Retrospective analysis of a nonforecasted rain-on-snow flood in the Alps – a matter of model limitations or unpredictable nature?

A rain-on-snow flood occurred in the Bernese Alps, Switzerland, on 10 October 2011, and caused significant damage. As the flood peak was unpredicted by the flood forecast system, questions were raised concerning the causes and the predictability of the event. Here, we aimed to reconstruct the anatomy of this rain-on-snow flood in the Lötschen Valley (160 km2) by analyzing meteorological data from the synoptic to the local scale and by reproducing the flood peak with the hydrological model WaSiM-ETH (Water Flow and Balance Simulation Model). This in order to gain process understanding and to evaluate the predictability. The atmospheric drivers of this rain-on-snow flood were (i) sustained snowfall followed by (ii) the passage of an atmospheric river bringing warm and moist air towards the Alps. As a result, intensive rainfall (average of 100 mm day-1) was accompanied by a temperature increase that shifted the 0° line from 1500 to 3200 m a.s.l. (meters above sea level) in 24 h with a maximum increase of 9 K in 9 h. The south-facing slope of the valley received significantly more precipitation than the north-facing slope, leading to flooding only in tributaries along the south-facing slope. We hypothesized that the reason for this very local rainfall distribution was a cavity circulation combined with a seeder-feeder-cloud system enhancing local rainfall and snowmelt along the south-facing slope. By applying and considerably recalibrating the standard hydrological model setup, we proved that both latent and sensible heat fluxes were needed to reconstruct the snow cover dynamic, and that locally high-precipitation sums (160 mm in 12 h) were required to produce the estimated flood peak. However, to reproduce the rapid runoff responses during the event, we conceptually represent likely lateral flow dynamics within the snow cover causing the model to react "oversensitively" to meltwater. Driving the optimized model with COSMO (Consortium for Small-scale Modeling)-2 forecast data, we still failed to simulate the flood because COSMO-2 forecast data underestimated both the local precipitation peak and the temperature increase. Thus we conclude that this rain-on-snow flood was, in general, predictable, but requires a special hydrological model setup and extensive and locally precise meteorological input data. Although, this data quality may not be achieved with forecast data, an additional model with a specific rain-on-snow configuration can provide useful information when rain-on-snow events are likely to occur.

Seedling resistance, tolerance and escape from herbivores: insights from co-dominant canopy tree species in a resource-poor African rain forest

* Although plants can reduce the impacts of herbivory in multiple ways, these defensive traits are often studied in isolation and an understanding of the resulting strategies is incomplete. * In the study reported here, empirical evidence was simultaneously evaluated for the three main sets of traits available to plants: (i) resistance through constitutive leaf traits, (ii) tolerance to defoliation and (iii) escape in space, for three caesalpiniaceous tree species Microberlinia bisulcata, Tetraberlinia bifoliolata and T. korupensis, which co-dominate groves within the lowland primary rain forest of Korup National Park (Cameroon). * Mesh cages were placed around individual wild seedlings to exclude insect herbivores at 41 paired canopy gap and understorey locations. After following seedling growth and survival for c. 2 years, caged and control treatments were removed, leaves harvested to determine nutrient and phenolic concentrations, leaf mass per area estimated, and seedling performance in gaps followed for a further c. 2 years to quantify tolerance to the leaf harvesting. * The more nutrient-rich leaves of the weakly shade-tolerant M. bisulcata were damaged much more in gaps than the two strongly shade-tolerant Tetraberlinia species, which had higher leaf mass per area and concentrations of total phenols. Conversely, the faster-growing M. bisulcata was better able to tolerate defoliation in terms of height growth (reflushing capacity), but not at maintaining overall leaf numbers, than the other two species. * Across gaps, insect-mediated Janzen–Connell effects were most pronounced for M. bisulcata, less so for T. korupensis, and not detectable for T. bifoliolata. The three species differed distinctly in their secondary metabolic profiles. * Taken together, the results suggested a conceptual framework linking the three sets of traits, one in which the three co-dominant species adopt different strategies towards herbivore pressure depending on their different responses to light availability. This study is one of the first in a natural forest ecosystem to examine resistance to, tolerance of, and escape from herbivory among a group of co-occurring tropical tree species.

Tree size and fecundity influence ballistic seed dispersal of two dominant mast-fruiting species in a tropical rain forest

Seed production, seed dispersal, and seedling recruitment are integral to forest dynamics, especially in masting species. Often these are studied separately, yet scarcely ever for species with ballistic dispersal even though this mode of dispersal is common in legume trees of tropical African rain forests. Here, we studied two dominant main-canopy tree species, Microberlinia bisulcata and Tetraberlinia bifoliolata (Caesalpinioideae), in 25 ha of primary rain forest at Korup, Cameroon, during two successive masting events (2007/2010). In the vicinity of c. 100 and 130 trees of each species, 476/580 traps caught dispersed seeds and beneath their crowns c. 57,000 pod valves per species were inspected to estimate tree-level fecundity. Seed production of trees increased non-linearly and asymptotically with increasing stem diameters. It was unequal within the two species’ populations, and differed strongly between years to foster both spatial and temporal patchiness in seed rain. The M. bisulcata trees could begin seeding at 42–44 cm diameter: at a much larger size than could T. bifoliolata (25 cm). Nevertheless, per capita life-time reproductive capacity was c. five times greater in M. bisulcata than T. bifoliolata owing to former’s larger adult stature, lower mortality rate (despite a shorter life-time) and smaller seed mass. The two species displayed strong differences in their dispersal capabilities. Inverse modelling (IM) revealed that dispersal of M. bisulcata was best described by a lognormal kernel. Most seeds landed at 10–15 m from stems, with 1% of them going beyond 80 m (<100 m). The direct estimates of fecundity significantly improved the models fitted. The lognormal also described well the seedling recruitment distribution of this species in 121 ground plots. By contrast, the lower intensity of masting and more limited dispersal of the heavier-seeded T. bifoliolata prevented reliable IM. For this species, seed density as function of distance to traps suggested a maximum dispersal distance of 40–50 m, and a correspondingly more aggregated seedling recruitment pattern ensued than for M. bisulcata. From this integrated field study, we conclude that the reproductive traits of M. bisulcata give it a considerable advantage over T. bifoliolata by better dispersing more seeds per capita to reach more suitable establishment sites, and combined with other key traits they explain its local dominance in the forest. Understanding the linkages between size at onset of maturity, individual fecundity, and dispersal capability can better inform the life-history strategies, and hence management, of co-occurring tree species in tropical forests.

Plant and arthropod community sensitivity to rainfall manipulation but not nitrogen enrichment in a successional grassland ecosystem

Grasslands provide many ecosystem services including carbon storage, biodiversity preservation and livestock forage production. These ecosystem services will change in the future in response to multiple global environmental changes, including climate change and increased nitrogen inputs. We conducted an experimental study over 3 years in a mesotrophic grassland ecosystem in southern England. We aimed to expose plots to rainfall manipulation that simulated IPCC 4th Assessment projections for 2100 (+15 % winter rainfall and −30 % summer rainfall) or ambient climate, achieving +15 % winter rainfall and −39 % summer rainfall in rainfall-manipulated plots. Nitrogen (40 kg ha−1 year−1) was also added to half of the experimental plots in factorial combination. Plant species composition and above ground biomass were not affected by rainfall in the first 2 years and the plant community did not respond to nitrogen enrichment throughout the experiment. In the third year, above-ground plant biomass declined in rainfall-manipulated plots, driven by a decline in the abundances of grass species characteristic of moist soils. Declining plant biomass was also associated with changes to arthropod communities, with lower abundances of plant-feeding Auchenorrhyncha and carnivorous Araneae indicating multi-trophic responses to rainfall manipulation. Plant and arthropod community composition and plant biomass responses to rainfall manipulation were not modified by nitrogen enrichment, which was not expected, but may have resulted from prior nitrogen saturation and/or phosphorus limitation. Overall, our study demonstrates that climate change may in future influence plant productivity and induce multi-trophic responses in grasslands.

Density-dependent dynamics of a dominant rain forest tree change with juvenile stage and time of masting

Although negative density dependence (NDD) can facilitate tree species coexistence in forests, the underlying mechanisms can differ, and rarely are the dynamics of seedlings and saplings studied together. Herein we present and discuss a novel mechanism based on our investigation of NDD predictions for the large, grove-forming ectomycorrhizal mast fruiting tree, Microberlinia bisulcata (Caesalpiniaceae), in an 82.5-ha plot at Korup, Cameroon. We tested whether juvenile density, size, growth and survival decreases with increasing conspecific adult basal area for 3245 ‘new’ seedlings and 540 ‘old’ seedlings (< 75-cm tall) during an approximately 4-year study period (2008–2012) and for 234 ‘saplings’ (≥ 75-cm tall) during an approximately 6-year study period (2008–2014). We found that the respective densities of new seedlings, old seedlings and saplings were positively, not and negatively related to increasing BA. Maximum leaf numbers and heights of old seedlings were negatively correlated with increasing basal areas, as were sapling heights and stem diameters. Whereas survivorship of new seedlings decreased by more than one-half with increasing basal area over its range in 2010–2012, that of old seedlings decreased by almost two-thirds, but only in 2008–2010, and was generally unrelated to conspecific seedling density. In 2010–2012 relative growth rates in new seedlings’ heights decreased with increasing basal area, as well as with increasing seedling density, together with increasing leaf numbers, whereas old seedlings’ growth was unrelated to either conspecific density or basal area. Saplings of below-average height had reduced survivorship with increasing basal area (probability decreasing from approx. 0.4 to 0.05 over the basal area range tested), but only sapling growth in terms of leaf numbers decreased with increasing basal area. These static and dynamic results indicate that NDD is operating within this system, possibly stabilizing the M. bisulcata population. However, these NDD patterns are unlikely to be caused by symmetric competition or by consumers. Instead, an alternative mechanism for conspecific adult–juvenile negative feedback is proposed, one which involves the interaction between tree phenology and ectomycorrhizal linkages.

Limitation of seedling growth by potassium and magnesium supply for two ectomycorrhizal tree species of a Central African rain forest and its implication for their recruitment

In the ectomycorrhizal caesalpiniaceous groves of southern Korup National Park, the dominant tree species, Microberlinia bisulcata, displays very poor in situ recruitment compared with its codominant, Tetraberlinia bifoliolata. The reported ex situ experiment tested whether availabilities of soil potassium and magnesium play a role. Seedlings of the two species received applications of K and Mg fertilizer in potted native soil in a local shade house, and their responses in terms of growth and nutrient concentrations were recorded over 2 years. Amended soil concentrations were also determined. Microberlinia responded strongly and positively in its growth to Mg, but less to K; Tetraberlinia responded weakly to both. Added Mg led to strongly increased Mg concentration for Microberlinia while added K changed that concentration only slightly; Tetraberlinia strongly increased its concentration of K with added K, but only somewhat its Mg concentration with added Mg. Additions of Mg and K had small but important antagonistic effects. Microberlinia is Mg-demanding and apparently Mg-limited in Korup soil; Tetraberlinia, whilst K-demanding, appeared not to be K-limited (for growth). Added K enhanced plant P concentrations of both species. Extra applied Mg may also be alleviating soil aluminum toxicity, and hence improving growth indirectly and especially to the benefit of Microberlinia. Mg appears to be essential for Microberlinia seedling growth and its low soil availability in grove soils at Korup may be an important contributing factor to its poor recruitment. Microberlinia is highly shade-intolerant and strongly light-responding, whilst Tetraberlinia is more shade-tolerant and moderately light-responding, which affords an interesting contrast with respect to their differing responses to Mg supply. The study revealed novel aspects of functional traits and likely niche-partitioning among ectomycorrhizal caesalps in African rain forests. Identifying the direct and interacting indirect effects of essential elements on tropical tree seedling growth presents a considerable challenge due the complex nexus of causes involved.

Litter nutrients and retranslocation in a central African rain forest dominated by ectomycorrhizal trees

In the strongly seasonal, but annually very wet, parts of the tropics, low-water availability in the short dry season leads to a semi-deciduous forest, one which is also highly susceptible to nutrient loss from leaching in the long wet season. Patterns in litterfall were compared between forest with low (LEM) and high (HEM) abundances of ectomycorrhizal trees in Korup National Park, Cameroon, over 26 months in 1990–92. Leaf litter was sorted into 26 abundant species which included six ectomycorrhizal species, and of these three were the large grove-forming trees Microberlinia bisulcata, Tetraberlinia bifoliolata and Tetraberlinia moreliana. Larger-tree species shed their leaves with pronounced peaks in the dry season, whereas other species had either weaker dependence, showed several peaks per year, or were wet-season shedders. Although total annual litterfall differed little between forest types, in the HEM forest (dominated by M. bisulcata) the dry-season peak was more pronounced and earlier than that in the LEMforest. Species differed greatly in their mean leaf litterfall nutrient concentrations, with an approx. twofold range for nitrogen and phosphorus, and 2.5–3.5-fold for potassium, magnesium and calcium. In the dry season, LEM and HEM litter showed similar declines in P and N concentration, and increases in K and Mg; some species, especially M. bisculcata, showed strong dry-wet season differences. The concentration of P (but not N) was higher in the leaf litter of ectomycorrhizal than nonectomycorrhizal species. Retranslocation of N and P was lower among the ectomycorrhizal than nonectomycorrhizal species by approx. twofold. It is suggested that, within ectomycorrhizal groves on this soil low in P, a fast decomposition rate with minimal loss of mineralized P is possible due to the relatively high litter P not limiting the cycle at this stage, combined with an efficient recapture of released P by the surface organic layer of ectomycorrhizas and fine roots. This points to a feedback between two essential controlling steps (retranslocation and mineralization) in a tropical rain forest ecosystem dominated by ectomycorrhizal trees.

Light and seed size affect establishment of grove-forming ectomycorrhizal rain forest tree species

• Regeneration of the dominant ectomycorrhizal tree Microberlinia bisulcata in groves in Korup, Central Africa, is very poor. The hypothesis was tested that this species is more shade intolerant than other co-occurring species. • In two 1-yr trials, each with M. bisulcata and four other species at a nursery close to Korup, growth was measured under five PAR levels, with ± added P and ± watering in the dry season. In parallel experiments the effects of PAR with two R : FR ratios were investigated. • Increasing PAR had a consistent effect on the rates of increase in plant mass and on changes in the other variables. Doubling soil P, watering and halving the R : FR ratio had almost no effect. However, across species, mass at low PAR and relative growth rate related positively and negatively, respectively, to seed mass. • One contributing factor for the poor recruitment of M. bisulcata is therefore its low survival and slow growth at low PAR, due to its small seed size. The two codominant ectomycorrhizal grove species of Tetraberlinia, with larger seeds, were less affected by low PAR.

Tree architecture in a Bornean lowland rain forest: intraspecific and interspecific patterns

Intraspecific and interspecific architectural patterns were studied for eight tree species of a Bornean rain forest. Trees 5--19 m tall in two 4-ha permanent sample plots in primary forest were selected, and three light descriptors and seven architectural traits for each tree were measured. Two general predictions were made: (1) Slow growing individuals (or short ones) encounter lower light, and have flatter crowns, fewer leaf layers, and thinner stems, than do fast growing individuals (or tall ones). (2) Species with higher shade-tolerance receive less light and have flatter crowns, fewer leaf layers, and thinner stems, than do species with lower shade-tolerance. Shade-tolerance is assumed to decrease with maximum growth rate, mortality rate, and adult stature of a species.

Water Table Level as Influenced by Rainfall, Crop Requirements, and Tiling Method during the past Three Years

In 1979, a portion of the research farm was pattern tiled including the large tillage plots. This was used as an opportunity to compare tile installation methods: a conventional trenching machine (used widely prior to late 70s), and a trenchless “tile plow” machine. The tile plow inserted plastic tile using a mole approach, which is the current primary tiling method. This research showed that plow and trenching tiling methods were not significantly different and both provided adequate drainage. It also showed that water table measurements were influenced more by timing of water needs of the crop being grown and intensity of the rainfall event than tiling method. This report focuses on continued research completed on these trial plots from 2009 to 2011 measuring water table level.

Fallout and concentration of aerosol-borne radioactivity over the Atlantic (Appendix)

Measurements of atmospheric radioactivity attached to aerosols are described. Fallout was collected in a vessel of large area. Emphasis was on separation of "wet" and "dry" samples. For strontium 90 a ratio of "wet" to "dry" fallout of 5:1 has been found independent of latitude. The total fallout was smaller than comparable values from continents because of very small amounts of rainfall in the equatorial zone. In order to achieve consistency in the global balance a better knowledge not only of radioactivity but also of precipitation over the ocean is required. Fallout of Ra-D clearly shows the ITC as a barrier for the latitudinal movement of near sea-surface air masses. The concentration of short-lived emanation daughters shows large variations according to varying geographic conditions. A variation with time could not be explained. The specific activity of long-lived radioactive substances shows the expected effect of the ITC as well as a seasonal diminuation of average concentration, similar to that measured at Heidelberg.

Soil, snow, weather, and sub-surface storage data from a mountain catchment in the rain-snow transition zone

A comprehensive hydroclimatic data set is presented for the 2011 water year to improve understanding of hydrologic processes in the rain-snow transition zone. This type of dataset is extremely rare in scientific literature because of the quality and quantity of soil depth, soil texture, soil moisture, and soil temperature data. Standard meteorological and snow cover data for the entire 2011 water year are included, which include several rain-on-snow events. Surface soil textures and soil depths from 57 points are presented as well as soil texture profiles from 14 points. Meteorological data include continuous hourly shielded, unshielded, and wind corrected precipitation, wind speed, air temperature, relative humidity, dew point temperature, and incoming solar and thermal radiation data. Sub-surface data included are hourly soil moisture data from multiple depths from 7 soil profiles within the catchment, and soil temperatures from multiple depths from 2 soil profiles. Hydrologic response data include hourly stream discharge from the catchment outlet weir, continuous snow depths from one location, intermittent snow depths from 5 locations, and snow depth and density data from ten weekly snow surveys. Though it represents only a single water year, the presentation of both above and below ground hydrologic condition makes it one of the most detailed and complete hydro-climatic datasets from the climatically sensitive rain-snow transition zone for a wide range of modeling and descriptive studies.

Isotopic composition of terrestrial plant waxes (dD and d13C of n-alkanes) of sediment core SO188_342 from the Northern Bay of Bengal for the last 18 ka

The Indian Summer Monsoon (ISM) is a major global climatic phenomenon. Long-term precipitation proxy records of the ISM, however, are often fragmented and discontinuous, impeding an estimation of the magnitude of precipitation variability from the Last Glacial to the present. To improve our understanding of past ISM variability, we provide a continuous reconstructed record of precipitation and continental vegetation changes from the lower Ganges-Brahmaputra-Meghna catchment and the Indo-Burman ranges over the last 18,000 years (18 ka). The records derive from a marine sediment core from the northern Bay of Bengal (NBoB), and are complemented by numerical model results of spatial moisture transport and precipitation distribution over the Bengal region. The isotopic composition of terrestrial plant waxes (dD and d13C of n-alkanes) are compared to results from an isotope-enabled general atmospheric circulation model (IsoCAM) for selected time slices (pre-industrial, mid-Holocene and Heinrich Stadial 1). Comparison of proxy and model results indicate that past changes in the dD of precipitation and plant waxes were mainly driven by the amount effect, and strongly influenced by ISM rainfall. Maximum precipitation is detected for the Early Holocene Climatic Optimum (EHCO; 10.5-6 ka BP), whereas minimum precipitation occurred during the Heinrich Stadial 1 (HS1; 16.9-15.4 ka BP). The IsoCAM model results support the hypothesis of a constant moisture source (i.e. the NBoB) throughout the study period. Relative to the pre-industrial period the model reconstructions show 20% more rain during the mid-Holocene (6 ka BP) and 20% less rain during the Heinrich Stadial 1 (HS1), respectively. A shift from C4-plant dominated ecosystems during the glacial to subsequent C3/C4-mixed ones during the interglacial took place. Vegetation changes were predominantly driven by precipitation variability, as evidenced by the significant correlation between the dD and d13C alkane records. When compared to other records across the ISM domain, precipitation and vegetation changes inferred from our records and the numerical model results provide evidence for a coherent regional variability of the ISM from the Last Glacial to the present.

Separating ITCZ- and ENSO-related rainfall changes in the Galápagos over the last 3 kyr using D/H ratios of multiple lipid biomarkers

We present a 3000-yr rainfall reconstruction from the Galápagos Islands that is based on paired biomarker records from the sediment of El Junco Lake. Located in the eastern equatorial Pacific, the climate of the Galápagos Islands is governed by movements of the Intertropical Convergence Zone (ITCZ) and the El Niño-Southern Oscillation (ENSO). We use a novel method for reconstructing past ENSO- and ITCZ-related rainfall changes through analysis of molecular and isotopic biomarker records representing several types of plants and algae that grow under differing climatic conditions. We propose that ?D values of dinosterol, a sterol produced by dinoflagellates, record changes in mean rainfall in El Junco Lake, while dD values of C34 botryococcene, a hydrocarbon unique to the green alga Botryococcus braunii, record changes in rainfall associated with moderate-to-strong El Niño events. We use these proxies to infer changes in mean rainfall and El Niño-related rainfall over the past 3000 yr. During periods in which the inferred change in El Niño-related rainfall opposed the change in mean rainfall, we infer changes in the amount of ITCZ-related rainfall. Simulations with an idealized isotope hydrology model of El Junco Lake help illustrate the interpretation of these proxy reconstructions. Opposing changes in El Niño- and ITCZ-related rainfall appear to account for several of the largest inferred hydrologic changes in El Junco Lake. We propose that these reconstructions can be used to infer changes in frequency and/or intensity of El Niño events and changes in the position of the ITCZ in the eastern equatorial Pacific over the past 3000 yr. Comparison with El Junco Lake sediment grain size records indicates general agreement of inferred rainfall changes over the late Holocene.