Influence of microclimate and geomorphological factors on alpine vegetation in the Western Swiss Alps

Among the numerous environmental factors affecting plant communities in alpine ecosystems, the influence of geomorphic processes and landforms has been minimally investigated. Subjected to persistent climate warming, it is vital to understand how these factors affect vegetation properties. Here, we studied 72 vegetation plots across three sites located in the Western Swiss Alps, characterized by high geomorphological variability and plant diversity. For each plot, vascular plant species were inventoried and ground surface temperature, soil moisture, topographic variables, earth surface processes (ESPs) and landform morphodynamics were assessed. The relationships between plant communities and environmental variables were analysed using non-metric multidimensional scaling (NMDS) and multivariate regression techniques (generalized linear model, GLM, and generalized additive model, GAM). Landform morphodynamics, growing degree days (sum of degree days above 5°C) and mean ground surface temperature were the most important explanatory variables of plant community composition. Furthermore, the regression models for species cover and species richness were significantly improved by adding a morphodynamics variable. This study provides complementary support that landform morphodynamics is a key factor, combined with growing degree days, to explain alpine plant distribution and community composition

Causes and mechanisms of synchronous succession trajectories in primeval Central European mixed Fagus sylvatica forests

1. Natural succession trajectories of Central European forest ecosystems are poorly understood due to the absence of long‐term observations and the pervasive effects of past human impacts on today's vegetation communities. This knowledge gap is significant given that currently forest ecosystems are expanding in Europe as a consequence of global change. 2. Annually laminated sediments were extracted from two small lowland lakes (Moossee 521 m a.s.l.; Burgäschisee 465 m a.s.l.) on the Swiss Plateau. We combine high‐resolution palaeoecological and quantitative analyses to assess changes in vegetation during the Neolithic. We test for regionally synchronous land‐use phases and plant successional patterns that may originate from complex interactions between human and climatic impacts. 3. Mixed Fagus sylvatica forests dominated the Swiss Plateau vegetation over millennia. During the period 6,500-4,200 cal year bp, pronounced forest disruptions accompanied by increased fire and agricultural activities occurred at c. 6,400-6,000 cal year bp, 5,750-5,550 cal year bp, around 5,400 cal year bp and at 5,100-4,600 cal year bp. Biodiversity increased during these land‐use phases, likely in response to the creation of new open habitats. After decades to centuries of land‐use, arboreal vegetation re‐expanded. In a first succession stage, heliophilous Corylus avellana shrubs were replaced by pioneer Betula trees. These open arboreal communities were out‐competed within 150-200 years by late‐successional  F. sylvatica and Abies alba forests. Most strikingly, cross‐correlations show that these successions occurred synchronously (±11 years) and repeatedly over large areas (>1,000 km2) and millennia. 4. Synthesis. First notable human impact shaped the primeval mixed Fagus sylvatica forests in Central Europe from c. 6,800-6,500 cal year bp on. Agrarian societies were susceptible to climate changes and we hypothesize that climate‐induced, simultaneous agricultural expansion and contraction phases resulted in synchronous regional forest successions. Currently, forests are expanding in Central Europe as a result of land abandonment in marginal areas. Our results imply that mixed Fagus sylvatica forests with Abies alba and Quercus may re‐expand rapidly in these areas, if climate conditions will remain within the range of the mid‐Holocene climatic variability (with summers c. +1-2°C warmer than today)

Summary and Recommendations from Working Group 1: model uncertainty representations in convection-permitting / shorter lead-time / limited-area ensembles

WG3 discussed both the pros and cons of existing schemes as Working group 1 considered the treatment of model uncertainty (MU) in high-resolution ensembles, at grid spacings of order 1-5 km. These systems are often run for regional weather forecasting, perhaps over a single country, and for lead times of up to 5 days. Looking ahead, ECMWF’s strategy seeks to deliver global medium-range ensemble forecasts with 3-4 km grid spacings by 2030. It is questionable for what grid spacing we should dispense with a deep convection parameterization, but it will be either switched off or damped in these systems, such that deep convection can be assumed to be dominated by explicit motions. One of the problems with limited-area ensemble systems at this scale is that spread depends not only on the modelling system itself but also on the variability inherited from the large-scale boundary conditions. There is often thought to be a lack of spread in our high-resolution EPS (ensemble prediction systems), but this could reflect a lack of diversity on larger scales. The relative importance of lateral-boundary diversity and the model uncertainty mechanisms is regime dependent. The lateral boundaries will generally be more important in midlatitude winter but less so for summertime convection in relatively weak synoptic flow

Elevational ground/air thermal gradients in the Swiss inner Alpine Valais

The dependence of air temperature on elevation (i.e., its elevational gradient) in the mountains is well known. However, the elevational gradient of near-surface ground temperatures and derived thermal parameters is much less understood. In this study, we investigated how these parameters depend on elevation by one-year temperature measurements along a transect in the Valais Alps (Switzerland) between 700 and 2,600 m a.s.l. In addition, we studied the effect of differences in slope aspect (north/south) and land cover (open field/forest). Air temperatures were measured as a reference. The results show that the ground thermal regime distinctly differs from that of the air. These differences could mainly be attributed to radiation, snow cover, and ground heat transfer. Our findings have far-reaching implications for ecosystems, agriculture, and forestry in mountains because a large portion of the living biomass is underground and thus affected by ground thermal processes

dphase_cosmoch2: COSMO model forecasts (2.2 km) run by MeteoSwiss for the MAP D-PHASE project

- preoperational model (planned to become operational in 2008) - configuration: Runge Kutta time integration scheme (dt=20sek); multi layer soil module; no parameterized deep convection; 60 levels; prognostic TKE, rain, snow and graupel - model runs are started at 00UTC 03UTC 09UTC 12UTc and 18UTC. Forecast range is 24h, except 09 and 18 run ranging upt to 30h. To complete the timeseries, dummy text files have been generated for 06UTC, 15UTC, 21UTC. Missing time steps are filled with dummy text files as well. Note: From 12th of July 2007 on, +24h forecasts are produced for 06, 15 and 21 UTC as well. Grid description: CDOM: xfirst: -2.76 yfirst: -0.02 xsize: 174.0 ysize: 141.0 xinc: 0.02 yinc: 0.02 xnpole: -170.0 ynpole: 43.0 DDOM: xfirst: -5.5 yfirst: -3.8 xsize: 500.0 ysize: 330.0 xinc: 0.02 yinc: 0.02 xnpole: -170.0 ynpole: 43.