Controlling Alien Species
By Jennifer Holmes

Controlling Alien Species

IPBES 2023 report: What have plants got to do with it?

We asked marine scientist and ecologist Eloise M. K. Holmes Msc. Bsc. for her thoughts on the latest report on alien species. Here she unpicks the key takeouts and points to the ‘winning strategy’.


In their recent report, IPBES warn that invasive alien species can take control of “people, economies, water security, human health and food supply”. Following our previous blog, here’s how plants factor in to the “dramatic and, in some cases, irreversible changes” being inflicted on nature globally [1].

A global overview

Invasive species drive 60% of extinctions worldwide, yet current policies to manage biological invasions are insufficient, say IPBES. Meanwhile, invasive alien plants are the taxonomic group most frequently reported to negatively impact terrestrial ecosystems. Reportedly, 6% of all established alien plants are invasive on a global scale. This may seem trivial at first glance, but in fact equates to 1061 species [1].

Ecosystem and human impacts

  • Production of allergenic pollenProsopis juliflora (Mesquite) and Ambrosia artemisiifolia (Common ragweed) [1]. Other studies have identified this can provoke respiratory problems in humans [2].
  • Increased fire risk – flammable properties in invasive trees and grasses promote more intense and frequent fire regimes causing risks to nature, people, and increased carbon release to the atmosphere [1].
  • Out-competition of native agricultural species – impacting livelihoods of farmers and rural communities [1].
  • Reduced water availability – many studies have confirmed that differences in size, rooting depth and leaf phenology (seasons) between invasive alien plants and native species lead to reduced river flows and mean annual run-off [3]. The greater the differences between alien and native species, the greater the impact is likely to be [4].

Areas most impacted by invasive alien plants

A general trend suggests that areas already susceptible to climate change are expected to suffer more from invasive alien plant establishment [1].

Bitter vine growing up a tree

  • Islands – alien plants outnumber native plants on more than ¼ of islands globally. Impacts of invasive alien species are stronger on islands than continents [1].
  • Coastal heathlands and mires – in Northwestern Europe, Picea sitchensis (Sitka spruce) “severely alters” these habitats which are vital for threatened and endangered native plants, birds, and other species [1].
  • Cultivated areasMikania micrantha (Bitter vine) shown above, is one of the most impactful invasive alien plants in agricultural systems in the Asia-Pacific region [1].
  • Temperate and boreal forests – forest regeneration is impacted by shade-tolerant invasive alien species, which compete with tree seedlings for light, water and soil nutrients [5].
  • Drought-plighted regions – invasive shrubs and trees can reduce water availability and exacerbate conditions already expected to worsen due to climate change [1].

Scenic rural landscape with river passing trough blooming goldenrod (solidago) field

What is driving alien invasive plant establishment and spread?

  • Herbivore introduction – grazing by alien ungulates (horses, camels, buffalo, pigs) can suppress native species and facilitates alien species causing habitat loss, erosion and altered nutrient dynamics. For instance, grazing spreads ectomycorrhizal fungi which are beneficial for establishment of alien pine trees [1].
  • Online trade – a “major contribution” to invasive alien species introduction [1].
  • Horticulture – 46% of invasive plant species worldwide are spread this way.
  • Land and sea use – activities such as forest logging and wetland flooding creates beneficial environmental conditions for invasive species, whilst threatening native plants [1]. Overuse of pesticides in farming means numerous invasive species have developed resistance to the synthetic chemicals [6]. Herbicide usage can be minimised by adopting an Integrated Weed Management (IWM) approach.
  • Climate change – there is a positive feedback loop with alien plants and climate change, in that altered environmental conditions favour invasions, and alien plants’ modifications of the environment can exacerbate the effects of climate change [7].

What’s happening to stop this?

Control methods we use such as herbicide, mechanical, biological and cultural are effective in controlling plants as long as they are carried out in a way such that non-target species are not impacted. To tackle control further, biosecurity regimes using risk-based regulatory frameworks have been developed under the international plant protection convention [1].

How successful have we been?

  • Controls for alien invasive plants have been successful in >60% of documented cases, with 1/3rd needing no further action alongside benefits to biodiversity and improved ecosystem resilience [1].
  • Often, failure to measure the initial status of native vegetation has rendered quantifying the effectiveness of ecosystem restoration impossible [1].
  • Prevention is the winning strategy with invasive alien plants, but this requires expert knowledge on species identification and ecology [1].

So why are plants so tricky?

It is important to carry out surveillance to detect and remove alien plant species before they germinate and reproduce. This is because many species have a seed bank, or other similar cryptic stage of life, meaning dormant seeds remain viable in soil without experts knowing it [1, 8]. A great example of this being Himalayan balsam (below) with its explosive seed heads. It is unsurprising that plants did not take centre stage in the IPBES report, since their cryptic nature and longevity in soil makes eradication a long-term battle.

A copse of Himalayan balsam

This report is the most widespread attempt at assessing invasive species to date, yet there remains a lack of comprehensive information on plants in the literature. IPBES has clearly demonstrated the need for more frequent reassessment, cohesive policies, and effective management frameworks, and paves the way for invasive alien species prevention on a global scale.

What are we, as an industry doing to help?

As stated above prevention is the winning strategy. By curbing plant growth via the method(s) that are most suited to the species and the habitat it’s invaded – we gain control. The key to ‘winning’ the invasive plant war is to catch it early. But identifying invasive species is not easy, it takes a highly trained eye to spot some plants, especially in their dormant or early growth stages.

Having a professional survey by experts in invasive plants and water weeds will give you the information you need; what the problem is and how to treat or remove it.

Book a survey with us today.



[1] Roy HE, Pauchard A, Stoett P, Renard Truong T, Bacher S, Galil BS, Hulme PE, Ikeda T, Sankaran KV, McGeoch MA, Meyerson LA. IPBES Invasive Alien Species Assessment: Summary for Policymakers.

[2] Hussain MI, Shackleton RT, El-Keblawy A, Del Mar Trigo Pérez M, González L. Invasive Mesquite (Prosopis juliflora), an allergy and health challenge. Plants. 2020 Jan 22;9(2):141.

[3] Le Maitre DC, Blignaut JN, Clulow A, Dzikiti S, Everson CS, Görgens AH, Gush MB. Impacts of plant invasions on terrestrial water flows in South Africa. InBiological Invasions in South Africa 2020 Mar 11 (pp. 431-457). Cham: Springer International Publishing.

[4] Le Maitre DC, Gush MB, Dzikiti S. Impacts of invading alien plant species on water flows at stand and catchment scales. AoB Plants. 2015 Jan 1;7:plv043.

[5] Langmaier M, Lapin K. A systematic review of the impact of invasive alien plants on forest regeneration in European temperate forests. Frontiers in Plant Science. 2020 Sep 3;11:524969.

[6] Siddiqui JA, Fan R, Naz H, Bamisile BS, Hafeez M, Ghani MI, Wei Y, Xu Y, Chen X. Insights into insecticide-resistance mechanisms in invasive species: Challenges and control strategies. Frontiers in Physiology. 2023 Jan 9;13:1112278.

[7] Turbelin A, Catford JA. Invasive plants and climate change. InClimate change 2021 Jan 1 (pp. 515-539). Elsevier.

[8] Key GE, Moore NP. Tackling invasive non-native species in the UK Overseas Territories. Island invasives: scaling up to meet the challenge. 2019;637.