1,721,151 research outputs found
The vanished Alnus-dominated forests along the Tyrrhenian coast
No full textThe development and decline of alder floodplain forests and alder carrs along the Tyrrhenian coasts, in relation to sea level changes, geomorphological processes, human activity, and climate change are presented and discussed. A number of 22 pollen records, complemented by Alnus macrofossil data, document the presence of widespread alder populations in the coastal Tyrrhenian floodplains throughout the Holocene, although with different density from one site to the other, mostly depending on local hydrological conditions. The role of climate changes in the dynamics of floodplain forests appears uncertain. In the last two centuries, major reclamation works disrupted this natural vegetation to obtain fertile plains that are now exploited for agricultural purposes, industrial activities, urban areas and related infrastructures. Only a few remnants of the original alder forests are preserved by international conservation conventions, as biodiversity reservoirs of severely endangered habitats. However, the vanished alder forests, which proved to be able to rapidly recover several times through the Holocene, may still have some potential to be restored
Buxus in Europe: Late quaternary dynamics and modern vulnerability.
No full textThe suggested location of broadleaved evergreen trees in Europe during the last full-glacial has traditionally
favoured a southerly refugial model, which proposes survival in the Mediterranean peninsulas
and recolonization of central and northern Europe during the Holocene. This hypothesis is not always
substantiated by thorough reviews of original past and modern occurrence data, or considered in the
light of plant traits and autoecology. Our approach focuses on the genus Buxus with the aim of exploring
(i) the relationship between the location of refugia and post-glacial population dynamics, (ii) past
processes determining density, fragmentation and local extinctions of modern populations, and (iii) the
vulnerability of Buxus in the context of the undergoing environmental changes. We compiled a database
of over 3600 modern occurrences and 676 fossil sites to reconstruct the distribution of Buxus in Europe
since 30 ka cal BP. The location of fossil finds and the plant traits of Buxus indicate that it persisted widely
across its modern distribution through the last glacial period with modes varying from region to region.
The E Pyrenees, W Alps, and Jura Mts hosted dense populations, which expanded exponentially during the
whole Holocene, and resulted in a modern continuous distribution area. In contrast, the Mediterranean
Peninsulas hosted sparse populations, which increased exponentially only during the first half of the
Holocene, clearly decreased in the last 4.5 ka BP and resulted in a highly fragmented modern distribution
area, most likely in relation to the climate trends towards dry conditions of the last few millennia. These
results challenge the common view that the Mediterranean regions are the exclusive and most important
refuge areas for evergreen broadleaved trees and stress the importance of considering long-term population
dynamics based on fossil data to evaluate the vulnerability of modern fragmented plant populations
in view of conservation actions.
© 2012 El
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
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