Scientists have found that flowering time in plants can advance as much as 3.6 days for every 1°C the climate warms, but why does this matter?
The United Nations designated the first Monday of October of every year as World Habitat Day to reflect on the state of our habitats, and remind the world of its collective responsibility for the future of the human habitat. But what has become increasingly apparent is that biodiversity provides human society with many benefits, and that the destruction of biodiversity undermines the foundations of our societies and wellbeing.
Plants not only provide us (and our livestock and pets) with many of the foods we eat, fibres such as cotton and hemp for our clothes, oils for cooking and other uses, medicines and skincare ingredients, and building materials; they also offer other critical services including absorbing carbon dioxide and pollution, filtering our water, offering flood defences and providing the oxygen we breathe. One plant may provide food and shelter for hundreds of other species. We are all tied up within a delicate ecosystem. If one thing changes, many things need to be able to adapt with it for the whole ecosystem to survive.
Leading climate scientists have observed impacts and projected risks to a range of habitats on a global scale. These changes include increases in both land and ocean temperatures, more frequent heatwaves, an increase in the frequency, intensity and/or amount of heavy precipitation events, as well as an increased risk of drought in the Mediterranean region. It is estimated that around one million animals and plants are threatened with extinction – more than ever before in human history.
Since the industrial revolution, human-induced global change has threatened species and ecosystems. Climate warming can cause shifts in the timing of annual life-history events of plants and animals, including earlier flowering of plants. Herbarium specimens from natural science collections provide millions of specimens worldwide that demonstrate the evidence of these long-term changes over hundreds of years.
Building up a picture from the smallest of habitats
Goldilocks buttercup (Ranunculus auricomus), Wild garlic (Allium ursinum) and Paris quadrifolia from the Museum’s collection
Responses to climate change not only vary among species but also vary across space. At smaller scales, this can be because of microclimatic differences, and at larger scales (across broad regions) may occur because sensitivities to cues such as temperature may differ between regions. Botanical data from natural science collections can be clustered around where collectors live or travel – for this reason, combining data from a large variety of natural science collections, including large national institutions with global collections and smaller local institutions with very localised specimens, provides more balanced evidence for these sorts of studies to be carried out. Willems et al. (2022) studied over 6000 digitised herbarium specimens (over 10% from NHM London) of 20 spring-flowering forest plants to understand how timing for flowering had changed during the last century. The group studied includes the goldilocks buttercup (Ranunculus auricomus), edible wild plants such as wild garlic (Allium ursinum) and plants that are in decline such as Paris quadrifolia which is on the Red List for Threatened species in Iceland due to loss of habitat. This study demonstrates that it is crucial to combine the analysis of herbarium data around the world with spatial modelling when testing for long-term trends across large areas.
Willems et al. focused on early-flowering understory plants because they have a critical time window for flowering. These plants are referred to as understory plants as the habitat they grow in exists beneath the forest canopy and has a lower requirement for light. These plants flower before the deciduous trees of the forest produce their leaves. Understory plants may also be exposed differently to climate change because climate warming is buffered under forest canopies. The study found that on average plants now flower over 6 days earlier than at the beginning of the last century. These changes were strongly associated with warmer spring temperatures, with flowering time advancing on average 3.6 days per 1°C warming. This study indicates that forest wildflowers in Europe now flower earlier in response to climate change, but that these shifts differ geographically. While no relationship was found due to elevation – plants at higher altitudes had no difference in flowering time – a significant north-south divide was found. Plants from northern and eastern Europe were found to flower up to 60 days later than plants from central and southern Europe.
The earlier flowing of plants can create an ecological mismatch as many insects, birds and other wildlife have co-evolved to synchronise their life stages with their food plant. Galium, also known as woodruff, is eaten by at least 18 species of caterpillars. To adapt, moths will have to have earlier mating times so that their eggs are laid earlier and caterpillars hatch at the right time to consume these flowers. While this is yet to be studied in moths, Wilson et al. (2022) have looked at this in British and Irish butterflies. Wilson et al. applied computer vision to digitised photographs of 24 species of the Museum’s British butterflies and found that the seasonal events of the butterflies that they looked at are indeed earlier in 17 of the species studied, in warmer years. Both of these studies indicate that to understand the wider impact that these shifts in annual timing of events in plants and insects will have on the wider the health of the ecosystem, more research is needed
What can we do?
The IPBES global assessment report found that global goals for conserving and sustainably using the world’s habitats cannot be met by current trajectories. Goals for 2030 and beyond may only be achieved through transformative changes across economics, politics and technology. Researchers at the Museum have worked to develop a tool called the Biodiversity Trends Explorer to track biodiversity change and share our knowledge with those that can enact change. Our scientists have used this to speak with policy makers about the importance of preserving a world in which people and the planet can both thrive. The change captured in the Biodiversity Trends Explorer is given as the Biodiversity Intactness Index (BII), an estimated percentage of the original number of species that remain and their abundance in any given area, despite human impacts. The BII complements other biodiversity indicators that tell the story of extinction risk, such as the Sampled Red List Index for Plants that uses the IUCN Red List Criteria to assess plant extinction rates.
More research is still needed to understand species and their abundance. “We still don’t know all there is to know about which species are which, and which are in danger. Without understanding how many species are threatened it’s extremely hard to protect them from extinction” Neil Brummitt, Principal Researcher, Plants Under Pressure. The Plants Under Pressure programme used a small sample of plant species selected at random, in partnership with the Royal Botanic Gardens, Kew, to represent broad patterns of plant diversity across the world and obtain a first value for the IUCN Sampled Red List for Plants indicator. These data were sourced from specimens within the Museum’s herbarium and others around the world, but by digitising the collection and geolocating each specimen, this enables researchers to more accurately understand which species are at risk. The Museum’s digitisation team have already digitised over 1 million of the Museum’s plants, which is around 20% of the Herbarium collection at the Museum, and Kew are under going a massive effort to digitise their collection of 7 million plants and fungi in the next five years. “Our work so far has shown us that at least 25% of plant species on earth meet the criteria as threatened under the IUCN Red List. We know that the biggest threat to both plants and animals is land use change, particularly in the tropics where there are really high levels of biodiversity or on islands where there are a lot of species that are endemic to that area”.
Providing free and open access to global biodiversity data is shifting the way in which scientists are studying the natural world. Analytical tools enable us to understand how our data is used so that we can demonstrate the impact of our work. By ensuring that our data abides by international data standards and contributes to larger data aggregators such as the Global Biodiversity Information Facility (GBIF), the Museum contributes a valuable resource to science and is part of wider solutions to the challenges facing humans today.
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Want to see what we’ve already digitised? Check out the Museum’s Data Portal and explore.