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Monitoring insect defoliation in forests with time-series of satellite based remote sensing data - near real-time methods and impact on the carbon balance

Olsson, Per-Ola LU (2016)
Abstract (Swedish)
Popular Abstract in Swedish

Skogar är av stor betydelse ur klimatsynpunkt på grund av deras stora förmåga att binda kol. Skogar på de nordligare breddgraderna spelar en viktig roll med sitt stora kolupptag, men eftersom dessa nordliga skogar troligen kommer att påverkas av klimatförändringarna i hög grad är det osäkert hur framtida kolupptag kommer att utvecklas. Ett varmare klimat kommer sannolikt att öka tillväxten och därmed öka skogarnas upptag av koldioxid från atmosfären. Samtidigt beräknas det att ett varmare klimat kommer att öka mängden skogsskador, såsom insektsangrepp, vilket kan resultera i stora förluster av koldioxid till atmosfären. Insektangrepp är i allmänhet inte inkluderade i kolbudgetar vilket kan... (More)
Popular Abstract in Swedish

Skogar är av stor betydelse ur klimatsynpunkt på grund av deras stora förmåga att binda kol. Skogar på de nordligare breddgraderna spelar en viktig roll med sitt stora kolupptag, men eftersom dessa nordliga skogar troligen kommer att påverkas av klimatförändringarna i hög grad är det osäkert hur framtida kolupptag kommer att utvecklas. Ett varmare klimat kommer sannolikt att öka tillväxten och därmed öka skogarnas upptag av koldioxid från atmosfären. Samtidigt beräknas det att ett varmare klimat kommer att öka mängden skogsskador, såsom insektsangrepp, vilket kan resultera i stora förluster av koldioxid till atmosfären. Insektangrepp är i allmänhet inte inkluderade i kolbudgetar vilket kan resultera i överskattningar av mängden kol som binds i skogar. Därför är det viktigt att utveckla metoder för att kartera insektsangrepp samt att beräkna hur dessa angrepp påverkar kolbalansen. Det övergripande syftet med avhandlingen var att utveckla metoder för kartläggning av insektsangrepp med satellitdata samt att beräkna effekterna av dessa angrepp på skogens kolupptag.

Studien visade att tidsserieanalyser av satellitdata kunde användas för att bestämma vilket år ett utbrott av den invasiva ungerska gransköldlusen i sydvästra Skåne startade. Resultaten visade också på möjligheten att utveckla system för övervakning av skogsskador med hjälp av satellitdata. Om ett sådant övervakningssystem hade varit aktivt hade sannolikt angreppen av gransköldlusen upptäckts redan samma år som de startade, vilket var ett år tidigare än det upptäcktes i fält. För invasiva insektsarter är en tidig upptäckt viktig för att minska risken för vidare spridning.

Studien visade också att satellitdata med låg rumslig upplösning (pixelstorlek 250x250 m) kan användas för nära realtidsövervakning av insektsskador. 74 100% av pixlarna med björkmätarangrepp i fjällbjörkskog i norra Sverige detekterades med en felklassning av ostörd björkskog på 39 56%, beroende på tröskelvärden i detekteringsmetoden. Metoden kan även användas för att studera hur ett insektsangrepp utvecklas över tid och kartera björkskog som återhämtar sig senare under samma växtsäsong som insektsangreppen. Detta är stora fördelar jämfört med metoder som klassificerar pixlar som angripna eller ostörda för en hel växtsäsong. Den låga rumsliga upplösningen är emellertid en begränsning i fragmenterade skogar som är uppsplittrade i många mindre skogsbestånd av varierande storlek och ålder. En metod för kartering av insektsangrepp baserad på säsongsmax av ett vegetationsindex visade att detektionsgraden för tallstekelskador i fragmenterade tallskogar med intensivt skogsbruk i östra Finland var låg i jämförelse med de mer homogena fjällbjörkskogarna i norra Sverige.

Studien visade också att satellitdata i kombination med meteorologiska data kan användas för att kartera effekterna av insektsangrepp på skogens kolupptag med hjälp av en s.k. light use efficience (LUE) modell. LUE modellen kalibrerades med fluxmätningar av skogens kolupptag och metoden för nära realtidsövervakning användas för att kartera angreppen. Dessa resultat visade på stora effekter på kolupptaget orsakade av insektsangrepp samt att det är möjligt att utveckla metoder för att övervaka och kartera insektsangrepp samt att kvantifiera effekterna av dessa angrepp på kolupptaget med satellitdata. Sådana metoder är viktiga för att minska osäkerheten i hur insektsangrepp påverkar skogarnas kolupptag. (Less)
Abstract
Forests are of major importance to climate change mitigation due to their strong capacity to sequester carbon. Nearly half of the terrestrial carbon is stored in forests, and forests contribute to half of the terrestrial primary productivity, with forests in the mid- and high latitude ecosystems as major contributors. These high latitude forests are, however, projected to be strongly influenced by climate change. A warmer climate is likely to have a positive effect on forest productivity and increase the ability to absorb CO2 from the atmosphere. At the same time it is projected that a warmer climate will increase the impact of forest disturbances, such as insect outbreaks. Insect outbreaks are, however, generally excluded in large scale... (More)
Forests are of major importance to climate change mitigation due to their strong capacity to sequester carbon. Nearly half of the terrestrial carbon is stored in forests, and forests contribute to half of the terrestrial primary productivity, with forests in the mid- and high latitude ecosystems as major contributors. These high latitude forests are, however, projected to be strongly influenced by climate change. A warmer climate is likely to have a positive effect on forest productivity and increase the ability to absorb CO2 from the atmosphere. At the same time it is projected that a warmer climate will increase the impact of forest disturbances, such as insect outbreaks. Insect outbreaks are, however, generally excluded in large scale carbon modeling. In addition, there are large uncertainties in the quantitative effects of insect outbreaks on the carbon balance. Hence, it is important to develop methods to monitor insect disturbances and to quantify the impact of these disturbances on the carbon balance. The general aim of this thesis was to develop methods for mapping of insect outbreaks with satellite data, and to quantify the impact of these outbreaks on primary productivity.

The results demonstrated that time-series of satellite data could be applied to find what year an outbreak by the invasive Hungarian spruce scale in southern Sweden started, and showed the potential of developing an early warning system. An early warning system would most likely have detected the outbreak the year before it was detected in field; for invasive species early detection is important to enable rapid counter-measures to decrease the risk that new species establish populations.

The results also showed that coarse spatial resolution satellite data (MODIS 250x250 m pixels size) can be used for near real-time monitoring of insect induced defoliation with the aid of Kalman filtering and cumulative sums (CUSUM). Of the defoliated MODIS pixels in mountain birch forests in northern Sweden 74–100% were detected with a misclassification of undisturbed pixels of 39–56%, depending on threshold settings. In addition, the developed method facilitates studies of the intra-seasonal dynamics of an insect outbreak as well as mapping of potential refoliation; these are major advantages compared to methods that classify a pixel into defoliated or undisturbed for an entire season. The coarse spatial resolution of MODIS is, however, a limitation in fragmented forests. A method based on z-scores of seasonal maximum values of a vegetation index showed that detection accuracies were low in fragmented and heavily managed pine forests in eastern Finland compared to the more homogenous mountain birch forests in northern Sweden.

The thesis also demonstrated that satellite data and meteorological data can be used to map the impact of insect outbreaks on gross primary productivity (GPP) with the aid of a light use efficiency (LUE) model. The LUE model was calibrated with eddy covariance measurements, and the near real-time monitoring method was applied to monitor defoliation. An extensive set-back to the carbon uptake in deciduous semi-arctic forests due to insect defoliation was recorded. These results demonstrated the potential to develop methods to both monitor insect disturbances and to quantify the impact of these disturbances on primary productivity. Such methods would be important to decrease the uncertainties in estimates of insect outbreaks impact on the carbon balance. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Senior Research Scientist, PhD Wulder, Mike, Canadian Forest Service, Natural Resources Canada
organization
publishing date
type
Thesis
publication status
published
subject
pages
156 pages
publisher
Department of Physical Geography and Ecosystem Science, Lund University
defense location
Pangea, Geocentrum II, Sölvegatan 12, Lund
defense date
2016-04-14 10:00
ISBN
978-91-85793-55-6
language
English
LU publication?
yes
id
96b08992-da8f-4e11-b005-eccd64c6bb17 (old id 8860253)
date added to LUP
2016-03-29 11:59:23
date last changed
2016-09-19 08:45:02
@phdthesis{96b08992-da8f-4e11-b005-eccd64c6bb17,
  abstract     = {Forests are of major importance to climate change mitigation due to their strong capacity to sequester carbon. Nearly half of the terrestrial carbon is stored in forests, and forests contribute to half of the terrestrial primary productivity, with forests in the mid- and high latitude ecosystems as major contributors. These high latitude forests are, however, projected to be strongly influenced by climate change. A warmer climate is likely to have a positive effect on forest productivity and increase the ability to absorb CO2 from the atmosphere. At the same time it is projected that a warmer climate will increase the impact of forest disturbances, such as insect outbreaks. Insect outbreaks are, however, generally excluded in large scale carbon modeling. In addition, there are large uncertainties in the quantitative effects of insect outbreaks on the carbon balance. Hence, it is important to develop methods to monitor insect disturbances and to quantify the impact of these disturbances on the carbon balance. The general aim of this thesis was to develop methods for mapping of insect outbreaks with satellite data, and to quantify the impact of these outbreaks on primary productivity. <br/><br>
The results demonstrated that time-series of satellite data could be applied to find what year an outbreak by the invasive Hungarian spruce scale in southern Sweden started, and showed the potential of developing an early warning system. An early warning system would most likely have detected the outbreak the year before it was detected in field; for invasive species early detection is important to enable rapid counter-measures to decrease the risk that new species establish populations.<br/><br>
The results also showed that coarse spatial resolution satellite data (MODIS 250x250 m pixels size) can be used for near real-time monitoring of insect induced defoliation with the aid of Kalman filtering and cumulative sums (CUSUM). Of the defoliated MODIS pixels in mountain birch forests in northern Sweden 74–100% were detected with a misclassification of undisturbed pixels of 39–56%, depending on threshold settings. In addition, the developed method facilitates studies of the intra-seasonal dynamics of an insect outbreak as well as mapping of potential refoliation; these are major advantages compared to methods that classify a pixel into defoliated or undisturbed for an entire season. The coarse spatial resolution of MODIS is, however, a limitation in fragmented forests. A method based on z-scores of seasonal maximum values of a vegetation index showed that detection accuracies were low in fragmented and heavily managed pine forests in eastern Finland compared to the more homogenous mountain birch forests in northern Sweden. <br/><br>
The thesis also demonstrated that satellite data and meteorological data can be used to map the impact of insect outbreaks on gross primary productivity (GPP) with the aid of a light use efficiency (LUE) model. The LUE model was calibrated with eddy covariance measurements, and the near real-time monitoring method was applied to monitor defoliation. An extensive set-back to the carbon uptake in deciduous semi-arctic forests due to insect defoliation was recorded. These results demonstrated the potential to develop methods to both monitor insect disturbances and to quantify the impact of these disturbances on primary productivity. Such methods would be important to decrease the uncertainties in estimates of insect outbreaks impact on the carbon balance.},
  author       = {Olsson, Per-Ola},
  isbn         = {978-91-85793-55-6},
  language     = {eng},
  pages        = {156},
  publisher    = {Department of Physical Geography and Ecosystem Science, Lund University},
  school       = {Lund University},
  title        = {Monitoring insect defoliation in forests with time-series of satellite based remote sensing data - near real-time methods and impact on the carbon balance},
  year         = {2016},
}