1,720,962 research outputs found
Drought and fire stress influence seedling competition in oak forests: fine-root dynamics as indicator of adaptation strategies to climate change
Full text linkIncreased summer drought and wildfires as a consequence of continuing climate change are expected to lead to disturbance of Mediterranean ecosystems. Seedlings recruitment is sensitive to both stresses and, therefore, any adaptation and restoration strategy devised to protect these forests should take into account a careful study on their effects on seedling development. As a substantial fraction of net primary productivity of forested ecosystems is channelled in the belowground compartments, the knowledge of how roots behave under stressful conditions becomes of primary importance to select the right management strategy to be implemented. This work tries to enlighten the events occurring in the fine root portion of the root system in young
seedlings of three co-existing oak species (Quercus ilex, Quercus trojana and Quercus virgiliana) under controlled conditions. We have made a comparative analysis of the effect of these two stresses, alone or in combination, with the aim to evaluate the tolerance level of these seedlings and, therefore, to obtain an indication of their recruitment potential in the field. The parameters investigated were biomass and a number of morphological traits. Data obtained suggest that a decrease in diameter could be part of a tolerance strategy in all three oaks tested together with a reduction of root length. In addition, tolerance to water shortage could require a reduction of carbon allocated belowground, in particular in the very fine roots, which leads to an overall reduction of the root system dimension. Q. trojana seedlings seem to be the fastest in resuming growth after stress interruption but a good recovery was also found for the remaining two oak species. Although our study provides interesting information regarding a possible tolerance strategy taking place in the fine root compartment when seedlings of these three oak species undergo water stress and fire treatment, more information is needed before any suggestion can be made as to which species would be best suited to make these forests more resistant to global changes
Forest canopy reduction stimulates xylem production and lowers carbon concentration in fine roots of European beech
No full textForest canopy reduction is well known to affect the coarse and fine root biomass production. Seasonality,
to the same extent, is acknowledged to vary the non-structural carbon content. However, the fine root
response in terms of carbon concentration to both canopy cover and seasonal change remains unclear.
To this aim, morphological and anatomical traits like xylem percentage, carbon concentration and
starch content were measured in mid-summer and early-fall on fine roots of three beech stands differing
in canopy cover and basal area.
The results highlighted a significant effect of canopy cover on the xylem area percentage throughout
the <2 mm diameter fine root population, as the lower the canopy cover is, the larger the xylem area
is. Moreover, an inverse relationship occurred between carbon concentration and xylem area percentage,
highlighting the key role played by this anatomical trait. In order of magnitude, the significant carbon
concentration decrease observed 5 years after felling was 15 kg ha1 for a mean fine root biomass of
200 g m2. For a given xylem percentage, starch concentration seasonal change partially explained the
carbon concentration decrease with the incipient dormancy. Root tissue density significantly decreased
with soil depth in mature and 15-yr-old conversion stands, whereas it did not in recently cut (5-yrold)
conversion stand.
Outcomes are that canopy closure in the mature stand, which increases the fine root standing crop, produced
a higher total carbon input into the soil. Moreover, fifteen years since felling appeared sufficient for
detecting a clear trend in the recovery of fine root biomass to pre-thinning levels
Competition for seedling establisment between three oak species in a Mediterranean forest affected by summer drought and fire".
No full text
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
Variations on the Author
Full text link“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
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