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9:00 Amanda Cooper: What is the Story in the Understorey: Does Boreal Forest Trees Diversity Affect Diversity Below the Canopy?
Boreal forest plant diversity is predominantly found in the understorey. Understorey plants provide vital ecosystem services, including resources for animals (such as berries), water regulation, and carbon storage. Trees control understorey plant communities by regulating light availability, intercepting precipitation, and controlling nutrient availability. We hypothesize that increased tree diversity will positively effect understorey plant diversity as this will drive variability in understorey habitat. To test the impact of tree species diversity on the understorey, a survey of understorey plants, including edible berry species, was conducted in the Satakunta Boreal Forest Diversity Experiment during the summers of 2019 & 2020. Satakunta, located in southwest Finland, consists of twenty-year-old forest plots that range in tree species richness from single species to plots with up to five tree species: Scots pine (Pinus sylvestris), Norway spruce (Picea abies), silver birch (Betula pendula), black alder (Alnus glutinosa), and Siberian larch (Larix sibirica). Preliminary analysis showed that tree species richness had no effect on understorey plant species richness. However, increased proportion of Norway spruce and Siberian larch in plots had a negative effect on understorey plant species richness whereas increased proportion of silver birch had a positive effect. Cover of three berries species, raspberry (Rubus idaeus), bilberry (Vaccinium myrtillus), and cowberry (Vaccinium vitis-idaea), was not affected by tree species richness, but bilberry cover was higher when pine was present in the overstorey. This study demonstrates that tree species identity, rather than tree species richness, had stronger effects on understorey species richness and edible berry cover. This may be due to variation in the canopy structure between tree species, causing differences in light and precipitation available to the understorey. Further work will explore variation in tree canopy structure and tree density as controlling mechanisms for understorey plant diversity.
9:15 Caitlin Lewis: Snapshots in time of soils during the forest restoration process
Following timber shortages in the early part of the 20th century, vast areas of the UK’s native broadleaf forests were replaced with faster growing, non-native coniferous plantations. Whilst providing a valuable source of timber, these plantations are frequently associated with potentially negative impacts on surface water and groundwater quality due to high levels of nitrogen accumulation in their soils.
As the world faces both a biodiversity crisis and a climate crisis, the restoration of broadleaf forest on these plantation sites is needed to enhance native biodiversity and forest resilience to climate change, but little is known about the potential negative consequences of this conversion on nitrate leaching fluxes. Although established mature broadleaved forests are usually associated with enhanced water quality, a conversion of coniferous woodland typically stimulates breakdown of organic matter, leading to a release of nitrogen which cannot be retained up by the nascent broadleaved forest.
Here, we present the initial findings from a chronosequence study running from summer 2021-2022 at Thetford Forest, East Anglia. During this study we are measuring throughfall chemistry, soil nitrate leaching fluxes, soil C/N ratios and microbial nitrogen transformation processes, in a series of 30 stands which are at different stages in the conversion process. We go on to discuss how we will use this research in future to model the long-term impact of forest conversions on groundwater nitrate concentrations to fully understand the legacy of coniferous plantations on water quality after forest restoration.
9:30 Hollie Folkard-Tapp: Optimising the Recovery of Degraded Tropical Rainforests
Tropical forests comprise 40% of the planet’s terrestrial carbon sink (Malhi, 2010; Ciais et al., 2014) but can act as both a sink and a source of CO2. Human activity such as logging impacts this natural carbon flux controlled by growth and decomposition (Riutta et al., 2018). Up to 70% of the world’s remaining forests have been affected by selective logging, yet these degraded forests are under-studied compared to old-growth forests. Previous research also focuses primarily on live aboveground biomass. This study aims to quantify the carbon flux and biomass recovery rate of logged forests in Borneo, including aboveground and belowground biomass, comprising live wood, deadwood, and soil. Initial results show that the live biomass recovery is affected by the former logging regime, with areas that have been shielded from logging displaying greater increases in aboveground biomass between 2011 and 2019. Models show optimum biomass increase to occur in forests with an initial biomass of around 320 t/ha, over the course of a decade. Subsequent analysis of tree mortality and deadwood stocks will confirm whether this optimum value also holds for minimising C loss, or is restricted to maximising C sequestration. If applied to forest management, these findings could inform sustainable logging limits and REDD+ accreditation schemes.