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Bumblebees are vitally important pollinators of wild flowering plants and agricultural crops across the world. However, populations of bumblebees have seen massive declines around the globe, driven by the climate crisis caused by human activities, including land use changes, commercial rearing of bees, competition with invasive species, diseases and agrochemical use.

They are able to fly in cooler temperatures and lower light levels than many other pollinators, such as honeybees and flies. Bumblebees can improve the quality and quantity of crops like peas, beans and tomatoes through pollination, ensuring food security, and they actively contribute to the recovery of degraded ecosystems, maintaining plant biodiversity. They also play a significant role in sustainable development projects and programs by providing an extra source of income to traditional and low-income communities.

How does climate change affect bumblebees?

According to a study analysing the climate crisis in the Eastern Amazon., anthropogenic climate change is a major menace for bumblebee species worldwide. The impacts of climate shift affect species’ abundance, distribution, morphology and phenology. The bumblebee’s fuzzy body also makes it difficult for them to survive in the heat. A new study from the University of Ottawa suggests that temperature spikes and extreme heat waves have driven some local bumblebee populations in Europe and North America to the edge of extinction. Researchers analysed more than 500 000 records of 66 bumblebee species from 1901 to 1974 and from 2000 to 2014. The results demonstrated that the number of places populated with bumblebees have declined by 46% in North America and by 17% in Europe from 2000 to 2014 compared to the baseline period of 1901 to 1974. The rusty patched bumblebee, a species native to eastern North America, is an example of local population decline. The species is no longer found in Canada and is classified as endangered in the US under the Endangered Species Act. 

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Bumblebees have been hardest hit in southern regions, such as Spain and Mexico, as a result of more frequent extreme warm years. The decline of bumblebees amid accelerating climate change would lead to cascading ecological effects and loss of biodiversity and eventually economic damage, as there are less bees for crop pollination. Bees contribute more than $15 billion to the US economy by pollinating crops, making them vital for food security in the US and beyond. Therefore, the climate crisis must be mitigated to manage the bumblebees’ habitats by reducing exposure to the growing frequency of temperatures that may exceed the species’ optimum range of tolerance; bumblebees can maintain high thoracic temperatures at ambient temperatures between ~ 9 and 30 °C. NASA released a report in mid-2019 in which it says that under 1.5 degrees Celsius warming, the hottest days at Earth’s mid-latitudes will be up to 3 degrees warmer, while at 2 degrees warming, the hottest days will be up to 4 degrees warmer, placing the bees’ tolerance temperatures at risk.

The study focused mainly on species decline in Europe and North America and there is still an insufficient number of studies on bumblebee declines with reference to extreme climate events. Therefore, more studies should be conducted in the future and applied in all parts of the world. The importance of bees to our future is vastly underestimated; it is to our detriment that we’ve allowed bee populations to plummet so drastically. There needs to be wide-scale programs that focus on restoring their numbers so the planet can continue to benefit from the ecosystem services they provide. 

When we talk about ozone, the image that most often springs to mind is the ozone layer in the stratosphere that protects us from harmful ultraviolet (UV) rays from the sun. The depletion of this ozone layer increases surface UV levels, making its protection vital. However, ozone pollution can also be detrimental to the health of plants. How does it do this and what does it mean for a warming planet?

How does ozone form?

The ozone layer depletion- called the ‘ozone hole’- over the North and South Polar regions has been a pervasive problem throughout the 20th century. Caused by pollutants such as chlorofluorocarbons (CFCs) and other anthropogenic pollutants such as halons- gases found in aerosols and refrigerants- more UV rays are able to reach the Earth’s surface and can increase rates of skin cancer. The Montreal Protocol signed in 1987 has greatly reduced the emission of CFCs; studies show that the global climate would be at least 25% hotter today without the Protocol and new satellite images show that the largest hole ever observed in the ozone layer over the Arctic has closed.

While these events provide a sense of hope that efforts to reduce aspects of the climate crisis are working, there is another threat associated with ozone that affects human health and particularly plants that has recently come to light- surface ozone pollution. 

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What is ozone?

Discovered by a Dutch chemist named Van Marum in 1840, ozone gas is a colourless gas that is used as a disinfectant and water treatment option because of its strong oxidative property that kills microorganisms. The gas is also used in ozone therapy, which is when ozone is injected into a patient’s body to disinfect the area around the bacteria, improving the body’s intake and use of oxygen and activating the immune system. Some have claimed that ozone therapy can be used as a treatment for the COVID-19 virus, however the Food and Drug Administration in the US has asserted that ozone is a toxic gas and ‘has no known useful medical application’. Scientists and medical professionals have asserted that ozone therapy can cause respiratory irritation, heart problems, poor circulation, strokes and other afflictions. 

Among various air pollutants, surface ozone- mostly produced photochemically from anthropogenic precursor gases such as nitrous oxide from vehicles and volatile organic compounds (VOCs) from solvents- is of particular concern due to the significant harm it can pose to both human and ecosystem health. The phytotoxicity of ozone has been shown to impair photosynthesis, reduce gas exchange, induce early leaf senescence (ageing) and hamper growth in both natural vegetation and crops. 

Ozone-Sensitive Plants

As plants play a vital role in regulating the ambient environment, ozone-induced damage in plants may further accelerate environmental degradation, with severe consequences for human health. The increasing ozone trend could be the result of increased temperature and reduction of humidity in subtropical climates, which induce stress in plants and in return reduce the ozone absorption ability of plants, increasing ozone concentration in the atmosphere.

Ozone is one of the most difficult pollutants to control because it is not directly emitted. Instead, dangerous compounds and nitrous oxides released from vehicles, power plants, landfills and other biomass and fossil fuel burning facilities react with sunlight to form this secondary pollutant. According to Hong Kong’s Environmental Protection Department’s 2019 air quality monitoring results, the average ozone level has been increasing over the past 20 years, despite government efforts to clean the air and overall air quality and other major pollutants’ level improving steadily. 

To investigate the impact of ozone on plants, Dr. Felix Leung from the Chinese University of Hong Kong established a free-air experimental garden to monitor, quantify and understand the mechanisms of ozone damage on plants. In this experimental field, dubbed the ‘ozone garden’, the team grew cultivars of beans with different ozone sensitivities as a bioindicator of the local air pollution impacts on ecosystems. 

The beans showed a distinctive red mottled pattern on the leaves according to the level of ozone in the atmosphere. There are two genotypes of beans that show different sensitivity to ozone. Dr. Felix Leung and his team found that the ozone-sensitive genotype bean suffered higher ozone-induced foliar damage, with more red mottles and a higher death rate. This shows that ozone level in Hong Kong is high enough to cause significant damage to plants even in the countryside.

Professor Amos Tai from the Faculty of Science says, “the data obtained from this garden is essential to not only demonstrate the impacts of air pollution on plants under locally specific environmental conditions, but can also be used to derive important parameters of ecophysiology and biometeorology that can be used to build a regionally relevant earth system model for predictive purposes. Such an ozone garden has also been shown to provide great opportunities for public education. The differences in visual damage on ozone-sensitive, normal and ozone-tolerant plants are often striking, and can be used in publicity and educational events to raise awareness of pollution impacts on life and to galvanize corresponding technical and policy solutions to protect regional ecosystems and agriculture against pollution threats.”

To specifically tackle ozone pollution, the governments of Hong Kong, Guangdong and Macau have committed to a 3-year joint study from 2020-2023 to better understand the origins of ozone precursors, its formation and its transportation. Hong Kong and Guangdong are also adding real-time VOCs monitoring in the regional air quality monitoring network and wind profiles at higher altitudes to track the transportation of pollutants over Hong Kong, with a view to tackle ozone pollution. 

The Hong Kong government should add more incentives to encourage the use of electric cars and convert existing public transport modes to electric. Additionally, more ozone-tolerant trees should be planted along the roadside to improve air quality. It is only through these proactive measures that ozone pollution can be tackled and mitigated; it is therefore imperative that more studies such as the one conducted at CUHK are undertaken to better understand the problem.

With rising temperatures brought on by the climate crisis, summer comes early, prompting plants to sprout and bloom earlier than usual. Until recently, scientists were not particularly worried about this premature blooming, as thriving plants might help mitigate the climate crisis by sequestering carbon dioxide. However, research shows that plants are actually growing less. What can be done?

With the results published in the journal, Nature, scientists studied three decades of satellite data and concluded that many regions can’t keep their early spring growth going through summer and into the fall because early growth sucks water out of the soil, leaving little left over for the main growing season. 

How does climate change affect flowers?

Wolfgang Buermann, who led the study, says, “Because of climate change, plants bloom earlier and more in spring, but they cannot sustain this until summer and autumn. That means over the entire year, the effect of warm springs on photosynthesis is small. Plants need water to grow. If plants start to bloom earlier, they take up water earlier from the soils, and then the water is missing in the drier summer season to sustain the growth.

He adds, “If leaves emerge earlier, they will also die earlier and hence cannot do photosynthesis in late summer.” The scientists believe that some existing climate models overestimate the amount of carbon that plants absorb due to early growth. 

Scientists measured the amount of green colour in satellite photos to determine how much vegetation covered the Earth’s surface by season and year, and they used temperature data to search for those years with colder or warmer than average springs. After this, spring temperature was compared with the vegetation productivity in spring, summer and autumn; this comparison was done for every point at the globe to the north of the 30th parallel north, from southern Europe and Japan to the most northerly tundra regions. 

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longer summers plants
Satellite images show that warmer springs produce more vegetation in the spring but less vegetation in the summer (Source: Nature). 

The results showed that the northern hemisphere becomes greener in the spring, but these effects reverse in summer, causing an overall loss of plant growth, meaning more heat-trapping CO2 in the atmosphere and less water in the soil. 

Deviations from normal weather conditions can have adverse impacts of plant growth. 

Extremely hot or cold temperatures can also hamper plant growth, as well as affect seed germination. Cool temperatures in autumn trigger the plant to reduce growth and store energy. Extreme temperatures can also inhibit fruit set on tomatoes and other garden plants, and hot weather can cause cool-season vegetables to bolt– the premature production of a flowering stem on a plant before it can be harvested- resulting in reduced production and changes in flavour. Temperature can also have indirect effects on plants. A warm winter may result in a larger insect population the following season, which may have resulted in this year’s locust invasion in West Africa.

Many plants require a chilling period of a certain number of days before growth resumes in spring. Repeated freezing and thawing of groundwater and soil- called heaving- can happen in shallow-rooted plants, resulting in their roots being pushed out of the ground.

Generally, plants bloom earlier and grow faster with increasing air temperatures to a point. Extreme heat will slow growth and also increase moisture loss. Temperatures for optimal plant growth vary with the type of plant. 

Heat waves and droughts will occur more often under the climate crisis; if plants use all the water in spring, this could mean that droughts will become even worse in summer. 

As the planet warms, spring has been coming earlier. The northern hemisphere spring equinox fell on March 19 this year, the earliest equinox the hemisphere has seen in 124 years. While this is basically inconsequential with the equinox usually falling on March 20, the warmer spring weather is far more noticeable a change. 

Thanks to anthropogenic climate change, spring is happening about 2.5 days earlier every decade. 

A study conducted in 2016 of 276 parks across the United States used NASA Earth Observatory images to observe flowering periods over the years in the parks. The study found that around 75% of the parks have been experiencing earlier springs that year and half saw the earliest springs recorded in 112 years. In Olympic National Park in Washington, the first leaves are now appearing 23 days earlier than they did a century ago, while the Grand Canyon is seeing leaves appear about 11 days earlier. 

National parks in the Sierras, along the Appalachian Trail and in Utah are seeing leaves appear five to 10 days earlier.

Changes in blooming seasons will affect bee populations. Despite the longer blooming season, plants aren’t producing more flowers. With the same number of flowers blooming over a longer period of time, bees could face a situation where there are fewer in bloom at any given time, which could increase competition between pollinators for these resources. If bees experience continued population loss, that will in turn impact the plants that depend on the insects for pollination. 

Meanwhile, Norway experienced a rare heatwave for early January, when temperatures should normally be below freezing. The highest temperature, measured in the village of Sunndalsora, was 19 degrees Celsius- more than 25 degrees Celsius above the monthly average, making it Norway’s warmest January since records began. 

The heatwave is due to an abnormally warm foehn wind, warm gusts that occur on the downwind side of mountain ranges. 

Japan is famed for its pink cherry trees that line the streets in the springtime. Hundreds of thousands of people plan their journeys specifically to see this beautiful sight, but planning may become more difficult in the future, as the cherry blossom season is arriving earlier than usual due to the climate crisis. 

Usually occurring in Japan for two weeks between late March and mid-April, this year’s cherry blossom season saw flower buds sprouting on March 14, the earliest date since the trees began being monitored in 1953. In October 2018, there were many cases of cherry blossom trees blooming completely out of season. 

A 2017 report from the Japan Meteorological Agency showed that the cherry blossoms have been flowering earlier every year over the last six decades, with a trend of one day earlier per decade. 

National Park Service ecologist, John Gross, says, “Changes in leaf and flowering dates have broad ramifications for nature. Pollinators, migratory birds, hibernating species, elk, and caribou all rely on food sources that need to be available at the right time.” While it may seem innocuous that plants bloom earlier, when temperatures start to misalign with usual seasonal changes, those species suffer.

A new study has indicated that 31.7% of tropical African flora species are at risk of going extinct, affecting those countries that rely on its biodiversity for tourism and fuel.

In the study, tropical flora was assessed across the continent. The findings were published in the Science Advances Journal and used an assessment process outlined by the International Union for Conservation of Nature (IUCN) Red List criteria.

The research demonstrated that 6,990 of the 22,036 species studied, or 31.7%, are at risk of extinction. Much of western African countries, Ethiopia, and parts of Tanzania and the Democratic Republic of Congo are the hardest-hit regions, standing to lose more than 40% of their flora. The species both at risk and potential risk include trees, shrubs, herbs and woody vines.

Biodiversity Loss in Africa

Loss of biodiversity will be particularly problematic in tropical Africa, “a region of incredible diversity but with major social and political challenges and expected rapid population growth over the next decades,” said lead researcher Dr Thomas Couvreur, a botanist at The French National Institute for Sustainable Development.

The situation could get worse. As well as the species that are at risk of extinction, a further 33.2% of the species studied are rare and could potentially be threatened with extinction. Major threats to biodiversity, especially in areas of exceptional plant diversity, primarily in the tropics, are often linked to industrial-scale activities such as timber exploitation or large plantations, mining and agriculture.

Research projects such as these are vital; while almost 90% of mammals and two-thirds of birds have been assessed, less than 8% of plants have been assessed, a surprising find considering how crucial plants are to the Earth’s ecosystems. This lack of data is especially true for tropical regions, such as the ones found in Africa, where the flora is extremely diverse, but have been poorly documented. 

Biodiversity going extinct has a knock-on effect. For example, some of the plant species that the African forest elephant eat can only germinate by passing through the animal’s digestive tract. Without these tree species, the elephants cannot eat and without the elephants, the tree species cannot reproduce, further emphasising the need to preserve these ecosystems.

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Commiphora is listed as endangered in four regions of Africa, including Ethiopia. (Source: Vinayaraj)

This assessment process aims to provide information on the conservation status of large numbers of species, following the guidelines of Preliminary Automated Conservation Assessments (PACA). By using PACA, the entire flora of a given area can be assessed. This allows species, both at threat and requiring additional attention, to be identified. 

The new approaches used in the study also provide useful guidelines for others to follow; they reduce cost, time and increase the potential of carrying out large-scale assessments. This is important as information can be gleaned quicker and at a cheaper rate. 

Professor Bonaventure Sonké, Professor at the Laboratory of Systematic Botany and Ecology of the Ecole Normale Supérieure (University Yaounde 1, Cameroon), says that the results were possible ‘because the partners involved agreed to share their data’. He adds that this creates ‘a strong signal to encourage researchers to share their data’.

The importance of sharing data is being realised and there is hope that this collaborative approach will produce solutions quicker. However, it may not be quick enough. The UN Environment Programme says, “No continent will be struck as severely by the impacts of climate change as Africa. Given its geographical position, the continent will be particularly vulnerable due to its considerably limited adaptive capacity, which will be exacerbated by widespread poverty.”

Despite this, perhaps the immensity of the challenges facing the continent can be mitigated through new approaches such as the ones used in the study. Dr Covreur says that “this study is the first large-scale assessment of the potential conservation status of the tropical African flora, explicitly using the IUCN’s methodology. While the results of the study are concerning, it is important that more studies such as these are conducted, so that threats facing biodiversity can be ascertained and managed.”

Article 14 of the UN Convention on Biological Diversity explicitly states that environmental impact assessments (EIAs) should be conducted before implementing projects that could impact on biodiversity in an area. To reduce risks linked to environmental concerns, EIAs should identify adverse impacts by projects on biodiversity and indicate measures to avoid, minimise and offset these impacts. This process must be followed to ensure that the richness of these countries’ biodiversity is preserved. 

The first ever global analysis of plant extinction found that over 570 species of plants have gone extinct in the last 250 years. Researchers believe even these numbers underestimate the true levels of the ongoing extinction.

571 plant species have completely disappeared from Earth in the last 250 years- more than twice the number of bird, mammal and amphibian species to have gone extinct in the same period combined.

The extinction rate is 500 times greater now than before the industrial revolution. The study was conducted by a team of researchers at the Royal Botanic Gardens, Kew, and Stockholm University.

The pattern of extinction of plants is strikingly similar to that of animals, though it doesn’t seem to be based on evolutionary patterns, as it is with the latter.

The majority of plant extinctions occurred in biodiversity ‘hotspots’ in the Tropics and the Mediterranean, including places like Australia, India, and Hawaii. Of all the extinct plant species numbered throughout the world, half were once found on islands and 18 percent once flourished in the Pacific.

“This probably reflects the high proportion of unique species (endemics) in island biotas and their vulnerability to biological invasion,” the authors suggest. “Consistent with this, we found that extinct species have narrower ranges than seed plants as a whole. We also found that most extinct plants were woody perennials and from the wet tropics or subtropics.”

Why do plants go extinct?

Many new plant species might also be headed for extinction because of habitat loss, climate change, and human exploitation. Around a third of the 90,000 species the team analysed could be considered threatened in some way.

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The Saint Helena olive, Nesiota elliptica, first discovered in 1805. It went extinct in 2003.
Photograph: Kew Gardens

To reach these conclusions, the researchers scoured every journal and plant database at their disposal, beginning with a 1753 compendium by pioneering botanist Carl Linnaeus and ending with the regularly updated IUCN Red List of Threatened Species, which maintains a comprehensive list of endangered and extinct plants and animals around the world. After combining and cross-checking the various extinction reports, the team compared the results to the natural or “background” extinction rates for plants, which a 2014 study calculated to be between 0.05 and 0.35 extinctions per million species per year.

Despite the gloomy outlook for planet Earth, the study does provide a glimmer of hope. The team found that 430 plant species which were thought to have gone extinct were rediscovered in the period they investigated. However, it should be noted that 90 percent of these rediscovered plants have a high extinction risk.

Researchers called for a number of measures to stop plant extinction: recording all the plants across the world, supporting herbaria, which preserve plant specimens for posterity, supporting botanists who carry out vital research, and teaching our children to see and recognise local plants. “We urge botanists to compile data on search effort, species density, abundance and detectability and to engage local people in the search for their missing biodiversity.” the authors say. “Such efforts will improve our understanding of genuine extinctions and help target future conservation action.”

Featured image: An artist’s rendering of extinct plant Sigillaria

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