NI: MAST-NET: masting responses to climate change and impacts on ecosystems

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Most plants do not produce regular annual seed crops, but switch between years of bumper seed crops (known as "mast years") and years with low seed production. Intriguingly, these bumper crops occur simultaneously in plants living alongside each other, and synchronisation can extend across hundreds of kilometres. For example, we have previously shown that in 1976, 1992, 1995 and most recently in 2011, beech trees across Western Europe (including the UK, Germany, France and Poland) all produced heavy seed crops in the same year. Interestingly, 1992 and 1995 were also bumper years for pine-cone production in spruce forests in the same region.This highly variable production of seeds is an important process in ecosystems. Producing seeds is a key step towards successfully establishing the next generation of plants. Masting is beneficial for plants because in years of bumper seed crops, seed predators cannot consume all the available seeds, which ensures that some survive to germinate the next spring. In ecosystems that are influenced by disturbance such as wildfires, windstorms and logging by humans, the timing of the next bumper seed year is also crucial to the ability of plants to regenerate. However, the importance of masting extends beyond plants. Bumper seed crops in forest trees represent a pulse of food resources, and cause population booms in small mammals (e.g. voles and mice) and seed-eating birds (e.g. woodpeckers and great tits). Low seed crops in sequential following years can eventually result in population crashes. These boom-and-bust cycles of small animals have further impacts on ecosystems. One of the most important for humans is the effect on tick numbers, which fluctuate in response to the number of host animals. Ticks act as a host for the Lyme disease pathogen, and research has shown that Lyme infection rates in humans peak two years after bumper seed crops in forest trees, including beech and oak. Masting is not just important in natural ecosystems, however. Many fruit and nut crops come from "masting" species. In agriculture, this phenomenon is usually known as "alternate cropping". Fruits grown in the UK, including apples and cherries, show this characteristic year-to-year variation in crop size, which causes variation in annual crop yield for farmers. It is also important in many other commercially valuable species, including olives, almonds and pistachios. For these reasons, we need to be able to predict seed crops in "masting" species accurately. This information is necessary for the management of natural ecosystems and agricultural systems that rely on masting species. Furthermore, predicting bumper seed crops will allow us to forecast years of high risk from infectious diseases carried by animal feeding vectors, such as Lyme. An important question is how seed production in masting species will change in the future with changes in climate. This project is designed as the first crucial step to achieving these objectives. It will establish an international network of researchers to build the datasets necessary to understand the causes of bumper seed crops, and to predict seed production in masting species. We will draw together data from the tropics with data from boreal forests to understand how masting varies between species, and will use long-term monitoring conducted by members of the network to understand how seed production varies over time, and what triggers bumper seed years. We will also search archives and scientific literature for useful data: in a previous project we found useful data on seed crops collected by 18th century foresters, demonstrating that in some species, there is potential to develop very long records of seed production. The datasets that we will build in this project will then act as a spring-board for future research, including projects linked to public health, habitat management, and agriculture, taking advantage of the wide range of network expertise.