Figure 1.
Spatial distribution of mangrove trees in 4 field sites at Gazi Bay.
The dots show the location of each tree. The diameter of the dots is proportional to the diameter of the stem above the root. The colour of the dots represents the tree species: Dark blue is Avicennia marina, light blue is Bruguiera gymnorrhiza, green is Ceriops tagal, orange is Rhizophora mucronata and brown is Xylocarpus granatum. Together site 1 and 2 form a complete section of the forest; from low tide shore to terrestrial vegetation (supralittoral level). The y-axis of site 1 starts at the terrestrial vegetation and ends at the beginning of site 2. The y-axis of site 2 ends at the last tree at the creek side. Site 3 had closed canopy, while site 4 had open canopy.
Figure 2.
Spatial point patterns representing 6 possible vegetation distributions (from left to right and from top to bottom): Random, semi-regular, aggregated, random with a density trend, semi-regular with a density trend and aggregated with a density trend.
Table 1.
An overview of the plotless sampling methods evaluated in this study.
Table 2.
The aggregation indices (R) for the field sites.
Table 3.
The aggregation indices (R) for the vegetation patterns.
Table 4.
Tree density estimations using plotless sampling in four field sites (30 sampling points, 10 replicates).
Table 5.
Tree density estimations using plotless sampling within six vegetation patterns (30 sampling points, 10 replicates).
Figure 3.
Tree density estimations by applying plotless sampling methods to field data.
The density estimations found by applying plotless sampling method to the field data. The field data consisted of mangrove tree locations in four sites. In each graph the horizontal lines are the real tree densities in the sites. The closed squares are the mean of 10 estimations with 30 random sampling points. The verticals crossing the means are the 95% confidence intervals. NN = Nearest Neighbour; BD = Basic Distance; O1 = Ordered distance 1; VY = Variable Area Transect in the y-direction with 3 trees; VX = Variable Area Transect in the x-direction with 3 trees; P1 = Point Centred Quarter Method with the nearest tree in each quadrant.
Figure 4.
Tree density estimations by applying plotless sampling methods to 6 vegetation patterns.
In each graph, the horizontal lines are the real densities (0.2 points per m2 for all patterns). The closed squares are the mean of 10 estimations with 30 random sampling points. The verticals crossing the means are the 95% confidence intervals. NN = Nearest Neighbour, BD = Basic Distance, O1 = Ordered distance 1, O2 = Ordered distance 2, O3 = Ordered distance 3, P1 = PCQM 1, P2 = PCQM 2, P3 = PCQM3, VX = Variable Area Transect in the x-direction with 3 trees, VY = Variable Area Transect in the y-direction with 3 trees.