Growth response of temperate mountain grasslands to inter-annual variations in snow cover duration

P Choler

doi:10.5194/bg-12-3885-2015

Abstract

Abstract. A remote sensing approach is used to examine the direct and indirect effects of snow cover duration and weather conditions on the growth response of mountain grasslands located above the tree line in the French Alps. Time-integrated Normalized Difference Vegetation Index (NDVIint), used as a surrogate for aboveground primary productivity, and snow cover duration were derived from a 13-year long time series of the Moderate-resolution Imaging Spectroradiometer (MODIS). A regional-scale meteorological forcing that accounted for topographical effects was provided by the SAFRAN–CROCUS–MEPRA model chain. A hierarchical path analysis was developed to analyze the multivariate causal relationships between forcing variables and proxies of primary productivity. Inter-annual variations in primary productivity were primarily governed by year-to-year variations in the length of the snow-free period and to a much lesser extent by temperature and precipitation during the growing season. A prolonged snow cover reduces the number and magnitude of frost events during the initial growth period but this has a negligible impact on NDVIint as compared to the strong negative effect of a delayed snow melting. The maximum NDVI slightly responded to increased summer precipitation and temperature but the impact on productivity was weak. The period spanning from peak standing biomass to the first snowfall accounted for two-thirds of NDVIint and this explained the high sensitivity of NDVIint to autumn temperature and autumn rainfall that control the timing of the first snowfall. The ability of mountain plants to maintain green tissues during the whole snow-free period along with the relatively low responsiveness of peak standing biomass to summer meteorological conditions led to the conclusion that the length of the snow-free period is the primary driver of the inter-annual variations in primary productivity of mountain grasslands.

Highlights

Temperate mountain grasslands are seasonally snow-covered ecosystems that have to cope with a limited period of growth (Körner, 1999)
To better understand the growth response of alpine grasslands to changing snow cover duration, it seems pivotal (i) to assess the contribution of the different components of the growth response, the duration of the favorable period of growth and the peak standing biomass; (ii) to account for the effect of meteorologi
The contribution of the first part of season was slightly higher for GPPint, though it largely remained under

Summary

Introduction

Temperate mountain grasslands are seasonally snow-covered ecosystems that have to cope with a limited period of growth (Körner, 1999). Several studies have pointed to the increasing risk of spring frost damage and summer water shortage following an early snowmelt and the associated detrimental effects on biomass production (Baptist et al, 2010; Ernakovich et al, 2014; Inouye, 2000). Both soil microbial nitrogen immobilization and accumulation of inorganic nitrogen are enhanced under deep and long-lasting snowpacks (Brooks et al, 1998), and plants may benefit from increased flush of nutrients and ameliorated soil water balance following unusually long winters. To better understand the growth response of alpine grasslands to changing snow cover duration, it seems pivotal (i) to assess the contribution of the different components of the growth response, the duration of the favorable period of growth and the peak standing biomass; (ii) to account for the effect of meteorologi-

Methods

Results

Discussion

Conclusion