VEGETATION SURVEY

AIM

Although the Ifotaka Forest has been broadly described and characterised, a detailed survey of the vegetation has not been conducted. The aim of the present study was to;

METHODS

The study area was consistent with that previously surveyed for lemur populations. The vegetation survey was conducted using nineteen 32m x 16m quadrats, each positioned at random and geographically referenced using a Global Positioning System (GPS). Within each quadrat, the identity (vernacular and scientific name), relative density and relative cover-abundance of all trees greater than 2.5cm diameter at breast height (dbh) were recorded. Relative density and relative cover-abundance were estimated using the following indices;

Index of density

  1. – Very dispersed (1-4 individuals/quadrat)
  2. – Dispersed (5-14 individuals/quadrat)
  3. – Not very numerous (15 – 29 individuals/quadrat)
  4. – Numerous (30 – 99 individuals/quadrat)
  5. – Very numerous (>100 individuals/quadrat)

Index of Cover-Abundance

  1. Few individuals, low coverage
  2. Numerous individuals, low coverage
  3. Very numerous individuals covering a minimum of 5% of surface
  4. Few or many individuals covering 25-50%
  5. Individuals covering 51 – 75%
  6. Individuals covering 76 – 100%

RESULTS

A total of 162 tree species were recorded during the vegetation survey, representing 52 families. Enterospermum sp. (Rubiaceae), Alluaudia procera (Didiereaceae), Euphorbia leucodendron (Euphorbiaceae), Strychnos madagascarensis (Loganiaceae), Combretum sp. (Combretaceae), Croton bevilaniensis (Euphorbiaceae) and Grevvia sp. (Tiliaceae) had the greatest median density and cover-abundance scores (2 and 1, respectively) and were recorded in sixteen or more of the nineteen quadrats. The estimated density of these species, based on the median density score, would have been equivalent to 98-273 individuals per hectare. The abundance of Alluadia procera was particularly significant since it was the species on which Propithecus v. verreauxi (Verreauxi’s Sifaka) was most frequently encountered during investigations of habitat preference (Plate 1).

Euphorbiaceae was the most common family with a total of sixteen species recorded and three species within the twelve most abundant trees. Fabaceae, Mimosaceae and Rubiaceae were the next most commonly represented families with six, seven and eight species recorded, respectively. A full species list including the identity (vernacular name and scientific name), relative density (median Index of Density coefficient and proportion occurrence) and relative cover (median Index of Cover Abundance coefficient) of tree species recorded during the vegetation surveys will be included in the final report.

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