- Decalonbathus peltatus is listed as an invasive species
- It is a widespread Indo-Pacific species found in Africa, Asia, Australia and the Pacific
- Even though it is native, many countries try to unsuccessfully eradicate it
- Samoan research shows that leaving it alone helps the rainforest regenerate
- Find out why
Decalobanthus peltatus formally known as Merremia peltata is a very common vine with large leaves in the rainforests of Far North Queensland. It is in the same family as the sweet potato and morning glory.
Decalobanthus peltatus is a widespread Indo-Pacific species found from Madagascar and Tanzania in Africa, across the Indian Ocean to South East Asia, down though Indonesia, Papua New Guinea and across the Pacific to Tahiti. Joseph Banks collected samples in Tahiti in 1769. Sydney Parkinson, the botanical artist on the Endeavour, painted the elegant picture depicted above.
It is a pioneer species that quickly grows over rainforests that have been damaged by clearing or cyclones. It an edge specialist, so it can often be seen on the edge of rainforests, especially roadsides or where rainforests adjoin cleared land.
Decalobanthus peltatus is a classical example of a misunderstood plant. It is listed internationally as an invasive species because of the way it rapidly grows and colonises disturbed rainforests. It is believed that it smothers and strangles the rainforest trees eventually killing them. Despite being a native species, several countries spend huge amounts of money on herbicides and wages to eliminate it with no evidence of success.
In Australia it is not treated as an invasive weed because it is a native species. It is seen as a natural part of the environment even if it is believed by some to be strangling its host trees. In Samoa they researched allowing nature to take its course when it grows over cyclone damaged forests and cleared land. They found that a ground cover of Decalobanthus peltatus suppresses most non-native invasive species. Very importantly, the research showed when it grows up into the canopy, instead of smothering and killing the trees, as previously assumed, it assisted succession from the pioneer species, which first come up in degraded rainforests, to primary rainforest species. Decalobanthus peltatus rather than damaging the forest, was actively assisting it to regenerate from secondary regrowth to a primary rainforest. Over time as the primary forest regenerates and matures, Decalobanthus peltatus becomes one of hundreds of species instead of overtaking it.
So why, when it is obvious that Decalobanthus peltatus grows over the tops of the rainforest trees and looks like it is smothering them, it is in fact assisting the rainforest to regenerate?
To solve this problem we need to understand how and why the misconception over the roles and function of this species were formed.
The Samoan experience is in stark contrast to the failed eradication campaigns of other countries, such as Vanuatu. Those eradication campaigns are based on the simplistic notion that weeds outcompete other species. People see a huge vine overgrowing a forest and assume it will outcompete and strangle the forest.
These types of data free assumptions about many weeds and invasive plants are the result of the widespread misinterpretation of the notion of survival of the fittest – where the strongest species will out-compete and dominate the ecosystem to the detriment or exclusion of other species.
Darwin used the term ‘natural selection’ however, later adopted the concept of ‘survival of the fittest’ which was coined by Herbert Spencer, a social scientist in 1852. In Darwin’s concept, the fittest is not the strongest or the most competitive species that dominate and prosper. The fittest meant that the species that had special and unique adaptations to the environment were more enabled to evolve and survive. Survival of the fittest morphed into competition theory, where only the strongest dominated through competitive exclusion. It is often portrayed as a violent struggle where the strongest and the most aggressive are the winners.
Competition theory has roots in the reductionist school of science, based on Ockham’s razor. The concept came from an English Franciscan friar William of Ockham (1287–1347) where all systems are reduced to the simplest model to understand them. This further evolved into Cartesian reductionism based on the philosophy of René Descartes (1596 – 1650), a French philosopher, mathematician, and scientist. Cartesian reductionism essentially reduced the understanding of systems to simplistic mechanical equations. It is a useful scientific method and has been very important in the development of our modern civilization.
Ockham’s razor and Cartesian reductionism are incorrect when applied to complex systems. Some examples are: designing software systems for computers, understanding how the immune, metabolic and hormone systems contribute to homeostasis, and understanding ecosystems.
Competition theory is a gross misinterpretation of Darwin’s original concept of natural selection. The concept of competition theory has been used and misused as the basis of the evolution of species, politics, controlling societies, racism, genocide, free markets, economics, ecosystems and weed eradication.
Competition theory based on the concept strongest and the most aggressive species outcompeting the others in an ecosystem is incorrect. Complex rainforests are excellent examples. They should not exist under this theory as a single species or a few of the most competitive species would have outcompeted and dominated all the other species.
Competition theory is being replaced with the new and evolving science of whole-of-systems approach that looks at the importance of the complexity of natural systems.
This whole-of-systems concept uses multiple sciences to understand how ecosystems operate over long time periods – decades, centuries and millennia. They include using botany, microbiology, entomology, biology, wildlife dynamics, epigenetics, anthropology and other sciences to understand how complex systems interact over time.
As an example the new science of epigenetics shows how all living organisms are exquisitely sensitive to changes in the environment and that the adaptation to these changes can be passed on to future generations. This gives living species the ongoing ability to actively adapt to constantly changing environmental conditions. The science of epigenetics did not exist when Darwin published his ground breaking research. His theory was reasonable based on the state of science at that time. However science has moved on considerably since then.
The reductionist model has led to many misconceptions, especially when managing the complex systems like the natural environment or farming systems. It is now being replaced with ecosystems analysis that look at the system as a whole composed of numerous complex and dynamic parts that interact in multiple ways over time such as through competition, mutualism and synergy.
Mutualism and synergy are critically important to understand the true dynamics of an ecosystem. The old competition theory is based on the belief that when a new species is introduced to a system it will now compete with the existing species for space and resources, causing problems for them. Current weed management is still based on this outmoded reductionist concept, where competition is used as the single criteria based on the belief that weeds/invasive species will outcompete the desired plants for water, nutrients, sunlight and space therefore lowering crop yields or outcompete and/or kill/displace the native species.
The ecological whole-of-systems approach shows that the interaction of the new species can be based on a range of dynamics such as mutualism. This is where it brings benefits to crops or native species. It becomes mutually beneficial to have both of them growing in the ecosystem and instead of displacing other species they can assist in increasing the number of species in the ecosystem. Regenerative agriculture is now applying these concepts to a whole suite of practices such as cover cropping, intercropping and polycultures to replace the dominant paradigm of monocultures with great success.
Synergy is where the benefits of species growing together are much greater than if one species was on its own. The sum is greater than the whole. Coral is an example of synergy. The coral polyp builds a home for itself and to host zooxanthellae. The zooxanthellae uses photosynthesis to produce glucose that it feeds to its host. This in turn creates habitat for numerous other species and the basis of the coral reef system being some of the most diverse habitats on our planet.
Coral bleaching occurs when the zooxanthellae are stressed by either by excess heat causing it to vacate the coral polyp, when turbid water and/or algal overgrowth due to excess soluble nutrients stop photosynthesis or herbicides causing the zooxanthellae to die. The coral polyps will eventually die due to lack of glucose, killing the reef. This in turn damages the whole habitat causing a decline in all the other species dependant on the reef.
The new understanding of forests is that they are complex dynamic systems mediated by the soil microbiome. All terrestrial ecosystems are dependant on the soil, however the ecology of the soil is largely ignored when analyzing and managing ecosystems.
The soil microbiome is composed of trillions of microbes and other soil species such as worms, beetles etc. It is the region of greatest biodiversity on the planet. A spoonful of healthy soil can contain billions of species. The highest concentration of microorganisms is found around the roots of plants. This region is called the rhizosphere. The reason for this is similar to the synergy of coral polyps and the zooxanthellae. Living plant roots excrete organic molecules made from glucose to feed these organisms. These organisms have multiple roles that benefit the plants. They make the soil minerals available to plants, they protect their host from pests and diseases, they build soil structure and fertility, they improve soil water holding capacity as well as soil aeration and multiple other benefits. The multiple benefits of the soil microbiome and its interaction with plants will be explored in further articles.
Most pioneer plant species have this role. They produce the organic molecules, through photosynthesis that feed the soil microbiome and increase soil organic matter, regenerating soil health thereby providing multiple ecosystem services to allow the regeneration of the ecosystem.
Decalobanthus peltatus needs to be understood through this lens, rather than the reductionist competition theory lens. The massive leaf area of this fast growing species produces huge amounts of glucose through photosynthesis to feed the soil microbiome via its roots to regenerate soil fertility and health. This benefits of all the species in the system.
Another important lens is how it shades out the shorter lived pioneer species that need full sun, rather than the longer lived primary forest species that can either tolerate being partly shaded under a canopy or are fast growing emergent species. Many weed species tend to be short lived pioneer species and this is why the Samoan research showed that it could control most of these.
The massive leaf area of this fast growing species produces huge amounts of glucose through photosynthesis to feed the soil microbiome via its roots to regenerate soil fertility and health. This benefits of all the species in the system.
The other lens is to observe it over long time periods, decades, to document how it effects the forest and interacts with other species in that time. This is what they did in Samoa, rather than assuming it would out-compete the other species. These lenses show why its role in regenerating disturbed ecosystems is so important.
The experience in Samoa shows that left alone Decalobanthus peltatus actively helps the disturbed rainforests to regenerate and over time it becomes just one of the many species in contributing diversity and ecosystem services to these dynamic and diverse ecosystems.
ABOUT THE AUTHOR / André Leu is the International Director of Regeneration International, a global NGO that promotes food, farming and land use systems that regenerate and stabilise eco systems, climate systems, the health of the planet and people. He, along with the other founders of Regeneration International, started the world wide regenerative farming movement. André is the Author of the ‘Myths of Safe Pesticides’ and ‘Poisoning our Children’. He is the co-author with Dr Vandana Shiva of ‘Biodiversity, Agroecology, Regenerative Organic Agriculture – Sustainable Solutions for Hunger, Poverty and Climate Change’. André first came to the Douglas Shire in 1971 and has, with his wife Julia, an organic tropical fruit farm in Lower Daintree.