Re: Letter to the Editor (July 15) stating that Albizia has replaced acres and acres of native forest. It went on to suggest that eventually the only native trees on Rarotonga will be those in our backyards.
I arrived in 1980, many of the inland slopes and lower ridges were monocultural
fernlands of Tangle Fern (Tuanu‘e), while many other lower-slopes had a broad
band of Tree Hibiscus (‘Au). Some outer slopes supported native forest. Uphill
of the Fernland and Hibiscus slopes there was a near pristine native forest.
(1985) did not mention Albizia (‘Ārapitia) among the exotic trees of the
Fernland, but in 1995 McCormack mentioned Albizia making “pure stands in many
former Fernland slopes.” Its spread
continued and now there are very few outer-slope fernlands left. Also, during
the 1980s and ‘90s, the Ministry of Agriculture planted exotic trees, mainly
Caribbean Pine and various Acacias, on many areas of the upper fernlands.
its abundance in former fernlands, Albizia has shown very little tendency to
invade native forest except where it has been seriously disturbed.
inland native forest remains in relatively good condition although exotic trees
such as Cecropia (Rau-māniota) and African Tulip (Kō‘ī‘ī /Pititī Vai) continue
to spread and much of the understory is now dominated by exotic shrubs,
especially Night-blooming Cestrum (Tiare Ariki-va‘ine) and Inkberry/Ardisia.
Various invasive vines continue to spread, such as Balloon Vine, Red
Passionfruit and Mile-a-minute.
the biggest threat to the native forest is the massive-leaved Peltate
Morning-glory. Whether this vine is native or introduced is uncertain, but what
is certain is that since the 1980s it has spread rapidly over the tops of many
trees in many parts of the inland. In the 1980s I wrote that Grand Balloon Vine
was the “green cancer” of our native forest, but today, I realise that the real
“green cancer” of the native forest is Peltate Morning-glory.
the gradual invasion of the inland native forest by exotic trees, shrubs and
vines, it is still one of the most pristine native forests in the tropical
South Pacific. I have visited about 70 islands between Fiji and Rapa Nui and
the Rarotonga inland forest, upslope of the bands of Albizia and Tree Hibiscus,
is still at the top of my list of pristine forests.
reason the extensive native forest still exists is worth repeating. The very
steep slopes and the lack of large-trunked millable trees kept those early
European timber enthusiasts at bay. What a blessing.
50 per cent of the inland trees are Cook Islands Homalium (Mato), which has
relatively small multiple trunks of very hard wood. Its extensive shallow roots
are also a major anti-erosion device. For its anti-milling and anti-erosion
efforts, the Cook Islands Homalium deserves much credit.
the Albizia forest were removed, would native trees repopulate the old fernland
slopes? It is extremely unlikely. The fernlands were very infertile, which is
why they rarely supported regenerating native forest. Albizia improves soil
fertility by the decomposition of its nitrogen-rich leaves and it also provides
increased shade and moisture for regenerating shrubs. Unfortunately, the shrubs
are mainly fast-growing invasives, rather than natives.
the Albizia forest undisturbed is probably the best policy, except for small
areas where somebody is going to nurse transplanted native trees and shrubs for
Islands Natural Heritage Trust
problematic Albizia trees lining the mountains at Raemaru Park should be an
former MP that operates his business next door to Raemaru Park should attend to
this invasive species, instead of cutting trees all over the island.