Abstract
Mixed-species forests have become widely studied in the recent years because of their potential to mitigate risks associated with climate change. However, their growth dynamics are often difficult to predict because species interactions vary with climatic and edaphic conditions, stand structure and forest management. We examined species interactions in mixtures of Scots pine (Pinus sylvestris) and pedunculate oak (Quercus robur) under climate change and for varying soil conditions in the Netherlands, over a period of 30 years. We parameterized, calibrated and validated the 3-PGmix model for mixing effects in Scots pine and oak mixtures and analysed these effects under climate change. 3-PGmix performed well for the variety of forest stands examined throughout the Netherlands. Furthermore, it was also able to reproduce mixing effects for each species in mixtures compared to monocultures for the growing conditions examined. Simulated climate change resulted in lower productivity of oak and higher productivity of Scots pine, compared to the current climate. This was observed for both monospecific stands and mixtures. The mixture of Scots pine and oak showed clear but limited overyielding (mixture yield greater than the mean of the monocultures), which was mainly attributed to oak. This was maintained under the most extreme climate scenario for 2050, implying that for oak, increased growth due to mixing with Scots pine was larger than the reduction in productivity under the future climate. On resource-limited soils, Scots pine competitiveness was increased, and this was maintained under a warmer and drier climate. Our results suggest that projected changes in climate will influence species interactions and result in increased Scots pine productivity, notably on poor sandy soils, which are typical of the Netherlands.
Highlights
Climate change is expected to increasingly impact forest ecosystems worldwide
Our results suggest that projected changes in climate will influence species interactions and result in increased Scots pine productivity, notably on poor sandy soils, which are typical of the Netherlands
The comparisons between predicted and observed stem and total biomass and the variables directly derived from them were slightly better for monocultures than for mixtures, since the criteria for model performance showed lower mean values for monocultures than for mixtures (e% =4.39, MAE%=18.52, MSE = 374.6, N = 36)
Summary
Climate change is expected to increasingly impact forest ecosystems worldwide. Mixtures are considered increasingly important in the face of climate change. Over the last few decades, the share of mixed forests in temperate regions has increased, and currently more than two-thirds of Europe’s forests are dominated by two or more tree species (Forest Europe, 2015). Mixed forests provide more resilience and resistance to various biotic and abiotic climate-related disturbances, such as patho gens, herbivores, drought, wind and fire (Bauhus et al, 2017). Species interactions in mixtures may result in higher productivity (Vilà et al, 2013; Pretzsch et al, 2015a; Jactel et al, 2018) and forests with more tree species may provide higher levels of multiple ecosystem ser vices simultaneously (Gamfeldt et al, 2013). If the productivity of mixed-species stands exceeds the weighted mean productivity of the monocultures, this is called overyielding, or transgressive overyielding when it exceeds the productivity of the most productive monoculture (Hector et al, 2002)
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