John Ewel

University of Florida, Department of Botany

Lessons learned from early work with invaders

• Intact communities are not only more resistant to invasion, but some are, in fact, non-invasible.
• Subtle changes in regional hydrology increase the vulnerability of otherwise resistant ecosystems to invasions.
• Fuel loads produced by invaders, and the flammability of invaders, can divert succession.
• Native species often form strong and essential biotic links with aliens (e.g. pollination, dispersal, scarification).

Lessons from self-designed seeded tropical successive communities

• More diversity is not necessarily better with respect to rates of loss of leaf tissue, plant productivity, and nutrient loss via leaching.
• Some patches of a single species are more invasion-resistant than are diverse mixtures.
• Big divisions are those that take place on the life-form level.
• Move toward greater simplicity in research. Use simple plantations of fast-growing plants; one or two life forms in a non- constraining environment.

Early outcomes

• Successful dominants preclude invasion, even when grown in monospecific stands.
• In most cases, light availability is more important than nutrient availability in controlling invasions.
• Stands of trees that demand lots of both light and nitrogen are vulnerable to invasion if below ground competition is reduced.
• Site invasion may be high initially, then very low, then somewhat higher (due to changing light and shade from canopy).
• Alien plant species now outnumber natives in Hawaii.
• The pig (an invasive species) is considered sacred by a substantial portion of the community, so control efforts must consider cultural factors.