20.4. Comparison of field inventory methods and use of airborne laser scanning for assessing coarse woody debris

 Public examination of a doctoral dissertation in the field of forestry

Doctoral candidate: M.Sc. Annukka Pesonen 

Date and venue: 20.4.2011 at 12 noon, Borealis, Joensuu campus 
 

ABSTRACT 

The sustainable use of forests, which is one of the key principles of forest management in Finland, for instance, includes the goal of maintaining forest biodiversity. Dead wood (coarse woody debris, CWD) has been recognized as one of the main indicators of biodiversity in boreal forests and it plays a major role in nutrient cycling, for example. Much effort has therefore been put into the development of new cost-efficient methods for assessing CWD. However, if data are collected for large areas, field inventory may be expensive even when a sample-based method is used. In this thesis, sample-based CWD inventory methods were studied and since airborne laser scanning (ALS) is nowadays regarded as one of the most promising remote sensing methods and is gradually being adopted for predicting living tree characteristics, the possibilities for utilizing ALS data in CWD inventory were investigated.

The material comprised data from three areas. Data for a conservation area in Koli were used to study the use of ALS data for estimating downed and standing dead wood volumes in natural forests, and data for commercially managed forests in Sonkajärvi and Juuka were used to study the efficiency of sample-based field inventory methods for assessing CWD. The sampling methods were compared in terms of the accuracy of the estimated mean CWD volume with a fixed input effort specified in fieldwork hours. Furthermore, it was studied how much the use of auxiliary information derived from ALS data or other sources could improve the sampling efficiency, i.e. reduce the standard error of the mean given the same inventory costs. The auxiliary information was used either in the design phase, for ‘probability proportional to size’ (PPS) sampling, or in the estimation phase, for ratio or regression estimation.

ALS data proved useful for predicting CWD volumes in natural forests. The RMSEs for downed and standing dead wood, and for the total CWD volume estimates were 51.6%, 78.8% and 54.2%, respectively. It was also observed that ALS-based estimates for downed dead wood volume were substantially more accurate than those based on living tree characteristics measured in the field. The sample-based inventory methods developed for assessing CWD or other rare characteristics were observed to be most efficient field inventory methods, and especially the relascope-based sampling methods were highly efficient. The use of PPS sampling notably improved the efficiency of the CWD inventory, but efficiency was modest when auxiliary information was used in the estimation phase. The improvement in efficiency varied considerably between different inventory methods and CWD materials. Although the efficiency of other inventory methods could be improved more by introducing PPS sampling, relascope-based sampling methods remained the most efficient methods for assessing CWD. It was also observed that the sampling efficiency was not markedly better if ALS data were combined with either aerial photographs or stand-register data, and it was usually preferable to use ALS data alone as the auxiliary data source. 

The doctoral dissertation of Annukka Pesonen entitled Comparison of field inventory methods and use of airborne laser scanning for assessing coarse woody debris will be examined at the Faculty of Science and Forestry. The opponent in the public examination is Professor Göran Ståhl SLU, Sweden and the custos is Professor Matti Maltamo of the University of Eastern Finland. 

Photo available for download at http://www.uef.fi/vaitoskuvat

Contact: Annukka Pesonen, annukka.pesonen(at)uef.fi

Publishing year: 2011

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