**3.2.3 Low diversity regional and local scale results**

202 Remote Sensing of Biomass – Principles and Applications

sites in N RFE (Figure 4). Even with the increased biomass of the larch canopy created with the introduction of *L. decidua* the transition from larch to *Pinus* spp. in late succession still occurs under increased temperature conditions (Figure 5c), with strong similarity to the

Fig. 4. Non-parametric factorial ANOVA results for climate sensitivity analyses in two high diversity sites of the Amur region in the Russian Far East: northern Russian Far East (N RFE) and southwestern Russian Far East (SW RFE). 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* 

Fig. 5. Simulated species biomass dynamics (tC ha-1) for high diversity Burukan site in northern Amur region of the Russian Far East (N RFE). Species composition by dominant genera is shown over 500 simulated years starting from bare ground for the base historical climate **(a),** temperature increase **(b),** and temperature increase with

species shift seen without inclusion of *L. decidua* (Figure 5b).

spp., and evergreen conifer (EC) biomass.

*Larix decidua* **(c).**

The 279 sites across Siberia and the remainder of the RFE have an average of 9 individual tree species, and are classified as low diversity for this analysis. Similar to the continental response, within the low diversity regions the non-parametric factorial ANOVA results showed a consistent response (p<0.001) to temperature and *L. decidua* treatments for biomass of the total forest, *Larix* spp., and evergreen conifers when compared to baseline biomass values (Figure 6). Specifically the temperature increase in low diversity regions affects total forest and *Larix* spp. biomass early in succession and prior to year 200 (Figure 6). These regions also display a synchrony or lag response with total forest and *Larix* spp. biomass being closely connected in terms of the timing of the significant departure from baseline biomass. In all low diversity regions analyzed, except central Siberia, the response of evergreen conifer biomass to warming occurs after the response of total forest and *Larix*  spp. biomass. The effect of the precipitation treatment was significant (p<0.001) in only one low diversity region analyzed, central Siberia.

Fig. 6. Non-parametric factorial ANOVA results for climate sensitivity analyses in low diversity sites of Siberia. Shown in colors corresponding to figure legend are comparisons to baseline biomass values for treatment effects of temperature, precipitation, and *Larix decidua* that were significant to p<0.001 for total forest, *Larix* spp., and evergreen conifer (EC) biomass. NW Siberia is the northwestern Siberia region. E and W Irkutsk regions are in southern Siberia.

Resilience and Stability Associated with Conversion of Boreal Forest 205

Biomass patterns from simulation of mature forest under historical climate conditions reflect the idea that areas with increased plant diversity have increased productivity (Tilman and Downing 1994; Chapin et al., 1997, Bengtsson et al., 2000), with areas of higher biomass located in the areas of increased diversity in the Amur region of the RFE. The 93 high diversity sites are all located in the Amur region of the RFE and have an average of 38 individual tree species. The remaining 279 sites have an average of 9 individual tree species. The Amur region of the RFE also has higher average temperatures and precipitation values than across Siberia and the remainder of the RFE which allows a more diverse group of species to actively compete and achieve optimal biomass without climate limitations. Similar biomass results from past simulations which allow 44 individual tree species to grow at all sites without range limitation across Siberia and the RFE suggest it is the severe climate, and not a decreased species diversity, which limits the amount of total biomass

Successional dynamics across the study area under base climate reflect fundamental competition dynamics among species. Larch (*Larix* spp.) is highly tolerant of cold temperatures, but is one of the most shade-intolerant genera in the region (Nikolov and Helmisaari 1992). As the forest matures, competition for light becomes a key factor in determining which species becomes dominant. In northwestern Siberia, the cold temperatures prevent many species from competing with the cold-tolerant larch. Central and southern Siberia do not experience the severely cold temperatures of northwestern Siberia, and evergreen conifers actively compete with larch. Due to the shade-intolerance of larch, these forests transition to evergreen dominance as seen in the base climate simulation (Figure 2a,b,c). The transition from larch to evergreen conifer is also a product of the lack of insect or wildfire disturbance in these simulations. At each site the results are a landscapelevel approximation of succession, which includes the natural disturbance caused by the death of individual trees. Warming climate is expected to cause increases in total area burned, fire-season length, and the severity of fire (Overpeck et al., 1990; Kasischke et al., 1995; Stocks et al., 1998; Soja et al., 2004; Soja et al., 2007). Similarly, the incidence of insect disturbance is also expected to become more prevalent with warming conditions (Holling 1992, Volney and Fleming 2000; Logan et al., 2003). Understanding the intrinsic successional dynamics isolates the direct response of the system to changing climate. Establishing the response of the system without the added changes of disturbance provides a strong basis for

**4. Discussion** 

**4.1 Model simulation across Siberia and RFE** 

across the interior of Russia (Shuman and Shugart 2009).

deconstructing the complexities of the system response to climate change.

Larch is shade-intolerant and, in all but the coldest regions, evergreen conifers naturally replace larch over time, especially when no disturbance occurs that can rejuvenate the larch by providing open gaps of sunlight (Nikolov and Helmisaari 1992). The shift from deciduous larch to evergreen conifer forest is accelerated across Siberia under warming conditions (Figure 2), and implies a significant change in albedo. Following 200 years of forest development, larch-dominated forests are replaced with evergreen conifer-dominated forests in areas across Siberia. In southern Siberia, where forests are vulnerable to early replacement of larch by evergreen conifer, there would be a local significant albedo shift of

**4.2 Climate sensitivity analysis 4.2.1 Continental scale discussion** 

The low diversity regions under historical site conditions have a successional pattern of increasing *Larix* spp. biomass to year 200, followed by the slow establishment of evergreen conifers with *Larix* spp. maintaining a significant presence to the end of simulation (Figure 7a). The temperature treatment accelerates the establishment of evergreen conifers and at some sites causes a complete collapse of larch biomass in many of the low diversity sites around year 200 when the temperature has increased by 4C (Figure 7b). Successional dynamics in northwestern Siberia represent an exception to this general pattern. The colder regional temperatures in northwestern Siberia do not promote transition from *Larix* spp. to evergreen conifer, rather there is persistent *Larix* spp. dominance (Figure 7d). Northwestern Siberia does not experience the collapse of larch that is seen at sites further south (Figure 7b), but does transition to forests dominated by evergreen conifers in late successional stages in response to warming (Figure 7e). This late successional transition is similar to the natural succession dynamics of central and southern Siberia under base climate conditions (Figure 7a). The effect of the *L. decidua* treatment on *Larix* spp. biomass is immediate and continues to the end of simulation in all low diversity regions (Figure 6), indicating that *L. decidua* easily establishes and contributes to overall biomass in these regions. The inclusion of *L. decidua* in the low diversity regions under base climate conditions delays and suppresses the transition to evergreen conifers. *L. decidua* acts to prevent the collapse of larch in response to warming that is observed in low diversity areas in central Siberia (Figure 7b,c).

Fig. 7. Simulated mixed species biomass dynamics (tC ha-1) for low diversity sites in Siberia. Species composition by the dominant genera over 500 simulated years starting from bare ground for the base historical climate **(a,d),** temperature increase **(b,e),** and temperature increase with *Larix decidua* **(c,f)**.
