Influence of human disturbance on carbon efflux in a subarctic boreal forest
Authors: Vas Dragos , Corriveau Elizabeth , Baxter William , Gaimaro Lindsay , Barbato Robyn 
Published: March 2024

Soil respiration plays a crucial role in the carbon cycle and has significant implications for climate change. Understanding the dynamics of soil respiration in the subarctic and arctic is essential to more accurately predict carbon fluxes and their potential responses to disturbances, as these systems hold an estimated 1,400 Pg of carbon (National Snow and Ice Data Center). This research focuses on two primary objectives: (1) to compare soil respiration rates between undisturbed and disturbed areas located in a boreal forest ecosystem near the town of Fairbanks, Alaska, and (2) to identify the key environmental and geochemical factors influencing soil respiration in these environments. Vegetation at the undisturbed site consists of a black spruce (Picea mariana) canopy, woody shrubs dominated by Labrador tea (Rhododendron tomentosum and groenlandicum), low shrubs (Vaccinium spp.), several mosses (Sphagnum and Spinulum), and reindeer lichen (Cladonia rangiferina). Grasses (Poaceae), sedges (Cyperaceae), and woody shrubs (Salix spp. and Rhododendron tomentosum) constitute the vegetation structure at the disrupted location. The disturbance was caused by trail construction and firewood harvesting.&#160; We used an automated carbon dioxide (CO2) and methane (CH4) efflux closed chamber system to measure soil respiration rates over the course of one year. Environmental parameters, including soil temperature, volumetric water content, and seasonal thaw depth, were also measured to assess their influence on soil respiration and to investigate their utility as environmental tracers for impacting C flux, seasonally.Preliminary results indicate that soil respiration rates measured at the disturbed site were higher, 2.43 +/- 0.14&#160; g of C-CO2 m&#8722;2/day&#8722;1, as compared to the undisturbed area, 2.13 +/- 0.23 g of C-CO2 m&#8722;2/day&#8722;1. Average soil temperature and water content were -0.53 &#176;C and 0.24 m3/m3 respectively in the undisturbed soils. The disturbed site had a higher average soil temperature of 0.30 &#176;C, while maintaining the same soil water content value of 0.24 m3/m3. Maximum seasonal thaw depths at the undisturbed sites were approximately 1/3, -58 +/- 3 cm, as compared to the disturbed sites, -148 +/- 29 cm. These differences are likely due to the change in vegetation cover, which contributes to elevated soil respiration rates.These findings show that disturbance events enhance soil respiration rates, possibly due to the deepening of the active layer, unlocking carbon in organic matter that is metabolized by the soil microbial communities. The increased soil respiration in the disturbed area may be attributed to the disruption of the original vegetation cover (e.g., moss and black spruce), which leads to an increased soil temperature and accelerated decomposition of organic matter. These findings highlight the importance of considering land disturbances for carbon models and suggest that vegetation disturbance can be used as a proxy for landscape-scale active layer dynamics in subarctic regions. The results contribute to our understanding of the carbon cycle in these ecosystems. Further research is needed to investigate the long-term effects of disturbances on soil respiration and to refine our understanding of the underlying mechanisms driving these processes.