Landscape-Scale Model Relating the Nordic Mountain Birch Forest Spatio-Temporal Dynamics to Various Anthropogenic Influences, Herbivory and Climate Change

Abstract

The main focus of the HIBECO model has been to prepare a virtual arena where general growth and dispersion patterns for subalpine, subarctic moun- tain birch forests can be simulated in a fairly realistic manner for the purpose of studying the consequences of various management and perturbation regimes.Under model conditions of stable and changing climate conditions, scenarios related to various anthropogenic influences and herbivory influ- ences from ungulates and leaf-consuming insects with periodic outbreaks have been studied at a preliminary level of detail.Our current implementation of moth outbreaks is a strong simplification of the intrinsic and extrinsic forces that influence the complex spatio-temporal fluctuations in severe defo- liation events.However, the HIBECO model may be expanded at a later stage with a more explicitly defined population dynamic submodel for the actual moth species and their main predators and parasitoids (see Chaps. 9 and 12 and Fig. 21.3,where conceptual models for some of the elements in this kind of submodel are described). In the current scenario example, grazing effect from ungulates is modeled to be stronger in cells dominated by young stands, such as recently logged areas and pioneer forest growth in the expanding front under improved cli- matic conditions, than in medium- and old-aged stands. In general terms,we have assumed in the model that medium and old-growth sites are generally less penetrable and have less grazing resources (due to less light penetration Landscape-Scale Model 299 to the forest floor) than sites dominated by young stands (cf. Chap. 22).How- ever, a more complex pattern may emerge if the grazing is strong and long- lasting (many years). In this case, the understorey may be opened up due to local habitat facilitation.At this stage we have not implemented this complex effect in the model. The current version of the HIBECO model is still in an early developmen- tal phase with respect to the level of detail that is necessary before it can be distributed as a tool for applied science to produce scenarios and analyses connected to particular areas and specific management contexts.At this stage, efforts are concentrated on aspects related to general management principles, and simplified, virtual landscapes are used for this purpose.The advantage of a virtual landscape is that it allows for a structure that is optimized for explo- ration of the basic mountain birch ecosystem processes in the context of var- ious management and climate scenarios. The focus is then more stringently aimed at capturing the main system processes typical or representative of a broad region rather than a specific, local area with all its particular and explicit landscape details. When the model behavior is sufficiently under- stood at the current generic level,one can bring in more details to the simula- tions in the next turn.