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Arnold Arboretum

The forest at Wai Dongkong

March 11, 2014 by Cam Webb

A spectacular fig overhanging the river

A spectacular fig overhanging the river

We’ve almost finished the fieldwork!

Last week I completed the morphotyping of the 582 trees in the four 0.25-ha sample plots, and the collecting crew has nearly finished obtaining samples of the ca. 117 taxa we recorded there. All but about 10 of these taxa were collected by either using a 10 m aluminum pole with a clipper on the end, by climbing the trees, or by a combination of both. While the local Manggerai people have less need to climb trees that the bird-collectors we met in Seram, many are none-the-less brave and skilled; Serpon and Adi have been our star tree climbers on this trip. We have found no small individuals of the remaining 10 tree taxa (i.e., less than 20 m tall!), and so will have to make do with DNA and botanical samples from leaves or twigs shot down with catapulted rocks, and wood samples (for wood density analysis) chiseled carefully from the bole. This week I’ll hopefully be interviewing some elders in the village to add to the ethnobotanical data we have been collecting from our long-term village assistants. Of all of them, Paul has spent most time in the forest (as a chainsaw operator), and has offered much useful information on timber species and their wood properties. However, these days few of the younger men or women are collecting medicinal plants from the forest, and so we need to chat with the older folk.

Varanus komodoensis!

Varanus komodoensis!

Our team of biologists is also finally (nearly) complete. Endro Setiawan (who along with Acun has been on each trip so far and has helped me since 2009) was able to leave his job at the Gunung Palung National Park for a couple weeks, and Dr. Teguh Triono, our counterpart scientist from 2010-2013, has just arrived for a short visit. Only Arief Hidayat and Yessi Santika from Bogor Herbarium are not with us. Since we will not get another chance, we took the opportunity yesterday to see the Komodo dragons on nearby Rinca island, a long-awaited natural history goal for Teguh, Acun, and Endro!

The rank-abundance curve* of tree species in the first 0.25-ha plots at each of the Papua, Seram, and Flores sites

The rank-abundance curve* of tree species in the first 0.25-ha plots at each of the Papua, Seram, and Flores sites.

So, what have we found out about the forest?

  1. Structurally, it is around 20-30 m tall, with a fairly even canopy, a mean tree diameter of 17 cm and only 32 (out of 582) trees being larger than 50 cm in diameter. There are few palms in the understory and it is fairly easy to walk through, and dominated by a small Mallotus (Euphorbiaceae). There is a relatively high abundance of large diameter lianas. Underfoot, the leaf litter is sparse, and the dark-brown soil has been brought up to the surface in the mounds of worm casts, showing everywhere between the many surface rocks.
  2. As expected, there are no dipterocarps (the family of trees that dominate the wet forests of Western Indonesia), and the large trees belong primarily to the families Malvaceae (genera Colona, Kleinhovia, Pterocymbium, Pterygota and Pterospermum), and Moraceae (Artocarpus and Ficus). Most of these genera are “pioneer-giants,” germinating and growing fast in the full sun of forest gaps but reaching giant proportions. This taxonomic composition of the large trees, along with some aspects of the forest structure, indicates that these forests are either frequently naturally disturbed, or have been disturbed by humans. The villagers have confirmed that there was extensive logging in the area until about 10 years ago, when the forest department stepped up its protection activities. What is striking is that there are so few stumps around, and that the forest structure is so healthy. The recovery has been rapid and the understory has opened out, and I missed the post-logging signs on my first recce. Seeing evidence of this rapid recovery is always very comforting to me, and helps remind me of the tremendous capacity for forest to heal, if fire can be avoided.
  3. Despite the “secondary” nature (a forestry term) of the forest (in two of the four plots), most of the species are obviously “primary forest” species, germinating in the dark understory and growing slowly towards the canopy in fits and starts. And while it is true that this forest is less diverse than the others I have visited on this project (see graphic), it is richer that I expected. I don’t recognize most of the species as species (but for a few, e.g., the widespread Maranthes corymbosa, Chrysobalanaceae), but do seem to recognize most species to their genus, and many of these genera do not occur in the Whitmore et al. checklist for this region. If they are not new species, they will definitely be new records for the flora of this part of southeast Indonesia.
  4. One surprise has been the number of species of the Meliaceae (ca. 12 species), and their abundance among the smaller trees in the forest. I have always had a sense (gained from Gunung Palung) that Meliaceae (especially Aglaia) diversity and Euphorbiaceae diversity provides an indicator of soil fertility. This Wai Dongkong site seems to support this hypothesis, as various other observations indicate that the soils here are quite rich.
  5. Overall, I have been very surprised at how “wet,” and “West Malesian” the forest here seems to be. Definitely not the dry deciduous forest I was expecting, and which we saw on our trip yesterday to Rinca. It seems Mount Mbeliling is causing much rain to fall on both its lower and upper slopes, creating a pocket of high diversity among the generally lower-diversity dry forests. It is going to be very exciting to work out the identity of our collections, and their phylogenetic relationships, and see “how far” these taxa, or their ancestors, have traveled from the wetter forests of the west and the east.

*A “rank-abundance distribution” plots the rank of each taxon on the x-axis against the number of individuals of that taxon on the y-axis. It thus indicates both the richness (the length of the “tail”) and the evenness of species abundances: a steep curve is uneven, a more level curve is more even, i.e., there are fewer dominant species.


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