1,721,039 research outputs found
A Multidimensional Statistical Framework to explore seasonal profile, severity and land-use preferences of widfires in a Mediterranean country
No full textThis study analyses spatio-temporal patterns of wildfires in Greece using a multidimensional statistical framework based on non-parametric correlations, principal component analysis, clustering and stepwise discriminant analysis. Specifically, we assess the frequency, seasonal profile, severity and land-use type of 135 178 wildfires which occurred between 2000-2012 in Greece, one of the countries most affected by fire in Europe. Our results show that both the number of fires and the average size of the area covered by fire show a specific seasonal pattern with a marked increase during the dry season. Principal component analysis identifies three dimensions linked with the main type of land-use affected by the fires: (i) medium and large fires primarily affected landscapes composed of forests, mixed woodlands/shrublands and croplands; (ii) small fires mainly affected fragmented landscapes, i.e. those with mosaics of different crops, market gardens and non-vegetated, abandoned or marginal areas; (iii) fires affecting wetlands and pastures occurred particularly in late summer and showing medium-low severity. Hierarchical clustering highlights similarities in spatio-temporal patterns between fire indicators (ignition date, burnt land cover classes, fire size, fire density). K-means clustering allows us to distinguish between low-severity fires occurring in the wet season from intense and frequent fires occurring in the dry season but with distinct land-use selectivity. The research reported here contributes insight into the complexity of wild fires in the Mediterranean region and supports the design of more effective fire prevention measures including sustainable forest management practices and careful regional planning to minimise risk factors
A multidimensional statistical framework to explore seasonal profile, severity and land-use preferences of wildfires in a Mediterranean country
Full text linkThis study analyses spatio-temporal patterns of wildfires in Greece using a multidimensional statistical framework based on non-parametric correlations, principal component analysis, clustering and stepwise discriminant analysis. Specifically, we assess the frequency, seasonal profile, severity and land-use type of 135 178 wildfires which occurred between 2000–2012 in Greece, one of the countries most affected by fire in Europe. Our results show that both the number of fires and the average size of the area covered by fire show a specific seasonal pattern with a marked increase during the dry season. Principal component analysis identifies three dimensions linked with the main type of land-use affected by the fires: (i) medium and large fires primarily affected landscapes composed of forests, mixed woodlands/shrublands and croplands; (ii) small fires mainly affected fragmented landscapes, i.e. those with mosaics of different crops, market gardens and non-vegetated, abandoned or marginal areas; (iii) fires affecting wetlands and pastures occurred particularly in late summer and showing medium-low severity. Hierarchical clustering highlights similarities in spatio-temporal patterns between fire indicators (ignition date, burnt land cover classes, fire size, fire density). K-means clustering allows us to distinguish between low-severity fires occurring in the wet season from intense and frequent fires occurring in the dry season but with distinct land-use selectivity. The research reported here contributes insight into the complexity of wild fires in the Mediterranean region and supports the design of more effective fire prevention measures including sustainable forest management practices and careful regional planning to minimise risk factors
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Long-term comparison of in situ and remotely-sensed Leaf Area Index in temperate and mediterranean broadleaved forests
No full textMonitoring vegetation structure and functioning is critical for modelling terrestrial ecosystems and energy cycles. Leaf area index (LAI) is an important structural property of vegetation used in many land-surface, climate, and forest monitoring applications. Remote sensing provides a unique way to obtain estimates of leaf area index at spatially extensive areas. However, the analysis and extraction of quantitative information from remotely-sensed data require accurate cross-calibration with in situ forest measurements, which are generally spatially- and temporally-limited, thereby limiting the ability to compare the seasonal dynamic patterns between field and remotely-sensed time series. This is particularly relevant in temperate broadleaved forests, which are characterized by high level of complexity, which can complicate the retrieval of vegetation attributes from remotely-sensed data. In this study, we performed a long-term comparison of MODIS LAI products with continuous in situ leaf area index measurements collected monthly in temperate and Mediterranean forests from 2000 to 2016. Results indicated that LAI showed a good correlation between satellite and ground data for most of the stands, and the pattern in seasonal changes were highly overlapping between the timeseries. We conclude that MODIS LAI data are suitable for phenological application and for up-scaling LAI from the stand level to larger scales
Climate, tree masting and spatial behaviour in wild boar (Sus scrofa L.): insight from a long-term study
No full textEarly and long-term impacts of browsing by roe deer in oak coppiced woods along a gradient of population density
No full textOver the last few decades, wild ungulate populations have exhibited relevant geographic and demographic expansion
in most European countries; roe deer is amongst the most widespread ungulate species. The increasing roe deer densities have led
to strong impact on forest regeneration; the problem has been recently recognized in coppice woods, a silvicultural system which is
widespread in Italy, where it amounts to about 56% of the total national forested area.
In this study we investigated the effect of roe deer browsing on the vegetative regeneration of Turkey oak few years after coppicing,
along a gradient of roe deer density. A browsing index revealed that browsing impact was high at any given roe deer density but
increased at higher density, with the browsing rate ranging from 65% to 79%. We also analyzed the long-term impact of browsing
six and eleven years after coppicing under a medium roe deer density. Results indicated the early impact are not ephemeral but
produced prolonged impacts through time, with an average reduction in volume of -57% and -41% six and eleven years after coppicing,
respectively. Based on these results we proposed integrating browsing monitoring with roe deer density estimation to allow
identifying ungulate densities which are compatible with silvicultural and forest management objectives. The proposed browsing
index can be regarded as an effective management tool, on account of its simplicity and cost-effectiveness, being therefore highly
suitable for routine, large scale monitoring of browsing impact
Reproductive phenology and conception synchrony in a natural wild boar population
No full textReproductive synchrony among gregarious mammals has a strong adaptive value and may lead to
cooperative behaviors aimed at maximizing offspring survival. Additionally, temporal clustering of
estrus has important implications on individual mating tactics and ultimately affects the degree of
polygamy in a population. Although several studies have examined the reproductive biology of wild
boar (Sus scrofa), much remains to be understood about the patterns of timing and synchrony of reproduction
in natural populations. We analyzed the spatiotemporal distribution of conception dates
in an Italian wild boar population taking into account the effects of environmental and individual
factors, in order to determine the main variables influencing the timing of reproduction and to detect
the signs of a socially-driven reproductive synchrony. Specifically, for each litter belonging to
354 pregnant sows culled between 2006 and 2013 in a mountain area of Tuscany, we determined
the conception date (CD) from an estimate of the mean fetal age and the culling date. We then investigated
which factors drove the variation in CD, by implementing linear mixed models, Mantel
tests and spatial autocorrelation analyses. The selected model showed significant effects of rainfall,
temperatures, and previous and current productivity on CD, as well as a strong correlation of CDs
among sows culled in close spatial and temporal proximity (i.e., in the same hunting ground and
hunting season). Likewise, autocorrelation analyses and Mantel tests consistently indicated that
closer sows had similar conception dates. Overall, our results confirm the effect of resource availability
and climate on wild boar reproductive phenology, and suggest socially-driven reproductive
patterns, in spite of a high turn-over in social groups due to hunting. Finally, possible advantages
and evolutionary implications of reproductive synchrony in wild boar are discussed
Characterizing the climatic niche of mast seeding in beech: Evidences of trade-offs between vegetation growth and seed production
No full textMasting is a complex mechanism which is mainly driven by a combination of internal plant resources and climatic conditions. While the driving role of climate in masting is being intensively studied, the interplay among climate, seed production, vegetation growth and phenology still needs further investigation. The objectives of this study were to identify the climatic determinants of different levels of seed production and of NDVI-based vegetation growth and phenology in European beech, and to evaluate if exists a trade-off between these two plant processes. To answer these questions, we used a 25-year-long dataset of beech seed production. We exploited the concept of ecological niche assuming that a mast year can be modeled like a species with variable preferences for different resources, which are the underlying annual climatic conditions; we performed an Ecological Niche Factor Analysis (ENFA), a presence-only modeling tool conventionally used in zoology and botany, and used seasonal (spring, summer, autumn) Standardized Precipitation-Evaporation Index (SPEI) observations, considering the current year (y−0), and up to one (y−1) and two (y−2) years before the masting event. For analyzing the role of vegetation growth and phenology, we used seasonal Normalized Difference Vegetation Index (NDVI) values and associated NDVI-based phenological metrics derived from Landsat imagery. Results indicated the driving role of climate for masting, especially in VHSP years. A moist summer and dry spring at y−2 and a dry summer at y−1 represented the main driving climatic conditions for masting; while a moist spring during the observation year represented the key condition for triggering higher intensities of seed production. Summer NDVI at y−0 and y−1 represented the variables discriminating best between masting and non-masting years and resulted as driven by opposite summer climatic conditions than seed production, thus indicating a trade-off between seed production and vegetation phenology. We concluded that reproduction and vegetation growth act as two different climate-dependent plant responses in beech, in a way that certain conditions through the years promote mast seeding and the opposite conditions favor vegetation growth. The understanding of climate-growth-masting relationships represents indispensable knowledge for providing a holistic view of masting mechanisms and developing adaptive forest management strategies in this species
Long-term response to thinning in a beech (Fagus sylvatica L.) coppice stand under conversion to high forest in Central Italy
Full text linkEuropean beech (Fagus sylvatica L.) forests have a long history of coppicing, but the majority of formerly managed coppices are currently under conversion to high forest. The long time required to achieve conversion requires a long-term perspective to fully understand the implication of the applied conversion practices. In this study, we showed results from a long-term (1992–2014) casestudy comparing two management options (natural evolution and periodic thinning) in a beech coppice in conversion to high forest. Leaf area index, litter production, radiation transmittance and growth efficiency taken as relevant stand descriptors, were estimated using both direct and indirect optical methods. Overall, results indicated that beech coppice showed positive and prompt
responses to active conversion practices based on periodic medium-heavy thinning. A growth efficiency index showed that tree growth increased asthe cutting intensity increased. Results from the case study supported the effectiveness of active conversion management from an economic (timber harvesting) and ecological (higher growth efficiency) point of view
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