Boscutti, F.

Casolo, V.

D\u2019Ambrogio, M.

Rixen, C.

Salzillo, F.

BOSCUTTI, Francesco

CASOLO, Valentino

D’Ambrogio, M.

Archivio istituzionale della ricerca - Università degli Studi di Udine

RESULTSINTRODUCTIONEnhanced shrub growth and shrub expansion due to climate warming have been observed in many arctic and alpineecosystems. Warmer temperatures and shrub expansion could cause major changes in plant community structure,affecting both species composition and diversity.Studying interrelations between climate, shrub growth, shrub cover and plant diversity may improve ourunderstanding of the ongoing changes in plant communities of the alpine tundra.To get new insight on such processes, we studied growth of bilberry (Vaccinium myrtillus L.) and its plantcommunities along an elevation gradient in the eastern Alps.METHODSData analysisLinear mixed models were applied usingpiecewise structural equation modelling(Lefcheck, 2016) to examine the complexrelationships between ecological drivers andvegetation responses. We thus structured acause-and-effect map to explain variableeffects on plant diversity. Effects on beta-diversity were assessed by regression ondistance matrices (MRM) (Lichstein, 2007).All analyses were performed in R StatisticalSoftware 3.1.1 (R Core Team, 2015)DISCUSSIONOur results demonstrate the importance to study a range of variables from traits of key species to community structure to interpret changes inecosystems. Shoot growth of V. myrtillus enhanced shrub cover, which subsequently decreased plant diversity. Elevation, as a proxy fortemperature, influenced growth parameters of V. myrtillus but had no direct effect on shrub cover or plant diversity. Hence, our findings suggestthat enhanced shrub growth might be a direct driver of plant diversity whereas temperature could be only an indirect one.Sampling designSampling was conducted with a nesteddesign in two valleys (i.e. blocks) of theCarnic Alps. In each valley, sampling areas(i.e. plots) of 25 m2 were randomly selectedwithin dwarf-shrubs communities along anelevation gradient (from c.a. 1600 to 2200 masl), each 30 m . In total, 37 plots weresurveyed (20 1st block +17 2nd block).Data collectionVaccinium myrtillus traits:Ten ramets of V. myrtillus were gathered inevery plot and analyzed by overall 370 crosssections counting their xylem rings andmeasuring ring widths. In field, the length ofthe top shoot of the same ramets was alsorecorded.Vegetation survey:In each plot, the cover of all occurringvascular plants was estimated inpercentage. Dwarf shrubs cover was alsorecorded.All the surveys were conducted in summer2014.Shrub cover rather than climate is a direct driver of plant diversity in alpine tundraF. Boscutti*1, V. Casolo1, M. D’Ambrogio1, F. Salzillo1, C. Rixen21 Department of Agricultural, Food, Environmental and Animal Sciences, University of Udine, via delle Scienze 91, 33100 - Udine, Italy; 2 WSL Institute for Forest, Snow and Landscape Research SLF, Unit Ecosystem Boundaries, Alpine Ecosystems, Flüelastr. 11, CH-7260 Davos, Switzerland*francesco.boscutti@uniud.itFigure 2 Effect of elevation on V.myrtillus traits (a, b, c), V. myrtillusshoot length on shrub cover (d), andof shrub cover on alpha- (e) andbeta-diversity (f)REFERENCESLefcheck, J. S. (2016). piecewiseSEM: Piecewise structural equation modelling in r for ecology, evolution, and systematics. Methods in Ecology and Evolution, 7: 573–579 Lichstein, J. W. (2007). Multiple regression on distance matrices: a multivariate spatial analysis tool. Plant Ecology, 188: 117–131R Core Team (2015). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria.Acknowledgements: research has been financed by the province of Udineshrub coverr2c= 0.53Figure 1 Path diagram showinginfluence of studied variables on plantdiversity. Solid lines indicatesignificant relations (p<0.05), dashedlines indicate tested relations with nosignificant values(a)(b)(c)ring widthr2c=0.62species richnessr2c= 0.58shoot lengthr2c=0.41ager2c=0.53 -0.73-0.81-0.450.60-0.72elevationAt higher elevation, ramets of V. myrtillus were younger, with shortershoots and smaller year rings, whereas elevation and shrub coverwere unrelated (Fig. 1a, Fig. 2a-b-c).In turn, shrub cover was positively related with shoot length of V.myrtillus (Fig. 1b, Fig. 2d).Enhanced shrub cover had a negative effect on species (alpha-, Fig.1c, Fig. 2e) and community (beta-, Tab. 1, Fig. 2f) diversities, whichwere, on the other hand, not explained by elevation.Table 1 MRM outcomes showingeffects of elevation and shrub coveron beta-diversity

Shrub cover rather than climate is a direct driver of plant diversity in alpine tundra

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Shrub cover rather than climate is a direct driver of plant diversity in alpine tundra

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