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J. W. F. Slik, Macaranga and Mallotus (Euphorbiaceae) as Indicators for Disturbance in the Lowland Dipterocarp Forests of East Kalimantan.

J. W. F. Slik, Macaranga and Mallotus (Euphorbiaceae) as Indicators for Disturbance in the Lowland Dipterocarp Forests of East Kalimantan. Leiden: Tropenbos--Kalimantan Series 4, 2000, ISBN 90-5113-045-7, 224 pp.

This fourth volume in the Kalimantan Series focuses on two genera of the Euphorbiaceae, or Rubber family, that are common throughout Borneo, both in gaps in the primary forest and in (highly) disturbed areas, which are unfortunately more common than primary forest in these lowlands. Silk states that the "aim of this study is to quantify disturbance in lowland dipterocarp forest in East Kalimantan (Indonesia) with the use of a small set of indicator plant species (Macaranga and Mallotus, Euphorbiaceae). These indicator plant species can be used to develop a rapid assessment method for measuring and monitoring forest disturbance in lowland dipterocarp forest." Silk's publication therefore aims to assess the indicator value of the many species of these two genera for determining the history of disturbance of a particular site.

Essentially, however, the book is a taxonomic volume, which is hardly surprising given that it has been produced under the auspices of the National Herbarium in Leiden. Of the book's 224 pages, only 28 pages are actually about Macaranga and Mallotus as indicator species for disturbance, while the remainder deals with various aspects of their taxonomy. In that sense, the title is a bit misleading, although there is still enough of interest to non-taxonomists. As with all the publications in the series, this volume has beautifully drawn line drawings of all taxa, which eases identification and at the same time makes the volume more attractive.

Both Macaranga and Mallotus are generally small to medium-sized, and although there has been some confusion regarding their taxonomy in the past, they are relatively easy to identify. However, as the Euphorbiaceae have yet to be dealt with by Flora Malesiana, identification has always been a major chore. Airy Shaw's 1975 publication on the Euphorbiaceae of Borneo was essentially not much more than a key and checklist--there were generally no descriptions, drawings were completely absent, and was therefore of little use to non-taxonomists. Slik provides excellent descriptions, drawings of all species, and his keys are primarily based on vegetative characteristics. Slik's book covers far less, but is much more user-friendly, and will be welcomed by a wider audience.

The book is divided into seven chapters: Chapter 1 provides an introduction, Chapters 2 and 3 are about disturbance and using Macaranga and Mallotus as indicators, Chapter 4 is about historic relationships between the two genera, Chapter 5 provides a key and descriptions of all Macaranga and Mallotus species in East Kalimantan, while Chapters 6 and 7 consist of taxonomic revisions of sections of the genus Mallotus. For the broader audience, chapters 2, 3 and 5 are of greater interest.

Chapter 2 deals with the effects of selective logging and forest fires on the forest structure and tree species composition. Slik's study shows that in selectively logged forest the total number of trees recovered within 5-10 years, while the number of tree species recovered to pre-logging levels within 10-20 years. In burnt areas, tree numbers also recovered within 5-10 years, but tree species numbers lagged well behind, as the new trees mainly belonged to only a few pioneer (Macaranga) tree species. However, the difference is not as marked as one would expect: Slik found that burnt forests had about 50 tree species on average per 0.3 ha plot, compared to 80 in primary forest. He concludes that most of the tree-disturbance tree species diversity can still be found 15 years after the fire. Surprisingly, diversity one year after disturbance was significantly higher for burnt than for selectively logged forest. Apparently, fire affected dominant tree species more than rare species, while selective logging affected rare species more than dominant species. Slik attributes this to selective logging of dipterocarps, which are dominant as a family, but often rare as individual species. However, his data set is too small to draw fully reliable conclusions. Most of his plots were in primary forest (10), selectively logged (22), and selectively logged and burnt (8) areas, rather than in areas of burnt primary forest (5). Also, the 5 plots of burnt primary forest were all in one locality (Wanariset), and without knowing the size of the burnt area and distance to primary forest, one cannot rule out that the diversity found in burnt areas was simply due to recruitment from nearby primary forest.

Slik found a difference in recruitment of Macaranga species between selectively logged and burnt areas, with a low recruitment in selectively logged areas (meaning that Macaranga was on its way out), and a high level of recruitment in burnt areas (meaning that Macaranga will remain a feature in these forests for much longer). Six species of Macaranga specifically studied were found to be dependent on presence of mature specimens for their initial recruitment, rather than on light availability.

Chapter 3 is where Slik assesses the role of "Macaranga and Mallotus species (Euphorbiaceae) as indicators for disturbance in the mixed lowland dipterocarp forest of East Kalimantan (Indonesia)." Slik counted and identified all individual specimens (>30cm tall) of these two genera in 45 plots, representing nine different forest types, and all with a varying level of disturbance. The level of disturbance was determined by measuring nine forest structure parameters, and the occurrence of Macaranga and Mallotus was found to be closely related to the level of disturbance in a forest. Most Macaranga species are characteristic for high disturbance levels, while most Mallotus species prefer intermediate to low levels of disturbance. However, both genera have species at both extremes, and Slik recognizes three groups: i) primary forest "remnant" species, ii) generalist pioneer species, and iii) high disturbance pioneer species. He concludes that small sets of Macaranga and Mallotus species could be used to predict the level of forest structure disturbance in a forest, but that a geographic component complicated this, suggesting that the method would need to be adapted to new study areas.

While these chapters provide very interesting information on the ecology of Macaranga and Mallotus in disturbed habitats, Slik does not bring us much closer to having a tool at hand for determining levels of disturbance on the basis of a few indicator species. If the method needs to be adapted to each new area, the calibration exercise will provide much of the information we are seeking. Also, if an ecologist, forester, manager of a protected area, or someone interested in forest resources wants to know the disturbance history of a forest, they are unlikely to (only) use indicator species. Satellite images and aerial photographs will provide more reliable information on disturbance, and the former are available from the early 1970s onwards, covering almost the entire period of intense disturbance. Also, now that images have become much cheaper, this technique is also much more accessible than previously. (Wim Giesen, ARCADIS Euroconsult, PO Box 441, 6800 AK Arnhem, The Netherlands,
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Author:Giesen, Wim
Publication:Borneo Research Bulletin
Article Type:Book review
Date:Jan 1, 2005
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