## 4 Discussion
### Drought Impact under Different Biophysical Conditions  
Forest phenology and green biomass production is related to site-specific environmental characteristics. This relation was further shaped by drought conditions. Elevation had the most important influence on diversification of forest growth during the discussed meteorological stress. The impact of altitude varied between locations and drought impact classes. Although [87] demonstrated Pan-European forest productivity decline in 2003, our study revealed GPP and CF drop only for stands growing below 1400 m a.s.l. within the 3 nNDVI class 1 response. Forest at higher elevations showed GPP and CF increases in 2003, which for some location was noted also in 2004. Furthermore, the 3 nNDVI class 3 indicated the productivity gain already at 700 m a.s.l. Abovementioned discrepancy from [87] could arise from higher spatial resolution of data used in our study. Moreover, our findings agree with demonstrated by [80] diverse effect of altitude on different tree species under heat wave conditions, as well as productivity increase observed at higher elevations due to drought-released temperature gradient [73; 75; 82]. The shift towards earlier SBD showed for some stands growing below 1400 m a.s.l. (3 nNDVI class 1 and 4 nNDII7 class 3), possibly reflects climate alternation towards warmer and dryer conditions [84], which is particularly vivid at lower altitudes [82]. Finally, the counterintuitive relation between elevation and CF could be explained by larch trees, as well as canopy openings, both being more frequent towards the upper tree line. Remarkably, the upturn in seasonal productivity was not coupled with prolongation of vegetation season. Drought impact on forest green biomass production and phenology showed moderate diversification in relation to exposition. In most of the cases, all aspect classes followed alike, index-specific temporal variability and revealed only minor drought-induced differences. Disparities in forest status among aspects originate presumably from species distribution and exposition governed water scarcity [27; 28], which explains enhanced inter-exposition variation under drought stress conditions. Since [88] showed SBD to be controlled by temperature rather than precipitation, as well as highlighted influence of photoperiod on growth and competitive strategies of various tree species, we assumed the observed SBD and SL differences emerged from stand composition and site-specific adaptations to drought (e.g., [75; 89]). Although this presumption is supported by the observed CF variability, it should be further confirmed by local surveys, and in the case of SL additional inspection of drought induced earlier senescence. The analysis of forest type specific response to drought was limited to the 3 nNDVI class 1 footprint. The sooner vegetation onset in 2003 observed within coniferous stands is supported by results of [88], additionally enhanced by the released temperature gradient [73; 82]. Following the horizontal distribution of vegetation belts, mixed forests are located at lower altitudes, which subjects them to more intense drought impact [82; 90]. Consequently, despite hardwood species being better adjusted to drought [14; 76] the 2003 CF decline in mixed stands suggests that trees mitigation abilities were exceeded. Persistent stress conditions during the following years evidently enforced aridity adaptation strategies (for example an increase in root biomass [89]), leading to rise of forest green biomass production. Higher CF reported interestingly for coniferous stands, not mixed stands, could result from forest openings or extended larch presence. This phenomenon should be inspected further. Since inclination governs water discharge and soil formation processes, an apparent relation between steepness increase and deterioration of forest productivity was expected. The presented results not always supported this assumption, demonstrating very complex and often irregular and counterintuitive variability.