Untersuchungen über Produktion und Konsum von Honigtau in Hecken Oberfrankens

Zusammenfassung Im Rahmen einer einjährigen Arbeit wurde die Produktion von Honigtau in oberfränkischen Hecken und dessen Nutzung durch die Arthropodenfauna untersucht. Dazu wurde das Artenpektrum und die Phänologie der phloemsaugenden Insekten mit Hilfe der Klopfprobemethode über die gesamte Vegetationsperiode hinweg erfaßt.Von den 25 an den heckentypischen Gehölzarten festgestellten Phloemsaugern traten die Psylliden an Weißdorn und die Aphididen an Schlehe in besonders großen Individuenzahlen auf. Sie stellten im Untersuchungszeitraum die ergiebigsten Honigtauproduzenten in den bearbeiteten Hecken.Die Honigtauabgabe erreichte an den meisten Heckengehölzen ihr Maximum im Frühjahr, mit einem Abklingen in den Sommermonaten und einem erneuten kleineren Anstieg im Herbst. Demgegenüber dauerte die Blattlausentwicklung an der Schlehe und der Eiche den Sommer über an und ermöglichte so ein kontinuierliches Honigtauangebot für nahrungssuchende Insekten über die ganze Vegetationsperiode.An der Schlehe konnten insgesamt 139 Insekternarten als Honigtau-Besucher festgestellt werden. Die Syrphiden waren dabei mit 16 Arten am zahlreichsten vertreten, wobeiEpisyrphus balteatus (Deg.) die mit Abstand häufigste Honigtau-Besucherin stellte.

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Studies on production and consumption of honeydew in hedges of upper frankonia

In a one-year study, the production of honeydew in hedges of Upper Frankonia and its utilization by food-searching insects were investigated. The phloemfeeding fauna and its seasonal development on hedgeshrubs were assessed by means of the beating method.Out of the 25 sap-sucking species recorded on the shrubs typical for hedges, the Psyllidae on hawthorn (Crataegus spec.) and the Aphididae on blackthorn (Prunus spinosa) were most abundant during the period of investigation producing considerable amounts of honeydew.On most hedgeplants honeydew production reached a maximum in spring with a sharp decline in summer and a second but smaller peak in autumn. In contrast, the development of the aphids on blackthorn and oak persisted throughout the summer and therefore there was a continous honeydew supply for foodsearching insect species in the hedges during the season.On blackthorn a total of 139 insect species were recorded taking up honeydew from the plant's surface. In species number as well as in individual number the syrphids were the most frequent honeydew visitors. EspeciallyEpisyrphus balteatus (Deg.) was observed to feed in great numbers on the excretions of aphids.

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Mit 3 Abbildungen und 5 Tabellen     

Radiation-use efficiency and gas exchange responses to water and nutrient availability in irrigated and fertilized stands of sweetgum and sycamore

We investigated how water and nutrient availability affect radiation-use efficiency (epsilon) and assessed leaf gas exchange as a possible mechanism for shifts in epsilon. We measured aboveground net primary production (ANPP) and annual photosynthetically active radiation (PAR) capture to calculate epsilon as well as leaf-level physiological variables (light-saturated net photosynthesis, Asat; stomatal conductance, gs; leaf internal CO2 concentration, Ci; foliar nitrogen concentration, foliar [N]; and midday leaf water potential, Psileaf) during the second (2001) and third (2002) growing seasons in sweetgum (Liquidambar styraciflua L.) and sycamore (Platanus occidentalis L.) stands receiving a factorial combination of irrigation and fertilization at the Savannah River Site, South Carolina. Irrigation and fertilization increased PAR capture (maximum increase 60%) in 2001 and 2002 for both species and annual PAR capture was well correlated with ANPP (mean r2 = 0.77). A decreasing trend in epsilon was observed in non-irrigated stands for sweetgum in 2001 and for sycamore in both years, although this was only significant for sycamore in 2002. Irrigated stands maintained higher gas exchange rates than non-irrigated stands for sweetgum in 2001 and for sycamore in both years, although foliar [N] and Psileaf were generally unaffected. Because Ci decreased in proportion to gs in non-irrigated stands, it appeared that greater stomatal limitation of photosynthesis was associated with decreased Asat. On several measurement dates for sweetgum in 2001 and for sycamore in both years, epsilon was positively correlated with gas exchange variables (Asat, gs, Ci) (r ranged from 0.600 to 0.857). These results indicate that PAR capture is well correlated with ANPP and that gas exchange rates modified by irrigation can influence the conversion of captured light energy to biomass.     

Do the size and landscape context of forest openings influence the abundance and breeding success of shrubland songbirds in southern New England?

Early successional birds have declined in the northeastern United States due to the regeneration of forest on abandoned farm fields and the suppression of natural disturbances that once provided appropriate habitat. These species have become increasingly dependent on early successional habitats generated by such activities as timber harvesting. Recent approaches of timber harvesting, which range from single-tree harvesting to clearcutting, create forest openings of different sizes and configurations embedded in landscapes with different land use patterns. To assess the importance of forest openings created by timber harvesting for shrubland birds, we surveyed birds on 50 m radius plots in 34 harvest sites (0.5–21 ha). We collected data on multi-scaled habitat variables ranging from plot-level vegetation characteristics to land use patterns within 1 km of each study site. We also monitored mating and nesting success of Blue-winged Warblers (Vermivora pinus) in 10 forest openings.

The abundance of most shrubland species was influenced by plot-level habitat variables, such as tree density and vegetation height, rather than shrubland area or the composition of land uses in the surrounding landscape. Only Eastern Towhees (Pipilo erythrophthalmus) were more frequent in survey plots in larger forest openings. In contrast, neither abundance nor reproductive activity of Blue-winged Warblers was correlated with the size of the forest opening. Their abundance was negatively related to vegetation height, however. Only 54% of the territorial male Blue-winged Warblers in forest openings were mated. We documented relatively low nest success rates of 21.1% during the egg laying and incubation nest stages, but increased success rates during the later stages of nesting.

Our results indicate that even small forest openings with low vegetation provide habitat for Blue-winged Warblers and other shrubland birds. The overall reproductive rate of territorial male Blue-winged Warblers in forests openings was low during the 2 years of the study, however. Further studies are needed to assess the long-term value of this type of habitat for sustaining shrubland bird populations.     

Diurnal and seasonal variability in the radial distribution of sap flow: predicting total stem flow in Pinus taeda trees

We monitored the radial distribution of sap flux density (v; g H2O m(-2) s(-1)) in the sapwood of six plantation-grown Pinus taeda L. trees during wet and dry soil periods. Mean basal diameter of the 32-year-old trees was 33.3 cm. For all trees, the radial distribution of sap flow in the base of the stem (i.e., radial profile) was Gaussian in shape. Sap flow occurred maximally in the outer 4 cm of sapwood, comprising 50-60% of total stem flow (F), and decreased toward the center, with the innermost 4 cm of sapwood (11-15 cm) comprising less than 10% of F. The percent of flow occurring in the outer 4 cm of sapwood was stable with time (average CV < 10%); however, the percentage of flow occurring in the remaining sapwood was more variable over time (average CV > 40%). Diurnally, the radial profile changed predictably with time and with total stem flow. Seasonally, the radial profile became less steep as the soil water content (theta) declined from 0.38 to 0.21. Throughout the season, daytime sap flow also decreased as theta decreased; however, nighttime sap flow (an estimate of stored water use) remained relatively constant. As a result, the percentage of stored water use increased as theta declined. Time series analysis of 15-min values of F, theta, photosynthetically active radiation (PAR) and vapor pressure deficit (D) showed that F lagged behind D by 0-15 min and behind PAR by 15-30 min. Diurnally, the relationship between F and D was much stronger than the relationship between F and PAR, whereas no relationship was found between F and theta. An autoregressive moving average (ARIMA) model estimated that 97% of the variability in F could be predicted by D alone. Although total sap flow in all trees responded similarly to D, we show that the radial distribution of sap flow comprising total flow could change temporally, both on daily and seasonal scales.     

The influence of timber harvest on the structure and composition of riparian forests in the Coastal Redwood region

The composition and structure of riparian forests in the coast redwood region were analyzed in relation to the length of time since timber harvest, and the width of riparian buffer zone. Ten sites were sampled in the central range of the coast redwood forest type within a variety of post-harvest age groups and riparian buffer zone widths. Data was collected using randomly selected sample plots adjacent to perennial coastal steams. Correlation Fisher's r to z tests and two-tailed t-test were used to examine the relationship between the sample variables and the experimental parameters “years since harvest”, and “width of buffer.” Results indicate that canopy cover was negatively correlated to “years since harvest” with the highest level of canopy cover found on the youngest sites and the lowest level found on the old-growth sites. The hardwood to conifer dominance ratio and the basal area of Alnus rubra (red alder) were correlated negatively to both “years since harvest” and “buffer width” indicating that timber harvest favored hardwood species. Late seral associates such as Oxalis oregana (redwood sorrel), Anthyrium filix-femina (lady fern), and Vaccinium parviflorum (billberry) were found preferentially in older forests and sites with wider buffer zones, while non-native species such as Hedera helix (English ivy), Pampas cortedaria (pampas grass), and Myosotis latifolia (forget-me-not) were found preferentially in younger forests and areas with smaller buffer zones.     

Toward pollen sterility in German chamomile (Matricaria chamomilla)–Conventional breeding approaches of cytoplasmic/genic male sterility and chemical emasculation

Pollen sterility (PS) in mother lines is crucial for hybrid crossings in plant breeding. 21 di- (2x) and tetraploid (4x) accessions of the hermaphroditic chamomile were screened for spontaneous, thermic or gametocide induced PS. Two crossing trials with the diploid accessions 'Bona' (BON) and 'Hungary 2' (HUN2) should specify maternally inherited cytoplasmic male sterility (CMS). Progeny thereof showed increased PS. BON as mother (BH) entailed means of 30 and 22% PS, versus 8% and 20% after reciprocal crossings. Backcrosses of BH with HUN2 in paternal and maternal direction revealed increasing mean PS (24% and 32%), without verification of CMS. A split plot design of 100 individuals treated with four chemical gametocides analyzed PS, seed set, germination rate and whole plant damage. Tri-iodobenzoic acid caused the highest PS (43%). Progeny of two plants (2x, 4x) with degenerated anthers without pollen, showed 100% PS either in tetraploid F₁ and F₂ (4% and 11%) or in diploid F₂ and F₃ (26% and 23%). High temperature (30/28°C day/night) decreased the male fertility to some extent.     

Modelling soil temperature in forest clearcuts using climate station data

A physically based numerical model was developed to estimate the time courses of soil temperature in forest clearcuts from measured solar irradiance, air temperature and wind speed. The model is based upon a finite difference solution of the one-dimensional soil heat flow equation with a surface boundary condition determined from aerodynamic heat transfer and energy balance theory.Modelled soil temperatures were compared with data from two other studies reported in the literature and with temperatures measured in a forest clearcut during 6 and 16 day periods in the summer. The model calculated surface and subsurface soil temperatures accurately over these long intervals. Modelled soil temperatures were relatively insensitive to air temperature, soil thermal properties and the lower boundary soil temperature but quite sensitive to solar irradiance, wind speed and surface roughness.