A kipuka is land surrounded by lava flows. Hawaiʻi has many examples of many different ages. They are particularly interesting areas to study ecological processes. An easy place to see kipukas is along Saddle Road above Hilo.
A brief description is here: https://en.wikipedia.org/wiki/K%C4%ABpuka.
An interesting study conducted was A study of Long-term effects of fragmentation and fragment properties on bird species richness in Hawaiian forests, Flaspohler et al. (2010): https://www.fs.fed.us/psw/publications/giardina/psw_2010_giardina(flaspohler)003.pdf
An important finding is summarized in this paragraph from the paper:
“Within a matrix of relatively young lava, even very small mid-elevation forest remnants of 3 ha or less are used by all but one native bird species, the Hawaiian hawk. These smaller forest patches also contained a larger proportion of native species than did the larger kipuka and the continuous forests that also attracted non-native species. Overall, the dominance of small kipuka by native bird species support the findings of Boelman et al. (2007) that native birds are capable of excluding or inhibiting invasion by non-native birds.”
Hawaiʻi Biodiversity 