In our new post, Julia Koricheva—a researcher at Royal Holloway University of London, UK—discusses her interest in effects of plant diversity on ecosystem functioning. Having worked extensively on long-term forest diversity experiments in Finland, Julia is particularly interested in the biodiversity and functionality of boreal forest ecosystems. She also works on the evolution and ecology of plant-herbivore interactions, including mechanisms of plant defense.
As more and more species are lost from ecosystems due to human activities, it is important to understand what impact biodiversity has on the functioning of ecosystems and services that they provide to humans. In managed ecosystems (e.g. agricultural fields and forestry plantations) plant diversity is often reduced to a single crop/timber species and these monocultures are often more susceptible than mixed stands to pest outbreaks, disease epidemics, and abiotic stresses. By increasing plant species and genetic diversity in managed ecosystems we can alleviate these negative effects. A lot of research on the effects of plant diversity has been conducted on crops in agricultural systems and in grasslands, but less is known about effects of tree species and genetic diversity on ecosystem functioning in forest ecosystems.
Profile
The research in my lab focuses on three main topics: relationship between forest biodiversity and ecosystem functioning, plant-herbivore interactions, and research synthesis and meta-analysis in ecology. While numerous studies over the last few decades have shown that plant diversity affects ecosystem functioning and ecosystem services, many of these studies have been short-term. To understand the temporal dynamics of plant diversity effects in ecosystems composed of long-lived species such as trees, we need long-term studies following the development of tree diversity effects from stand initiation through forest succession. We also need experimental studies in which plant diversity is directly manipulated so that diversity effects can be disentangled from effects of other environmental factors. I am fortunate enough to be using these long-term experimental sites in my research.
In addition, the relative importance of different mechanisms behind plant diversity effects on ecosystem functioning is not well understood. For instance, reduced herbivory commonly observed in mixed species stands—as compared to monocultures—is often attributed to reduced abundance or apparency of host plants or increased activity of natural enemies. But there might be other mechanisms as well, for instance, differences in shading or nutrient regimes of focal trees in pure and mixed stands might affect their quality to herbivores. Research in my lab is exploring the relative importance of different mechanisms behind forest diversity effects on herbivore resistance and other ecosystem processes and services.
Where in the world are you?
My main study sites for the last 20+ years have been the Satakunta forest diversity experiments in south-western Finland—established by myself and colleagues from University of Turku in 1999–2000. One of our experiments is manipulating tree species diversity and another is one manipulating within-species genetic diversity. Taken together, these long-term experiments provide a unique opportunity to compare effects of trees species and intraspecific genetic diversity on boreal forest ecosystem functioning and services.
The Satakunta tree species diversity experiment consists of 3 areas, each containing 38 plots (20 x 20m) planted with monocultures, 2-, 3- and 5-species mixtures of Scots pine, Norway spruce, Siberian larch, silver birch and black alder. The Satakunta birch genetic diversity experiment consists of a single area planted with 8 different genotypes of silver birch which differ in their growth and leaf characteristics as well as in resistance to herbivores and pathogens. Plots are randomly assigned to either single-genotype plots or 2-, 4- and 8-genotype mixtures.
Over the years we have collaborated with a number of researchers across Europe to study the effects of tree diversity on many aspects of ecosystem functioning, including: tree growth and mortality; herbivory; predation; litter decomposition; fungal pathogens and mycorrhizal fungi; soil microbial processes; and understory vegetation. Our most recent research focuses on exploring the effects of tree diversity on canopy structure using drones (part of Mandy Cooper’s PhD thesis) and effects of neighborhood diversity on leaf chemical and physical traits which are important for herbivores (part of Juri Felix’s PhD studies).
Planting a forest makes you appreciate how many biotic and abiotic stresses trees have to deal with before they mature. In their first few years after planting, many of our tree seedlings were badly damaged by voles and large pine weevils, and we had to replant some of the plots, particularly those with high proportion of conifers. For the next few years our saplings, particularly birch and pine, experienced lots of damage by moose. Moose are quite abundant in Finland and can cause considerable damage to young forest plantations, particularly in winter when other food sources are scarce. However, the surviving trees eventually become tall enough to avoid moose browsing.
Forest ecosystems in general—and trees in particular—are incredibly resilient. Despite many biotic and abiotic challenges over the years, our forest stands are thriving. Some of the trees that were pronounced dead in previous plot inventories have sprung to life in subsequent years by producing new stems from the same root stock. These might not be the type of trees that foresters want to harvest for timber, but they still provide important ecosystem services and support diversity of other organisms. Given the low diversity of tree species in boreal forests, I was surprised by the sheer diversity of species that these trees support. For instance, we have recorded 28 different species of leaf-miners (insects which tunnel the leaf tissues) on silver birch alone and 121 different understory vascular plant species in our plots.
Tips for fieldwork
Summer days in Finland are long and field work can be monotonous, with hundreds of trees and plots to survey, measure or sample—it is important to take a break now and then. When the weather is rainy, it might be more productive to spend a day entering the data already collected, catching up on emails, using sauna, or just watching TV. Speaking of rainy weather, proper waterproof clothes (jacket AND trousers) are a must! There is nothing that makes you more miserable in the field than been soaked to the bone.
It’s important to think creatively. For example, we used plasticine caterpillars to study avian predation, which has been great fun! When birds attempt to predate plasticine caterpillars, they leave beak marks on them, so predation attempts can be quantified and compared between plots. Bird species differ in their preferences with regards to which tree species they mainly forage on, and we have noticed particularly many predation attempts of plasticine caterpillars on Scots pine. To establish the identity of the bird species responsible for predation attempts on pine, we have installed camera traps on pine trees. After several days of waiting and the excitement of going through the footage, we have found the culprit—Great tits!
Enjoying your work is vital. One enjoyable ‘side-effect’ of doing fieldwork at the Satakunta experimental site over the summer is the profusion of edible mushrooms : chanterelles; penny buns; orange birch boletes (my personal favorites)—we get them all. Fortunately, everyone in my lab loves eating mushrooms, so our dinner menu during the field season has a distinctive mushroom theme and tends to alternate between mushroom risotto, tagliatelle ai funghi, and other dishes involving mushrooms. We don’t just eat mushrooms from our experiment, we study them too, in collaboration with Leho Tedersoo’s group from the University of Tartu, Estonia. Using a novel DNA meta-barcoding approach—which allows us to identify species of fungi and other eucaryotes directly from soil—we have shown that tree diversity has a positive effect on species richness of ectomycorrhizal fungi which include chanterelles, boletes, and other edible mushrooms.
The future
I hope to continue following the development of the forest diversity effects in the Satakunta experiments for many more years. After all, within forest succession time scales, our sites are still quite young. But I also enjoy opportunities of working at other study sites. I am currently involved in the project TreEPlaNat which is part of ‘Future of UK Treescapes’ research program and is exploring social and ecological consequences of woodland creation using tree planting and natural colonisation. We have many study sites in England with different histories of establishment and I am hoping to be able to visit some of them. I have also recently read a wonderful book “The Lost Rainforests of Britain” by Guy Shrubsole and I would love to do some field work in the remaining fragments of temperate rainforest in Britain. Trees covered by epiphytic ferns and lichens are absolutely magical, and this ecosystem is severely understudied in the UK.
The Satakunta forest diversity experiments are part of TreeDivNet, a global network of forest diversity experiments which currently includes 29 experimental sites in different forest biomes. I am interested in research synthesis and meta-analysis and I see a tremendous potential in combining results from different TreeDivNet experiments to compare the effects of tree diversity and tree species composition on various ecosystem processes and services across different biomes as well as exploring how these effects change over time through forest succession in different types of forests.
