Inference On Forest Attributes and Ecological Diversity of Trees-outside-forests Based On Two-phase Inventories

Tree-outside-forests (TOF) play important roles in national economies, ecosystems and international efforts for sustainability. Recently, international programmes on global forest resource assessments recognize the TOF role not only in sustainable land management, but also in carbon sequestration, thus allowing for climate changes mitigation. Indeed, in the past, TOF tend to be left out of natural resource assessment, but in 1996 a FAO expert meeting addressed the need of data on TOF and, as a result, the FAO Forestry Department included TOF in the National Forest Monitoring and Assessment Programme. From this perspective, a large-scale investigation was planned in 2008 for the Molise Region, an administrative district of approximately 450000 ha located in Central Italy. The first years were devoted to the collection and storage of 1 m geometric resolution aerial ortho-photos, covering the entire study area and allowing the identification of small groups of trees by visual onscreen analysis. The entire collection of 52796 TOF units scattered throughout the region were subsequently identified. Clearly, the very large population size rendered any complete investigation prohibitive. In 2013, a two-phase sample survey was planned to estimate some attributes of interest and diversity measures, such as the abundance vector, the basal area, the volume and the carbon storage. In the first phase, the Molise Region was covered by a grid of 4693 hexagons of size 100 ha, and a point was randomly selected within each hexagon. Then, to reduce the sampling effort, a sample of 2347 points/hexagons were selected in a second phase by means of the one per stratum stratified sampling. Finally, in accordance with the point sampling protocol, all of the TOF units intercepted at least by one of these 2347 points were sampled and visited on the ground.