Scottish Atlantic oak woods or temperate rainforest are rare and threatened habitats that support a vast array of biodiversity, particularly lichens and bryophytes. Much of this unique habitat was converted to conifer plantations (known as Plantations on Ancient Woodland Sites – PAWS) last century for commercial timber production. Many PAWS are undergoing restoration in attempts to reinstate the former structure and functional diversity of the oakwoods.
While there are studies examining how the initial establishment of PAWS and subsequent restoration efforts have impacted aboveground biodiversity, there are no data on belowground functional and taxonomic biodiversity responses to the same changes in management. The current work is addressing this knowledge gap.
Stage
Work in ProgressDirectory of Expertise
Purpose
Soils support rich communities of organisms from across all seven Kingdoms of life (Archaea, Bacteria, Chromista, Fungi, Planta, Protozoa). This myriad of taxonomic biodiversity is also functionally diverse and vital for maintaining essential ecosystem processes including carbon and nutrient cycling and directly impacts on diversity of plant and animal communities aboveground. Relationships between above and belowground diversity are reciprocal and drastic changes aboveground can have major impacts on functional biodiversity belowground.
Figure 1. The mycelia of fungi, like that shown in the image, have multiple essential roles in ecosystems, functioning as recyclers of organic matter, symbiotic partners of plants, food sources for small soil animals, and creating and building soil structure.
The conversion of Atlantic oakwoods to PAWS has a dramatic negative impact on biodiversity above ground – as shown in the paired lead images above. How this impact translates below ground is unknown. Similarly, it is unknown how efforts to restore former PAWS back to oak rainforest influence soil communities. Are soil communities able to recover following restoration? Long-term sustainability of restored sites will depend on understanding what has changed following PAWS establishment and on how effective restoration efforts are at rebuilding the assemblages of organisms which sustain existing oak rainforests.
In order to fill these knowledge gaps, we must determine the following:
1) The soil communities and functions that are characteristic of existing, near-pristine oak rainforests.
2) The impact of PAWS establishment on soil communities and ecosystem processes.
3) The trajectories of soil communities and associated functions following removal of conifers from PAWS.
The effectiveness of restoration efforts will likely take decades to be appreciated, but establishing baselines in pristine rainforest sites and in PAWS enables the ends of the gradient to be determined against which soil communities and functions in restoration sites can be compared.
Results
A study site was established at Glen Creran, NE of Oban, in collaboration with Richard Thompson (Forest and Land Scotland). The site was chosen because the management history of this site is known, it is undergoing active restoration, and it still contains an area of PAWS.
Six areas were chosen which represented different managements:
1. near pristine oak woodland (the desired habitat)
2. managed oakwood – where understorey trees had been removed
3. PAWS – with existing conifer trees
4. young regeneration ca. 7 years after conifer removal
5. older regeneration (ca. 20 years) on rich soil
6. and older regeneration (ca. 20 years) on poorer soil
Seven small plots were established within each area, where we determined soil chemistry, decomposition rates, and characterised the soil biodiversity using molecular markers.
Nutrient mineralisation rates and nitrogen and carbon concentrations differed markedly among management regimes.
In general, pristine oak plots had:
a) the lowest C:N ratios - mainly attributable to higher N concentrations
b) higher decomposition rates of labile carbon substrate, and surprisingly
c) the highest levels of soil nitrate together with the regeneration plots on rich soils
Levels of other soil nutrients showed more variable patterns amongst the management regimes.
The soil fungal communities were strikingly different under the management regimes (Figure 2), which were strongly related to the fungal communities associated with the roots of the plants present. The other components of the biodiversity (bacteria and Eukaryotes) were more strongly influenced by soil conditions. Differences in the fungal communities are likely to be reflected in the observed functional differences between the management areas.
Figure 2. Relatedness of the fungal communities in plots in the different management regimes at Glen Creran. The closer two points are the more similar the communities are between the plots. (Targ – pristine oak, Rich – rich regeneration, Plant – PAWS area, Poor – regeneration on poor soil, Man – area of managed oakwood, Young – area of 7-year-old regeneration).
Planting oak woodlands with non-native conifers clearly has a significant impact on nutrient and carbon cycles. These changes are likely to be a direct consequence of the massive change in the fungal communities, the organisms most responsible for the nutrient cycling and the decomposition of organic matter in woodland systems. The uniqueness of the fungal communities under each of the management regimes highlights their responsiveness and usefulness as indicators of change. Fungal communities underpin many ecosystem processes and services (Figure 1) and changes in fungal community composition and structure create bottom-up effects at higher trophic levels. The plots in the semi-natural oak stands supported not just different species from the PAWS plots (Figure 2) but had > 45% greater species richness. The study discovered new fungal species to Scotland and the UK including two truffle species.
Benefits
This is the first study that has examined the impact of the conversion of Atlantic oak woodland to PAWS and the subsequent initial restoration process. The combined approach of determining soil chemistry and functional biodiversity provides unique insights on the potential ecosystem consequences for these dramatic shifts in woodland management. In addition, the study highlighted both how little we know about the biodiversity in Scottish soils, and emphasised the extraordinary biodiversity associated with temperate rainforests.
The study provides new baseline comparative data as evidence for the significant impacts of PAWS formation on below ground communities and functions in Atlantic oak woods. In particular, the study demonstrated that converting temperate rainforest to PAWS devastated soil fungal communities by reducing species richness by almost half. Additionally, the study highlights the feasibility of capturing large within site variation to allow robust comparisons of the impacts of different management approaches on functional biodiversity. The study forms the basis for tracking the progress of restorative management practices aimed at reversing the disastrous impacts of creating PAWS on biodiversity hotspots such as Oak temperate rainforest.
All Image Credits: AFS Taylor (case study author).
Project Partners
The James Hutton Institute
Forest and Land Scotland