Controlling Invasive Plants

Controlling Invasive Plants
CURRENT

PROJECT:

Control of Invasive Plants in the Highlands of Galapagos

PARTNER:

Charles Darwin Foundation

STATUS:

Funded in 2014; ongoing

 

Controlling quinine at Media Luna on Santa Cruz. (© Lorea Cardas)

Scientists monitor a plot of controlled quinine in the Santa Cruz highlands. (Photo © Lorea Cardas)

 

Background

The unique animals and plants of the Galapagos archipelago have experienced few extinctions, mainly due to late colonization by humans and the high level of protection provided by the Government of Ecuador. Nevertheless, native species have been seriously affected by land use change and invasive species, particularly on the five inhabited islands of Santa Cruz, San Cristóbal, Floreana, Isabela, and Baltra. In the case of plants, there are 866 recognized introduced species present in Galapagos — of which approximately 65% were brought to the Islands deliberately for agricultural or domestic use. Many of the plants introduced for cultivation have spread and threaten native species and habitats. This project focuses on developing effective control techniques, including the potential for biological control, for two of the most invasive plant species in Galapagos: quinine and blackberry.

Quinine

A scientist monitors quinine in the Santa Cruz highlands

Project lead Heinke Jager monitors quinine. (© Lorea Cardas)

Quinine (Cinchona pubescens) is one of the most invasive woody species in Galapagos, and is adversely impacting the natural vegetation on Santa Cruz Island. After this tree was introduced in the 1940s, it added new growth to the formerly treeless environment of the Santa Cruz highlands and has now spread to cover more than 12,000 hectares. Quinine is considered a “transformer,” changing plant species composition and community structure of the Santa Cruz highlands. Although it is currently being controlled by the Galapagos National Park Directorate (GNPD), it is so widespread on Santa Cruz that manual and chemical control measures are not feasible on a broad scale. A long-term study of the effects of quinine management techniques have also revealed that manual and chemical control may produce more harm than good. Future investigations will focus on improving the effectiveness of management techniques for this invasive tree while exploring other control options.

Blackberry

Blackberry (Rubus niveus) is a spiny shrub from Asia that was introduced to the islands of Santa Cruz and San Cristóbal in the 1970s  It can now be found on Isabela, Floreana, and Santiago Islands as well, and has the potential to cover 90,000 hectares — approximately 12% of the entire archipelago. Blackberry invades the wetter parts of the Islands, forming dense thickets up to 13 feet tall. This species grows vigorously and has a massive seed bank, preventing recruitment of native seedlings and impacting native plant communities such as the unique Scalesia forest.

Cutting trails into dense blackberry

Researchers cutting trails into dense blackberry. (© Heinke Jager)

Over the last 20 years, large areas of Los Gemelos (twin volcanic craters located in the highlands of Santa Cruz) have been invaded by blackberry, and this area has been the focus of restoration efforts by the GNPD — including management actions to control the blackberry, and reforesting with nursery-grown Scalesia saplings. However, these significant efforts have not successfully contained blackberry, and there are concerns about other impacts to the forest from management attempts. In 2014, scientists from the Charles Darwin Foundation teamed up with the GNPD and with ornithologist Sabine Tebbich from the University of Vienna to implement an investigation of the short and long-term effects of blackberry management on the native flora and fauna. This long-term study will provide science-based advice on the direct and indirect effects of restoration programs at Los Gemelos.

Biological Control

Park Rangers Cutting Trails at Los Gemelos

Park rangers cutting trails at Los Gemelos. (© Heinke Jager)

This project will explore the potential use of biological control for blackberry and quinine, which involves the release of natural enemies of the target species such as disease or an insect species. Biological control is one of the best management solutions for widespread plant invasions, and can be a permanent and self-sustaining method for controlling invasive species over large areas. A biological control agent is chosen because it is specific only to the target species, weakening it and thus reducing its dominance over native vegetation. Pre-release testing, which may take several years, is critical to ensure that the agent will not negatively impact any other species than the target. In the interim, scientists are focusing on improving current blackberry management using Los Gemelos as a study system.