1,721,152 research outputs found
The more, the better? Water relations of Norway spruce stands after progressive thinning
No full textPredicted intense and prolonged drought events challenge forest management. Thinning is debated as a silvicultural measure for reducing drought risk in densely established forest stands. We report on a thinning experiment in a 26-year-old Norway spruce stand (Picea abies), comprising of two thinning intensities and one unthinnned control. The removal of 43% (moderate thinning, MT) and 67% (heavy thinning, HT) of the initial basal area led to increased water availability during the entire three year observation period. Stand-level transpiration (Es) was decreased by about 25% upon moderate, and by about 50% upon heavy thinning during the first year after the interventions had been carried out. However, differences in Es across the treatments decreased within three years after thinning mainly due to increased single-tree transpiration and additional understory evapotranspiration at HT. Nevertheless, due to lower interception and transpiration on the thinned plots three years after treatment MT and HT still showed a substantial surplus in extractable soil water. The results showed that the main determinants concerning the extent of the mitigation effect with increasing thinning intensity were the available soil water storage capacity and the emerging understory vegetation. We conclude that repeated moderate thinning, through enhancing the water availability to the remaining trees, can mitigate drought risk in young spruce stands and thus, represent a viable silvicultural measure in anticipating possible water limitations due to climate change
Close to the edge: effects of repeated severe drought on stem hydraulics and non-structural carbohydrates in European beech saplings
No full textSevere drought events threaten tree water transport system, productivity and survival. Woody angiosperms generally die when embolism-induced loss of hydraulic conductance (PLC) surpasses 80-90% under intense water shortage. However, the recovery capability and possible long-term carry-over effects of repeated drought events could dictate the fate of species' population under climate change scenarios. Potted saplings of European beech (Fagus sylvatica L.) were subjected to two drought cycles in two consecutive growing seasons, aiming to induce minimum leaf water potentials (Ψmd) of about -4 MPa, corresponding to hydraulic thresholds for survival of this species. In the first cycle, a well-irrigated (C) and a drought-stressed group (S) were formed, and, in the following summer, each group was divided in a well-irrigated and a drought-stressed one (four groups in total). The impact of the multiple drought events was assessed by measuring wood anatomical traits, biomass production, water relations, stem hydraulics and non-structural carbohydrate (NSC) content. We also investigated possible connections between stem hydraulics and carbon dynamics during the second drought event and following re-irrigation. S plants had lower Ψmd and maximum specific hydraulic conductivity (Ks) than C plants in the following growing season. Additionally, aboveground biomass production and leaf number were lower compared to C trees, resulting in lower water consumption. However, PLC was similar between groups, probably due to the production of new functional xylem in spring. The second drought event induced 85% PLC and promoted conversion of starch-to soluble sugars. Nevertheless, 1 week after re-irrigation, no embolism repair was observed and soluble sugars were reconverted to starch. The previous drought cycle did not influence the hydraulic performance during the second drought, and after re-irrigation S plants had 40% higher wood NSC content. Our data suggest that beech cannot recover from high embolism levels but multiple droughts might enhance stem NSC availability
Post-drought hydraulic recovery is accompanied by non-structural carbohydrate depletion in the stem wood of Norway spruce saplings
Full text linkHydraulic failure and carbon starvation are recognized as main causes of drought-induced forest decline. As water transport and carbon dynamics are strictly interdependent, it is necessary to clarify how dehydration-rehydration cycles are affecting the relations between stem embolism and non-structural carbohydrates (NSC). This is particularly needed for conifers whose embolism repair capability is still controversial. Potted Norway spruce saplings underwent two drought-re-irrigation
cycles of same intensity, but performed in two consecutive summers. During the second cycle, stem percent loss of hydraulic conductivity (PLC) and NSC content showed no carry-over effects from the previous drought, indicating complete long-term recovery. The second drought treatment induced moderate PLC (20%) and did not affect total NSCs content, while starch was converted to soluble sugars in the bark. After one week of re-irrigation, PLC recovered to pre-stress values (0%) and NSCs were depleted, only in the wood, by about 30%. Our data suggest that spruce can repair xylem embolism and that, when water is newly available, NSCs stored in xylem parenchyma can be mobilized over short term to sustain respiration and/or for processes involved in xylem transport restoration. This, however, might imply dependency on sapwood NSC reserves for survival, especially if frequent drought spells occur
Saisonale Dynamiken hinter dem CO2 Efflux von Rotbuche (Fagus sylvatica) und Fichte (Picea abies) – aufgedeckt mittels stabiler C Isotope
No full textThe study examined seasonal pattern in the CO2 efflux from non-leafy branches, trunks and coarse roots of ca. 60-year-old European beech (F. sylvatica) and Norway spruce (P. abies) trees. To this end, the natural δ13C of the CO2 efflux was measured on the monthly scale, covering the course of a whole year. In addition, seasonal changes in C allocation of recent photosynthates to respiratory C pools were examined by stable C isotope labeling of whole-tree canopies (isoFACE infrastructure). Pronounced seasonal dynamics were observed in each species and results were related to tree phenology, i.e. lignin synthesis during summer and CO2 refixation during winter. The study highlighted the dependency of beech on seasonal build-up and consumption of storage C and the abundance of two respiratory C pools. Both aspects were less pronounced in evergreen spruce.The study examined seasonal pattern in the CO2 efflux from non-leafy branches, trunks and coarse roots of ca. 60-year-old European beech (F. sylvatica) and Norway spruce (P. abies) trees. To this end, the natural δ13C of the CO2 efflux was measured on the monthly scale, covering the course of a whole year. In addition, seasonal changes in C allocation of recent photosynthates to respiratory C pools were examined by stable C isotope labeling of whole-tree canopies (isoFACE infrastructure). Pronounced seasonal dynamics were observed in each species and results were related to tree phenology, i.e. lignin synthesis during summer and CO2 refixation during winter. The study highlighted the dependency of beech on seasonal build-up and consumption of storage C and the abundance of two respiratory C pools. Both aspects were less pronounced in evergreen spruce.Die Studie untersuchte saisonale Muster im CO2 Efflux unbelaubter Zweige, Stämme und Grobwurzeln ca. 60-jähriger Rotbuchen (F. sylvatica) und Fichten (P. abies). Hierzu wurde ein Jahr lang der natürliche δ13C des CO2 Effluxes einmal pro Monat gemessen. Zudem wurden saisonale Änderungen in der C Allokation neuer Photosyntheseprodukte zu Respirations C-Pools durch die Markierung kompletter Baumkronen mittels stabiler C Isotope (isoFACE Markierungssystem) untersucht. In beiden Arten wurden ausgeprägte saisonale Dynamiken beobachtet, welche auf die Phänologie der Bäume zurückgeführt wurden, z.B. auf Lignin Synthese im Sommer und auf CO2 Refixierung im Winter. Die Studie machte die Abhängigkeit der Buche von saisonalen Speicherauf- und -abbau deutlich und deutete auf die Anwesenheit von zwei Atmungs-Kohlenstoffpools. Beide Aspekte waren für die immergrüne Fichte weniger ausgeprägt
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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