Scientific results of the Bryotrop expedition to Zaire and Rwanda : 7., life strategies of epiphytic bryophytes from tropical lowland and montane forests, ericaceous woodlands and the Dendrosenecio subpáramo of the eastern Congo basin and the adjacent mountains (Parc National de Kahuzi-Biega/Zaire, Forêt de Nyungwe/Rwanda)

Life strategies of epiphytic bryophytes are studied along an altitudinal gradient from the eastern Congo basin (tropical lowland zone) to the mountains of the East-African graben (tropical subalpine/alpine Zone; BRYOTROP III-transect). Three strategies, Colonists, Perennial shuttle species and Perennial stayers can be observed, which are further subdivided according to their reproduction tactic (high sexual reproductive effort, high asexual reproductive effort, moderately or low sexual and asexual reproductive effort). Of these, only taxa with a long life span (perennials) are of importance, indicating the unchanging and constant ecological conditions and long-lasting microsites, provided by the epiphytic habitats. The basis for the life strategy pattern analysis along the altitudinal gradient were plant sociological investigations and the determination of the mean percentage cover values for the different life strategy categories. By this, the distribution and occurrence of the different strategies within the communities and the altitudinal zones can be shown

Wissenschaftliche Ergebnisse der BRYOTROP-Expedition nach Zaire und Rwanda : 6., Lebensformen und Adaptionen zur Wasserleitung und Wasserspeicherung in epiphytischen Moosgesellschaften im östlichen Kongobecken und den angrenzenden Gebirgsstöcken (Parc National de Kahuzi-Biega/Zaire, Forêt de Nyungwe/ Rwanda)

Life forms, water conducting and water storing structures of epiphytic bryophytes are studied along an altitudinal gradient from the eastern Congo basin (tropical lowand zone) to the mountains of the East-African graben (tropical subalpine/alpine zone; BRYOTROP III-transect). Based on a phytosociological analysis, these adaptations were put in relation to the distribution pattern of the bryophyte communities, as well as to the ecological gradient. The interpretation is based on the mean percent cover of each group. The tropical lowland zone is dominated by the life form mat, which is distinctly correlated with watersacs and taxa of the Jubulaceae, Lejeuneaceae and Radulaceae. In the following perhumid montane zone a clear alteration concerning the life form and the adaptations can be observed. The physiognomy of the primary rain-forests now is dominated by fan-forming Plagiochila species which are standing off the phorophyte by its flattened shoots. They are able to condensate water vapour from the fogs as well as using the low light intensities. Within the epiphytes of the bamboo zone of the upper montane zone, similar adaptation strategies to those of the lowland zone can be observed. The communities of the anthropogeneous montane woodlands of this zone, which are rich in mosses, show an ecomorphological wide spectrum [weft and tall-turfs correlated with a central strand (hadrome), hyalocysts and rhizoids]. Within the tropical subalpine/alpine zone exposed to great diurnal variations of climate, mat, weft and cushion-forming tall-turfs dominate, indicating the more xeric conditions (drought stress) by 88 water storing structures (alar cells, central strand, hyalocysts, rhizoids). In this zone, also structures reach a high mean percent cover, which enables the condensation of water vapour from the fog and mist rising from the upper montane zone or which show a groove-like arrangement of the leaflets. This may be recognized as a mechanism enabling a permanent water supply as well as a drain off of surplus water.Aufbauend auf einer pflanzensoziologischen Analyse werden die Lebensformen und die wasserleitenden und wasserspeichernden Strukturen epiphytischer Bryophyten entlang eines Transektes vom östlichen Kongobecken (Tieflandstufe) zum zentralafrikanischen Grabenrand (tropischsubalpine/ alpine Stufe; BRYOTROP III-Transekt) analysiert und in Beziehung zu den Moosgesellschaften und dem ökologischen Höhenstufengradienten gesetzt. Grundlage für die Interpretation ist der mittlere Gruppenmengenanteil. In der tropischen Tieflandstufe dominiert die Lebensform Decke, die eine auffallende Korrelation zu dem Strukturmerkmal Wassertasche und Wassersack sowie Sippen der Verwandtschaftskreise Jubulaceae, Lejeuneaceae und Radulaceae zeigt. In der sich anschließenden humiden Bergwaldstufe kommt es zu einem deutlichen Wechsel im Lebensformen- und Anpassungsspektrum. Wedelbildende Plagiochila- Arten bestimmen die Physiognomie der primären Regenwälder, deren abstehendes, planares Sproßsystem sich sowohl zum Nebelkämmen (Wasserdampfkondensation) eignet als auch als Anpassung an die lichtarmen Bedingungen interpretiert wird. Sonderfälle stellen in der oberen Bergwaldstufe die Epiphyten der Bergbambuswälder, mit ähnlichen Anpassungssyndromen wie die der Tieflandstufe, und die der offeneren, anthropogenen Bergwälder dar, deren laubmoosreiche Gesellschaften ökomorphologisch reicher strukturiert sind (Korrelation von Filz und Hochrasen mit Hyalozyten, Rhizoidenfilz und Zentralstrang). In der durch starke Klimaschwankungen gekennzeichneten tropisch-subalpinen Stufe dominieren Decke, Filz und posterförmige Hochrasen, die durch wasserspeichernde Strukturen (Alarzellen, Hyalozyten, Rhizoidenfilz, Zentralstrang) auf die bereits xerischen Bedingungen (Trockenstress) hindeuten. Hohe Anteile im Spektrum erreichen hier aber auch Strukturen zum Nebelkämmen (Nutzung der aus der Bergwaldstufe häufig aufsteigenden Treibnebel) und die Rinnenbildung

Climatology of the semidiurnal tide at 52-56°N from ground-based radar wind measurements 1985-1995

Long-term wind measurements carried out at 6 northern midlatitude sites (Saskatoon, Sheffield, Juliusruh, Collm, Obninsk, Kazan) are investigated to establish a climatology of the semidiurnal tide in the mesopause region for the narrow latitudinal range between 52°N and 56°N. Comparison of zonal and meridional components shows that in general the horizontal components are circularly polarized. Intercomparison of amplitudes and phases generally shows good agreement between the results from the different measuring systems. The results are compared with an empirical model of the semidiurnal tide. The longitudinal variation of the semidiurnal tide is small in summer, but the tidal amplitudes in winter are larger at Saskatoon and Kazan, compared with the results from the other sites. The possible influence of wave-tidal interaction in the stratosphere on the interannual variability of this difference is discussed

Mesopause region semidiurnal tide over Europe as seen from ground-based wind measurements

Wind measurements carried out at 6 European sites are investigated to set up a climatology of the semidiurnal tide in the mesopause region over Europe for the latitudinal range between 50°N and 56°N. Intercomparison of amplitudes and phases generally shows good agreement of the results from the different measuring systems. The longitudinal variation of the semidiurnal tide is small. The results are compared with an empirical model of the semidiurnal tide

The wind regime of the mesosphere and lower thermosphere during the DYANA campaign-II. Semi-diurnal tide

Co-ordinated ground-based radar measurements carried out during the 15 January-15 March 1990 DYANA campaign at 14 different geographical sites have provided a good opportunity to investigate the characteristics of semi-diurnal tidal variations in the mesosphere/lower thermosphere over a wide spectrum of space/time scales. It is pointed out that significant differences of monthly mean tidal parameters observed at the various sites may be explained by latitudinal and longitudinal effects. Well-defined 2-3-week oscillations of the tidal parameters are found to be typical of all observational sites. Their estimated space scales do not contradict the hypothesis about a possible coupling between these oscillations and the low wave-number processes in the stratosphere. Tidal parameter oscillations with 2-5-day periods may be explained to be effects of the nonstationary processes with longitudinal wave numbers S > 3. © 1994

The wind regime of the mesosphere and lower thermosphere during the DYANA campaign-I. Prevailing winds

During the DYANA campaign, winds and tides at mesospheric and lower thermospheric altitudes were measured by 14 ground based experiments (MF radars, meteor radars and LF-drift systems). The experiments were located between 107°W and 102°E, mostly in northern mid-latitudes with well covered areas in Central and Eastern Europe. Emphasis is placed here upon the vertical profiles and height-time contours of the prevailing zonal and meridional winds with different resolution (15 d, 4d). Generally, westerly winds are observed at heights below 95 km with a strong mesospheric variability and with longitudinal differences between the data of Central Europe, Eastern Europe, Asia and Canada. Planetary waves and a minor stratospheric warming in the first 10 days of February 1990 are the cause of this behaviour. In connection with the stratospheric warming, a wind reversal to summer east winds reaching from the upper stratosphere up to 95 km is observed. The close connection of the behaviour of the stratosphere with the observed longitudinal differences in the mesospheric response on the stratospheric warming and with the occurrence of wind oscillations (10-15 d) is discussed. © 1994

Variability of the quasi-2-day wave observed in the MLT region during the PSMOS campaign of June-August 1999

A network of 15 northern hemisphere radars has been used to measure horizontal winds in the mesosphere and lower thermosphere during the PSMOS campaign of Summer 1999. The radars are sited at latitudes ranging from 21°N to 75°N and longitudes from 142°E to 157°W. The data were examined to investigate the Northern Hemisphere structure of the quasi-2-day planetary wave during the interval June-August. The amplitude of the 2-day wave was found to exhibit great day-to-day variability. In particular, significant periodic fluctuations in amplitude occurred with periods of 8-10 and 14-17 days. These modulations were strongest in July and largely absent in June and August. In July, the wave activity can be resolved into three westward-propagating waves with zonal wave numbers of 2, 3 and 4. The periods associated with these wave numbers were 53-56, 48-50 and 42-43 h, respectively. The simultaneous presence of at least two spectral components with periods close to each other may serve to explain the observed amplitude modulations as a result of a beating between different spectral components. An earlier analysis of the planetary-wave field during this interval has revealed a westward propagating ∼16-day wave with zonal wave number 1 (Journal of Atmospheric and Solar-Terrestrial Physics 64 (2002b) 1865-1896). A non-linear interaction between this ∼16-day planetary wave and the (3,0) Rossby-gravity mode (the 2-day-wave) provides a possible mechanism to generate the above ∼42 h/wavenumber 4 wave and the ∼55 h/wavenumber 2 waves as sum and difference secondary waves. A bispectral analysis was used to further investigate non-linear interactions between members of the planetary-wave field and suggested a number of interactions occur within the planetary-wave field, but that some of the interactions also involve the non-migrating diurnal tide with zonal wavenumber 6. © 2004 Elsevier Ltd. All rights reserved

New national and regional bryophyte records, 59

Peer reviewe

Changes in CO2 during ocean anoxic event 1d indicate similarities to other carbon cycle perturbations

Past greenhouse intervals of the Mesozoic were repeatedly punctuated by Ocean Anoxic Events (OAEs), major perturbations to the global carbon cycle and abrupt climate changes that may serve as relevant analogs for Earth’s greenhouse gas-forced climate future. The key to better understanding these transient climate disruptions and possible CO2 forced tipping-points resides in high-resolution, precise, and accurate estimates of atmospheric CO2 for individual OAEs. Here we present a high-temporal resolution, multi-proxy pCO2 reconstruction for the onset of mid-Cretaceous (Albian-Cenomanian Boundary) OAE1d. Coupling of pCO2 estimates with carbon isotopic compositions (δ13C) of charcoal, vitrain, and cuticle from the Rose Creek Pit (RCP), Nebraska, reveals complex phasing, including a lag between the well-documented negative δ13C excursion defining the onset of OAE1d and the CO2 increase. This lag indicates that increased CO2 or other C-based greenhouse gases may not have been the primary cause of the negative excursion. Our study reveals a pCO2 increase within the interval of the negative δ13C excursion, reaching a maximum of up to ~840 ppm (95% confidence interval -307 ppm/+167 ppm) toward its end. The reconstructed magnitude of CO2 increase (~357 ppm) is similar to that of Late Cretaceous OAE2 but of smaller magnitude than that of other major carbon cycle perturbations of the Mesozoic assessed via stomatal methods (e.g., the Toarcian OAE [TOAE], Triassic-Jurassic boundary event, Cretaceous-Paleogene Boundary event). Furthermore, our results indicate a possible shared causal or developmental mechanism with OAE1a and the TOAE

Global-scale tidal variability during the PSMOS campaign of June-August 1999: Interaction with planetary waves

During the PSMOS Global-scale tidal variability experiment campaign of June 1-August 31, 1999, a network of radars made measurements of winds, waves and tides in the mesosphere/lower-thermosphere region over a wide range of latitudes. Clear evidence was found that fluctuations in tidal amplitudes occur on a global scale in both hemispheres, and that at least some of these fluctuations are periodic in nature. Modulation of the amplitude of the 12 h tide was particularly evident at periods of 10 and 16 days, suggesting a non-linear interaction with planetary waves of those periods to be responsible. In selected cases, the secondary waves predicted from non-linear theory could be identified and their zonal wave numbers determined. In some, but not all, cases the longitudinal structure of the secondary waves supports the theory of planetary-wave/tidal interaction being responsible for the observed tidal modulation. It was noted also that beating between a 12.4-lunar and the solar tide could produce a near 16-day modulation of the 12 h tide amplitude that is frequently observed in late summer. © 2002 Elsevier Science Ltd. All rights reserved