Forest response to climate change
Changes in climate are causing significant changes in the functioning, composition and structure of Europe’s forests. For example, increased temperatures and drought stress, coupled with changes in atmospheric CO2, nutrient availability, disturbance dynamics and management are resulting in changes in the productivity of forests, with implications for carbon storage and the future of terrestrial carbon sink.
This research theme uses tree ring chronologies to create to create long time-series of tree and forest growth. Long-term changes in growth are linked to decadal patterns in climate (Hacket-Pain and Friend 2017), inter-annual variations in growth are used to assess the sensitivity of growth to seasonal climate variability (Muffler et al., 2020), and the response of growth to extreme climate events is used to quantify the sensitivity of forests to drought events (Hacket-Pain et al. 2017; Castagneri et al., In Review). Current research is focused on developing a distribution-wide network of tree ring chronologies. I am working with Dr Christian Zang (TUM, Germany) on this project (“European Beech Tree Ring Network”), which involves collaboration with a group of over 30 researchers from across Europe (Hacket-Pain et al., 2018; Zang et al. In Prep). We are using this network of tree ring chronologies to understand how the sensitivity of these species to drought and other climatic driver of growth varies within this species geographic distribution. This includes the effect of between-tree competition, with implications for how we can manage forest ecosystems to mitigate the impacts of future increases in drought frequency and severity (Castagneri et al., In Review).
However, forest responses to global environmental change are dependent not only the response of tree growth, but also on forest demographic processes. We are particularly interested in the links between climate, fire disturbance and tree mortality and recruitment. Recent work has included studying the mortality and recruitment in Alpine beech forests after novel fire disturbance (Maringer et al., 2019; Maringer et al., In Review), and a large-scale study to establish the links between climate teleconnections, drought, fire and seed production in North American boreal forests (Ascoli et al., 2019). You can read more about the links between climate, wildfire and seed production in boreal forest on The Journal of Ecology blog.
Understanding the drivers of tree growth
Tree growth is the primary process by which carbon fixed by photosynthesis is sequestered in forest ecosystems, but the supply of carbon from photosynthesis is not the only factor that controls tree growth (and productivity more generally). For example, the allocation of available resources plays a key role. The production of flowers, pollen, fruits and seeds all require significant investment of resources, which can result in a "trade-off" with growth. Consequently, year-to-year variation in allocation to reproduction is an important control on tree growth, and years with high investment in reproduction are associated with reduced growth (Hacket-Pain et al. 2017; Hadad et al., Submitted). Furthermore, as reproduction is influenced by weather conditions in various biologically relevant seasonal windows (Vacchiano et al. 2017), the interplay with reproduction creates important indirect mechanisms by which climate can influence growth (Hacket-Pain et al. 2018). Research has focused on European Beech, but the next step is to investigate these dynamics for other species (Hacket-Pain et al., 2019; Hadad et al, Submitted). For example, we are currently analysing new tree ring material from seven long-term seed monitoring plots along an elevation gradient in Paneveggio, Italy (sampled September 2018). I also have a project funded by the Royal Society to investigate the dynamics of climate, masting and tree growth in Araucaria araucana, a conifer native to northern Patagonia. In February 2020 I completed our first field trip to Patagonia, and the next trip is scheduled for February 2021.
In addition to resource supply and the allocation of resources, tree growth can also be limited by the potential rate at which a tree can use resources to build need tissue (i.e. wood tissues, though xylogenesis). The importance of this “sink limitation” on growth is currently a major topic of debate. Using a new model of tree growth, we have demonstrated the potential for growth limitation to switch between supply limitation (“source limited”, related to photosynthesis) and growth limitation (“sink limited”, related to xylogenesis) (Hayat et al. 2017). The next step is to integrate these ideas into global-scale models, to assess the potential implications for the dynamics of the global carbon cycle.
Masting is the synchronous and highly variable production of seeds and fruits, and is a characteristic reproductive strategy in many grass and woody species (Fernández-Martínez, 2019). 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, but the synchronisation can also extend across hundreds of kilometers (Vacchiano et al., 2017; Ascoli et al. 2020).
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 (Bogdziewicz et al., 2020a). 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. For example, I'm currently working with collaborators in Europe and North America to understand this interplay of climate, fire disturbance and masting in Canadian boreal forests (Ascoli et al., 2020), and mountain beech forests in the European Alps (Maringer et al., 2019). As part of the COST-Action project “PROFOUND”, I worked with foresters, field ecologists and modellers to investigate how masting can be incorporated into forest models, aiming to improve predictions of the response of forest dynamics to climate change (Vacchiano et al. 2018).
A series of papers has focused on understanding patterns and drivers of masting in two of the most widespread tree species in Europe - European Beech and Norway Spruce. In 2017 we drew together published data from the literature and our own datasets, and developed the largest published masting database (MASTREE, Ascoli et al. 2017a). The database contains >18,000 records from 28 countries, with the earliest datasets extending back to 1677. Analysis of this dataset has revealed distinct spatial structures in masting patterns, including the occasional occurrence of continent-wide mast years (i.e. simultaneous high seed production across Europe) (Vacchiano et al. 2017). Inter-annual variation in seed production in these two species is strongly related to a series of temperature “cues” (Hacket-Pain et al. 2015; Vacchiano et al. 2017), and consequently teleconnections that influence weather patterns across Europe also control the spatial synchronisation of masting (Ascoli et al. 2017b). A major motivation is to better understand the repsonse of masting to environmental change. We have shown that climate warming is associated with a "breakdown" in masting in UK beech trees (Bogdziewicz et al., 2020b), and future research will examine whether these changes are occurring in other species and regions, and what this means for forest regeneration under climate change.
In a new project funded by NERC (MAST-NET project) will expand this previously European-focused project to the global scale. The project brings together an new international network of researchers investigating the causes and consequences of masting in a range of different ecosystems. For example, we have a new paper providing an agenda for the experiments required to establish how plants regulate variability in seed production, and how they ensure that they achieve synchrony with other individuals and populations (Bogdziewicz et al., 2020a). We aim to improve prediction of bumper seed crop years, establish how masting will respond to environmental change (Bogdziewicz et al., 2020c), and understand what changes in masting will mean for ecosystems working with the NSF-funded MASTIF project. Our project will draw together data from tropical, temperate and boreal forests to understand how masting varies between biomes, species, and across climate gradients. Various members of the network maintain research programmes that monitor annual seed production, and we will bring these together to understand how seed production varies over time, and what triggers bumper seed years. We will also search archives and the scientific literature for additional data to develop a global-scale version of the MASTREE database ("MASTREE+"). These datasets 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 expertise contained in the network.
MonkeyPuzzle: Reconstructing mast events and climate in Patagonia using Araucaria araucana tree rings
ROYAL SOCIETY (OST)
December 2019 - December 2022
MAST-NET: masting responses to climate change and impacts on ecosystems
NATURAL ENVIRONMENT RESEARCH COUNCIL (NERC)
December 2018 - December 2021
Untangling climate drivers of wildfire in the Northwest Territories
DEPARTMENT FOR BUSINESS, ENERGY AND INDUSTRIAL STRATEGY (BEIS) (UK)
March 2018 - February 2019