Trees and climate change - again

Carbon dioxide, methane, nitrous oxide and chlorofluorocarbons are the principal human-produced greenhouse gases in our atmosphere. Carbon dioxide, CO₂, is our planet’s most important greenhouse gas. CO₂ in the atmosphere is responsible for more than half the rise in global temperatures.

The amount of CO₂ in the atmosphere is still rising rapidly. Atmospheric CO₂ levels have been recorded at the Mauna Loa Observatory in Hawaii for more than 60 years. The latest results from Mauna Loa show that the monthly average of CO₂ in the atmosphere for March 2024 was 425·38 ppm. In March 2023 it was 420·99 ppm.

Atmospheric concentrations of CO₂ are rising mostly because of the fossil fuels, that we are still burning.

All plants absorb CO₂. They use it to produce oxygen (which we breathe) and carbohydrates (which the plants use for energy and growth). It would seem obvious then, that to slow global warming we simply need to plant more trees and that would certainly help but there are some provisos.

First, to plant enough trees globally to absorb enough carbon, it is estimated that an area equivalent to nearly one and half times the size of Australia would be required. It would have to be land that could support the growth of forests – not desert and not snow-covered peaks, etc. Much of the land would have to be arable land that is needed for farming to feed an increasing global population.

When a tree dies, or burns, its carbon is returned to the atmosphere. Planting huge numbers of new trees might mean more trees die, or burn, thus adding to the problem. Different forest types sequester different amounts of carbon. Where the trees are planted becomes important too – generally, tropical forests take up more carbon than forests in temperate zones.

United Nations Climate Action warns: “Ocean habitats such as seagrasses and mangroves, along with their associated food webs, can sequester carbon dioxide from the atmosphere at rates up to four times higher than terrestrial forests can.”

There are many unanswered questions and despite new research that suggest terrestrial plants absorb more CO₂ than we first thought, it is still agreed that we cannot plant enough trees to slow climate change without reducing our emissions.

 

Spotted Gums make great urban trees

The Spotted Gum, Corymbia maculata, is one eucalypt that is easy to identify. And yes, it is a eucalypt despite the ‘corymbia’ part of its scientific name – corymbia and angophora are now considered as sub-genera of the eucalypt group. Korymbus is Greek for bunches of flowers or fruit and maculatus is Latin for spotted.

Spotted Gums in Princes Way Drouin

The Spotted Gum is endemic to south-east Australia, from south-east Qld to southern NSW. There is a disjunct population near Orbost in Victoria.

Spotted Gums are frequently used for urban plantings. They are attractive, grow straight, easy to establish and they tolerate poor urban conditions and have few lower branches to obstruct views.

When Spotted Gums replace their bark each season, they do it in patches, giving rise to the recognisable spots that can vary from green to tan to grey over time. Spotted Gums often flower profusely, attracting nectar-seeking birds, insects and mammals. Their broad, dense canopies provide shade and shelter and add beauty.

Musk and Rainbow Lorikeets love Drouin's Spotted Gums

Once credited with being ‘limb-droppers’, Spotted Gum varieties are now bred to minimize this characteristic.

C.maculata can grow large. Old Blotchy, ‘the world’s largest Spotted Gum’ at Termeil in NSW is 59m tall, has a trunk girth of 10·7m and is estimated to be over 400 years old.

As urban planners look toward planting more resilient trees to help mitigate the effects of a warming world, they could do a lot worse than choose the beautiful and rewarding Spotted Gum.

Some introduced avian ‘pests’

The Friends of Drouin’s Trees is in the middle of its autumn bird surveys for 2024. This might be the time to investigate the history and habits of some of our introduced bird species we call ‘ferals’.

In the mid nineteenth century in Australia and New Zealand acclimatisation societies were established to introduce exotic animals and plants. The much-vaunted Ferdinand von Meuller, Victoria’s first government botanist, was alone responsible for ‘distributing’ thousands of introduced plants and seeds! In its short life of just 11 years from 1861 to 1872, the Victorian Acclimatisation Society played a devastating role in this state’s ecology.

SPARROW

The very cosmopolitan House Sparrow was introduced to Victoria in the late 1860s. This little bird thrives wherever there is human habitation – farms, granaries, school yards, town squares, etc. It is a very sociable and gregarious species. The House Sparrow competes with native birds for food and nesting sites. Many references suggest the sparrow is host to a large number of parasites and diseases.

STARLING

The scientific name Sturnus vulgaris is very appropriate for this boisterous and aggressive introduced bird. Starlings are native to northern Europe where they are a migratory species. Here, they seem to have lost the need to migrate and might perform some seasonal local movements only. Their preference for cavities in buildings and trees for their nesting sites is perhaps their worst feature. Starlings quickly drive away native birds that are hollow-dependent for their breeding regimes. They were introduced in the vain hope of keeping pest insects under control. English starlings were introduced in the eastern states from 1863 onwards.

MYNA

Mynas and starlings are related – they belong to the Sturnidae family. The Common Myna was introduced to Melbourne in circa 1860 to help control caterpillars in market gardens. They were only partly successful and soon spread to other areas as well as being ‘shipped’ to north Queensland to control pests in sugar cane. Mynas seldom occupy places with dense vegetation, preferring open areas of parklands, streets, back yards, etc. In 2000, the Common Myna was listed among 100 of the world’s worst invasive species by the World Conservation Union. A nation-wide survey in Australia in 2005 placed the myna at number one pest – ahead of the Cane Toad, rabbit, feral cat, etc. Like starlings, mynas aggressively defend their territories and nesting sites, driving off native birds.

DOVE

The Spotted Dove was introduced in Melbourne in the 1860’s principally for aesthetic reasons. Their native range is the Indian sub-continent and south-east Asia. Some references suggest the Spotted Dove is not a pest to the degree of others in this list. It is believed to have displaced the native Peaceful Dove in some districts but now itself is considered to be ‘under pressure’ from the native Crested Pigeon which seems to be expanding its range. When they drink they only need to place their bill in water. They sort of inhale the water, using their bill like a straw. Other birds need to lift their heads after they take a drink so they can swallow water, but not doves and pigeons.

BLACKBIRD

Pioneers to Victoria found the birdsong of the native species unfamiliar and alien. Wealthy early settlers regarded blackbirds to be a worthy addition to their European-style gardens, principally for their song. The bird quickly spread throughout the state. Even today it is pretty much the most abundant bird in Melbourne and although mainly found in urban areas it is not unusual to see blackbirds in native bushland settings these days. The Common Blackbird is thought to be the principal vector for the spread of the invasive species Sweet Pittosporum.

GOLDFINCH

The European Goldfinch is a small bird in the finch family that is native to Europe, North Africa, and western and central Asia. In Victoria it was introduced in several locations in the late nineteenth century. Apparently, many of these introductions failed, but now the bird is well established, particularly in ‘wasteland’ areas on urban edges. Overseas, the bird is often called the Thistle Bird because of its preference for the seeds of the thistle plant. Goldfinches like to line their nests with mosses, lichens and plant down from thistles.