Forest stand reflectance at the canopy level results from various factors, such as vegetation chemical properties, leaf morphology, canopy structure, and tree sizes. These factors are dependent on the species, age, and health statuses of trees, as well as the site conditions. Sentinel-2 imagery with the high spatial, spectral, and temporal resolution, has enabled analysis of the relationships between vegetation properties and their spectral responses at large spatial scales. A comprehensive study of these relationships is needed to understand the drivers of vegetation spectral patterns and is essential from the point of view of remote sensing data interpretation. Our study aimed to quantify the site and forest parameters affecting forest stands reflectance. The analysis was conducted for common beech-, silver fir- and Scots pine-dominated stands in a mountainous area of the Polish Carpathians. The effect of stands and site properties on reflectance in different parts of the growing season was captured using the dense time series provided by Sentinel-2 from 2018-2019. The results indicate that the reflectance of common beech stands is mainly influenced by elevation, particularly during spring and autumn. Other factors influencing beech stand reflectance include the share of the broadleaved understory, aspect, and, during summer, the age of stands. The reflectance of coniferous species, i.e., Scots pine and silver fir, is mainly influenced by the age and stand properties, namely the crown closure and stand density. The age is a primary driver for silver fir stands reflectance changes, while the stand properties have a large impact on Scots pine stands reflectance. Also, the understory influences Scots pine stands reflectance, while there appears to be no impact on silver fir stands. The influence of the abovementioned factors is highly diverse, depending on the used band and time of the season. In the case of deciduous species, there is a large phenological variability caused by elevation-related temperature gradients and the local microclimate [ 35 – 37 ]. Typically, there is a negative correlation between leaf onset and elevation [ 36 ]. In remote sensing studies, the impact of The reflectance differences between the same tree species may also occur due to site fertility [ 42 , 43 ], which can also influence forest floor reflectance [ 44 , 45 ]. Still, the influence of all the aspects mentioned above on forest reflectance has not yet been fully explored at the stand level, as for example, that which is seen with high-resolution satellite imagery. With satellite imagery, it is now possible to study the vegetation properties and site conditions impact on reflectance at larger scales and with higher frequency. The high temporal resolution is essential, as the vegetation changes can be very rapid, particularly at the beginning and the end of the growing season. Regarding slope, in general, stands located on steeper terrain were characterized by a higher reflectance, particularly during spring. The differences in air temperature, as well as the soil fertility and temperature, resulting from the elevation, aspect and slope, may influence the phenophases, physiological processes, and chemical composition of leaves. The consequence of this can be probably observed in differences between stands reflectance. In spring and autumn, the sum of direct solar radiation daily heat on the south-facing slopes is much greater than that of the north-facing slopes [ 76 ]. Furthermore, according to Trepińska [ 77 ], as a result of the difference in the amount of solar radiation, the top layer of soil on southern slopes is significantly warmer than that of flat ground. Another hypothetical cause for the reflectance variations may be different humidity and the nutritional status of trees and, in particular, leaves. With an increasing elevation, there is higher precipitation, but weaker nutrition, and soils become increasingly deficient in minerals, particularly nitrogen. The influence of stand age and forest structure on coniferous species stands reflectance Stand age had the highest impact on the reflectance of silver fir-dominated stands. These effects of the understory can be noticed, for example, in Fig 4 , where beech stands with a higher share of broadleaved species had a higher SWIR reflectance during spring. Interestingly, at a leaf scale, there are also differences between understory and canopy leaf reflectance, and these differences are particularly prominent in the SWIR region [ 92 ]. Heiskanen et al. [ 22 ] reported the understory drying in coniferous stands from early May to early June. Therefore, seasonal variations in understory spectra may be due to the moisture regime/water content, and this may also be a reason for the high importance of the SWIR band. Also, Doninck et al. 1 = fully coniferous, 10 = fully broadleaved? Complete. Fig. 2- complete ‘.. in years 2018 and 2019’. Also, add in Methods that you combine the 2018 and 2019 dates to have higher scenes frequency within a year, while assuming that the reference stand data did not changed between 2008-2019, right? Tab. 2 Caption: “model’ or ‘models’? Complete meaning of numbers in bolt, same for tab. 3 Fig. 3 – correct x label axis in Red plot, May 2nd? Fig. 6 explain meaning of the dashed and solid lines? Fig. 16 – what is the differences between a-c? 16 – what is the differences between a-c? Consider to remove the background to exemplify that the lines are moving if this is the case (as the unfolding elevation), or in some other way clarify the message of the fig? Can you link better the reflectance and phenology? this can be also one of the main traits of the manuscript. The differences between a-c are in the elevation of leaf unfolding (in the background, you can see the Sentinel-2 image in true-color composition); the color lines represent contour lines (isohypses). We modified the figure description (now it’s Figure 11).