Photosynthetic responses to needle water potentials in Scots pine after a four-year exposure to elevated CO(2) and temperature

Effects of needle water potential (Psi(l)) on gas exchange of Scots pine (Pinus sylvestris L.) grown for 4 years in open-top chambers with elevated temperature (ET), elevated CO(2) (EC) or a combination of elevated temperature and CO(2) (EC + ET) were examined at a high photon flux density (PPFD), saturated leaf to air water vapor pressure deficit (VPD) and optimal temperature (T). We used the Farquhar model of photosynthesis to estimate the separate effects of Psi(l) and the treatments on maximum carboxylation efficiency (V(c,max)), ribulose-1,5-bisphosphate regeneration capacity (J), rate of respiration in the light (R(d)), intercellular partial pressure of CO(2) (C(i)) and stomatal conductance (G(s)). Depression of CO(2) assimilation rate at low Psi(l) was the result of both stomatal and non-stomatal limitations on photosynthetic processes; however, stomatal limitations dominated during short-term water stress (Psi(l) < -1.2 MPa), whereas non-stomatal limitations dominated during severe water stress. Among the nonstomatal components, the decrease in J contributed more to the decline in photosynthesis than the decrease in V(c,max). Long-term elevation of CO(2) and temperature led to differences in the maximum values of the parameters, the threshold values of Psi(l) and the sensitivity of the parameters to decreasing Psi(l). The CO(2) treatment decreased the maximum values of V(c,max), J and R(d) but significantly increased the sensitivity of V(c,max), J and R(d) to decreasing Psi(l) (P < 0.05). The effects of the ET and EC + ET treatments on V(c,max), J and R(d) were opposite to the effects of the EC treatment on these parameters. The values of G(s), which were measured simultaneously with maximum net rate of assimilation (A(max)), declined in a curvilinear fashion as Psi(l) decreased. Both the EC + ET and ET treatments significantly decreased the sensitivity of G(s) to decreasing Psi(l). We conclude that, in the future, acclimation to increased atmospheric CO(2) and temperature could increase the tolerance of Scots pine to water stress.     

Moisture content penetration in wood elements under varying boundary conditions

Knowledge of effects of moisture exposure on timber structures is important for serviceability and load bearing capacity of timber elements and systems. Varying climate affects the moisture content profiles in timber as the relative humidity changes in the ambient air. This paper presents methods for calculation of diffusion based moisture transport and corresponding results on how timber responds to varying moisture with regard to moisture penetration and distribution. The calculations are based on measured outdoor relative humidity and temperature at different climatic locations in Sweden. No remarkably large deviations between the different climatic locations were found in general, which is positive in a design code perspective.     

Beschädigungen in einer Wohnung durch Wespen

Ohne Zusammenfassung     

Shoot growth and crown development: effect of crown position in three-dimensional simulations

Trees have been increasingly considered as modular organisms, with individual shoots forming autonomous units that respond semi-independently to their surrounding environment. However, there is evidence for fairly strict hormonal control of tree crown development. Studies on the hydraulic architecture of trees suggest a closer functional connection between shoots and crown development than is postulated by the theory of branch autonomy. We studied how shoot growth pattern influences growth and crown architecture in young Scots pine trees simulated by the LIGNUM model assuming that (a) the growth of a shoot mainly depends on its light climate and (b) the growth of a shoot is influenced by its position within the crown. We determined shoot position within the crown based on a recently developed vigor index. The vigor index compares the relative axis cross-sectional area from the base of the tree to each shoot and gives a value of 1 to the pathway of the greatest cross-sectional area. All other shoots attain values between 0 and 1 depending on their cross-sectional areas and the cross-sectional areas of the branches leading there from the main axis. The shoot light climate is characterized by annually intercepted photosynthetically active radiation. We compared the results from simulations (a) and (b) against an independent data set. The addition of a within-shoot position index (the vigor index) to our simulation (simulation b) resulted in a more realistic tree form than that obtained with simulation (a) alone. We discuss the functional significance of the results as well as the possibilities of using an index of shoot position in simulations of crown architecture.     

Bridging process-based and empirical approaches to modeling tree growth

The gulf between process-based and empirical approaches to modeling tree growth may be bridged, in part, by the use of a common model. To this end, we have formulated a process-based model of tree growth that can be fitted and applied in an empirical mode. The growth model is grounded in pipe model theory and an optimal control model of crown development. Together, the pipe model and the optimal control model provide a framework for expressing the components of tree biomass in terms of three standard inventory variables: tree height, crown height and stem cross-sectional area. Growth rates of the inventory variables and the components of biomass are formulated from a carbon balance. Fundamentally, the parameters of the model comprise physiological rates and morphological ratios. In principle, the values of these parameters may be estimated by lower-level process models. Alternatively, the physiological and morphological parameters combine, under reasonable assumptions, into a set of aggregate parameters, whose values can be estimated from inventory data with a statistical fitting procedure.     

Zur Verbreitung und Entwicklung einiger höhlenbrütender Singvögel in Ostbayern

Zusammenfassung Die Verbreitung und Entwicklung des Kleibers (Sitta europaea), der beiden Baumläuferarten (Certhia familiaris undC. Brachydactyla), sowie des Trauerschnäppers (Ficedula hypoleuca), des Gartenrotschwanzes (Phoenicurus phoenicurus) und des Wendehalses (Jynx torquilla) wurde anhand von Aufzeichnungen über die Ergebnisse der Nistkastenkontrolle in Ostbayern für den Zeitraum von 1950 bis 1990 untersucht. Der Kleiber dominierte in den Laubwaldgebieten. Er nahm seit Beginn der der Wendehals bei Roding nachgewiesen. Der Anteil beider Arten erreichte zu Beginn der siebziger Jahre ein Maximum und war seitdem rückläufig. Besonders gravierend ist der Rückgang des Gartenrotschwanzes, der ehedem in einigen Revieren bei Mauth, Burglengenfeld und Zwiesel relativ häufig auftrat. Sein Anteil unter den Nistkastenbewohnern ging von ehemals 2,5% im gesamten Untersuchungsgebiet auf weniger als 0,2% zurück.

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Distribution and development of singing birds breeding in nesting boxes in eastern Bavaria

The occurrence ofJynx torquilla, Certhia familiaris, C. brachydactyla, Phoenicurus phoenicurus, Ficedula hypoleuca andSitta europaea in the eastern parts of Bavaria was investigated according to records of contents in nesting boxes from 1950–1990. The number of boxes checked each year rose from 560 in the year 1950 up to 13000 in 1985 (Abb. 2). The distribution of the species during the last decade from 1981–1990 is mapped (Abb. 1 and 3). The percentage of the boxes used by the nuthatch increased steadily by 0.3% per year since the begin of the observations. The flycatcher and the wryneck increased until 1976 and declined later. The tree creepers and the redstart decreased during the observed period of 41 years.

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Mit 4 Abbildungen und einer Tabelle

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Die Untersuchungen wurden vom Bayerischen Staatsministerium für Ernährung, Landwirtschaft und Forsten gefördert.     

Unkrautbekämpfung und Mäuse in Forstkulturen

Zusammenfassung In 25 Forstkulturen war die Mäusedichte im darauffolgenden Herbst nach dem Ausmähen allgemein etwas geringer als in vergleichbaren nicht gemähten Flächen. Die Erdmaus wurde von der Unkrautbekämpfung am stärksten betroffen. Auf den ausgemähten Flächen waren nur etwa halb so viele Fallen von dieser Wühlmausart belegt wie auf den nicht gemähten Flächen. Demgegenüber nahm die Dichte der Waldmaus auf den gemähten Flächen eher zu.Die Auswirkungen des Ausmähens waren jedoch zu gering, um die Mäusedichte nachhaltig zu dezimieren. Die Schadensgefahr kann erheblich verschärft werden durch eine Verletzung der jungen Bäumchen. Der austretende Assimilatsaft lockt Mäuse an, die an den verletzten Bäumchen das Benagen der Stämmchen erlernen können.

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Weed control and voles in forest cultivations

The vegetation in forest cultivations is an important factor for the occurrence of harmful voles which can gnaw the roots and the bark of the young trees. The influence of weed control upon the density of rodents was observed during ten years in several tree plantations in Bavaria. In 27 mowed cultivations the number of harmful voles was reduced by about one third in comparision to 25 untreated cultivations. However, there is a risk to injure the young trees by mowing. The voles are attracted by the effluent assimilates and can learn by this way to gnaw the bark from the wounded and subsequently also from the intact trees.

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Mit 2 Abbildungen