plants and lichens 320, and fungi 449. Three landscapes were sampled as long-term time series (>10 years). Seven hundred and eleven species are found in two or more landscapes. Consolidating the substantial amount of primary data available on biodiversity responses to fragmentation in the context of land-use change and natural disturbances is an essential part of understanding the effects of increasing anthropogenic pressures on land. The consistent format of this database facilitates testing of generalizations concerning biologic responses to fragmentation across diverse systems and taxa. It also allows the re-examination of existing datasets with alternative landscape metrics and robust statistical methods, for example, helping to address pseudo-replication problems. The database can thus help researchers in producing broad syntheses of the effects of land use. The database is dynamic and inclusive, and contributions from individual and large-scale data-collection efforts are welcome.
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Carbon-based forest conservation requires the establishment of ‘reference emission levels’ against which to measure a country or region's progress in reducing their carbon emissions. In East Africa, landscape-scale estimates of carbon... more
Carbon-based forest conservation requires the establishment of ‘reference emission levels’ against which to measure a country or region's progress in reducing their carbon emissions. In East Africa, landscape-scale estimates of carbon fluxes are uncertain and factors such as deforestation poorly resolved due to a lack of data. In this study, trends in vegetation cover and carbon for East Africa were quantified using moderate-resolution imaging spectroradiometer (MODIS) land cover grids from 2002 to 2008 (500-m spatial resolution), in combination with a regional carbon look-up table. The inclusion of data on rainfall and the distribution of protected areas helped to gauge impacts on vegetation burning (assessed using 1-km spatial resolution MODIS active fire data) and biome trends. Between 2002 and 2008, the spatial extents of forests, woodlands and scrublands decreased considerably and East Africa experienced a net carbon loss of 494 megatonnes (Mt). Most countries in the area were sources of carbon emissions, except for Tanzania and Malawi, where the areal increase of savannah and woodlands counterbalanced carbon emissions from deforestation. Both Malawi and Tanzania contain large areas of planted forest. Vegetation burning was correlated with rainfall (forest only) and differed depending on land management. Freely available global earth observation products have provided ways to achieve rapid assessment and monitoring of carbon change hotspots at the landscape scale.(Received March 23 2012)(Accepted September 27 2012)(Online publication December 10 2012)
Creel et al. argue against the conservation effectiveness of fencing based on a population measure that ignores the importance of top predators to ecosystem processes. Their statistical analyses consider, first, only a subset of fenced... more
Creel et al. argue against the conservation effectiveness of fencing based on a population measure that ignores the importance of top predators to ecosystem processes. Their statistical analyses consider, first, only a subset of fenced reserves and, second, an incomplete examination of ‘costs per lion.’ Our original conclusions remain unaltered.
Conservationists often advocate for landscape approaches to wildlife management while others argue for physical separation between protected species and human communities, but direct empirical comparisons of these alternatives are scarce.... more
Conservationists often advocate for landscape approaches to wildlife management while others argue for physical separation between protected species and human communities, but direct empirical comparisons of these alternatives are scarce. We relate African lion population densities and population trends to contrasting management practices across 42 sites in 11 countries. Lion populations in fenced reserves are significantly closer to their estimated carrying capacities than unfenced populations. Whereas fenced reserves can maintain lions at 80% of their potential densities on annual management budgets of $500 km−2, unfenced populations require budgets in excess of $2000 km−2 to attain half their potential densities. Lions in fenced reserves are primarily limited by density dependence, but lions in unfenced reserves are highly sensitive to human population densities in surrounding communities, and unfenced populations are frequently subjected to density-independent factors. Nearly half the unfenced lion populations may decline to near extinction over the next 20–40 years.
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Aim  Earth observation (EO) products are a valuable alternative to spectral vegetation indices. We discuss the availability of EO products for analysing patterns in macroecology, particularly related to vegetation, on a range of spatial... more
Aim  Earth observation (EO) products are a valuable alternative to spectral vegetation indices. We discuss the availability of EO products for analysing patterns in macroecology, particularly related to vegetation, on a range of spatial and temporal scales.Location  Global.Methods  We discuss four groups of EO products: land cover/cover change, vegetation structure and ecosystem productivity, fire detection, and digital elevation models. We address important practical issues arising from their use, such as assumptions underlying product generation, product accuracy and product transferability between spatial scales. We investigate the potential of EO products for analysing terrestrial ecosystems.Results  Land cover, productivity and fire products are generated from long-term data using standardized algorithms to improve reliability in detecting change of land surfaces. Their global coverage renders them useful for macroecology. Their spatial resolution (e.g. GLOBCOVER vegetation, 300 m; MODIS vegetation and fire, ≥ 500 m; ASTER digital elevation, 30 m) can be a limiting factor. Canopy structure and productivity products are based on physical approaches and thus are independent of biome-specific calibrations. Active fire locations are provided in near-real time, while burnt area products show actual area burnt by fire. EO products can be assimilated into ecosystem models, and their validation information can be employed to calculate uncertainties during subsequent modelling.Main conclusions  Owing to their global coverage and long-term continuity, EO end products can significantly advance the field of macroecology. EO products allow analyses of spatial biodiversity, seasonal dynamics of biomass and productivity, and consequences of disturbances on regional to global scales. Remaining drawbacks include inter-operability between products from different sensors and accuracy issues due to differences between assumptions and models underlying the generation of different EO products. Our review explains the nature of EO products and how they relate to particular ecological variables across scales to encourage their wider use in ecological applications.
Understanding of mechanisms underlying carbon flux dynamics in the Eastern Arc Mountains and their catchment areas is lacking, due to data shortage (e.g. biome specific canopy structure) and spatial heterogeneity of tropical ecosystems.... more
Understanding of mechanisms underlying carbon flux dynamics in the Eastern Arc Mountains and their catchment areas is lacking, due to data shortage (e.g. biome specific canopy structure) and spatial heterogeneity of tropical ecosystems. This study focuses on documenting leaf area index (LAI) for the main biomes in the Eastern Arc Mountains and their surroundings. In situ optical instruments, i.e. hemispherical photography and a SunScan device, were used to acquire ground LAI measurements. Spectral vegetation indices (VIs) extracted from Landsat Enhanced Thematic Mapper (ETM +) and Système Probatoire d'Observation de la Terre (SPOT) reflectance data were used, along with mean annual precipitation (MAP), as explanatory variables of LAI variation. The results indicate that LAI significantly increases with increasing MAP for woody biomes. Implementing long-term MAP as a second predictor variable into the VI–LAI models significantly improved LAI predictions by up to 10% using the normalised difference vegetation index (NDVI), modified soil adjusted vegetation index (MSAVI 2) and 2-band enhanced vegetation index (EVI 2). Varying forest disturbances and agricultural management practises may have contributed to observed discrepancies of LAI with MAP across biomes. The importance of altitudinal gradients is yet to be explained fully with more study required. However, LAI appears to be higher in low-altitude forests compared to forests at higher altitudes. Our results indicate that SPOT and Landsat-derived VIs, in combination with long-term MAP, may be a suitable tool to develop landscape maps of LAI in Eastern Africa. This study also presents the in situ LAI measurements for further validation of global products for areas that are currently under-represented in Earth Observation (EO) global validation networks.► We document leaf area index (LAI) for East African biomes. ► We present algorithms for LAI relationships with spectral vegetation indices (VI). ► LAI links to precipitation and decreases from forests to woodlands and bushlands. ► LAI–VI relationships are modified by mean annual rainfall. ► LAI–VI relationships are further shaped by disturbances and other factors.
We present a model-based investigation of the effect of discrete-return lidar system and survey characteristics on the signal recorded over young forest environments. A Monte Carlo ray tracing (MCRT) model of canopy scattering was used to... more
We present a model-based investigation of the effect of discrete-return lidar system and survey characteristics on the signal recorded over young forest environments. A Monte Carlo ray tracing (MCRT) model of canopy scattering was used to examine the sensitivity of model estimates of lidar-derived canopy height, hlidar to signal triggering method, canopy structure, footprint size, sampling density and scanning angle, for broadleaf and conifer canopies of varying density. Detailed 3D models of Scots pine (Pinus sylvestris) and Downy birch (Betula pubescens) were used to simulate lidar response, with minimal assumptions about canopy structure. Use of such models allowed the impact of lidar parameters on canopy height retrieval to be tested under a range of conditions typically not possible in practice. Retrieved hlidar was generally found to be an underestimate of ‘true’ canopy height, hcanopy, but with exceptions. Choice of signal triggering method caused hlidar to underestimate hcanopy by ∼ 4% for birch and ∼ 7% for pine (up to 66% in extreme cases). Variations in canopy structure resulted on average in underestimation of hcanopy by 13% for birch and between 29 and 48% for pine depending on age, but with over-estimates in some cases of up to 10%. Increasing footprint diameter from 0.1 to 1 m increased retrieved hlidar from significant underestimates of hcanopy to values indistinguishable from hcanopy. Increased sampling density led to slightly increased values of hlidar to close to hcanopy, but not significantly. Increasing scan angle increased hlidar by up to 8% for birch, and 19% for pine at a scan angle of 30°. The impact of scan angle was greater for conifers as a result of large variation in crown height. Results showed that interactions between physically modelled (hypothetical) within canopy returns are similar to findings made in other studies using actual lidar systems, and that these modelled returns can depend strongly on the type of canopy and the lidar acquisition characteristics, as well as interactions between these properties. Physical models of laser pulse/canopy interactions may provide additional information on pulse interactions within the canopy, but require validation and testing before they are applied to actual survey planning and logistics.
Aim  This study aims to link demographic traits and post-glacial recolonization processes with genetic traits in Himantoglossum hircinum (L.) Spreng (Orchidaceae), and to test the implications of the central–marginal concept (CMC) in... more
Aim  This study aims to link demographic traits and post-glacial recolonization processes with genetic traits in Himantoglossum hircinum (L.) Spreng (Orchidaceae), and to test the implications of the central–marginal concept (CMC) in Europe.Location  Twenty sites covering the entire European distribution range of this species.Methods  We employed amplified fragment length polymorphism (AFLP) markers and performed a plastid microsatellite survey to assess genetic variation in 20 populations of H. hircinum located along central–marginal gradients. We measured demographic traits to assess population fitness along geographical gradients and to test for correlations between demographic traits and genetic diversity. We used genetic diversity indices and analyses of molecular variance (AMOVA) to test hypotheses of reduced genetic diversity and increased genetic differentiation and isolation from central to peripheral sites. We used Bayesian simulations to analyse genetic relationships among populations.Results  Genetic diversity decreased significantly with increasing latitudinal and longitudinal distance from the distribution centre when excluding outlying populations. The AMOVA revealed significant genetic differentiation among populations (FST = 0.146) and an increase in genetic differentiation from the centre of the geographical range to the margins (except for the Atlantic group). Population fitness, expressed as the ratio NR/N, decreased significantly with increasing latitudinal distance from the distribution centre. Flower production was lower in most eastern peripheral sites. The geographical distribution of microsatellite haplotypes suggests post-glacial range expansion along three major migratory pathways, as also supported by individual membership fractions in six ancestral genetic clusters (C1–C6). No correlations between genetic diversity (e.g. diversity indices, haplotype frequency) and population demographic traits were detected.Main conclusions  Reduced genetic diversity and haplotype frequency in H. hircinum at marginal sites reflect historical range expansions. Spatial variation in demographic traits could not explain genetic diversity patterns. For those sites that did not fit into the CMC, the genetic pattern is probably masked by other factors directly affecting either demography or population genetic structure. These include post-glacial recolonization patterns and changes in habitat suitability due to climate change at the northern periphery. Our findings emphasize the importance of distinguishing historical effects from those caused by geographical variation in population demography of species when studying evolutionary and ecological processes at the range margins under global change.
The flowering pattern of plant species, including orchid species, may fluctuate irregularly. Several explanations are given in the literature to explain that pattern, including: costs associated with reproduction, herbivory effects,... more
The flowering pattern of plant species, including orchid species, may fluctuate irregularly. Several explanations are given in the literature to explain that pattern, including: costs associated with reproduction, herbivory effects, intrinsically triggered unpredictable variation of the system, and external conditions (i.e. weather). The influence of age is discussed, but is difficult to determine because relevant long-term field observations are generally absent in the literature. The influence of age, size, reproductive effort and climatic conditions on flowering variability of Himantoglossum hircinum are examined using data collected in a long-term project (1976–2001) in Germany. PCA and multiple regression analysis were used to analyse variability in flowering pattern over the years as a function of size and weather variability. We studied future size after flowering to quantify costs of reproduction. Flowering probability was strongly determined by plant size, while there was no significant influence of age class on flowering probability of the population. Costs associated with reproduction resulted in a decrease in plant size, causing reduced flowering probability of the plants in the following year. The weather explained about 50% of the yearly variation in the proportion of large plants and thus had an indirect, strong influence on the flowering percentage. We conclude that variability in flowering is caused mainly by the variability of weather conditions in the previous and current year, whereby reproductive effort causes further variability in flowering at the individual and, consequently, the population levels. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society, 2006, 151, 511–526.

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