Representation of species mixing in forest growth models. A review and perspective

Abstract

a b s t r a c tMixed-species forests can sometimes fulfil forest functions and services better than monocultures and are therefore receiving growing attention in forest science and practice. The productivity of mixtures and the interactions between species are influenced by the availability of different resources and climatic conditions, all of which change spatially and temporally. Models are a valuable tool for understanding and predicting how these interacting factors will influence the growth and other functions and services in mixed-species forests. However, concepts, models and theory are still mainly based on monocultures, which have dominated forest science since its beginnings. Recent empirical works report strong effects of mixing tree species on the environmental conditions within stands (e.g., vertical light profile, rooting space, humus layer), their functioning (e.g., photosynthetic rate, light use, growth), and tree and stand structure (e.g., crown and stem shape, shoot and root morphology). Process-based organ-or tree-level approaches reveal changed resource supply, flows and metabolic rates in high spatial and temporal resolution. Stand-level approaches usually provide predictions with a lower spatial and temporal resolution but can be more accurate in the longer-term. Many studies stress considerable effects of mixing tree species on growth dynamics, yield, resilience and stability, but these effects are still under-represented in existing models. We reviewed 54 forest growth models to show how they incorporate the variability of individual tree or species characteristics that occur in forests and how this variability influences the development and characteristics of the whole stand. While some organ-or tree-level models inherently integrate evident processes, stand-level models do not usually explicitly consider species interactions. Nevertheless, many processes that occur in mixtures can also be modelled at the stand level and are often included in stand-level monospecific models. Stand-level models are likely to offer a simpler alternative model structure for mixtures. We stress how both model approaches can be refined, benefit from mutual adjustment, and can be substantiated by further empirical research into mixed-species forests.

Joining of the historical research and future prediction as a support tool for the assessment of management strategy for European beech-dominated forests in protected areas

“…A combination of routine forest inventory data and the set of functions implemented in the transparent forecast system can be an important support tool for conservation planning in the frame of conservation forest biodiversity. Growth simulation models for the prediction of future forest development represent a promising tool for sustainable management of forest ecosystems (Pretzsch et al 2015, Simon et al 2014. However, growths models have not yet been fully integrated into the forest management practice (Porté andBartelink 2002, Machar et al 2016) and are rarely used to assess the forest management strategies in conservation areas (Sodtke et al 2004).…”

Mixing of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) enhances structural heterogeneity, and the effect increases with water availability

“…Increases in species diversity and heterogeneity of other structural attributes can, e.g., stabilize and raise the productivity (Bielak et al, 2014;Lei et al, 2009;Liang et al, 2007;Jucker et al, 2014;Pretzsch et al, 2013Pretzsch et al, , 2015aRío and Sterba, 2009), stability (Griess and Knoke, 2011;Jactel and Brockerhoff, 2007), reduced sensitivity to drought (Grossiord et al, 2014;Metz et al, 2013), habitat diversity (Tews et al, 2004), plant and animal richness (Brunet et al, 2010;Ishii et al, 2004;Roth, 1976), and the aesthetic value (Schütz, 2002;Stölb, 2005) of forest stands. On the other hand more heterogeneous structures can have a negative effect on some taxa (Paillet et al, 2010), on the wood quality (Pretzsch and Rais, 2016), on the effort of forest inventory, planning, and management (von Gadow, 1998;von Gadow et al, 2002), and on the costs of opening up the stands to harvest the timber (Keegan et al, 1995;Kellogg et al, 1996).…”

A Review of Processes Behind Diversity—Productivity Relationships in Forests

“…However, there is often interest in the effects of different climatic conditions and novel combinations of species or management. Validated process-based forest growth models could be used to examine these scenarios [35,36]. A recent review of forest growth models found that many could be used for mixed-species forests but very few have been validated by comparing their predictions of complementarity effects against measured complementarity effects [36].…”

“…Nevertheless, it is clear that this simple framework cannot simultaneously show all the different spatial or temporal gradients, or different processes, that are typically occurring in a single forest. The prediction of dynamics resulting from several simultaneously occurring processes can be achieved using process-based models that contain many of the processes or structural attributes listed in Table 1 [35,36].…”