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The potential impact of changing vegetation on thawing permafrost : effects of manipulated vegetation on summer ground temperatures and soil moisture in Abisko, Sweden

Torkelsson, Eric LU and Bengtsson, John LU (2012) In Student thesis series INES NGEK01 20121
Dept of Physical Geography and Ecosystem Science
Abstract
The Arctic region has experienced significant warming in the past decades and according to predictions further increases in air temperatures and precipitation will occur during the 21st century. Recent changes in climate have had widespread implications for the permafrost around the Arctic. Shorter periods of snow covering the Arctic regions significantly reduce the average annual albedo which dramatically increases the amount of energy being absorbed by the ground surface. In addition, the amount of snow has increased which results in even further warming of the ground through insulation during the winter. Warmer ground temperatures increase the available amount of organic material stored in the formerly frozen ground when the active... (More)
The Arctic region has experienced significant warming in the past decades and according to predictions further increases in air temperatures and precipitation will occur during the 21st century. Recent changes in climate have had widespread implications for the permafrost around the Arctic. Shorter periods of snow covering the Arctic regions significantly reduce the average annual albedo which dramatically increases the amount of energy being absorbed by the ground surface. In addition, the amount of snow has increased which results in even further warming of the ground through insulation during the winter. Warmer ground temperatures increase the available amount of organic material stored in the formerly frozen ground when the active layer (i.e. the upper layer that thaws and refreezes annually) becomes thicker. This can potentially lead to additional releases of greenhouse gases resulting in even further regional warming and permafrost degradation with implications for the global climate.
The Arctic vegetation has also changed due to higher air temperatures and altered precipitation patterns. Future predictions suggest more productive vegetation over the Arctic. This will likely increase the dominance of trees and shrubby vegetation leading to reductions in moss vegetation. Sub-arctic palsa mires in northern Sweden are experiencing a different shift in vegetation with higher graminoid abundance and declining shrub coverage due to increasing wetness. A change in the type of vegetation i.e. a change in plant functional types can alter the albedo together with the shading-, the evapotranspiration-, the snow trapping- and insulation potential. All these factors have the potential to change the ground temperature and the soil moisture content which affect the underlying permafrost. Changes like this have already been observed at the margin of where permafrost can exist, for example in the Abisko area in northernmost Sweden.
This report presents results from an experiment where different plant functional types (dwarf shrubs, graminoids, mosses and lichens) have been removed at the Storflaket mire in the Abisko area. During a five year period the vegetation has been manipulated in different plots to extract information on how soil moisture content and ground temperature (10 cm depth) respond to changes in vegetation. Ground temperatures were significantly warmer (0.2°C) where dwarf shrubs had been removed compared to the control plots. Removal of mosses and lichens significantly decreased the ground temperature by 0.7°C. Soil moisture was only significantly higher (6.6%) where mosses and lichens had been removed.
It is likely that ongoing vegetation changes on the mires i.e. a shift from dwarf-shrub dominated to graminoids dominated vegetation in the Abisko area will continue also in the future. The results suggest that the potential decrease of dwarf shrubs on the mires will lead to an additional increase in ground temperatures making the permafrost more sensitive to additional future changes in climate. (Less)
Abstract (Swedish)
Populärvetenskaplig sammanfattning
Arktis har under de senaste årtiondena upplevt betydande uppvärmning och enligt prognoser förväntas ytterligare höjningar av både lufttemperatur och nederbörd under det kommande århundradet. Det förändrade klimatet har haft omfattande konsekvenser för permafrosten (ständigt frusen mark) som format och kraftigt präglar stora delar av det arktiska landskapet. Med ökande temperaturer förkortas den period avsevärt under vilken marken är täckt av snö. Detta medför att markens genomsnittliga förmåga att reflektera solljus drastiskt minskar. Sett över året resulterar det i att marken blir varmare samtidigt som lufttemperaturen fortsatt stiger. Ökande nederbörd gör att snötäcket under vintern blir tjockare... (More)
Populärvetenskaplig sammanfattning
Arktis har under de senaste årtiondena upplevt betydande uppvärmning och enligt prognoser förväntas ytterligare höjningar av både lufttemperatur och nederbörd under det kommande århundradet. Det förändrade klimatet har haft omfattande konsekvenser för permafrosten (ständigt frusen mark) som format och kraftigt präglar stora delar av det arktiska landskapet. Med ökande temperaturer förkortas den period avsevärt under vilken marken är täckt av snö. Detta medför att markens genomsnittliga förmåga att reflektera solljus drastiskt minskar. Sett över året resulterar det i att marken blir varmare samtidigt som lufttemperaturen fortsatt stiger. Ökande nederbörd gör att snötäcket under vintern blir tjockare vilket också bidrar till en uppvärmning av marken genom att isolera och skydda markytan från låga lufttemperaturer under vintern. I kombination leder konsekvenserna av ett varmare Arktis till att temperaturökningen i regionen idag sker mycket snabbare än den förändring som ses globalt. Efterhand som permafrosten tinar och marktemperaturen blir högre ökar även den mikrobiologiska aktiviteten och nedbrytningen av det organiska materialet som tidigare varit otillgängligt i den frusna marken. Detta kommer troligen leda till ökade utsläpp av växthusgaser vilket på sikt kan påverka det globala klimatet.
Förändringar i det arktiska klimatet har också påverkat vegetationen genom förändringar i temperatur, samt påverkat tillgången till vatten och näring. Vegetationen i Arktis förväntas bli allt mer produktiv med fler träd och buskar, samtidigt som utbredningen av mossor förväntas minska. Palsamyrar i norra Sverige genomgår en förändring där arealer som domineras av risbuskar minskar på grund av allt fuktigare miljö som istället gynnar gräsdominans. Förändringar i artsammansättningen kan påverka den arktiska energibalansen på flera sätt. Ett skifte i vegetationen innebär förändringar i reflektionsförmåga, skuggningsegenskaper, evpotranspiration och isolering både sommar- och vintertid. Alla dessa faktorer påverkar hur en förändring i klimatet kan ha inverkan på vegetationen och markvatten som i sin tur avgör vad som händer med permafrosten.
För att undersöka hur permafrosten kan påverkas av vegetationen startades ett experiment på Storflaket, en palsmyr utanför Abisko, där olika typer av vegetation (risbuskar, mossor och lavar samt gräsväxter) togs bort på olika platser för att se effekten av dessa vegetationstypers frånvaro på markens temperatur och fuktighet. Under en femårsperiod manipulerades vegetationen och mätningar gjordes på marktemperatur och markfuktighet under sommaren. Det fastställdes att temperaturen ökar med 0.2°C när risbuskar tagits bort och att temperaturen sjunker med 0.7°C där mossor och lavar tagits bort. Markfuktigheten ökar med 6.6 procentenheter där mossor och lavar tagits bort.
Det är troligt att de pågående vegetationsförändringar på myrarna, det vill säga en övergång från risbuskar till gräsdominerad vegetation på myrarna kring Abisko kommer att fortsätta i framtiden. Resultaten från denna studie tyder på att den potentiella minskningen av risbuskar kan leda till ytterligare ökade marktemperaturer vilket kan leda till att permafrosten i området blir ännu mer känslig för framtida förändringar i klimatet. (Less)
Please use this url to cite or link to this publication:
author
Torkelsson, Eric LU and Bengtsson, John LU
supervisor
organization
course
NGEK01 20121
year
type
M2 - Bachelor Degree
subject
keywords
vegetation manipulation experiment, permafrost, climate change, physical geography, geography, Abisko, sub-arctic, naturgeografi, geografi, klimatförändring, manipulation av vegetation, subarktis
publication/series
Student thesis series INES
report number
244
language
English
id
2796854
date added to LUP
2012-08-09 16:31:17
date last changed
2012-08-09 16:31:17
@misc{2796854,
  abstract     = {The Arctic region has experienced significant warming in the past decades and according to predictions further increases in air temperatures and precipitation will occur during the 21st century. Recent changes in climate have had widespread implications for the permafrost around the Arctic. Shorter periods of snow covering the Arctic regions significantly reduce the average annual albedo which dramatically increases the amount of energy being absorbed by the ground surface. In addition, the amount of snow has increased which results in even further warming of the ground through insulation during the winter. Warmer ground temperatures increase the available amount of organic material stored in the formerly frozen ground when the active layer (i.e. the upper layer that thaws and refreezes annually) becomes thicker. This can potentially lead to additional releases of greenhouse gases resulting in even further regional warming and permafrost degradation with implications for the global climate.
The Arctic vegetation has also changed due to higher air temperatures and altered precipitation patterns. Future predictions suggest more productive vegetation over the Arctic. This will likely increase the dominance of trees and shrubby vegetation leading to reductions in moss vegetation. Sub-arctic palsa mires in northern Sweden are experiencing a different shift in vegetation with higher graminoid abundance and declining shrub coverage due to increasing wetness. A change in the type of vegetation i.e. a change in plant functional types can alter the albedo together with the shading-, the evapotranspiration-, the snow trapping- and insulation potential. All these factors have the potential to change the ground temperature and the soil moisture content which affect the underlying permafrost. Changes like this have already been observed at the margin of where permafrost can exist, for example in the Abisko area in northernmost Sweden. 
This report presents results from an experiment where different plant functional types (dwarf shrubs, graminoids, mosses and lichens) have been removed at the Storflaket mire in the Abisko area. During a five year period the vegetation has been manipulated in different plots to extract information on how soil moisture content and ground temperature (10 cm depth) respond to changes in vegetation. Ground temperatures were significantly warmer (0.2°C) where dwarf shrubs had been removed compared to the control plots. Removal of mosses and lichens significantly decreased the ground temperature by 0.7°C. Soil moisture was only significantly higher (6.6%) where mosses and lichens had been removed.
It is likely that ongoing vegetation changes on the mires i.e. a shift from dwarf-shrub dominated to graminoids dominated vegetation in the Abisko area will continue also in the future. The results suggest that the potential decrease of dwarf shrubs on the mires will lead to an additional increase in ground temperatures making the permafrost more sensitive to additional future changes in climate.},
  author       = {Torkelsson, Eric and Bengtsson, John},
  keyword      = {vegetation manipulation experiment,permafrost,climate change,physical geography,geography,Abisko,sub-arctic,naturgeografi,geografi,klimatförändring,manipulation av vegetation,subarktis},
  language     = {eng},
  note         = {Student Paper},
  series       = {Student thesis series INES},
  title        = {The potential impact of changing vegetation on thawing permafrost : effects of manipulated vegetation on summer ground temperatures and soil moisture in Abisko, Sweden},
  year         = {2012},
}