796 research outputs found
Regional variation in canopy transpiration of Central European beech forests
No full textForest hydrologists have hypothesised that canopy transpiration (E-c) of European temperate forests occurs at rather similar rates in stands with different tree species and hydrologic regimes. We tested this hypothesis by synchronously measuring xylem sap flow in four mature stands of Fagus sylvatica along a precipitation gradient with the aim (1) of exploring the regional variability of annual canopy transpiration (E-c(t)) in this species, and (2) of analysing the relationship between precipitation (P) and E-c(t). E-c(t) rates of 216, 225, 272 and 303 mm year(-1) corresponded to precipitation averages of 520, 710, 801 and 1,040 mm year(-1) in the four stands. We explored the regional variability of E-c(t) in Central European colline to sub-montane beech stands in two meta-analyses based on (1) existing sap flow data on beech (n=5 observations), or (2) all canopy transpiration data on beech obtained by different techniques (sap flow, micrometeorological or soil water budget approaches, n=25). With a coefficient of variation (CV) of 20%, the regional variability of E-c(t) (213-421 mm year(-1)) was smaller than the variation in corresponding precipitation (550-1,480 mm year(-1)). The mean E-c(t) for beech was 289 (+/- 58) mm year(-1) (n=25). A humped-shaped relationship between E-c(t) and P, with a broad transpiration maximum in the precipitation range from ca. 700 to 1,000 mm year(-1), was found which may indicate soil moisture limitation of transpiration for P 1,000 mm year(-1). Thus, the precipitation level significantly influences canopy transpiration of humid temperate forests; however, the size of the P influence on E-c(t) and, in part, the direction of its effect differ from forests in semi-arid or arid climates. European beech has the capacity to maintain high E-c rates in both humid and partly dry summer climates (P < 550 mm year(-1))
Functional role of forest diversity: Pros and cons of synthetic stands and across-site comparisons in established forests
No full textIn contrast to grasslands, forests have only rarely been the subject of functional biodiversity research. This paper addresses specific problems. which arise from applying the synthetic stand approach to long-lived plants, which can be taken to simulate the loss or addition of tree species or tree functional groups in forest stands. Planted synthetic stands often deviate from natural forests in several properties including trophic structure, tree age distribution, and horizontal and vertical canopy structures. Moreover, edge effects and the absence of a quasi-steady state in soil development limit the spectrum of processes which can be analysed for biodiversity effects in synthetic tree stands. We propose that these shortcomings can partly be overcome by combining the synthetic stand approach with observational Studies in existing forest stands of contrasting tree diversity. The potentials and limitations of comparisons among existing stands for functional biodiversity reseal-ell are briefly discussed using the example of the Hainich Tree Diversity Matrix, a species-rich temperate broad-leaved forest consisting of a small-scale mosaic of stands differing in tree diversity, which originated from a variety of historic forest-use practices. (C) 2008 Published by Elsevier GmbH oil behalf of Gesellschaft fur Okologie.DFG-Graduiertenkolle
Functional Crown Architecture of Five Temperate Broadleaf Tree Species: Vertical Gradients in Leaf Morphology, Leaf Angle, and Leaf Area Density
No full textThe morphology, inclination, and spatial distribution of leaves in different parts of tree crowns are important determinants of the radiation, momentum, and gas exchange between the canopy and the atmosphere. However, it is not well known how these foliage-related traits vary among species differing in successional status. We measured leaf size, leaf mass area (LMA), leaf inclination (angle to the horizontal), leaf area density (LAD), total leaf area (leaf area index, LAI), and leaf area distribution across the crown in adult trees of five common, early to late-successional tree species (Betula pendula Roth, Quercus petraea (Matt.) Liebl., Carpinus betulus L., Tilia cordata Mill., and Fagus sylvatica L.) using different canopy access techniques and the harvest of foliated trees (29 trees in total). Leaf size increased continuously with crown depth in B. pendula and T. cordata but peaked at mid-crown in Q. petraea, C. betulus, and F. sylvatica to decrease toward the shade crown. By contrast, LMA and leaf angle decreased continuously with crown depth in all species, but the pattern of vertical change varied. The mid/late- and late-successional species had higher LAI, lower shade-leaf LMA, lower leaf angles (shade and sun crown), and higher LAD in the uppermost sun crown in comparison to early successional B. pendula. We assume that the most peripheral sun leaf layer is partly acting as a shield against excess radiation, with foliage properties depending on the structure of the shade crown. We conclude that the vertical change in leaf morphology, inclination, and spatial distribution in tree crowns is highly species specific, with partial dependence on the species’ position in succession
Variation of soil and biomass carbon pools in beech forests across a precipitation gradient
No full textTemperate forests have recently been identified as being continuing sinks for carbon even in their mature and senescent stages. However, modeling exercises indicate that a warmer and drier climate as predicted for parts of Central Europe may substantially alter the source/sink function of these economically important ecosystems. In a transect study with 14 mature European beech (Fagus sylvatica L.) forests growing on uniform geological substrate, we analyzed the influence of a large reduction of annual precipitation (970-520 mm yr-1) on the carbon stocks in fast and slow pools, independent of the well-known aging effect. We investigated the C storage in the organic L, F, H layers, the mineral soil to 100 cm, and in the biomass (stem, leaves, fine roots), and analyzed the dependence of these pools on precipitation. Soil organic carbon decreased by about 25% from stands with > 900 mm yr-1 to those with < 600 mm yr-1; while the carbon storage in beech stems slightly increased. Reduced precipitation affected the biomass C pool in particular in the fine root fraction but much less in the leaf biomass and stem fractions. Fine root turnover increased with a precipitation reduction, even though stand fine root biomass and SOC in the organic L, F, and H layers decreased. According to regression analyses, the C storage in the organic layers was mainly controlled by the size of the fine root C pool suggesting an important role of fine root turnover for the C transfer from tree biomass to the SOC pool. We conclude that the long-term consequence of a substantial precipitation decrease would be a reduction of the mineral soil and organic layer SOC pools, mainly due to higher decomposition rates. This could turn temperate beech forests into significant carbon sources instead of sinks under global warming
In situ water absorption by tree fine roots measured in real time using miniature sap-flow gauges
No full text1. Root water uptake is a key process in the circulation of water in forest ecosystems. Until recently, water absorption by tree fine roots could not be measured in situ in undisturbed soil. 2. We present a new technique that allows continuous recording of the water absorption of fine root endings in mature stands without altering soil structure, hydrology or mycorrhizal infection. 3. The approach combines miniature sap-flow gauges mounted on small-diameter tree roots (3-4 mm) with a complete extraction and visual surface analysis of the adjacent absorbing fine root endings. This technique yields continuous data on water absorption per fine root surface area, and allows analysis of the spatial heterogeneity of root water uptake in the rhizosphere of forests. 4. We present the results of laboratory and field calibration experiments with Fagus sylvatica L. roots (3-4 mm), which show a good agreement between gauge flow data and synchronous gravimetric flow measurements for flows between 2 and >50 g h(-1) . Gauge readings were unreliable during low flows (<2 g h(-1) ) at night. In these periods, which cover approximate to10% of daily flow, we used an empirically derived linear relationship between root temperature difference and flow. 5. Measurements on F. sylvatica root endings during 10 summer days showed daily water absorption maxima ranging between 0.20 (rainy days) and 0.58 mmol m(-2) root surface area s(-1) (bright or overcast days). The corresponding daily maxima of leaf transpiration rate were approximate to10 times higher (2-4 mmol m(-2) leaf area s(-1) ). 6. The combination of miniature sap-flow gauges and determination of fine root surface area provides a promising tool for analysing water absorption by tree root systems in situ
Leaf water status and stem xylem flux in relation to soil drought in five temperate broad-leaved tree species with contrasting water use strategies
No full text• Five temperate broad-leaved tree species were compared with respect to their water consumption strategies under ample and restricted water supply. We measured synchronously leaf conductance in the sun canopy, xylem sap flux and leaf water potential (predawn, and noon, ) in adult trees in a mixed stand and related them to the fluctuations in vapor pressure deficit ( and soil moisture.
• Maximum was particularly high in F. excelsior, C. betulus and T. cordata and revealed a higher sensitivity. remained constantly high in A. pseudoplatanus, C. betulus and F. excelsior, but decreased in T. cordata and F. sylvatica with decreasing soil moisture.
• decreased linearly with decreasing soil matrix potential in all species except for F. excelsior. Apparent hydraulic conductance in the soil-to-leaf flow path was higher in A. pseudoplatanus than in the other species.
• F. sylvatica maintained a low maximum and reduced markedly upon drought, but faced severe decreases in and . F. excelsior represents an opposite strategy with high maximum and stable .
• The species drought sensitivity increases in the sequence F. excelsior C. betulus T. cordata A. pseudoplatanus F. sylvatica.Statut hydrique des feuilles et flux xylèmique dans le tronc en
relation avec la sécheresse du sol pour cinq espèces d'arbres
feuillus tempérés à stratégies de consommation
d'eau différentes. • Les stratégies de consommation d'eau de cinq espèces d'arbres
feuillus tempérés ont été comparées sous
approvisionnement en eau suffisant ou limité. De façon synchrone
nous avons mesuré la conductance hydraulique des feuilles dans
la partie du couvert exposée au soleil, le flux de sève
xylémique et le potentiel hydrique foliaire (potentiel de base
et potentiel minimum ) d'arbres adultes
en peuplement mixte et nous les avons reliés aux fluctuations du
déficit de pression de vapeur () et à l'humidité du sol.
• maximum était particulièrement élevée chez F. excelsior, C. betulus et
T. cordata et a révélé une plus grande sensibilité à D. est resté constamment élevé chez A. pseudoplatanus, . betulus et F. excelsior, mais a
diminué chez T. cordata et . sylvatica lorsque l'humidité du sol diminuait.
• a diminué linéairement avec le potentiel matriciel du sol pour
toutes les espèces excepté excelsior. La conductivité hydraulique
apparente du trajet sol-feuille était plus élevée chez A. pseudoplatanus que
dans les autres espèces.
• F. sylvatica a maintenu une faible maximum et a réduit sensiblement
face à la sécheresse, mais a connu de graves diminutions de
et . F. excelsior présentait une stratégie
opposée avec une maximum élevée et un
stable.
• La sensibilité des espèces à la sécheresse augmente selon
la séquence F. excelsior C. betulus T. cordata A. pseudoplatanus F. sylvatica
Soziale Traumatisierung durch Eltern und Gleichaltrige – unterschätzt und übersehen
No full textIffland B, Neuner F. Soziale Traumatisierung durch Eltern und Gleichaltrige – unterschätzt und übersehen. In: Müller J, Ruf-Leuschner M, Grimmer B, Knaevelsrud C, Dammann G, eds. Traumafolgen - Forschung und therapeutische Praxis . Psychotherapie in Psychiatrie und Psychosomatik. Stuttgart: Kohlhammer; 2022
Within-canopy variation in photosynthetic capacity, SLA and foliar N in temperate broad-leaved trees with contrasting shade tolerance
No full textThe leaf morphology and photosynthetic capacity of trees are remarkably plastic in response to intra-canopy light gradients. While most studies examined seedlings, it is not well understood how plasticity differs in mature trees among species with contrasting shade tolerance. We studied light-saturated net photosynthesis (A max), maximum carboxylation rate (V cmax), electron transport capacity (J max) and leaf dark respiration (R d) along natural light gradients in the canopies of 26 adult trees of five broad-leaved tree species in a mixed temperate old-growth forest (Fraxinus excelsior, Acer pseudoplatanus, Carpinus betulus, Tilia cordata and Fagus sylvatica), representing a sequence from moderately light-demanding to highly shade-tolerant species. We searched for species differences in the dependence of photosynthetic capacity on relative irradiance (RI), specific leaf area (SLA) and nitrogen per leaf area (N a ). The three shade-tolerant species (C. betulus, T. cordata, F. sylvatica) differed from the two more light-demanding species by the formation of shade leaves with particularly high SLA but relatively low N a and consequently lower area-based A max, and a generally higher leaf morphological and functional plasticity across the canopy. Sun leaf morphology and physiology were more similar among the two groups. The three shade-tolerant species differed in their shade acclimation strategies which are primarily determined by the species’ plasticity in SLA. Under low light, T. cordata and F. sylvatica increased SLA, mass-based foliar N and leaf size, while C. betulus increased solely SLA exhibiting only low intra-crown plasticity in leaf morphology and N allocation patterns. This study with mature trees adds to our understanding of tree species differences in shade acclimation strategies under the natural conditions of a mixed old-growth forest
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Xylem safety in relation to the stringency of plant water potential regulation of European beech, Norway spruce, and Douglas-fir trees during severe drought
No full textAbstract
Key message
Norway spruce operates with larger hydraulic safety margins (HSM) than beech and Douglas-fir despite the known drought sensitivity of spruce, questioning a pivotal role of HSM in drought tolerance.
Abstract
The exceptional 2018/2019 drought exposed Central Europe’s forests to severe stress, highlighting the need to better understand stomatal regulation strategies and their relationship to xylem safety under extreme drought. We studied diurnal, seasonal, and inter-annual variation in stomatal conductance (
g
s
) and leaf water potential (
Ψ
Leaf
) in co-occurring European beech (
F. sylvatica
), Norway spruce (
P. abies
), and Douglas-fir (
P. menziesii
) trees in the two summers and related them to hydraulic traits characterizing drought resistance. In 2018,
F. sylvatica
exhibited a continuous
Ψ
Leaf
decline from June to September, as is characteristic for an anisohydric strategy, while
P. abies
closed stomata early and reached the least negative
Ψ
Leaf
-values at the end of summer.
P. menziesii
showed low
Ψ
Leaf
-values close to
P
12
(the xylem pressure at onset of embolism) already in July. Both conifers closed stomata when approaching
P
12
and maintained low
g
s
-levels throughout summer, indicative for isohydric regulation. In 2019, all three species showed a linear decline in
Ψ
Leaf
, but
F. sylvatica
crossed P
12
in contrast to the conifers. The three species exhibited similar water potentials at turgor loss point (− 2.44 to − 2.51 MPa) and branch
P
50
(xylem pressure at 50% loss of hydraulic conductance; − 3.3 to − 3.8 MPa). Yet,
F. sylvatica
and
P. menziesii
operated with smaller hydraulic safety margins (HSM means: 0.79 and 0.77 MPa) than
P. abies
(1.28 MPa).
F. sylvatica
reduced leaf size and specific leaf area in 2019 and increased Huber value. Our species comparison during extreme drought contradicts the general assumption that conifers operate with larger HSMs than angiosperm trees. Contrary to expectation,
P. abies
appeared as hydraulically less vulnerable than Douglas-fir.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Georg-August-Universität Göttingen http://dx.doi.org/10.13039/50110000338
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