1,721,026 research outputs found
Modeling the carbon cycle and its interactions with management practices in grasslands
Get PDFThe world-wide geographical extension of grasslands consist in 20% of the land and in Europe of about 8% (EU-15). The annual sink of this kind of ecosystem is estimate to be about 0.5 Gt C y−1. The carbon accumulated in the soils of temperate grasslands was estimated to be between 150 and 300 Gt C. This quantity is about double the carbon stocked in the soils of temperate forests.
Anyway there are many uncertainties in these fluxes and stocks estimates. This uncertainties can in part be connected with the lack of knowledge in the applied and historical management. Frequently, these factors are only marginally accounted in ecosystem carbon budget while its importance was repeatedly stressed in literature. From this the importance of getting better insight in the interactions between carbon cycle and management practices in this type of ecosystem.
The process ecosystem model Biome-BGC is frequently used for simulating carbon cycle in forest ecosystems but its application to grasslands is uncommon.
This is linked to missing routines for simulating management. A first aim of the present work is to fill this lack. For this reason a module for simulating mowing and a module for simulating nitrogen fertilisation were implemented and tested.
A reason why there are uncertainties in ecosystem carbon budgets is that frequently the model input parameters are defined by literature without taking in consideration the uncertainties associated with the model and the characteristics of the single sites. This project aimed to suggest a solution to this problem by mean of sensitivity analysis and parameter optimisation. By mean of the mentioned aims this work is a contribution for gaining a better insight in the relationships between carbon cycle and management practices.Gli ecosistemi prato-pascolivi occupano il 20% della superficie terrestre e circa l’8% dell’Europa (EU-15). L’assorbimento globale di carbonio per questa tipologia ecosistemica `e stimato essere di 0.5 Gt y−1. Il carbonio accumulato nei suoli delle praterie nella fascia temperata `e stato quantificato tra i 150 ed i 300 Gt di C, questa quantit`a consiste in circa il doppio rispetto al carbonio contenuto nei suoli delle foreste temperate. Tuttavia, associate a queste stime, esistono diverse incertezze alle quali contribuisce una lacuna nella conoscenza delle modalit`a di gestione. Talvolta questa viene marginalmente considerata ai fini del calcolo di bilanci ecosistemici, mentre `e stato ripetutamente evidenziato che essa `e un fattore fondamentale nel determinare il ruolo di assorbimento o di emissione di una prateria gestita. Da questo emerge l’importanza dell’approfondimento della
conoscenza delle interazioni tra componenti del ciclo del carbonio e gestione in questo ecosistema.
Il modello ecosistemico Biome-BGC `e stato usato in numerosi casi per simulare il ciclo del carbonio in ecosistemi forestali ma la sua applicazione ad ecosistemi erbacei `e meno frequente. Questo `e dovuto all’assenza di routine che simulino le pratiche gestionali. Un primo obiettivo di questo progetto `e quello di colmare questa lacuna. Per questo motivo un modulo per simulare lo sfalcio ed un modulo per simulare la fertilizzazione sono stati implementati e testati.
Un altra causa nelle incertezze nei bilanci ecosistemici `e connessa al fatto che spesso i parametri di input di un modello sono definiti da valori medi di letteratura senza considerare la specificit`a del sito e del modello utilizzato.
Con il presente progetto si `e voluta colmare anche questa seconda lacuna attraverso un’analisi di sensitivit`a ed un’ottimizzazione dei parametri di input del modello pi ́u importanti. Con l’implementazione delle suddette routine e dell’ottimizzazione dei parametri si `e voluto contribuire ad una migliore comprensione delle interazioni tra pratiche gestionali e le diverse componenti del ciclo del carbonio
A Sentinel-2 Based Multi-Temporal Monitoring Framework for Wind and Bark Beetle Detection and Damage Mapping
Get PDFThe occurrence of extreme windstorms and increasing heat and drought events induced by climate change leads to severe damage and stress in coniferous forests, making trees more vulnerable to spruce bark beetle infestations. The combination of abiotic and biotic disturbances in forests can cause drastic environmental and economic losses. The first step to containing such damage is establishing a monitoring framework for the early detection of vulnerable plots and distinguishing the cause of forest damage at scales from the management unit to the region. To develop and evaluate the functionality of such a monitoring framework, we first selected an area of interest affected by windthrow damage and bark beetles at the border between Italy and Austria in the Friulian Dolomites, Carnic and Julian Alps and the Carinthian Gailtal. Secondly, we implemented a framework for time-series analysis with open-access Sentinel-2 data over four years (2017–2020) by quantifying single-band sensitivity to disturbances. Additionally, we enhanced the framework by deploying vegetation indices to monitor spectral changes and perform supervised image classification for change detection. A mean overall accuracy of 89% was achieved; thus, Sentinel-2 imagery proved to be suitable for distinguishing stressed stands, bark-beetle-attacked canopies and wind-felled patches. The advantages of our methodology are its large-scale applicability to monitoring forest health and forest-cover changes and its usability to support the development of forest management strategies for dealing with massive bark beetle outbreaks
Testing the Height Variation Hypothesis with the R rasterdiv Package for Tree Species Diversity Estimation
Get PDFAbstract: Forest biodiversity is a key element to support ecosystem functions. Measuring biodiversity
is a necessary step to identify critical issues and to choose interventions to be applied in order to
protect it. Remote sensing provides consistent quality and standardized data, which can be used
to estimate different aspects of biodiversity. The Height Variation Hypothesis (HVH) represents an
indirect method for estimating species diversity in forest ecosystems from the LiDAR data, and it
assumes that the higher the variation in tree height (height heterogeneity, HH), calculated through
the ’Canopy Height Model’ (CHM) metric, the more complex the overall structure of the forest
and the higher the tree species diversity. To date, the HVH has been tested exclusively with CHM
data, assessing the HH only with a single heterogeneity index (the Rao’s Q index) without making
use of any moving windows (MW) approach. In this study, the HVH has been tested in an alpine
coniferous forest situated in the municipality of San Genesio/Jenesien (eastern Italian Alps) at 1100 m,
characterized by the presence of 11 different tree species (mainly Pinus sylvestris, Larix decidua, Picea
abies followed by Betula alba and Corylus avellana). The HH has been estimated through different
heterogeneity measures described in the new R rasterdiv package using, besides the CHM, also other
LiDAR metrics (as the percentile or the standard deviation of the height distribution) at various
spatial resolutions and MWs (ALS LiDAR data with mean point cloud density of 2.9 point/m2 ).
For each combination of parameters, and for all the considered plots, linear regressions between
the Shannon’s H0 (used as tree species diversity index based on field data) and the HH have been
derived. The results showed that the Rao’s Q index (singularly and through a multidimensional
approach) performed generally better than the other heterogeneity indices in the assessment of the
HH. The CHM and the LiDAR metrics related to the upper quantile point cloud distribution at fine
resolution (2.5 m, 5 m) have shown the most important results for the assessment of the HH. The size
of the used MW did not influence the general outcomes but instead, it increased when compared to
the results found in the literature, where the HVH was tested without MW approach. The outcomes
of this study underline that the HVH, calculated with certain heterogeneity indices and LiDAR data,
can be considered a useful tool for assessing tree species diversity in considered forest ecosystems.
The general results highlight the strength and importance of LiDAR data in assessing the height
heterogeneity and the related biodiversity in forest ecosystems
Impact of salvage logging on short-term natural regeneration in montane forests of the Alps after large windthrow events
Get PDFWind disturbances are one of the main drivers of forest dynamics in Europe, shaping forest stands and modifying the ecosystem services provisioning. Salvage logging is often most common strategy adopted after a high-severity disturbance in managed stands. Understanding natural regeneration dynamics including their interaction with the logging operations, is crucial to understand how forests will be changing under a climate with increasing variability and to design adequate adaptive post-disturbance management strategies. In this study, we focused on 148 stands damaged by storm Vaia (2018). The aim was to analyze natural regeneration dynamics under different logging systems and to investigate influences of site characteristics and disturbance legacies on sapling growth and seedling emergence. The sampling protocol consisted of one transect per stand, perpendicular to one of the intact forest edges, and with a length of 80 m. Along the transect, we collected soil cover, natural seedling and sapling stem density, and deadwood quantity in four sample plots of 3 m radius each at distances of 0, 20, 40, and 80 meters from the edge (592 plots in total). Regeneration species composition was mainly driven by previous stand composition, with some exceptions depending on seed dispersal strategy. Distance from the edge significantly influenced seedlings and saplings occurrence in large gaps and affected the browsing damage percentage, together with deadwood presence. According to GLM’s models, distance from the edge, elevation, and logging methods influenced seedling establishment. At the same time, species characteristics, edge structure, deadwood and logging damages significantly influenced pre-storm seedlings and saplings presence and health. In conclusion site factors, disturbance legacies, and logging strategies are key points to consider in post-disturbance management for a fast forest recovery
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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