Spring greening in boreal forest ecosystems has been widely linked to increasing temperature, but few studies have attempted to unravel the relative effects of climate variables such as maximum temperature (TMX), minimum temperature (TMN), mean temperature (TMP), precipitation (PRE) and radiation (RAD) on vegetation growth at different stages of growing season. However, clarifying these effects is fundamental to better understand the relationship between vegetation and climate change. This study investigated spatio-temporal divergence in the responses of Finland’s boreal forests to climate variables using the plant phenology index (PPI) calculated based on the latest Collection V006 MODIS BRDF-corrected surface reflectance products (MCD43C4) from 2002 to 2018, and identified the dominant climate variables controlling vegetation change during the growing season (May–September) on a monthly basis. Partial least squares (PLS) regression was used to quantify the response of PPI to climate variables and distinguish the separate impacts of different variables. The study results show the dominant effects of temperature on the PPI in May and June, with TMX, TMN and TMP being the most important explanatory variables for the variation of PPI depending on the location, respectively. Meanwhile, drought had an unexpectedly positive impact on vegetation in few areas. More than 50 % of the variation of PPI could be explained by climate variables for 68.5 % of the entire forest area in May and 87.7 % in June, respectively. During July to September, the PPI variance explained by climate and corresponding spatial extent rapidly decreased. Nevertheless, the RAD was found be the most important explanatory variable to July PPI in some areas. In contrast, the PPI in August and September was insensitive to climate in almost all of the regions studied. Our study gives useful insights on quantifying and identifying the relative importance of climate variables to boreal forest, which can be used to predict the possible response of forest under future warming.

北方森林生态系统中的春季绿化与温度升高有着广泛的联系，但是很少有研究试图揭示气候变量的相对影响，例如最高温度（TMX），最低温度（TMN），平均温度（TMP），降水量（PRE） ）和辐射（RAD）对生长季节不同阶段的植被生长的影响。但是，弄清这些影响对于更好地理解植被与气候变化之间的关系至关重要。这项研究使用植物物候指数（PPI），根据2002-2018年最新的V006 MODIS BRDF校正表面反射产品（MCD43C4），计算了芬兰北方森林对气候变量的响应的时空差异，并每月确定生长季节（5月至9月）控制植被变化的主要气候变量。偏最小二乘（PLS）回归用于量化PPI对气候变量的响应并区分不同变量的单独影响。研究结果表明，温度在5月和6月对PPI具有显着影响，其中TMX，TMN和TMP分别是PPI随位置变化的最重要的解释变量。同时，干旱对少数地区的植被产生了意想不到的积极影响。PPI变化的50％以上由5月整个森林面积的68.5％和6月的87.7％的气候变量解释。在七月至九月期间，由气候和相应的空间范围解释的PPI变化迅速减小。尽管如此，在某些地区，RAD被认为是7月PPI的最重要的解释变量。相反，几乎所有研究的地区，8月和9月的PPI对气候都不敏感。我们的研究为量化和确定气候变量对北方森林的相对重要性提供了有益的见解，可用于预测未来变暖下森林的可能响应。