Alien Plant Invasion Threatens Tropical Biodiversity
Recent studies reveal a rapid spread of alien plant species across tropical ecosystems. This invasion is altering native flora and destabilising rich biodiversity. Climate change and human actions accelerate this trend. The Greater Tropics, home to most of Earth’s biodiversity and a billion people, face serious ecological and economic risks. Urgent research and restoration efforts are needed to address these challenges.
Scope of Alien Plant Invasion
Alien plants are species introduced outside their native regions by human activity. Since the 1950s, their spread has increased exponentially. Currently, about 4% of plant species globally—between 13,939 and 18,543—exist beyond their original ranges. In the Greater Tropics, nearly 9,831 alien plants are established. Islands are particularly affected, with some having more alien than native species. Examples include Guam with 66.5% and Tahiti with 73.8% alien flora.
Drivers of Invasion
The invasion is driven by human mobility, land use changes, and climate change. Moderate climates with high productivity and human disturbance see more invasions. Species like Lantana camara and Chromolaena odorata thrive in such conditions and spread widely. Land use changes in India, including agriculture and settlements, have altered fire and grazing patterns, enabling invasive species to cover 66% of natural areas.
Impact on Ecosystems and Biodiversity
Alien plants replace diverse native ecosystems with simpler, homogeneous ones. This reduces biodiversity and ecosystem resilience. In the Amazon, invasive grasses increase fire risks, causing forest dieback. This degradation disrupts native species and turns forests from carbon sinks into carbon sources, worsening climate change. Similar patterns occur in savannas and open forests, where woody alien species intensify fires and promote further invasions.
Interactions with Native Species
Alien plants affect native species in complex ways. For instance, Prosopis juliflora in India reduces native forage but supports blackbuck during dry seasons. These herbivores help disperse the alien plant, worsening native plant loss. Native species can also become invasive within regions, complicating ecosystem dynamics. Rising CO2 levels facilitate woody thickening, further changing habitat structures.
Economic and Social Implications
Controlling invasive plants is costly. India alone may need about US$13.5 billion, 36 times its current environmental budget, to manage invasions. The livelihoods of billions depending on tropical ecosystems are at risk. Alien plant invasions threaten food security, forest resources, and biodiversity-based economies, especially in the Global South.
Call for Research and Restoration
Experts urge long-term, interdisciplinary research to understand and mitigate impacts. Strengthening community awareness and documentation is vital. Restoration of native ecosystems must be prioritised. Coordinated global and regional efforts can help reduce the spread and protect tropical biodiversity.
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