NEP of a Swiss subalpine forest is significantly driven not only by current but also by previous year's weather

Abstract

Abstract. Understanding the response of forest net ecosystem productivity (NEP) to environmental drivers under climate change is highly relevant for predictions of annual forest carbon (C) flux budgets. Modeling annual forest NEP with soil-vegetation-atmosphere transfer models (SVATs), however, remains challenging due to unknown delayed responses to weather of the previous year. In this study, we addressed the influence of previous year's weather on the interannual variability of NEP for a subalpine spruce forest in Switzerland. Analysis of long-term (1997-2011) eddy covariance measurements showed that the Norway spruce forest Davos Seehornwald was a consistent sink for atmospheric CO 2 , sequestering 210 ± 88 g C m −2 yr −1 on average. Previous year's weather strongly affected interannual variability of NEP, increasing the explained variance in linear models to 53 % compared to 20 % without accounting for previous year's weather. Thus, our results highlight the need to consider previous year's weather in modeling annual C budgets of forests. Furthermore, soil temperature in the current year's spring played a major role controlling annual NEP, mainly by influencing gross primary productivity early in the year, with spring NEP accounting for 56 % of annual NEP. Consequently, we expect an increase in net CO 2 uptake with future climate warming, as long as no other resources become limiting.

Tree Density and Forest Productivity in a Heterogeneous Alpine Environment: Insights from Airborne Laser Scanning and Imaging Spectroscopy

“…Since the forest ecosystem shows a pronounced phenological cycle, estimated GPP are likely to be overestimated. In fact, Zielis et al [100] and Wolf et al [101] report maximum GPP values of 5 g C m −2 day −1 for a Norway spruce forest close to Davos, Switzerland, that is comparable to our observation taken at the peak season. Scaling their flux tower-based GPP estimates to annual values results in roughly 1000 g C m −2 year −1 , while we observed average values of 1255 ± 342 g C m −2 year −1 , confirming the expected overestimation of GPP when using a single snapshot in combination with the EVI approach.…”

Remote sensing of annual terrestrial gross primary productivity from MODIS: an assessment using the FLUXNET La Thuile data set

“…Recent studies have also suggested that lagged effects can significantly affect annual GPP (Gough et al, 2008;Marcolla et al, 2011). For example, Zielis et al (2014) used long-term eddy covariance data collected at a spruce forest site to show that inclusion of meteorological data from the previous year significantly improved estimates of net ecosystem exchange, suggesting that next generation models need to include lagged effects and functional responses to climate forcing in previous years.…”

Net ecosystem productivity and its environmental controls in a mature Scots pine stand in north-western Poland

“…2001; Pilegaard et al, 2001;Kolari et al, 2004;Zielis et al, 2014;Danielewska et al, 2015). Furthermore, according to comprehensive quantification of the C balance of different forests, using EC and biometric measurements, temperate evergreen forests sequester from 133 ± 47 up to 389 ± 42 g C m −2 y −1 depending on climatic conditions (Luyssaert et al, 2007).…”