## 4 Discussion  
\(T_{\mathit{spring}}\) is reported to cause both negative and positive direct impacts on ecosystem productivity [6; 16], but our results make a case for the latter being the dominant influence, at least in the mid- to high latitudes. Damage from, e.g., late spring frost events or acute frost desiccation does not seem to override the growth caused by warming, at least on a global scale. The only biome-type deviation from this trend is temperate shrulands, mainly located in north Africa and Turkey, in other words, close to the southernmost borders of our study area. These regions are known for their warm and dry climate. Warm springs in these regions likely bring adverse effects on water-stressed plants, causing a negative correlation. The cohesive correlation trend between spring temperatures and spring productivity does not persist in the same vein for the legacy effects. A warm spring will not necessarily lead to the same legacy effects to summer and autumn productivity, as an unusually lush and productive spring would. The fact that these two usually go hand in hand makes this result somewhat surprising, but also highlights the importance of keeping these qualities separate. The legacy effects from warmer springs with high ecosystem productivity also differ strongly between GPP products. There are several uncertainties in the data sets that could contribute to this. One possible explanation, pointed out in [37], is the difficulty to separate snow cover decrease from leaf area increase. The spring months, particularly in the northernmost regions, are often characterized by partially covered snow. Increasing temperatures might lower the fraction of snow cover in spring, leading to a false signal of greening. Our results also indicate that forests overall had the most prevalent negative responses from the legacy effects, whereas grasslands and shrulands showed an ambiguous response (Figure 4). The patterns (i.e., narrow spread of correlation coefficients in forests and wide spread of correlation coefficients in other types) are seen in all three GPP products. This result is much in line with previous studies (e.g., [16; 17; 18; 19]). The authors of [16] used the Global Inventory Modeling and Mapping Studies (GIMMS) NDVI data set [38] and actual evapotranspiration derived from the FLUXNET latent heat flux measurements [39] to investigate the legacy effects of earlier springs on boreal forests in North America. They found that earlier spring and associated drying in summer can cause a decline of vegetation productivity due to increased tree mortality and fire activity. Possibly, the long seasonal time frames that the legacy effects operate on better match the slow growth seen in forests. In general, grasslands and shrulands are rapidly growing and changing across the seasons, and respond more directly to current-season precipitation and soil moisture conditions. The importance from previous seasons was then less evident. The legacy effects that were visible for grasslands and shrulands mostly occurred during summer. Moreover, the soil moisture data sets used in this study only reflected water contents of the topsoil horizon (0-7 cm), which may explain that grasslands or shrulands with the low rooting depth are more sensitive to the topsoil moisture condition than forests. This agrees with a study [40] which is based on eddy covariance measurements of carbon flux for Swiss forests and grasslands. They found that grasslands are more sensitive to spring drought because forests can reduce their evapotranspiration to increase the water use efficiency reflecting a better adaptive strategy. Significant difference between GOSIF-GPP, NIRv-GPP, and FluxSat-GPP is a recurring theme for our results. Most likely, this is explained by fundamental differences in the models used to up-scale the data sets, as well as the measurement gaps that occur between different sensors. Satellite data sets of even higher spatial resolutions and quality might be necessary to bridge this gap and create a cohesive signal.