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Entries in rattan growth (4)


Searching For Significance

Mr. Dong and Mr. Phuong struggle with standard errors and confidence intervals in the WWF-Hue office as they search for significant differences between the size-specific growth rates of Daemonorops poilanei. [NOTE: Statistical significance was nowhere to be found, but they promised to collect more data].



Figure above shows size-specific growth rates for six rattan species from Laos and Cambodia. The data were collected over a four year period to provide a production baseline for defining a sustainable harvest of cane. In the absence of these data, the communities were operating under the assumption that 20% of the canes in the forest could be harvested each year on a sustainable basis. This assumption, which was provided as an interim indicator by the WWF rattan program, is valid if the commercial canes are growing at least 1.0 meter/year. i.e. it takes five years to produce a merchantable rattan cane such that 20% of the resource stock can be harvested each year.

The growth data shown above verify that a 20% harvest intensity is appropriate for all of the rattan species except Calamus tetradactylus. The merchantable canes (≥5.0 m long) of this species exhibit an average growth rate of 0.78 meter/year [NOTE: Average growth rates of merchantable canes are shown as a dotted horizontal line in each histogram] and annual harvest intensities, as a result, should be considerably less than 20%. Similarly, more than 20% of the merchantable canes could be harvested sustainably from other species, e.g. Myrialepis and Plectocomia, which are both growing well over 2.0 meters/year.

When you know the actual yield characteristics of the resource you are exploiting, you can be very precise in defining a sustainable offtake. [NOTE: These data are currently being written up in an article, so please do not copy, distribute, or cite. Thx].


Dakrong Workshop

Dr.Ninh Khac Ban (shown above; see Which Rattan Is That and Glimpses of Transects) and I gave a workshop yesterday at the Dakrong Nature Reserve in Quang Tri province on measuring the growth and yield of rattan. The workshop was attended by representatives from six protected areas in the Central Truong Son Mountains.

The image below shows three workshop participants (l to r), Le Van Huong, vice-Director of the Phong Dien Nature Reserve, Tran Van Thu Director of the Song Thanh Nature Reserve, and Hoang Ngoc Tien, Director of the Dakrong Nature Reserve. Together, these three young men are in charge of over 175,000 hectares of the best rattan habitat in Vietnam.  And they are listening attentively and taking notes on how to manage this resource on a sustainable basis. [NOTE: Mr. Thu, the Director of Song Thanh N.R., is currently doing a masters at Hue and I am a member of his advisory committee. For his thesis, he is developing a management plan for rattan in the reserve. Of which I am quite pleased]. 




I arrived last night to Vientiane, Laos and started a three-day workshop on rattan growth this morning at the local WWF office. Lectured for about two hours on the theory and methodology of sustainable resource harvest, and then spent the rest of the day processing four years of size-specific growth data with foresters from Laos and Cambodia. After flying 19 hours yesterday and ending up 12 hours on the wrong time zone, I was really wishing I had a hammock (see above) to stretch out in at about two o'clock this afternoon. [NOTE: Workshop seems to be going well and participants are enthusiastic about learning what do with all the growth measurements from their permanent sample plots. Off the the field tomorrow to have a look at some of these plots.]