Effects of delineation errors in forest stand boundaries on estimated areaand timber volumes

A 717 ha forest area dominated by Norway spruce [Picea abies (L.) Karst.] a nd Scots pine [Pinus sylvestris L.] was used to assess the effects of photo interpreter errors in the placement of stand boundaries on the estimated ar ea of different groups of forest stands (strata) and other land use classes , and on the total timber volume estimate of the forest. The boundaries bet ween thinning phase stands and clearcuts were classified into three differe nt groups according to the length of the tree shadows hindering ground visi bility in the aerial photographs. Different distributions of errors in stan d boundaries were assigned to the three groups of boundaries. By means of M onte Carlo simulations of errors in each boundary, the placement of each bo undary was altered according to a normally distributed random deviate. In t otal. 125 independent estimates of total timber volume and area of differen t land use classes were produced. For thinning phase forest, the difference between the mean area of the simulations and true area was -2.0% of true a rea. The corresponding difference for total timber volume of all stands was -2.1%. For individual simulations, the minimum and maximum biases in timbe r volume were -4.8% and 3.1%, respectively.