We've developed a framework to help World Heritage Sites manage invasive species

Over 250,000 protected areas make up around 15% of the globe's surface area. They include World Heritage Sites, national parks, provincial parks, nature reserves and many other sites on land or water.

These protected areas are crucial for preserving the world's biodiversity and ecosystem functions. They also support the well-being of millions of people.

Protected areas are increasingly under threat because of human induced drivers of global change. These include poaching, pollution, climate change and biological invasions caused by invasive alien species.

Invasive alien species are organisms that are moved by humans to new regions where they traditionally don't occur. For various reasons these species spread uncontrollably. They can negatively affect their new environments.

Invasive alien species are one of the leading threats to biodiversity in protected areas globally. For example in South Africa, invasive tree species on Table Mountain National Park are changing naturally occurring fire and water systems .

Managing invasive alien species is also a huge financial burden for many protected areas. For instance, South African National Parks and the Working for Water, an ecosystem restoration programme, spend on average R2 million (about $139,000) a year for invasive alien species control. This was done in the Kruger National Park, in northeastern South Africa, one of Africa's largest game reserves.

A team of researchers and managers working in invasion science have been monitoring invasive alien species in World Heritage Sites across the world. When reviewing documents about invasions in these sites, we found reports were hard to compare because no systematic method of reporting was followed.

We therefore developed a new framework to guide monitoring and reporting of invasive alien species in natural World Heritage Sites globally.

The framework allows assessors to assign an overall threat score to a World Heritage Site. This will help improve the monitoring and control of invasive alien species at these sites.

What we found

The review of United Nations Educational, Scientific and Cultural Organisation and International Union for Conservation of Nature documents about invasive alien species in World Heritage Sites revealed reporting problems. Essential data were often not reported in documents or not detailed enough to be useful. This made it difficult to assess changes to levels of threat or progress in the management of invasive alien species in the sites over time. Sunrise at the Serengeti National Park, Tanzania. shutterstock

The framework we developed has three components:

• The first focuses on monitoring and reporting of the current status of biological invasions. It relates to compiling lists of alien species, assessing how they were introduced into the sites, identifying and reporting their impact.

• The second component looks to the future and aims to predict future threats and management needs.

• The third component assesses knowledge gaps and the overall threat levels of invasive alien species to the site.

To test the framework, we did seven in-depth case studies in different social-ecological contexts on five continents. These include the Aldabra Atoll (Seychelles tropical islands), Serengeti National Park (Tanzania) and Vredefort Dome (South Africa).

We drew information from the literature and consulted local researchers and managers to get additional information about each site. Applying the framework yielded more information than past monitoring initiatives.

For example, the threat level showed in the 2017 World Heritage Outlook for the Serengeti and Vredefort Dome sites was “data deficient”. They're now categorised as facing moderate to high threats from biological invasions based on our assessment informed by the framework.

Just over half of the World Heritage Sites globally are formally listed as being threatened by biological invasions, from over 300 different invasive alien species. But the number of sites and invasive alien species is probably under-reported and likely to be much higher.

Use of the framework more than doubled the number of invasive species reported for all sites except for Aldabra. This site has less invasive alien species now due to effective eradication and control initiatives. The total number of invasive species in the site dropped from seven to five.

What needs to be done

A major issue that limits efficacious management is the availability and collation of data about invasions for many protected areas. This lack of information limits understanding and hinders the formulation of robust policy or control responses.

Better transparency and standardisation of long-term monitoring and reporting of biological invasions in protected areas will allow for meaningful analysis of trends over time. This will also guide adaptive management. Further research that collects baseline data and empirical evidence on invasions in protected areas is also crucial.

We hope that the framework we've developed will help to do this and become a global norm moving forward.

The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.

By Ross Shackleton, Post Doc student Conservation and invasion Biology, Stellenbosch University