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Errors in estimating volume increments of forest trees
Full text linkErrors in estimating volume increments of forest trees. Periodic tree and stand increments are often estimated retrospectively from measurements of diameter and height growth of standing trees, through the application of various simplifications of the general formula for volume increment rates. In particular, the Hellrigl method and its various formulations have been often suggested in Italy. Like other retrospective approaches, the Hellrigl method is affected by a systematic error, resulting from the assumption as a reference term of conditions at one of the extremes of the period considered. The magnitude of the error introduced by different formulations has been assessed in the present study through their application to mensurational and increment measurements from the detailed growth analysis of 107 Picea abies trees. Results are compared with those obtained with a new equation, which makes reference to the interval mid-point. The newly proposed method makes it possible to drastically reduce the error in the estimate of periodic tree increments, and especially its systematic component. This appears of particular relevance for stand- and national level applications
Towards an assessment of tree mortality and net annual increments in Italian forests. Which sustainability for the Italian forestry?
Full text linkSustainable forest management requires that fellings do not exceed increments in the medium term, once natural mortality is taken into account. Here we propose an assessment of the relevance of tree mortality in stands not regularly thinned, as prevailing in Italian forests. The amount of small-scale mortality losses is often neglected and cannot be directly estimated from available inventory data. From literature sources and using two alternative approaches, mortality losses could amount to 31.1-36.2% of gross annual increments. Fellings would therefore remove 57.7-62.6% of net annual increments of Italian forests, well above what often reported and not far away from the EU15 average. This new estimate confirms the overall sustainability of Italian forestry on a national level, but highlights the need for careful planning in the future use of forest biomass, a strategic renewable resource
Inhibition of photosystem 2 in starch-enriched Chlamydomonas reinhardtii cells prevents the efficient induction of H2 production in sulfur-depleted cultures
No full textIn sulfur-deprived Chlamydomonas reinhardtii cells the activity of photosystem 2 (PSII) has been shown to have a crucial role in the photosynthetic production of H2, since it allows the synthesis of internal reserves such as starch. In the present investigation, the PSII inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) was added in starch-enriched and sulfur-depleted C. reinhardtii cultures 1) at the very end of the aerobic phase, and 2) soon after the culture started to evolve H2. In the former case, production of H2 on
a volumetric basis was completely down-regulated, although starch mobilization was enhanced. In vitro tests showed that the hydrogenase enzyme was active, although its efficiency of utilization in vivo was lowered very soon in the experiment. When an inhibitor
of Rubisco such as glycolaldehyde was added under the same conditions, no substantial improvement in H2 production rates was noted. These findings indicate that, aside starch storage, PSII plays an active role in the induction of the H2 production process
Response to water stress of Italian alder seedlings from different geographic origin.
No full textThe morphological and physiological response to water stress was studied in 2-year-old potted Italian alder (Alnuscordata Loisel.) seedlings. Leaf area, transpiration, stomatal conductance, and xylem water potential were measured during May 1987 on seedlings from five geographic sources grown (i) with soil water content close to field capacity and (ii) with a severe drought. Significant differences in leaf area were found, at the end of the experiment, between drought-stressed and well-watered plants. As drought progressed, plants displayed a reduction of xylem water potentials and a decrease in stomatal conductance. However, transpiration did not stop completely, and seedlings were not able to maintain a favourable internal water status. Osmotic potentials for the undiluted cell sap, estimated from pressure–volume curves, were between −0.9 and −1.3 MPa. In June 1988, a similar experiment was carried out using seedlings from only one geographic source. A simultaneous decrease of transpiration, xylem potential, and net photosynthesis was observed in seedlings subjected to the drought treatment. During both experiments, a recovery of physiological parameters was observed, after rewatering. Some differences between provenances were detected. The provenance from Corsica showed the greatest sensitivity to water stress; a seed source from the province of Avellino (Campania, south Italy) was able to maintain a more favourable internal water status, as drought progressed
Contribution of diffusional and non-diffusional limitations to midday depression of photosynthesis in Arbutus unedo L.
No full textIt is still unknown whether the midday depression of photosynthesis under severe water stress, frequently observed in plants growing in a Mediterranean-type climate, is primarily a consequence of diffusional or non-diffusional limitations. We carried out combined measurements of gas exchanges and chlorophyll fluorescence in field-grown Arbutus unedo L. trees during late spring and mid summer, and a quantitative limitation analysis was performed to distinguish between the different limitations to photosynthesis, i.e., diffusional [D L = stomatal (S L) + mesophyll (MCL)] and non-diffusional (carboxylation capacity and electron transport, B L) limitations. Light-saturated assimilation at ambient CO2 (A max), stomatal conductance to water vapour (g sw) and maximum carboxylation rate (V cmax C i) showed a marked midday depression during both periods. The total limitations tended to increase during the day and were remarkably similar in June and July (50 and 48%, respectively); on a daily basis, D L was similar to B L (about 23%) in June; whereas, in July the former was predominant (38 and 4%, respectively). We concluded that the midday depression in photosynthesis was largely caused by diffusional limitations, with non-diffusional limitations playing a smaller role. Although stomatal closure was the main diffusional limitation, the decline in mesophyll conductance was not negligible during the hottest and driest period
Let's Exploit Available Knowledge on Vegetation Fluorescence
Full text linkThe potential to measure vegetation fluorescence from space (1) and to derive from it direct information on the gross primary productivity (GPP) of terrestrial ecosystems is probably the most thrilling development in remote sensing and global ecology of recent years, as it moves Earth observation techniques from the detection of canopy biophysics (e.g., fraction of absorbed radiation) and biochemistry (chlorophyll and nitrogen content) to the realm of ecosystem function.
The existence of a functional relationship
between fluorescence and photosynthesis
has been elucidated over the last decade
by several laboratories, notably as part of the
preliminary studies of the European Space
Agency Fluorescence Explorer (FLEX) Earth
Explorer Mission.
The empirical observation presented by
Guanter et al. (2) of a linear relationship
between fluorescence radiance and GPP,
however, provides the first experimental confirmation
of the feasibility of the approach
already thoroughly tested at leaf levelat the
desired scale, despite the confounding effects
associated with the satellite detection of such
a faint signal.
A word of clarification is needed here.
The use of fluorescence as a probe of leaf
photochemistry has been a staple of plant
ecophysiology for decades, rooted in a sound
understanding of photosynthetic energy dissipation.
However, most past studies had to
rely for the interpretation of results on active
(pulse-saturated) techniques, making them
unsuitable for remote-sensing applications.
Over recent years, however, novel process based
models have been developed for the
interpretation of steady-state, solar-induced fluorescence at the leaf to canopy scale (3).
We are therefore in a position to move beyond
the mere empirical observation of an
association between GPP and fluorescence
radiance.
In particular, Guanter et al. (2) base their
analysis on the assumption of a constant ratio
between photosynthetic and fluorescence
light use efficiencies (equation 3 in ref. 2).We
know, however, that the ratio is not constant,
but changes widely in response to light, CO2,
stomatal limitations, and extreme stress (4,
5). Whats more, we can make sense of such
changes, thus extracting valuable information
from the very scatter that is apparent in
their data.
However, this process will require the
availability of more tailored instruments,
such as the one planned for the FLEX
mission. As already stressed by Guanter
et al. (2), the spatial resolution of the
Global Ozone Monitoring Experiment-2
sensor (40 80 km) makes it difficult to
compare meaningfully the fluorescence signal
with ground measurements, when only
6070% of the footprint consists of the desired
land-cover type (table S1 in ref. 2),
suggesting that this could be largely responsible
for the low signals observed in
European grasslands. Moreover, the overpass
time of the MetOp-A satellite (9:30 AM)
implies that fluorescence is generally measured
under light-limiting conditions, when
fluorescence is only marginally affected by
stomatal closure even under stress conditions.
This result could explain the seasonal
mismatch with daily GPP observed
in natural ecosystems in the absence of irrigation
(figure 4 in ref. 2). We hope, therefore, that this welcome
contribution to this fast-advancing field will
help demonstrate the potential of the new
technique, and pave the way for more refined
studies under both a technological and scientific
point of view
The impact of sea erosion on coastal Pinus pinea stands. A diachronic analysis combining tree-rings and ecological markers
No full textCoastal erosion is a widespread phenomenon on sandy coasts throughout the Mediterranean region;
along the Thyrrenian coast of Tuscany (Italy), stone pine (Pinus pinea L.) stands originally planted for the
protection of agricultural crops further inland are often damaged. In the present study, a pairwise
comparison of stands at different distance from the sea at eroded and control sites highlighted the effects
of coastal erosion alone on pine growth and function. Dendroecological analyses made it possible to
determine the temporal dynamics of the phenomenon since 1930 and the interactions with climate,
whilst additional structural (LAI, sapwood area) and functional (carbon isotope discrimination)
measurements were used to discriminate between stress mechanisms. Salty winds, exacerbated by the
removal of dunal vegetation, were found to be the most likely cause of the observed growth decline. The
presence and, in more recent times, the reduction of surfactants in sea water played an important
synergistic effect. The intrusion of salty water in the water table, on the contrary, played a marginal role at
the site. Finally, stressed trees were more sensitive to the inter-annual variability in precipitation; at all
sites, growth was stimulated by June, November and December precipitation in the current and two
preceding years
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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