Energy-systems accounting in industrial-natural systems; An energy analysis of a managed forest ecosystem including food web biomass dynamics

Abstract

Managed forests are industrial-natural systems established and maintained by human inputs that provide biomass to society while, given their long-successional growth period, also supporting a multitude of interacting species in food webs. Yet, energy analyses have overlooked food web impacts resulting from forest management. Addressing this gap, a dynamic energy analysis of a managed forest stand together with its supported food web was performed under differing forest management scenarios over a 100-year period. The model allows for a dynamic comparison of the exogenous energies invested to establish, manage, and harvest the stand, alongside the time-series impacts on food web biomass stocks compared to a reference no-harvest scenario. Over the first 25 years, food web biomass improved by ∼18 to 31 GJ/ha under management scenarios with forest thinnings prior to the initial harvest, which enhanced dead wood production relative to no-harvest scenarios. However, after 100 years, magnitudes of food web biomass losses exceeded exogenous investments in the forest stand by factors of three to five depending on management type. These results highlight a critical imbalance between the external inputs supporting the forest and the resultant food web impacts driven by those inputs. Taken together, such results suggest a large-scale losing energy tradeoff between civilization and the biosphere.