The effect of warmer or cooler winters on European beech phenology carries over the phenophases of next growing season

Phenology of trees of temperate regions has become an important research topic for global change issues over the last two decades because of its major role in regulating ecosystems processes such as carbon cycle and species interactions. While spring phenology has often been studied, autumn phenology is still poorly understood. Most of the studies focus on specific phenophases, such as budburst or flowering, and generally do not consider the carry over effect of a phenophase on following ones during the same annual cycle (e.g. budburst and bud set). Using beech saplings in a reciprocal transplanting experiment between two elevations in the Swiss Jura, we hypothesized that: (i) cooler or warmer winter conditions would affect the following spring and autumn phenophases, as well as the spring phenology of the following year. (ii) These changes could be related to non-structural carbohydrates (NSC) storage and/or to a shift in the dormancy release driven by chilling and forcing temperature requirements. Our results showed that the advance and the delay of budburst timing induced by warmer and cooler winter conditions, respectively, has impacted the following autumn phenology: an advanced spring budburst has led to an earlier autumn bud set. This suggests that the potential delay in senescence processes due to global warming might be smaller than expected and that the assumption of longer growing season does not necessarily apply. The dependency of these two phenophases might be explained by the building up of the NSC storage. Furthermore, no carry over effect was found between the advanced or the delayed budburst timing in 2014 and the spring phenology of 2015, indicating that the following year, the current climatic variables were the dominant drivers of spring phenology. Adapting phenological models to the whole annual phenological cycle would improve predictions of tree phenology under future climate warming conditions.

Subalpine Pasture-Woodlands in a Changing Climate

Konstantin Svetlozarov Gavazov

Climate change in temperate mountain systems and associated increase in temperature and decrease in precipitation are expected to have strong implications for vegetation productivity, species diversity and carbon turnover in subalpine grasslands. Little is known, however, about the interaction between the effects of climate change and those of local land use management and possible changes in landscape structure. Pasture woodlands in the Swiss Jura Mountains are a traditional landscape, resulting from a long-lived sustainable use of grasslands and woodlands, and as such provide a suite of important ecosystem services to human society. These range from carbon sequestration and biodiversity preservation, to provision of timber and forage for livestock, and last but not least an aesthetic value, much appreciated by tourism. In this thesis various aspects of ecosystem functioning have been studied, investigating the combined effects of experimental climate change and land use on structurally different wooded pastures. An altitudinal gradient method has been used to simulate future climate change conditions, by imposing warmer and drier climate on subalpine turfs transplanted at lower elevation. The resulting gradient in mean annual temperature and precipitation – ranging from cold and wet in the subalpine zone, to warm and dry in the colline zone – has allowed for the detection of tipping points and altered states of ecosystem functioning in response to the treatments. The method employed provided also the possibility for a direct comparison of three land use types: unwooded pastures, sparsely wooded pastures, and densely wooded pastures (the result of pasture management intensity), in their response to climate perturbation. During the four years of experimental work, a series of observations have been made at the plot scale (square metre) in terms of plant performance and biogeochemical cycles, as well as at the landscape scale (hectare) in terms of forage production. A general threshold level for ecosystem resistance to experimental climate change was detected between the moderate IPCC scenario (+2 K mean annual temperature; -20 % annual precipitation) and the intensive IPCC scenario (+4 K mean annual temperature; -40 % annual precipitation). A concomitant gradient in ecosystem response to climate change was observed across the three land use types. The intensively managed unwooded pasture type was consistently more affected by the experimental treatment and rarely exhibited signs of resistance, especially under the intense climate change scenario. A drastic loss of plant species diversity, reduction of herbaceous biomass, impaired litter decomposition and soil microbial metabolic activity have all contributed to the altered state of ecosystem functioning. In contrast, the two extensively managed wooded pasture types showed considerable resistance to climate perturbation in terms of both above and belowground ecosystem processes. The reported inter-annual variation in herbaceous diversity and biomass production within these land use types demonstrated their resilience (recovery) potential too. Using a modelling approach for upscaling these results to the heterogeneous landscape of pasture woodlands in the Swiss Jura Mountains, has proven that extensively used wooded pastures could grant sustainable ecosystem services in terms of forage provision for cattle under climate change. Considering that the two experimental climate change intensities implemented this study are the projected ‘best’ and ‘worst’ case scenarios for the coming decades, the reported resistance of wooded pastures to climate change has to be embraced, and sustainable land use set as a goal in high altitude mountain pastures.

EPFL2013

Asymmetric effects of cooler and warmer winters on beech phenology last beyond spring

Alexandre Buttler, María Paula Sanginés De Cárcer, Rodolphe Schlaepfer, Constant Signarbieux, Ester Toledano Díaz, Yann Vitasse

In temperate trees, the timings of plant growth onset and cessation affect biogeochemical cycles, water, and energy balance. Currently, phenological studies largely focus on specific phenophases and on their responses to warming. How differently spring phenology responds to the warming and cooling, and affects the subsequent phases, has not been yet investigated in trees. Here, we exposed saplings of Fagus sylvatica L. to warmer and cooler climate during the winter 2013-2014 by conducting a reciprocal transplant experiment between two elevations (1,340 vs. 371m a.s.l., ca. 6 degrees C difference) in the Swiss Jura mountains. To test the legacy effects of earlier or later budburst on the budset timing, saplings were moved back to their original elevation shortly after the occurrence of budburst in spring 2014. One degree decrease in air temperature in winter/spring resulted in a delay of 10.9 days in budburst dates, whereas one degree of warming advanced the date by 8.8 days. Interestingly, we also found an asymmetric effect of the warmer winter vs. cooler winter on the budset timing in late summer. Budset of saplings that experienced a cooler winter was delayed by 31days compared to the control, whereas it was delayed by only 10 days in saplings that experienced a warmer winter. Budburst timing in 2015 was not significantly impacted by the artificial advance or delay of the budburst timing in 2014, indicating that the legacy effects of the different phenophases might be reset during each winter. Adapting phenological models to the whole annual phenological cycle, and considering the different response to cooling and warming, would improve predictions of tree phenology under future climate warming conditions.

Wiley2017

Assessing the responses of Sphagnum micro-eukaryotes to climate changes using high throughput sequencing

Alexandre Buttler, Vincent Eric Jules Jassey, Mariusz Lamentowicz, Enrique Lara, Edward Mitchell

Current projections suggest that climate warming will be accompanied by more frequent and severe drought events. Peatlands store ca. one third of the world's soil organic carbon. Warming and drought may cause peatlands to become carbon sources through stimulation of microbial activity increasing ecosystem respiration, with positive feedback effect on global warming. Micro-eukaryotes play a key role in the carbon cycle through food web interactions and therefore, alterations in their community structure and diversity may affect ecosystem functioning and could reflect these changes. We assessed the diversity and community composition of Sphagnum-associated eukaryotic microorganisms inhabiting peatlands and their response to experimental drought and warming using high throughput sequencing of environmental DNA. Under drier conditions, micro-eukaryotic diversity decreased, the relative abundance of autotrophs increased and that of osmotrophs (including Fungi and Peronosporomycetes) decreased. Furthermore, we identified climate change indicators that could be used as early indicators of change in peatland microbial communities and ecosystem functioning. The changes we observed indicate a shift towards a more "terrestrial'' community in response to drought, in line with observed changes in the functioning of the ecosystem.

PEERJ INC2020

Subalpine Pasture-Woodlands in a Changing Climate

Konstantin Svetlozarov Gavazov

EPFL2013