One week later. JK here at the peripheries of the site is currently in a rapid state of aggressive growth; its rate of spread and establishment are far greater than JK already established within the site's boundaries.
Given good daylight, heavy moisture, a fertile and regularly disturbed soil, regular and widely-scattered disturbance of plant material......the JK's establishment is already secure here.
Its present growth here is itself a testimony to having been already repeatedly under-estimated and dealt with without full information.
The rapidly-growing threadlike cilia on the plant's rhizome structures lie at much greater depths than the visible root crowns which seem to remain superficially-rooted.
However, superficial roots mean that earth disturbances break off viable plant material more readily(remember its use of its volcanic environment in its primary homeland.
JK growth at this site is currently unchecked this growing season(May 2012); test-pits will need to be dug several metres out into this field to ascertain the approximate limits of JK growth.
This cannot be underestimated: one can expect viable or dormant JK to exist even over 5-6 metres horizontally AND 4 metres vertically away(invisible in other words).
Underestimation of this has contributed to its recent establishment: a barbed exclusion fence has been placed some time after site closure, with earth disturbance that suggests excavation of material or the ratifying of a boundary ditch. However, its placement belies its inadequacy, as JK is visibly established some 2 metres out into the field.