Four ways to define the growing season

Abstract

What is addressed as growing season in terrestrial ecosystems is one of the main determinants of annual plant biomass production globally. However, there is no well‐defined concept behind. Here, we show different facets of what might be termed growing season, each with a distinct meaning: (1) the time period during which a plant or a part of it actually grows and produces new tissue, irrespective of net carbon gain (growing season sensu stricto). (2) The period defined by developmental, that is, phenological markers (phenological season). (3) The period during which vegetation as a whole achieves its annual net primary production (NPP) or a net ecosystem production (NEP), expressed as net carbon gain (productive season) and (4) the period during which plants could potentially grow based on meteorological criteria (meteorological season). We hypothesize that the duration of such a ‘window of opportunity’ is a strong predictor for NPP at a global scale, especially for forests. These different definitions have implications for the understanding and modelling of plant growth and biomass production. The common view that variation in phenology is a proxy for variation in productivity is misleading, often resulting in unfounded statements on potential consequences of climatic warming such as carbon sequestration.

Recurrent summer drought affects biomass production and community composition independently of snowmelt manipulation in alpine grassland

“…It was previously argued that adverse effects of freezing temperatures during earlier snowmelt outweigh beneficial effects of a longer growing season (Wipf et al, 2009) but particularly graminoids exhibit a high freezing resistance even in a fully active state (von Büren & Hiltbrunner, 2022). In addition, internal controls over growth and senescence could restrain plants from extending growth when the season prolongs (Körner et al, 2023), as recently evidenced for alpine Carex curvula grassland (Möhl et al, 2022).…”

“…A major outcome of this study is therefore that the dominant species profits from the simulated scenarios, perhaps explaining the several millennia of persistence of individual Carex clones in this grassland (de Witte et al, 2012). Given the unresponsiveness of biomass production to variable snowmelt dates, our study warns against projections that assume proportionality between biomass production and season length (see Körner et al, 2023). In contrast to drought, systematic variation of snowmelt date did not affect species composition, a surprising result in view of the classical species gradients across snowmelt gradients.…”

Spatial replication can best advance our understanding of population responses to climate

“…minimum and maximum temperatures, Bennie et al 2008). These conditions can be leveraged in studies that use climatic predictors with a direct physiological interpretation, such as growing degree days (Körner et al 2023). While such physiological predictors require daily weather data, these can be measured via data loggers, or derived from gridded climatic data (Maclean et al 2019, Kearney andPorter 2020).…”

Vegetation Greening and Climate Warming Increased the Propagation Risk From Meteorological Drought to Soil Drought at Subseasonal Timescales

“…Here, the first 5 pentads (2 pentads) in 1980 were omitted in computing SPI (SSMI) due to no 6‐pentad (3‐pentad) accumulated values in this case. In this study, we focused on droughts in the growing season (with pentad‐mean surface air temperature above 5°C) (Frich et al., 2002; Körner et al., 2023).…”