## 1 Introduction  
Ecosystem productivity in the boreal forest is often constrained by short growing seasons, lack of winter sunlight, temperature, permafrost, low soil nutrient levels [1, 2], and disturbance [3, 4, 5]. Furthermore, ecosystem productivity is increasingly limited by mid-summer moisture stress [6, 7, 8, 9]. Northwestern North America (and northern latitudes in general) is predicted to continue warming throughout the 21 st century, and climatic changes over the last century have already resulted in warmer springs accompanied by an earlier start of growing season [4, 10], warmer summers, and much warmer winters [11]. Altered weather patterns are due in part to the shift in the Pacific Decadal Oscillations (PDO) in the 1970s [12]. These changes, combined with ongoing warming, will likely alter the structure [13, 14], composition [15, 16], distribution [7, 17, 18], disturbance regimes (increasing severity and frequency of insect outbreaks and fire) [15, 19, 20], ecosystem services or productivity [2, 21, 22, 23], postfire succession [24], and ecosystem goods and services of the boreal forest. Warming and drying weather conditions throughout the 20 th century have been linked with reduced radial growth of white spruce in the Alaskan boreal forest [6]. Remote sensing studies have observed similar patterns of boreal \"browning\" since the 1980s [9, 25]. The warming climate may change the limiting factor of tree growth from temperature to moisture [2, 7, 23], particularly in mid-summer [7, 26]. These changes will likely result in increased burned area, fire frequency, and fire severity [27]. Severe fires often expose bare mineral soils in which deciduous propagules have great success [28] and dominate early to mid-successful communities [29] and result in increases in long-term deciduous forests. Boreal deciduous species have been reported to respond more positively to climate change [15, 16, 25] and drought [30] than boreal coniferous species, and are likely to increase in a warmer climate [16, 20, 28, 31, 32, 33]. Since mature deciduous stands often have greater ecosystem productivity [5, 16, 29, 33, 34], greater carbon uptake [30, 35, 36], and a longer fire return interval than coniferous stands, an increase in their cover/extent is likely to increase overall ecosystem productivity. While climate change may be associated with decreasing coniferous productivity and abundance, its net effect on overall long-term boreal productivity is uncertain. The strength and direction of future productivity patterns in the boreal forest depends largely on changes to the quantity and timing of precipitation, continuing increases in greenhouse gases, the strength of the CO\({}_{2}\) fertilization effect [22], species diversity and beneficial interactions [37], PDO patterns, and corresponding changes to the disturbance regime [20]. Interannual variation in weather influences the temporal signal of vegetation recovery following a disturbance event [17] and obscures ecosystem \"performance\", or productivity, trends related to succession and climate change [8]. How well vegetation responds to growing conditions such as weather and site conditions (soils, elevation/aspect, permafrost, _etc._) is described here as \"ecosystemperformance\", which is assessed with growing season integrals of remotely sensed vegetation indices [38, 39, 40, 41] that are associated with photosynthetic potential or vegetation greenness. Healthy, robust vegetation will respond to moisture stress, insect infestations, and other plant stressors in a robust manner (normal performance) while a degraded or previously stressed vegetation stand may have a larger reduction in productivity given the same stressors (underperformance). Disturbances such as stand replacing fires will be readily represented as severe performance departures from that expected for a mature forest given site conditions.