14Specific leaf area (SLA, leaf area per unit dry mass) is a key canopy structural characteristic, a 15 measure of photosynthetic capacity, and an important input into many terrestrial process models. 16 Although many studies have examined SLA variation, relatively few data exist from high 17 latitude, climate-sensitive permafrost regions. We measured SLA and soil and topographic 18 properties across a boreal forest permafrost transition, in which forest composition changed as 19 permafrost deepened from 54 to >150 cm over 75 m hillslope transects in Caribou-Poker Creeks 20 Research Watershed, Alaska. We characterized both linear and threshold relationships between 21 topographic and edaphic variables and SLA and developed a conceptual model of these 22 relationships. We found that the depth of the soil active layer above permafrost was significantly 23 and positively correlated with SLA for both coniferous and deciduous boreal tree species.
24Intraspecific SLA variation was associated with a fivefold increase in net primary production, 25 suggesting that changes in active layer depth due to permafrost thaw could strongly influence 26 ecosystem productivity. While this is an exploratory study to begin understanding SLA variation 27 in a non-contiguous permafrost system, our results indicate the need for more extensive 28 evaluation across larger spatial domains. These empirical relationships and associated 29 uncertainty can be incorporated into ecosystem models that use dynamic traits, improving our 30 ability to predict ecosystem-level carbon cycling responses to ongoing climate change. 31 32 3 33 4 55Global analyses reveal that specific leaf area varies with climatic and edaphic gradients 56 [16,17]. In contrast, SLA variation within a species is less well understood. Intraspecific SLA 57 variation has been shown to contribute significantly to total trait variability [18][19][20][21], and used to 58 understand local and regional community assembly processes and explain the coexistence of 59 multiple species across environmental gradients [22][23][24].
60In boreal systems underlain by permafrost, the thaw depth of the seasonally-thawed active 61 layer [9] is coupled to soil moisture and nutrient availability, and is hypothesized to govern leaf 62 area and plant productivity [25][26][27]. While SLA of boreal vegetation has been shown to vary 63 with environmental conditions, including tree species and soil resources [20,[28][29][30], the effect of 64 permafrost on SLA variation is not well understood, due in large part to the lack of empirical 65 SLA data across a broad range of permafrost conditions.
66Because SLA is linked to forest productivity through photosynthetic potential, 67 understanding the environmental controls on SLA variation is also important for predictive 68 ecosystem modeling [31], especially in climate-sensitive permafrost systems. Most ecosystem 69 models assign a specific leaf area value based on plant functional types [32], and efforts have 70 been made to improve mean canopy estimates ...