## 3 Results and Discussion
### Influence of Climate Change on Expected Ecosystem Performance  
EEP model extrapolation was extremely rare when applied to future climate projections (<1% of the area). Training the EEP model on multiple years and a large number of random locations resulted in robust EEP predictions across a wide range of climatic conditions within the future climate data sets. Climate change is expected to influence mature boreal forest ecosystem performance throughout the 21 st century (Figure 5). The climate projection [88] suggests a 12.4% average increase in precipitation between the 2000-2008 average and 2040, and a 23.8% increase by 2070. Under the same scenario, mean annual temperature is expected to increase by an average of 2.2 \({}^{\circ}\)C by 2040 and 4.1 \({}^{\circ}\)C by 2070 compared to the 2000-2008 baseline. The geographic patterns of warming and increased precipitation in the future are strongly related; areas with increased temperatures are also likely to be wetter (R\({}^{2}>0.80\) for both periods). Our model suggests that undisturbed EEP will increase 5.6% and 8.7% in 2040 and 2070, respectively, relative to the 2000-2008 baseline. Figure 5: Change (%) in Expected Ecosystem Performance (EEP) between the study period (2000–2008) and 2040 (**A**) change in in EEP between 2000–2008 and 2070 (**B**). Histograms of projected future EEP suggest that climate change will tend to broaden the range of undisturbed EEP, creating greater spatial diversity in performance. Most (92.6%) of the study area boreal forest is projected to have an increased undisturbed EEP by 2040 relative to the 2000-2008 average. Areas of decreased EEP by 2040 are concentrated in the drier portions of Yukon, Canada, and in the Yukon Flats region (Figure 5A), most of which reverse in direction to a net positive undisturbed EEP change by 2070, with 97.8% of the study area expected to have net increased undisturbed EEP by 2070. Results broadly suggest increased performance in undisturbed forests in the west and reduced to unchanged performance in the east, following precipitation contours (Figure 1), a pattern suggested by previous researchers [25, 96]. Moreover, our model predicts a sharpening of the west to east performance gradient. Declining trends in Alaska boreal forest productivity have been documented by [3, 24], although large areas of no trend were also found, especially in unburned areas. Often very small, but statistically significant, declines in NDVI were documented [96]. Spruce tree ring analysis indicates declining tree growth scattered across Alaska and pan Arctic boreal forests [7, 18] which may indicate opening niches for deciduous forest species advancement and increased boreal biodiversity and productivity. Conversely, more recent work in interior Alaska has demonstrated a positive correlation between black spruce tree ring growth and air temperature after the mid 1990s [97]. Increasing deciduous forest components and forest productivity in Alaska boreal forests is further supported by widespread consistent increasing trends in annual maximum NDVI on non-burned areas based on the (1982-2010) Long Term Data Record collected by the Advanced Very High Resolution Radiometer [98] and MODIS NDVI [99] and an new improved NDVI dataset with higher quality in high latitude regions (GIMMS\({}_{3g}\)) [100]. Increases in burned area and fire severity have been observed, especially in the late season, a pattern expected to continue in the future with warming [20, 27], which will likely result in increased habitat availability for deciduous forest (Figure 4B). Our results of net increased ecosystem performance in the future for undisturbed forest supports the commonly reported hypothesis that the highly productive [5, 16, 29, 33, 34] deciduous component of boreal forests will increase [16, 20, 28, 31, 32, 33], leading to further carbon uptake [30, 35, 36, 97] and productivity increases through complementary diversity [37].