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.
Photo 2: Pauline and Maruiti assessing fern diversity and abundance in 2x2 m quadrats (delimited by 2 m long woody sticks) located around the 10x10 m permanent plot (delimited by measuring tapes) set up at about 600 m in a Miconia invaded rainforest.
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) !
Délégation à la Recherche de la Polynésie française