Quantifying land use and disturbance intensity in forestry, based on the self-thinning relationship

Forest management and disturbances affect forest soils and biomass carbon stocks, emissions to the atmosphere, and radiative forcing. The conventional approaches to quantifying the intensity of land management based on net primary productivity (NPP) are limited because they lack a sound ecological basis. These limitations are especially evident for forests. This study proposes a new way of characterizing the degree of management and disturbance in forest stands that do not experience a change in classification, i.e., they remain forests. The proposed index, called land use and disturbance intensity (LUDI), uses the relationship between stand density and diameter at breast height for a relatively unmanaged/ pristine baseline forest and different management schemes, in conjunction with the selfthinning relationship, to calculate the difference between potential and actual biomass storage. The LUDI distinguishes between the long and short timescales associated with management and disturbance. This capacity sets it apart from the conventional NPP-based approaches currently used to quantify the disturbance intensity. The study uses a semi-qualitative validation approach to demonstrate that the proposed index reproduces textbook knowledge on management and disturbance intensity. However, our quantitative approach that distinguishes between timescales adds insight into the effects of forest management on the living biomass stock. Further, data from the German national forest inventory were used to demonstrate that the proposed index does not require knowledge about the management scheme. Although LUDI is constrained to aboveground living biomass, we believe that the approach is useful in the context of broadening our capability in large-scale management reconstruction and through this understanding the effects of land use on the carbon cycle, beyond effects of deforestation and afforestation.