Visit of Esther Baumann / project ECOPOTENTIAL

E. Baumann is a Master'student (M2) from the University Of Bayreuth supervised by Pr. Carl Beierkunhlein and visiting the island to acheive the fieldwork of her project. She describes her experience.

On the 10th of August I arrived on the Island of La Reunion to conduct the fieldwork for my Master Thesis, which is embedded in the ECOPOTENTIAL project (H2020). The study aims at detecting patterns in leaf coloration along an elevational gradient in the subalpine shrublands of La Réunion island.

Beyond that aim, stands the concept that the elevational gradient is considered as a proxy for changing environmental conditions, as e.g. increased UV-radiation and increased wind speeds.

Leaf coloration can also be considered as a proxy for reflection of light, leading to the assumption, that a brighter leaf coloration implies a higher albedo. Therefore, it is favorable for plants at higher altitude, experiencing higher UV- radiation, to have brighter leaves. Another circumstance that might lead to a brighter leaf coloration in high altitudes is the specific surface character of a leaf under certain conditions: to cope with the rough environmental conditions, plants evolved to having hairs or even a whitish pelt around their leafs. This leaf property offers advantages in terms of water storage and transpiration by providing protection e.g. from the increased wind speeds in high altitudes.

The aim of the fieldwork therefore is to test the following hypothesis:

With increasing altitude, the proportion of shrubs with bright leaves increases as well.

To do so, I first of all had to quantify the patterns of the different leaf colors in the subalpine shrubland. For that I drove on the 11th of August to the shurblands below the Piton de la Fournaise (2632 m) accompanied by two students from the University of La Reunion (Sohan and Sebastien, M2 BEST) to get familiar with the species present in the subalpine shrubland. On the following day I started with my first plots in the same area, where I sampled throughout the whole stay a total of 16 plots.

A. On the way up to Grand Bénare; B. Sunset on the sea of clouds, Maïdo, C. Piton des Neiges, view from Maïdo, D. Observatory for the physics of the Atmosphere, OPAR

A. On the way up to Grand Bénare; B. Sunset on the sea of clouds, Maïdo, C. Piton des Neiges, view from Maïdo, D. Observatory for the physics of the Atmosphere, OPAR

Another 15 plots are located in the area around the Grand Bénare (2898 m), for which I was accompanied for two days by Claudine Ah-Peng and stayed for one night at the observatory (OPAR) there. This was a very nice experience, as we also got a little tour through the facility and we could see the green laser in action at night. The other days of work in this areas I completed alone, while I was able to pitch a tent nearby at Jacques Fournel's endemic horticulture. This saved me a lot of time as I did not have to drive back and forth every day. Another series of plots was sampled around the Piton de Neiges (3069 m). To reach the area of interest there, I hiked up from Cilaos to the guesthouse, pitched my tent there and stayed there for two nights. Unfortunately, I was not able to stay longer, therefore I only managed six plots at the Piton de Neiges. Only one plot was done in Roche Ecrite (2276 m), as the vegetation was more patchy and less adapted for this protocol. In total this sums up to 40 plots, covering the three highest elevations of the Island. For reasons of efficiency I decided on placing my plots along hiking paths and streets, to be able to access the shrublands without problems, as I was often working mostly alone in the field. I covered in total an elevational gradient from 2000 to 2800 m.a.s.l for this study (no more shrubs above 2800 m) and ascended all the peaks.

On the field. A) Setting up the transect with the GPS compas B) looking at leaf coloration o

On the field. A) Setting up the transect with the GPS compas B) Looking at leaf coloration

Each of those plots consisted of three transects (always in North- South, Northeast- Southwest and Northwest- Southeast direction) of each 20 m long. Reference point for these transects was always one GPS point placed in the center. Along each of those transects I estimated the cover for each individual shrub encountered via the line intercept method. Additionally, I measured the average growth height for every individual. The cover for open soil, rocks and bryophytes was recorded as well. The colour estimation was then done on the species level: I sampled within one plot species specific leaf colors (with the Munsell- Scala for plants) and the leaf area by measuring 10 representative leafs for each  shrub species found. To account for open soil, rock and bryophytes and its impact on the reflectance signal, I also measured their color (with the Munsell- Scala for soils in case of soil and rock).

Mansell Plant tissues

Munsell Plant tissues

Another aspect of my thesis will be the combination of the sampled field data on leaf colours with satellite imagery. For that I got together with Claudine Ah-Peng and Erwann Lagabrielle (SEAS-OI, UMR Espace-Dev) to discuss possible methods to combine the aquired field data with remote sensing techniques, as I think that remote sensing would proof to be a useful tool to detect patterns at a larger scale, as observed patterns are almost always a simple matter of scale. Assistance from Romain Goeury (SEAS-OI) for the satellite coverage and data availability was much appreciated.

Overall, I enjoyed my stay at this wonderful Island very much, as it was not only fruitful and fascinating in professional terms but also as the organisation on site was very smooth and the people I met during my stay made me feel very welcome. Additionally, I was very lucky, as my stay coincidentally overlapped with the total eclipse at the 1st of September!

The Eclipse, Esther and Erwann

The Eclipse, Esther and Erwann