title: Indirect approach for estimation of forest degradation in non-intact dry forest: modelling biomass loss with Tweedie distributions.
abstract: BACKGROUND
  Implementation of REDD+ requires measurement and monitoring of carbon emissions from forest degradation in developing countries. Dry forests cover about 40 % of the total tropical forest area, are home to large populations, and hence often display high disturbance levels. They are susceptible to gradual but persistent degradation and monitoring needs to be low cost due to the low potential benefit from carbon accumulation per unit area. Indirect remote sensing approaches may provide estimates of subsistence wood extraction, but sampling of biomass loss produces zero-inflated continuous data that challenges conventional statistical approaches. We introduce the use of Tweedie Compound Poisson distributions from the exponential dispersion family with Generalized Linear Models (CPGLM) to predict biomass loss as a function of distance to nearest settlement in two forest areas in Tanzania.
  
  
  RESULTS
  We found that distance to nearest settlement is a valid proxy variable for prediction of biomass loss from fuelwood collection (p < 0.001) and total subsistence wood extraction (p < 0.01). Biomass loss from commercial charcoal production did not follow a spatial pattern related to settlements.
  
  
  CONCLUSIONS
  Distance to nearest settlement seems promising as proxy variable for estimation of subsistence wood extraction in dry forests in Tanzania. Tweedie GLM provided valid parameters from the over-dispersed continuous biomass loss data with exact zeroes, and observations with zero biomass loss were successfully included in the model parameters.
authors.affiliation: Informi GIS, Stationsparken 37, 2600 Glostrup, Denmark.
authors.forename: Klaus
authors.initials: K
authors.lastname: Dons
authors.affiliation: United Nations Development Programme, UN House, Pulchowk, GPO Box 107, Lalitpur, Kathmandu, Nepal.
authors.forename: Sushma
authors.initials: S
authors.lastname: Bhattarai
authors.affiliation: Faculty of Science, University of Copenhagen, Rolighedsvej 23, DK-1958 Frb C, Copenhagen, Denmark.
authors.forename: Henrik
authors.initials: H
authors.lastname: Meilby
authors.affiliation: Faculty of Science, University of Copenhagen, Rolighedsvej 23, DK-1958 Frb C, Copenhagen, Denmark.
authors.forename: Carsten
authors.initials: C
authors.lastname: Smith-Hall
authors.affiliation: Faculty of Science, University of Copenhagen, Rolighedsvej 23, DK-1958 Frb C, Copenhagen, Denmark.
authors.forename: Toke Emil
authors.initials: TE
authors.lastname: Panduro
keywords: Compound Poisson distribution; Forest monitoring; REDD+; Spatial analysis; Tanzania