More Growth Rings

And speaking of growth rings, the rings widths on these Pinus patula boards at the INFOMASC (Industria Forestal Maderera de Santiago Comaltepec) sawmill in Oaxaca are pretty impressive. Not surprising, really, because I know that these forest are very well managed - and FSC certified. 

As emphasized by the sign in front of the sawmill, "Profitable Forests" (Bosque Rentable) are "Sustainable Forests" (Bosque Sustentable). [NOTE: Our tree growth workshop (see Growth Bands in Comaltepec) was held in a restaurant right in front of this sawmill. Fitting].

Counting the Rings (From The Archive)

Mark Ashton (left), Morris K. Jesup Professor of Silviculture at Yale, and Yang Chenghua (right), botanist at the Guizhou Forestry Academy, count the rings on a large cross section of Cunninghamia lanceolata (Lamb.) Hook to estimate its age and growth rate.  This valuable timber species, known locally as "shamu", is used by the Miao to build their houses (see Miao Still Life) and it is widely planted and managed in local forests. We spent the day in the drizzling rain running inventory transects in the forests outside of Wudong to quantify the density and size-class structure of Cunninghamia trees. We got soaked - but we finished 2,000 m² of transects. A good day.

[NOTE: I post this again because I am teaching Introduction to Indigenous Silviculture: Ecology, Livelihoods, and Policy at the Yale School of Forestry and Environmental Studies this semester and I see Mark every Monday. We reminisce about counting rings in southwestern China - among other things]. 

Growth Rings

Because of the aseasonality of the climate in which they grow, the great majority of tropical trees do not produce growth rings.  The few species that do exhibit visible discontinuities in their secondary xylem have rarely produced these on a reliable, annual basis.  The lack of growth rings in tropical trees causes a lot of problems for ecologists and foresters. Foresters cannot easily determine how fast their trees are growing, and ecologists are left with no way of accurately determining tree age or reconstructing forest dynamics. 

Myrciaria dubia (see Camu-camu), a riparian shrub from lowland Amazonia, spends a large part of the year underwater. Once the floodwaters recede, the tree has three to four months to grow, flower, and fruit before being submerged again.  Not surprisingly, cross sections of the wood from this species (shown above) exhibit well-defined growth rings. And given that the Amazon River rises and falls only once a year, these growth rings are produced annually.

You can determine the age and growth history of Myrciaria dubia by counting rings and carefully measuring ring widths.  The species produces larger rings during years with low flooding (i.e. it is out of the water for a longer period of time), and smaller rings during years of heavy flooding. [NOTE: The trunk of a large adult may contain up to 40 years of floodpeak data].