What makes us uniquely Canadian?  That is a vast topic, for different bloggers to tackle.

In terms of wildlife, however, and more specifically plant wildlife, our interest was piqued by a recent CBC article profiling research called “Ours to Save.” The study apparently achieved a Canadian first.

As the report’s authors and sponsors describe, “NatureServe Canada and the Nature Conservancy of Canada (NCC), in consultation with experts from across the country, have developed the first comprehensive list of plants, animals and fungi that can only be found in Canada.”

This select group of 308 of Canada’s “nationally endemic species” occur only in Canada.

The report systematically identifies wildlife species and sub-species that are unique to each province and territory, and flag more than 200 vulnerable species that “only Canada can save from extinction”.

Here we will keep our focus on the findings related to plant wildlife, illustrating example species and profiles of provinces and territories.

The authors hope that, “The results of this project can be used to prioritize conservation actions and to inspire public support for species and habitat protection in Canada.”

Readers who want to learn more about a specific region, and/or the other wildlife addressed in the study (e.g., animals, insects) may read the full report (75 pages) here  https://bit.ly/2MGZVQq, and species profiles at https://bit.ly/3h95bKT.

Endemic Plants

“There are 109 nationally endemic plants in Canada. Almost 60% are full species and the remainder are subspecies and varieties. Only 12 are ranked by NatureServe as globally Secure or Apparently Secure. These secure plants include species with restricted ranges that are abundant and not threatened, such as Ogilvie Range Locoweed (Oxytropis nigrescens var. lonchopoda) in Yukon, and species that are more widespread but their global range is restricted to Canada. This includes Limestone Scurvygrass (Cochlearia tridactylites) and Limestone Willow (Salix calcicola var. calcicola).”

“Endemic plants occur in every province and territory, with BC and Quebec having the greatest number. The territories, Newfoundland and Labrador, and Saskatchewan are also relatively rich in endemic flora. Key areas for endemic vascular plants in Canada include the Athabasca Sand Dunes, coasts of the Gulf of St. Lawrence and St. Lawrence River freshwater estuary, islands of Canada’s West Coast, mountainous regions in Yukon and limestone plains on the island of Newfoundland.”

“Canada has 14 species of mosses, liverworts, lichens and fungi that are nationally endemic. Only one of these is a subspecies. All are of global conservation concern or are Unranked. These species occur across the country, including a beard lichen (Usnea fibrillosa) endemic to Nova Scotia, Slender Notchwort (Crossocalyx tenuis) endemic to Ontario and Carlott’s Wijkia Moss (Wijkia carlottae) endemic to Haida Gwaii.”

Example Endemic Plant Species Profiles

“Lake Louise arnica” is a small, perennial herbaceous plant in the sunflower family, named for Lake Louise in the Canadian Rockies.

This species’ pale-yellow colour and drooping shape help distinguish it from similar arnica species in the region.

Lake Louise arnica is unique to Canada and is found only in the Canadian Rockies of Alberta and BC. It grows in alpine meadows and on rocky, exposed slopes at high elevations.

This species is globally imperiled with observations in only about 20 locations.” https://bit.ly/37fG04E

“The Gulf of St. Lawrence Aster is a fleshy annual plant with clusters of small, white to pinkish flowers.”

“Its leaves are lance-shaped and range from 1.1 to 6.5 centimetres in length and from two to 9.8 millimetres in width. The tip of its leaves is slightly rounded.”

“Gulf of St. Lawrence aster produces dry fruits, called achenes, with silky tufts, which help the seeds to be dispersed by wind. This plant is also self-fertile and can reproduce on its own without other plants.”

“There are only 29 known populations of this species, whose range is limited to Quebec’s Magdalen Islands, New Brunswick and Prince Edward Island.”

“This species grows on moist sandy soils. It can be found on coastal habitats: beaches, dunes, lagoons and dry areas in salt marshes.”

“The Gulf of St. Lawrence aster is assessed as threatened by the Committee on the Status of Endangered Wildlife in Canada.”

“Hairy braya was first collected during the Franklin expedition in 1826. Journals from the expedition were used to relocate this wildflower more than 150 years after its discovery. It is restricted to a small area along the northern coast of the Northwest Territories and is highly threatened by climate change and rising sea levels.”

Yukon draba: This delicate, white wildflower lives in dry open meadows in southwestern Yukon and is restricted to just a handful of sites. It is a relic of the land bridge that stretched between Russia and the Yukon during the last Ice Age.

Example Profiles for Provinces and Territories

The following  excerpts give an illustrating flavour of the way findings are reported for each province and territory.

“Alberta has 54 nationally endemic species — the third highest in Canada (behind British Columbia and Quebec). Fifteen of these are subspecies or varieties, and four species have unresolved taxonomic questions. Alberta’s nationally endemic species include 16 vascular plants and two species of tiger beetles. Alberta also includes a portion of the breeding habitat for Whooping Crane (Grus americana) in Wood Buffalo National Park.”

Most Canadian endemic species occurring in Alberta are associated with the Rocky Mountains, Lake Athabasca and Cypress Hills. Many of the Rocky Mountain endemics can be found in Banff, Jasper and Waterton Lakes national parks and surrounding areas. Lake Louise Arnica (Arnica louiseana) is a colourful wildflower that can be found on exposed alpine slopes and calcareous rock slides at high elevations. There are also a few nationally endemic species that occur in the prairie region of the province. This includes Margaret’s Diving Beetle (Agabus margaretae), a predaceous beetle that only lives in vernal ponds in the northern prairies of Alberta and Saskatchewan.

“British Columbia has 105 nationally endemic species. This is the highest in all of Canada and represents over one-third of Canada’s nationally endemic species. This includes 36 subspecies or varieties, and five species with questionable taxonomy. Over 70% of the nationally endemic species from BC are vascular plants and invertebrates. The province holds the vast majority of Canada’s endemic mammals and birds. There are 76 nationally endemic species found only in BC, by far the highest number in Canada. Many of these occur on Vancouver Island, Haida Gwaii and other islands that probably acted as refugia during the last period of glaciation. Vancouver Island and Haida Gwaii both have several endemic mammals and birds including Vancouver Island Marmot (Marmota vancouverensis), Vancouver Island Water Shrew, (Sorex navigator brooksi) Queen Charlotte Hairy Woodpecker (Dryobates villosus picoideus),Queen Charlotte Pine Grosbeak (Pinicola enucleator carlottae), and several subspecies of the Townsend’s Vole (Microtus townsendii) (Cornely & Verts, 1988).”

“For its size, Nova Scotia has an extraordinary richness of nationally endemic species. Twenty-eight species have been documented, a richness similar to larger regions, including Ontario, Manitoba and Nunavut.”

“Over 40 percent of the national endemic species found in Nova Scotia do not occur in other jurisdictions (Table 11). This percentage of subnational endemics is only greater in British Columbia and Yukon.”

“Nunavut Canada’s largest territory has 29 nationally endemic species. This includes 13 subspecies or varieties.”

“Five Canadian endemic species are found only in Nunavut (Table 12), including two butterflies. Johansen’s Sulphur (Colias johanseni) is only found on the dry tundra at Bernard Harbour in Nunavut. Rankin Inlet Sulphur (also known as the Kivaliq Sulphur) (Colias rankinensis) is more widespread and has been recorded in several locations across mainland Nunavut (Schmidt, 2018).”

“Ontario has a total of 28 endemic species. One-third are subspecies or varieties, and three species have questionable taxonomy. Most nationally endemic species found in Ontario are vascular plants and invertebrates. Nine of Ontario’s endemic species are entirely restricted to the province (Table 13). These species include a small scavenger beetle (Hydnobius autumnalis) that is only known from eastern Ontario; Slender Notchwort (Crossocalyx tenuis), a liverwort that has only been found on the Bruce Peninsula and Eugenia Falls on the Niagara Escarpment; a lichen (Myriolecis carlottiana) that only occurs on the Bruce Peninsula and Manitoulin Island; and Cain’s Screw Moss (Syntrichia cainii), that is restricted to alvars. The only other moss species restricted to Ontario is now believed to be extinct. Macoun’s Shining Moss (Neomacounia nitida) was first found in 1864 in elm and cedar swamps near Belleville and has only ever been known from those original collections. The original site had been cleared by 1892, and this moss has never been found again despite searches in 1972 and 2001 (COSEWIC, 2002).”

“Quebec has 57 nationally endemic species, the second highest number in Canada. This includes 17 subspecies or varieties, and six species have questionable taxonomy. Over 40% of the nationally endemic species from Quebec are vascular plants and seven are butterflies or moths.”

Which Trees are Best for Reducing Air Pollution?

We are often asked which trees are “best” for climate action.

This May 2020 article in the BBC highlights research findings by “Future Planet” on this question, which to no surprise involves many variables and as such, is complicated to answer.

Nonetheless – our topline take-aways, for Readers who want to cut to the skinny – conifers and low-VOC (volatile organic compound)-emitting trees.

The article starts by giving us examples of urban tree projects intended to help reduce air pollution, with the reminder that of course it is always better “to reduce emissions of pollutants in the first place.”

“Trees have a remarkable range of traits that can help reduce urban air pollution, and cities around the world are looking to harness them. In January 2019, the mayor of London announced that 7,000 trees would be planted before the end of the following year. Meanwhile, China’s Hebei Province, home to Beijing, has been working on a “green necklace” of plants that could help reduce pollution from factories that surround the capital. And Paris is planning an urban forest that will encompass its most iconic landmarks in an effort to adapt to climate change, and also improve the city’s air quality.”

Ecosystem’s “Lungs” and “Liver”

“Trees can improve air quality in direct and indirect ways. Indirectly, they can help by shading surfaces and reducing temperatures. If buildings are shaded by trees, it reduces the need for conventional air conditioning, and the emissions of greenhouse gases that come with it. Plus, lower temperatures decrease risk of harmful pollutants like ground level ozone that commonly spike on hot days in urban areas.”

“But trees also play a vital role in directly removing pollutants from the air. Plants are often seen as the “lungs” of an ecosystem because they absorb carbon dioxide and emit oxygen, says Rita Baraldi, a plant physiologist at the Institute of Bioeconomy of the Italian National Research Council. But they also act as an ecosystems “liver” too, filtering atmospheric pollutants like sulphur dioxide and nitrogen dioxide through their leaves.”

“Trees are particularly effective at removing particulate matter (PM), Nowak adds. PM comes in the form of tiny particles of organic chemicals, acids, metals and dust, emitted from fossil-fuel-burning vehicles and factories, as well as construction sites.” 

“Fine particulate matter can easily penetrate into human respiratory system, causing lung and cardiovascular diseases or exacerbating respiratory illness. It has also been linked to inflammation and heart disease. By one estimate, 8.9 million deaths a year globally could be attributable to exposure to outdoor fine particulate matter.”  Trees matter!!

Clearing the air

Our top line take aways: Trees help reduce air pollution through dispersion and deposition of particulate matter (PM). Bigger tree canopies and leaf types with rough, rugged hairy surfaces are the best filters. Silver birch, yew, elder trees, silver maple, honey locusts and conifers, like pines and cypresses, are the most effective. Urban planners are advised to favour conifers and deciduous trees that are low producers of volatile organic compounds (VOCs).

“From an urban planning perspective, plants act as a readily available set of PM purifiers. “Trees can help reduce PM in two main ways,” says Prashant Kumar, the founding director of the Global Centre for Clean Air Research at the University of Surrey.”

“The first one is dispersion – by crashing into trees and plants, concentrated clouds of minuscule particles get dispersed and so diluted by the air, decreasing the risk of inhalation by humans. The second one is deposition. PM can easily get trapped in the waxy, hairy leaves of trees and shrubs. When it rains, most of these particles are washed away by water into drains.”

“The extent to which each species performs such filtering activity depends mostly on canopy size, leaf size and leaf structure,” says Baraldi. Bigger canopies can trap more particles than smaller ones, and larger leaves can trap more pollutants than small ones. When it comes to leaf type, it is those with rough, rugged and hairy surfaces that act as the “best filters” for PM.”

“Recent research suggests that tiny hairs on plant leaves in particular may play a big role in trapping the solid and liquid particles that make up PM. In one recent study, Barbara Maher and colleagues at the University of Lancaster tested the ability of nine tree species to capture PM in wind-tunnel experiments. Silver birch, yew and elder trees were the most effective at capturing particles, and it was the hairs of their leaves that contributed to reduction rates of 79%, 71% and 70% respectively. In contrast, nettles emerged as the least useful of the species studied, though they still captured a respectable 32%.”

Alpine air

“Conifers, like pines and cypresses, are also good natural purifiers. In 2015, Jun Yang, an urban ecologist at the Center for Earth System Science, Tsinghua University, in Beijing, ranked the most frequently occurring species in cities based on their PM 2.5 absorption capacity. The ranking also took into account species’ ability to survive in urban contexts, and any negative impact on air quality, such as the production of allergens, and of volatile organic compounds (VOCs) – a set of substances that can interact with gases emitted by vehicles, like nitrogen dioxide. In the presence of sunlight, these reactions can contribute to ground-level ozone, which is harmful to human health. The effects can be considerable; when a heatwave hit Berlin in 2006, the ozone created by the interaction of plants’ VOCs and vehicles’ pollutants resulted in sudden decreases in air quality.”

“To Yang’s surprise, his ranking system showed that the most widespread species of trees were not the best pollution filters. “Of the 10 most recurring species, only the London plane, silver maple and honey locust ranked above average,” he says. It was conifers, such as pines and cypresses, that were the best pollution filters. Planting conifers, Yang concluded, would make most sense in polluted cities like Beijing to reduce PM2.5s. The Chinese capital routinely reports PM levels above 125 micrograms per cubic meter, more than 10 times greater than World Health Organization recommended threshold of 10 micrograms per cubic meter.”

“The reason for conifers’ success in reducing PM is partly down to their canopy structure – the dense canopy of needle-like leaves typical of conifers is very effective at trapping pollutants. And their seasonal biology helps too. “Conifers offer the best PM reduction because they are an evergreen species,” Nowak says. Unlike deciduous trees, who lose their leaves during winter, evergreen species act as year-round filters. “But that does not automatically make them fit for any context.”

“The issue with conifers, Nowak says, is that many species can be very sensitive to salt levels in soils, which tend to be high in urban areas especially where salt is used to de-ice roads. Compounding the issue, conifers’ year-round canopy can block sunlight from melting snow and ice, which can lead to road traffic problems in cities subject to cold temperatures, Nowak notes. These two drawbacks to conifers were also cited by Yang as caveats to be considered in his recommendations.”

Troubling trees

Our top line take aways: Overall, favour year round canopies offered by conifers, especially conifers with low-production of volatile organic compounds (VOCs) such as hemlocks and junipers and low-VOC deciduous trees like elm, horse chestnuts and basswood.

“Some deciduous species can also come with side-effects, Nowak says. For example, trees commonly found in cities of the northern hemisphere – such as poplars or black gum trees – can emit high levels of VOCs.

“Ideally, you want to be able to identify species that can maximise PM absorption but minimise ozone-precursor production,” says Margarita Préndez, an organic chemist at the University of Chile, who has studied how different species affect air quality in Santiago. Nowak cites conifers like hemlocks, junipers and deciduous trees like elms, horse chestnuts and basswood as examples of low-VOC plants.”

“Based on data from Santiago and other Chilean cities, native trees emit fewer VOCs than non-native trees,” Préndez adds. In Santiago, non-native species like the Prunus and the London plane tree can produce up to 30 times more VOCs than native species.”

“But this rule might not apply everywhere, and Yang says that you can’t generalise when it comes to endemic versus introduced trees. “Some of the best species for air pollution reduction are non-native,” he says. “We should not rule them out for ideological reasons.”

Which trees, where to plant them?

Our top line take aways: Seek expert guidance on which trees to plant and where to plant them to maximize tree benefits for improving urban air quality. It is complicated. Fortunately , there is an expert report to guide urban planners, by the Global Centre for Clean Air Research, University of Surrey, called, “Implementing Green Infrastructure for Air Pollution Abatement: General Recomendations for Management and Plant Species Selection”. The document “summarizes best practice regarding Green Infrastructure implementation for improved urban air quality and reduced pedestrian exposure to air pollution. Generic (i.e. not site-specific) recommendations are offered for typical urban environments.”

“It’s a finely balanced business to find the right trees for a city. But that’s just the start, says Nowak. The next question is where to plant them.”

“Many well-meaning schemes have suffered because of poorly planned planting. “Some cities like Beijing and Mexico City have planted trees pretty far from the city centers,” says Rob McDonald, lead scientist at The Nature Conservancy. ‘That may not be that beneficial.’”

“McDonald, who works with municipal governments to manage urban forests, says that as a rule of thumb, trees need to be planted close to where people – and sources of pollution – are.”

“And as wind direction and landscape structure can affect the way pollution moves, trees need to be planted accordingly, Nowak adds. In narrow streets surrounded by tall buildings, like those of downtown Manhattan, airflow can trap pollutants close to the ground. Planting tall trees with big canopies can make matters worse in this situation by preventing the pollution from dispersing. A recent tree planning scheme in Beijing ended up trapping pollution in certain areas, partly for this reason.”

“Kumar and his team recently issued specific recommendations for urban planners on this point. Hedges or green walls are generally to be preferred to trees in narrow streets flanked by tall buildings. While on broad roads surrounded by low-rise buildings, like those typical of the American suburbs, air can flow more freely so there is less risk of trapping pollutants, making both trees and hedges viable options. Examples of roadside hedges that work well include viburnum, red tip photinia, privet and bay laurel, Baraldi adds.”

“Ensuring biodiversity is also essential, even if one tree species is a standout winner in terms of its pollutant-trapping abilities. Kumar recommends that no more than 5-10% of an urban forest should be made of the same species or family. And a final factor that Nowak notes is that one should be realistic about maintenance and lifespan – plants that require little attention and that will last several decades are to be preferred.”

Implementing Green Infrastructure for Air Pollution Abatement: General Reccomendations for Management and Plant Species Selection – full report https://bit.ly/30qWUMb.

To access the full BBC article on Best Trees to Reduce Air Pollution (May 2020), that is the main source for this Blog post, see https://bbc.in/2XJuR94.