Talking Point

Natural ecosystems protect against climate change

The identification of natural carbon sinks and understanding how they work is critical if humans are to mitigate global climate change. Tropical coastal wetlands are considered important but, so far, there is little data to show the benefits. The study, led by the University of Göttingen with the Leibniz Centre for Tropical Marine Research in Bremen, and the University of Bremen showed that mangrove ecosystems need to be conserved and restored as part of the battle against rising carbon levels in the atmosphere.

Researchers conducted the study in the mangrove-fringed Segara Anakan Lagoon in Java, Indonesia. This coastal lagoon is known to be one of the most effective carbon sinks amongst mangrove ecosystems around the world. The researchers analysed a five-meter-deep core of sediment for its age and biogeochemical composition, as well as elements, pollen and spores. They investigated four different time periods across 400 years and varying climates, integrating data from ecological and societal changes with land and coastal changes. The results show that the environmental dynamics in the lagoon and carbon accumulation were controlled mainly by fluctuations in the climate and human activity. The researchers found that the interaction of these two factors affected the lagoon’s sediment and saltiness, which then went on to alter the composition of the organic matter (which contains carbon), and how it was deposited in the lagoon thus adding to the ‘sink of carbon’. They also found that the weather was the chief driver in washing carbon compounds, in the form of organic matter, to the lagoon from remote areas far from the coast. In earlier times, these remote areas consisted of natural mixed forest but more often now they are agricultural land. Coastal lagoons, such as Segara Anakan, are particularly threatened both by destruction of the mangroves by people and the effects of global environmental change, such as rising sea levels. The rising water in turn causes coastal erosion, extreme floods and habitat loss, which endangers society. “Our research shows that people need to prioritise mangrove ecosystems for conservation and restoration because mangroves absorb carbon efficiently,” says first author Dr Kartika Anggi Hapsari from the Department of Palynology and Climate Dynamics at Göttingen University. “It is not enough just to focus on cutting carbon emissions. Society needs to also identify efficient and natural ecosystems, like those dominated by mangrove vegetation, to remove carbon. This research also really emphasises the importance of interdisciplinary working,” Hapsari adds.

Greenland ice losses rising faster than expected

Greenland is losing ice seven times faster than in the 1990s and is tracking the Intergovernmental Panel on Climate Change's high-end climate warming scenario, which would see 40 million more people exposed to coastal flooding by 2100. A team of 96 polar scientists from 50 international organisations have produced the most complete picture of Greenland ice loss to date. The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) Team combined 26 separate surveys to compute changes in the mass of Greenland's ice sheet between 1992 and 2018. Altogether, data from 11 different satellite missions were used, including measurements of the ice sheet's changing volume, flow and gravity.

The findings show that Greenland has lost 3.8 trillion tonnes of ice since 1992 -- enough to push global sea levels up by 10.6 millimetres. The rate of ice loss has risen from 33 billion tonnes per year in the 1990s to 254 billion tonnes per year in the last decade -- a seven-fold increase within three decades. The assessment, led by Professor Andrew Shepherd at the University of Leeds and Dr Erik Ivins at NASA’s Jet Propulsion Laboratory in California, was supported by the European Space Agency (ESA) and the US National Aeronautics and Space Administration (NASA). In 2013, the Intergovernmental Panel on Climate Change (IPCC) predicted that global sea levels will rise by 60 centimetres by 2100, putting 360 million people at risk of annual coastal flooding. But this new study shows that Greenland's ice losses are rising faster than expected and are instead tracking the IPCC’s high-end climate warming scenario, which predicts 7 centimetres more. Professor Shepherd said: “As a rule of thumb, for every centimetre rise in global sea level another six million people are exposed to coastal flooding around the planet.” On current trends, Greenland ice melting will cause 100 million people to be flooded each year by the end of the century, so 400 million in total due to all sea level rise. “These are not unlikely events or small impacts; they are happening and will be devastating for coastal communities.” The team also used regional climate models to show that half of the ice losses were due to surface melting as air temperatures have risen. The other half has been due to increased glacier flow, triggered by rising ocean temperatures. Ice losses peaked at 335 billion tonnes per year in 2011 -- ten times the rate of the 1990s -- during a period of intense surface melting. Although the rate of ice loss dropped to an average 238 billion tonnes per year since then, this remains seven times higher and does not include all of 2019, which could set a new high due to widespread summer melting.

Killer whale grandmothers boost survival of calves

Post-menopausal killer whale grandmothers improve the chances of survival for their grand-calves, new research has found. The study found that grandmothers who were no longer able to reproduce had the biggest beneficial impact on the survival chances of their grand-offspring. This may be because grandmothers without calves of their own are free to focus time and resources on the latest generation, the researchers suggest. The research team also found that grandmothers had a particularly important role in times of food scarcity, as the impact on a calf of losing a post-menopausal grandmother was highest in years when salmon was scarce. Previous research has shown that post-reproductive female killer whales are the most knowledgeable and provide an important leadership role for the group when foraging in salmon grounds. These benefits to the group may help to solve the long-standing mystery of why the menopause has evolved in some species of whales and in humans, the authors of the study say.

Senior author of the study, Dr Dan Franks from the Department of Biology, at the University of York, said: The study suggests that breeding grandmothers are not able to provide the same level of support as grandmothers who no longer breed. This means that the evolution of menopause has increased a grandmother's capacity to help her grand-offspring. “The death of a post-menopausal grandmother can have important repercussions for her family group, and this could prove to be an important consideration when assessing the future of these populations. As salmon populations continue to decline, grandmothers are likely to become even more important in these killer whale populations.” The study involved an international research team from the Universities of York and Exeter (UK), the Centre for Whale Research (USA) and Fisheries and Oceans Canada. The scientists analysed 36 years of data gathered by the Center for Whale Research and Fisheries and Oceans Canada on two populations of resident killer whales. The populations (which include several pods, made up of multiple family groups) live off the North West Pacific Coast of Canada and the US and feed on Chinook salmon. In resident killer whales, both sons and daughters stay with their mothers for life, but they mate with individuals from a different family group. Male killer whales typically have a shorter lifespan than females with many not surviving beyond 30 years. Females usually stop reproducing in their 30s-40s, but just like humans they can live for many decades following menopause. Lead author, Dr Stuart Nattrass, from the University of York, added: “The findings help to explain factors that are driving the whales’ survival and reproductive success, which is essential information given that the Southern Resident killer whales -- one of the whale populations under study -- is listed as endangered and at risk of extinction.” Co-author of the study, Prof Darren Croft from the University of Exeter, said: “The menopause has only evolved in humans, killer whales and three other species of toothed whales and understanding why females of these species stop reproduction well before the end of life is a long standing evolutionary puzzle.”

New findings on how trees coexist

For a decade, researchers explore how tree species diversity affects the coexistence of trees and their growth performance in the largest biodiversity experiment with trees worldwide, the so-called ‘BEF-China’ experiment. One of the main interests of the BEF-China team is to explore the relationship between tree diversity and multiple ecosystem functions, specifically those benefitting society, such as wood production or the mitigation of soil erosion. For this purpose, an experimental site of c. 50 hectare in subtropical China was planted with more than 400,000 trees and shrubs. Trees have achieved a height of 10 to 15 m and their crowns have formed a dense canopy by that time. The findings now shed new light on tree-tree interactions: The local environment of a tree strongly determine its productivity, meaning that tree individuals growing in a species-rich neighbourhood produce more wood than those surrounded by neighbours of the same species.

“Particularly impressive is the finding that the interrelations of a tree with its immediate neighbours induce higher productivity of the entire tree community (i.e. the forest stand), and that such local neighbourhood interactions explain more than 50% of the total forest stand productivity,” says forest ecologist Dr Andreas Fichtner. The importance of local neighbourhood interactions in regulating forest stand productivity increases as forest stands were richer in tree species. These findings show that the coexistence of neighbouring trees and their small-scale interactions are substantial in explaining the productivity of species-rich mixed forests. The scientists were also able to identify mechanisms explaining why species-rich neighbourhoods promote tree productivity. Their findings show that competition is less prevalent in species-rich neighbourhoods and that species-rich neighbourhoods can even lead to facilitation by e.g. an improvement of the microclimatic conditions or by positive interactions with soil fungi. “These findings contribute to a deeper understanding of tree interactions and the functioning of forest ecosystems, and are particularly relevant for nature conservation and forestry,” says Prof Dr Goddert von Oheimb from the Department of Forest Sciences at the TU Dresden. For instance, afforestation programs in countries that have experienced dramatic deforestation in the past, may benefit from planting multiple native tree species at the smallest spatial scale (i.e., the local neighbourhood level) instead of planting monocultures or mixing monospecific patches at larger spatial scales. Furthermore, the study emphasizes the importance of long-term measures preserving global biodiversity. This in turn will benefit the multifunctionality of forest ecosystems and their associated ecosystem services benefitting the society. “This shows that biodiversity conservation is not exclusively an ecological or ethical issue, but rather a necessity ensuring socio-economic welfare,” says Dr Andreas Fichtner.