# Siberian Pine and Larch Response to Warming-Drying Climate in the Southern Boundary of Their Range
## 4 Discussion
### Siberian Pine and Larch Growth since the Warming Restart  
The warming restart significantly modified the dependence of both species' growth on the air temperature and moisture variables. Alongside that, winter wind speed changes coinciding with the warming restart strongly affected trees' growth within the treeline ecotone.  
Warming within the treeline stimulated the growth increase in both species since the end of the 1990s. Moreover, the growth increase in the treeline was stronger than in lower elevations (Figure 3). That may be attributed to the comparatively low species-species competition for nutrients and light within the sparse treeline communities. However, strong local depressions of the larch growth occurred during recent years. These growth depressions were also observed at lower (up to c. 1600 m) elevations (Figure 3a-c). Those depressions of the GI coincided with the outbreak of the insect defoliator _Zeiraphera griseana_, a larch tortrix. Defoliation of larch (even complete but single defoliation) did not lead to larch mortality, although it did decrease trees' growth. Outbreaks of larch tortrix regularly arose at high elevations (>1200 m) [43]. During the considered period of the outbreak within the study site (2020-2022), a megascale outbreak of _Zeiraphera griseana_ occurred also in the larch forests of Middle and Eastern Siberia. The area of that outbreak included larch forests within the huge range from 51\({}^{\circ}\) NL in the south to 64\({}^{\circ}\) NL in the north and from 92\({}^{\circ}\) EL in the west to 130\({}^{\circ}\) EL in the east.  
Since the warming restart, Siberian pine growth dependence on the moisture variables increased throughout all elevations. Thus, positive correlations with precipitation and soil moisture and negative ones with atmospheric drought (indicated by VPD) strongly increased. A significant negative correlation arose with air temperature throughout all elevations, including the treeline ecotone (Figure 6).  
A similar--but stronger--warming restart caused changes in growth-climate variables correlations for the drought-resistant larch. An increased negative influence of air temperature on growth was observed at low elevations, whereas at high elevations, i.e., in the area with sufficient precipitation, warming stimulated growth increase. At the lower elevations, i.e., the zone with a lower moisture supply, a positive dependence on the precipitation increased. However, at the high elevations, negative correlations with precipitation arose, and an increase in the positive correlation with VPD was observed. That effect is related to excessive moistening at high elevations. A similar negative influence of over-moistening on larch growth was reported for the wetlands [21]. Meanwhile, in the area with minimal moisture supply, i.e., a forest-steppe ecotone, larch growth was strongly limited by moisture variables as well as rising air temperature (Figure 7).  
The rising air temperature since the warming restart led to the rise in both tree species' dependence on soil moisture stored during the fall (September-October) of the previous year (Figure 8). A similar earlier dependence was reported for larch trees only within the forest-steppe ecotone [22]. Notably, Siberian pine positively responded to the restored soil moisture within all elevation belts, whereas larch responded mostly at low elevations. The strong dependence of larch regeneration on the stored moisture is explained by the shallow root system of the seedlings.