Time lags and the invasion debt in plant naturalisations

Ecological processes often exhibit time lags. For plant invasions, lags of
decades to centuries between species’ introduction and establishment in
the wild (naturalisation) are common, leading to the idea of an invasion
debt: accelerating rates of introduction result in an expanding pool of
introduced species that will naturalise in the future. Here, I show how a
concept from survival analysis, the hazard function, provides an intuitive
way to understand and forecast time lags. For plant naturalisation,
theoretical arguments predict that lags between introduction and
naturalisation will have a unimodal distribution, and that increasing
horticultural activity will cause the mean and variance of lag times to
decline over time. These predictions were supported by data on
introduction and naturalisation dates for plant species introduced to
Britain. While increasing trade and horticultural activity can generate an
invasion debt by accelerating introductions, the same processes could
lower that debt by reducing lag times.