Despite three months of almost continuous rains
between January and March 2013 in Tahiti, we were able to conduct several field surveys
between 900 and 1400 m elevation in dense montane cloudforest with my assistant
Maruiti TEROROTUA (Délégation à la Recherche de la Polynésie française) to find
suitable locations to set up a series of 10 x10 m permanent plots. Because of
the rough topography at that elevation range, with often steep slopes and deep
narrow gulches, it was not feasible to set up larger plots (e.g. 20 x 20 m), and
the choice of two 100 m² plots (one located in the upper part of the gulch, the
other in the lower part) appeared to be the best option.
Photo 1: a view of a gulch in montane cloud forest
between 1200 and 1300 m elevation
With the recent (the 17th of March)
arrival of Pauline BLANCHARD, a graduate student (Master 2 Recherche) from the
Université Pierre et Marie Curie of Paris 6, our small team started the following
measurements in this series of permanent plots:
(1)
a complete inventory of all
vascular plants, according to three main vegetation strata (canopy or tree
layer > 5 m, understorey or shrub layer between 1-5 m and herbaceous layer
< 1 m), including fern species found in different microhabitats (terrestrial
on the ground, dead wood and logs, rocks; and epiphytes below 2 m, above 2 m,
and found in the canopy),
(2)
the basal area of all woody
species (diameter at breast height of all stems above 1,3 m) to describe the
forest structure and composition, and assess the dominance of native (endemic
and indigenous) versus alien naturalized woody shrubs and trees.
We have also decided to set up 2x2m quadrats
around the 10x10 m permanent plots (for a total of 24 quadrats) to estimate the
abundance of fern species by counting the number of individuals (or patches)
per species and estimating their ground cover (%) in each quadrat. This
protocol has both the advantage to prevent human disturbances inside the
permanent plot, and increases our sampling area for fern diversity from 200 m²
to 392 m² in each site.
The most difficult part will be to set up
similar plots above 1400 m (two hours hike both way) up to the summit of Mt
Aorai at about 2000 m (overnight camping) !
Jean-Yves MEYER
Délégation à la Recherche de la Polynésie française