Guava, Psidium guajava, is a serious invasive species in various islands in the Galapagos. Scott Henderson, at the time working with the Charles Darwin Foundation, has investigated aspects of the invasion of guava which will help in planning its management, as well as providing information on the invasion process itself. Investigation of the role of disturbance in promoting guava invasion has confirmed preliminary suspicions that high disturbance facilitates guava germination, growth and survival in native fern-sedge and Scalesia vegetation zones. These areas are already considerably reduced in size, still under pressure, and are of high conservation values as they are inhabited by dozens of endemic plant species. This research demonstrates that disturbance similar to large animal trampling greatly facilitates guava
colonisation, so these animals must be excluded from the Galapagos National Park if this aggressive invader is not to spread further in the Park.
Bush fires on the slopes of southern Isabela island in 1985 and 1994 destroyed thousands of hectares of guava forest, but within one year the re-sprouting saplings were over 1m tall. There are now more than
40,000 ha of guava forest invading the pampa zone of Sierra Negra volcano and nearby Cerro Azul.
Experiments on the impacts of guava on native vegetation in three vegetation zones, Scalesia, Miconia and Fern-sedge, on Santa Cruz and San Cristobal islands, involved recording plant species, soils and microclimate (light, humidity, rain, air and soil temperature) in invaded and uninvaded areas. This allowed evaluation of the degree to which guava alters community composition and affects the abundance of endemic species as well as other introduced species of concern. Impacts were found to be greatest in areas where trees are naturally absent (fern/sedge) and least in naturally forested areas (Scalesia). The most important factor is probably the degree to which light levels are affected by canopy structure.
Source: Charles Darwin Foundation.