Why Everyone Should Care About Invasive Plants

A land which could not be conquered by kings and rulers of the world is being invaded silently. India is the second-most floral invasive cost-bearing country in the world. Invasive alien plant species have cost India’s economy Rs 8.3 trillion over the last 60 years.

Let’s clarify a few important concepts of Native and Non-native species before we dive deep. Native species are those which occur or may occur in each area as a result of natural ecological processes. Plant species which are not natural to any geographical area are called non-native or alien species (alien as they arrive from a foreign region).

A Non-native plant species if starts spreading widely and causes adverse ecological and economic impacts, is called as invasive species. A non-native species may or may not become invasive to other ecosystems. One of the simple examples is Gulmohar tree ( Delonix regia). It has origin from Madagaskar, planted vigorously as ornamental tree in India but has not become invasive. But being a nonnative tree it has little ecological value and does not support biodiversity much.

Some nonnative trees are from similar geographical and climatic regions adapt to local conditions and after a long period of time, known as naturalized. it is still a nonnative species. Best example of this is Tamarind or Imli.  It is a nonnative tree to India, has African origin, but a naturalized tree in Indian conditions and not invasive.

Invasive species are threat to the native plant communities, they degrade soil and deplete local biodiversity. They create far reaching economical damage to the native ecosystems when they disturb and alter the ecosystems. Invaded ecosystems do not support the natural ecological cycles of ground water recharge, flood control, natural regeneration, nutrient recycling among others.

These non-native species have got a very attractive name somehow over time, which is also helping their spread. They are called as “exotic plants”. Exotic as per Oxford dictionary is “from or in another country” or “Alien” in other words.  But Exotic has another meaning which is “seeming exciting and unusual because it is connected with foreign countries like exotic locations. People have confused “Alien” with “Exciting” and a negative connotation “exotic” has become a positive one.  Let’s correct this.  If someone tells you it is an Exotic plant you must ask, “is it native”?

Let’s understand how invasive species get entry in any ecosystem. Natural disturbances like forest fires, long term droughts, flooding, landslides provide opportunities for invasive species to become established in any area, but human disturbances have proved to be biggest cause for invasive species spread. Making roads or construction activity in natural areas invite invasive species to establish there. Introducing of non-native species as ornamental plants is creating havoc in the natural world.

Once inside any ecosystem, non-native species spread fast as they have few biological controls to keep them in check. As they are not natural to the given area, they are not in the food menu of the native wildlife either. Successful invader species are so well adapted that they outcompete native species easily.

Multiple factors promoting the invasion of non-native plant species in Indian conditions are-

1. Degraded soil

As body lacks nutrients. it slowly loses immunity and catch disease. Similarly, when soil is low in carbon, Nitrogen, Phosphate or micronutrients, soil becomes weak and non- native plants invade them easily. With lots of chemicals in soil pumped over the years in India, our soil is severely degraded.

2. Disturbed areas

Alteration in natural conditions of any area, creates disturbances and open opportunities for invasive species. For example, a natural forest is cut across and a road is constructed. Invasive species starts coming up on both side of this road initially and then start spreading inside forests.

3. Introduction of non-native plant species as ornamentals

When a plant arrives in a new region due to direct or indirect human intervention, it is called introduced species. Most of the invasive species in India are “introduced species”.

Few mentionable introduced invasive species and are being planted as ornamental trees, which are degrading Indian forests are-

• Australian acacia (Acacia auriculiformis)
• Gliricidia sepium
• Lantana (lantana camara)
• Cosmos (Cosmos sulphureus)
• Copperpod (Peltophorum pterocarpum )
• Conocarpus species
• Water hyacinth (Pontederia crassipes)
• Prosopis (Prosopis juliflora)
• Eucalupts species
  

4. Changing climate

Changing climate is bringing changes like increased temperatures, uneven rainfall, increased floods etc which are responsible for change in natural conditions of many regions and thus opening opportunities for invasive species.

5. Habitat destruction

Clearing or fragmenting forests, cutting hills, flattening undulating land, and altering natural conditions in other ways lead to loss of native vegetation, loss of biodiversity and is open invite for invasive species.

An invasive plant has the ability to thrive and spread aggressively outside its natural range. A naturally aggressive plant may be especially invasive when it is introduced into a new habitat. An invasive species that colonizes a new area often has an ecological advantage because the insects, diseases, and foraging animals that naturally keep its growth in check in its native range are not present in its new habitat.

Let’s try to understand what the invasive plants do, when they gain entry in any habitat.  Few of the disturbances caused by non-native invasive plants includes-

1. They radically alters the light, temperature, and soil chemistry destroying the ecological balance between plants, animals, soil, and water achieved over many thousands of years
2. Invasive species outcompete and displaces native plant species. They displace native plants by robbing moisture, nutrients, and sunlight, resulting in declines in habitat and food sources.
3. Loss in native grasses and shrubs leads to insects and herbivore decline in and then decline in top predators of the ecosystem. Eventually the ecosystem gets devoid of any biodiversity.
4. Invasive species are aggressive and competitive, and, in newly invaded areas, they lack sufficient predators from their native range, or local-occurring natural predators, to effectively control them.
5. These can interbreed with native plant species and dilute native gene pools and
6. Alter cultural landscapes, and excessive growth can threaten the integrity of historic and cultural sites and structures.
7. Few of these invasive species like conocorpus are known to cause health hazards. Adverse effects of the species’ pollen can lead to colds, coughs, asthma and allergies among individuals.

Not all invasive plants behave identical, some are worse than others. Many invasive plants are admired by gardeners or landscapers who may not be aware of their invasive nature. Others are recognized as weeds but are difficult for landowners to control. Some do not even become invasive until they are neglected for a long time. Some aggressively colonize only small areas. Others may spread and eventually dominate large areas in just a few years.Australian Acacia (Acacia Auriculiformis) invading western ghats, replacing native trees

Picture from Karnataka (2023)

Australian Acacia (Acacia Auriculiformis) invading western ghats

Picture from Northern Kerala (2024)

Australian Acacia (Acacia Auriculiformis) Planted along the roadside

Picture from Goa (2023)

Conocarpus Planted along the highway

Picture from Andhra Pradesh ( 2022)

Australian Acacia (Acacia Auriculiformis), Invasive species planted on road median on NH 66 ( 2022)

Invasion of Cosmos plant, replacing native grasses and shrubs

Picture from Outskirts of Pune (2023)

The problem of exotic tree species spread in India is mainly from unawareness and carelessness. Nurseries spread all over the country grow and keep these nonnative trees. These are sold out without the awareness of their toxic nature and effects.

Plantation along the roads and highways are carried out throughout the country but without the ecological knowledge. Nonnative and invasive trees are planted by contactors thousands in numbers.

Sprouting multi storied societies all over the country plant few trees in the society green space. Most of the times these are nonnative and invasive species planted as ornamentals.

Farmers near urban periphery plant nonnative, invasive species around their farms unknowingly. Forest departments have history of planting invasive trees in degraded areas as they grow fast.

Most of these plantations are catering to the need of growing trees fast in a shorter time.

Fast growing trees enable the grower to showcase the area as “Green” in no time. These small initiatives, spread all over the country, collectively make daunting impacts on natural world.

Let’s try to find solutions on how we can stop or minimize this destructive cycle on our level-

1. As an individual, or member of a society, a contractor or associated with any decision maker body always inquire about what species are being planted and in which ecosystem.
2. Whenever planting trees, always consult with a person who knows about native local trees.
3. In local nursery ask for native plants only. This way you are creating demand of native species and letting nurseries know that it is beneficial for them to know about native and nonnative trees.
4. Ask landscape architects to include native trees in their planting plans only.
5. Search or read online, if you are not sure about native distribution of any tree species.

For whatever reasons nonnative trees are being planted, lets try to stop this ecological destruction. If someone needs fast growth, there are many beautiful Indian (native) trees which grow fast like Gmelina arborea, Michelia champaca, Albizzia lebbek, Erythrina suberosa, Trema orientalis, Cordia dicotoma etc.

If anyone wants flowering trees as ornamental or as avenue trees, there are many beautiful Indian (native) flowering trees like Cassia fistula, Mimusops elengi, Saraca asoca, Lagerstroemia indica,

Trees which grow fast, need less water, are drought tolerant, are resistant to fire, for every region, for every terrain we have native Indian trees. The advantage of using native trees for planting is that they help the soil, the ground water, the ecological cycles, support biodiversity and ultimately help us.

PS. If you need help in identifying any tree as native/ nonnative or to ensure that if it is good for planting in any region, we will be happy to help always.