Permafrost thaw in boreal peatlands is rapidly altering forest community composition

Abstract in English and Slavey; article in English only.

English:

1. Boreal peatlands are frequently underlain by permafrost, which is thawing rapidly. A common ecological response to thaw is the conversion of raised forested plateaus to treeless wetlands, but unexplained spatial variation in responses, combined with a lack of stand‐level data, make it difficult to predict future trajectories of boreal forest composition and structure.
2. We sought to characterize patterns and identify drivers of forest structure, composition, mortality and recruitment in a boreal peatland experiencing permafrost thaw. To do this, we established a large (10 ha) permanent forest plot (completed in 2014), located in the Northwest Territories, Canada, that includes 40,584 mapped and measured trees. In 2018, we conducted a comprehensive mortality and recruitment recensus. We also measured frost table depth, soil moisture, soil humification and organic layer thickness within the plot between 2012 and 2018, and used habitat association tests to link these variables to forest characteristics and dynamics.
3. Forest composition and structure varied markedly throughout the plot and were strongly governed by patterns in permafrost presence and organic layer thickness. Overall, there was a net loss of trees from the plot at a rate of 0.7% year⁻¹. Mortality of black spruce, the dominant tree species, was more than double that of recruitment and was strongly associated with permafrost thaw. In contrast, recruitment of larch was over four times greater than mortality, and occurred primarily in low‐lying, permafrost‐free wetlands with mineral soil near the surface.
4. Synthesis. The trends in tree demography and underlying drivers suggest that spruce‐dominated permafrost plateaus will be converted into larch‐dominated wetlands as permafrost thaw progresses in boreal peatlands, particularly in areas where mineral soil is near the surface. In the longer term, thaw could increase the hydrologic connectivity of the landscape, resulting in widespread drainage and re‐vegetation by spruce, but we did not find evidence that this is occurring yet. Given the increasing rates of permafrost thaw, and positive feedbacks between thaw and forest change, we predict that larch abundance will continue to increase in boreal peatlands over the coming decades, leading to shifts in ecosystem function, wildlife habitat, albedo and snow dynamics.

Slavey:

1. Ndéh gotselé zhı́e ndéh tené, ndéh thekǫ́ t’áh nagoyı̨̨. Dechı̨ ndeé, ǫdı̨ godet’azıh hésı̨́ı̨̨, dı nagoyı̨ t’áh, deɂǫ́ gots’ele agodande odı̨h dechı̨ hų́le hésı̨́ı̨, kó meghǫ gondı łǫ hı́le, kaondı t’áh edáondı́ ek’éodejǫ holı́ı.
2. Odı̨ nagoyı̨ hésı̨́ı̨, nahe dhąą edágot’ı̨ chu megháıda, gulı́ı agodande gháts’enda. 2014 zhíe dı, kaots’ele gha, godı̨cha nı̨odéthı́t’ǫ, ká ezhı t’ats’ǫzę agų́t’e. Nahendeé, Dene Ndeé zhı́e, 40,584 kanéht’ee dechı̨ hegedı̨tá gots’ęh yégı̨́dzá. 2018 zhı́e, k’achu yeghǫ gıadá. Ndéh tené chuu ndéh tselé, edáodeh tselé, edáodéhjı́ yeghágı̨nda, dı azhǫǫ yégı̨̨́dzá, edáondı dechı̨táh yáonı̨́zhe ełénı̨la.
3. Dı ndeé k’éozhı́e góhthı́chúu, gų́lı̨́ı ahsı́ı yánı́hshǫ, ndéh tené k’eh ahsı́ı yánı́zhe, ezhı ts’ıɂóné, mothane azhı́ı yánı́zhe chu. Azhǫǫ got’áh, xaye tanet’e 0.7% dechı̨ hų́le ajá. Ts’u gółı̨́ı̨ dendah yánı́zhe, ezhı há dendah łǫǫdeh, ndéh tené ts’ı̨ɂǫ́. Gǫǫ́cho hothane xaye tanet’e, dı̨ı̨ koneshe, gots’ęh gozhı́ onı̨́tǫ́ǫ odı̨ ndéh tené gų́lı̨ hı́le, gots’ęh gonezų yáonı́zhe.
4. Dı gháts’enda ts’ı̨ɂǫ́, ezhı ndéh k’eh odı̨ ts‘u chu ndéh tené gų́lı̨, ndéh nayı̨ hénıdé, ndéh tselé héh gǫǫ́cho agot’ı̨́, odı̨ ahsı́ı gonezų yánı́zhe k’éozhı́e. Axǫh yundaa nı̨dhąą hénıdé, dı ndéh tselé taedéhtth’e hénıdé axǫǫ ts‘u yonı̨́zhe anagode gha, kó kı k‘ala meghǫ kıots’ı́ɂǫ hı́le. Naxı̨h nahe ghádé hoadhe t’áh, yundaa gogháıda t’áh, dı gǫǫ́cho kı́ ekaot’ee yanı̨zhe gha, ndéh tené edáxıı nayı̨ t’áh. Ndéh gųlı́ı adande t’áh, yet’ah yáenda hesı̨́ı̨ chu gulı agedande.