**3. Results**

### **3.1 Model simulation across Siberia and RFE**

Overall biomass dynamics across Siberia and the RFE for the baseline climate scenario shows the highest values across the Amur region of the RFE, moderate biomass within

Resilience and Stability Associated with Conversion of Boreal Forest 201

affects biomass in all groups (total forest, *Larix* spp., and evergreen conifer) at the continental scale for the entire simulation. There is an effect of precipitation change on biomass, but this effect occurs only later in succession, at year 140, and alters total forest and

Fig. 3. Non-parametric factorial ANOVA results for climate sensitivity analyses for 372 sites across Siberia and Russian Far East. Shown in colors corresponding to figure legend are comparisons to baseline biomass values that were significant to p<0.001 for treatment effects of temperature, precipitation, and *Larix deciuda* on total forest, *Larix* spp., and evergreen

Sites in the Amur region of the Russian Far East (RFE) have an average of 38 individual tree species, and are classified for this analysis as high diversity. Within the high diversity regions, the non-parametric factorial ANOVA results showed a sporadic response (p<0.001) to the temperature and European Larch (*L. decidua*) treatments for the biomass classes measured (Figure 4). In contrast to the continental effect, the high diversity regions showed minimal response to the treatment effects of temperature increase and *L. decidua* addition,

Local results for the high diversity regions are variable depending on local climate conditions. The southwestern RFE (SW RFE) region under the base climate has mixed deciduous forests in the early successional stages which mature into mixed deciduous and evergreen conifer forests. Larch is present in SW RFE region, but is not a dominant species at any point during succession. Local scale analysis in SW RFE shows that the increased temperature alters the late successional dynamics by drastically reducing or replacing evergreen conifers with mixed deciduous species as early as year 150; this is reflected in the response (p<0.001) of evergreen conifer biomass from year 120 until the end of simulation (Figure 4). The *L. decidua* treatment does not significantly affect biomass in SW RFE region. With base climate conditions at sites in the northern RFE (N RFE) there is an initial pioneering stage dominated by *Larix* spp. which then transitions to evergreen conifer (*Picea*  spp.) dominant forest (Figure 5a). The effect of temperature increase of 4°C across 200 years accelerates and alters the transition to a mixed-species forest dominated by *Pinus* spp. rather than *Picea* spp. (Figure 5b). This is reflected in the effect of the temperature treatment (p<0.001) on total forest biomass and *Larix spp.* biomass in late succession after year 200 for

evergreen conifer biomass, not *Larix spp.* biomass (Figure 3).

**3.2.2 High diversity regional and local scale results** 

and no response to the effect of precipitation change.

conifer biomass.

southern Siberia and low biomass across the northernmost sites. The successional dynamics across western Siberia in response to baseline climate feature a larch-dominated system persisting over time (Figure 2a). In the warmer southern portions of the region, larch forest undergoes a transition to mixed evergreen conifer and deciduous broad-leaved species beginning around year 230 (Figure 2b). This transition continues and by year 500, the southern portion of Siberia becomes a mixed larch and evergreen conifer forest (Figure 2c).

Fig. 2. Species distribution in western Siberia, a subset of the total area and dataset, for the baseline **(a, b, c)** and temperature increase **(d, e, f)** climates.

#### **3.2 Climate sensitivity analysis 3.2.1 Continental scale results**

Biomass response to the temperature treatment is significant (p<0.001), continues to the end of simulation for total forest and *Larix* spp. biomass (Figure 3), and is reflected in the shift in species distribution over time (Figure 2). By year 130, the effects of the response to warming can already be seen when compared to the base climate (Figure 2a) in the shift of species dominance from larch to evergreen conifer and other species at sites in southwestern Siberia (Figure 2d). The presence of evergreen conifers and other species, in what was larchdominated forest under the historical climate (Figure 2b), expands across more of southern Siberia by year 230 (Figure 2e), and by year 500 Siberia is no longer a larch-dominated forest under increased temperature conditions (Figure 2f).

At the continental scale non-parametric factorial ANOVA results for biomass (tC ha-1) under the temperature, precipitation, and European Larch (*Larix decidua*) treatments indicated that all classes of biomass were affected (p<0.001) (Figure 3). The temperature and *L. decidua*  treatments have the strongest and most persistent effect on biomass throughout the simulation. *L.decidua* appears to be well-adapted to establishing across the region and

southern Siberia and low biomass across the northernmost sites. The successional dynamics across western Siberia in response to baseline climate feature a larch-dominated system persisting over time (Figure 2a). In the warmer southern portions of the region, larch forest undergoes a transition to mixed evergreen conifer and deciduous broad-leaved species beginning around year 230 (Figure 2b). This transition continues and by year 500, the southern portion of Siberia becomes a mixed larch and evergreen conifer forest (Figure 2c).

Fig. 2. Species distribution in western Siberia, a subset of the total area and dataset, for the

Biomass response to the temperature treatment is significant (p<0.001), continues to the end of simulation for total forest and *Larix* spp. biomass (Figure 3), and is reflected in the shift in species distribution over time (Figure 2). By year 130, the effects of the response to warming can already be seen when compared to the base climate (Figure 2a) in the shift of species dominance from larch to evergreen conifer and other species at sites in southwestern Siberia (Figure 2d). The presence of evergreen conifers and other species, in what was larchdominated forest under the historical climate (Figure 2b), expands across more of southern Siberia by year 230 (Figure 2e), and by year 500 Siberia is no longer a larch-dominated forest

At the continental scale non-parametric factorial ANOVA results for biomass (tC ha-1) under the temperature, precipitation, and European Larch (*Larix decidua*) treatments indicated that all classes of biomass were affected (p<0.001) (Figure 3). The temperature and *L. decidua*  treatments have the strongest and most persistent effect on biomass throughout the simulation. *L.decidua* appears to be well-adapted to establishing across the region and

baseline **(a, b, c)** and temperature increase **(d, e, f)** climates.

under increased temperature conditions (Figure 2f).

**3.2 Climate sensitivity analysis 3.2.1 Continental scale results** 

affects biomass in all groups (total forest, *Larix* spp., and evergreen conifer) at the continental scale for the entire simulation. There is an effect of precipitation change on biomass, but this effect occurs only later in succession, at year 140, and alters total forest and evergreen conifer biomass, not *Larix spp.* biomass (Figure 3).

Fig. 3. Non-parametric factorial ANOVA results for climate sensitivity analyses for 372 sites across Siberia and Russian Far East. Shown in colors corresponding to figure legend are comparisons to baseline biomass values that were significant to p<0.001 for treatment effects of temperature, precipitation, and *Larix deciuda* on total forest, *Larix* spp., and evergreen conifer biomass.
