Trees

, Volume 29, Issue 1, pp 129–142

Sap flow responses to seasonal thaw and permafrost degradation in a subarctic boreal peatland

  • Rajit Patankar
  • William L. Quinton
  • Masaki Hayashi
  • Jennifer L. Baltzer
Original Paper

DOI: 10.1007/s00468-014-1097-8

Cite this article as:
Patankar, R., Quinton, W.L., Hayashi, M. et al. Trees (2015) 29: 129. doi:10.1007/s00468-014-1097-8
Part of the following topical collections:
  1. Long Distance Transport: Phloem and Xylem

Abstract

Key message

We demonstrate the negative impacts of ground thaw on sap flow in black spruce. Climate warming is accelerating permafrost thaw; our study may inform observed warming-related productivity declines in subarctic forests.

Abstract

Many of Canada’s northern boreal peatlands are situated on discontinuous permafrost. Here, permafrost provides the physical foundation on which forests persist. However, climate warming is leading to increased rates of permafrost thaw resulting in both increased active layer thickness (ALT) as well as shrinkage of the area underlain by permafrost due to lateral thaw at plateau margins. Such changes to the substrate likely impact growth and physiological processes of the trees. Despite this, little is known about the role of active layer development, and changes to it, including thaw of the underlying permafrost on tree water relations. Here, we measured sap flow in black spruce from a peatland experiencing rapid permafrost thaw and quantified drivers of changes in sap flow. Time series analyses revealed that of the environmental drivers examined, vapour pressure deficit was the strongest predictor of diurnal sap flow, while seasonal patterns were driven largely by energy inputs; however, the environmental drivers of importance did not change as a function of ground thaw conditions. To understand the implications of changing permafrost and active layer conditions, we quantified differences in sap flow between trees in interior positions of permafrost plateaus and trees on degrading plateau edges. We found >65 % reductions in sap flow in edge trees, attributable to reduced root function at waterlogged edges. Seasonal thaw processes also influenced sap flow. Paired measures of ALT indicated a negative linear relationship with sap flow that was stronger for interior trees. Greater ALT, which corresponds with deeper frost and water tables reduced sap flow by up to 60 % and is likely attributable to drying in surface soil layers where rooting occurs. Climate warming will accelerate permafrost thaw, which our data suggests will drive decreases in the productivity of black spruce-dominated subarctic forests. These findings may thus enhance our understanding of widespread reductions in productivity in boreal forests in northwestern North America.

Keywords

Evapotranspiration Ecohydrology Discontinuous permafrost Mackenzie River Basin Northwest Territories Tree growth and productivity Plant–soil feedbacks 

Supplementary material

468_2014_1097_MOESM1_ESM.docx (56 kb)
Supplementary material 1 (DOCX 56 kb)

Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Rajit Patankar
    • 1
  • William L. Quinton
    • 2
  • Masaki Hayashi
    • 3
  • Jennifer L. Baltzer
    • 1
    • 2
  1. 1.Department of BiologyWilfrid Laurier UniversityWaterlooCanada
  2. 2.Cold Regions Research CentreWilfrid Laurier UniversityWaterlooCanada
  3. 3.Department of GeoscienceUniversity of CalgaryCalgaryCanada

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