Carbon stocks down 12.9% at Lantapan watershed – study

MALAYBALAY CITY (MindaNews/28 April) — The total carbon stocks at the Manupali watershed in Lantapan town in Bukidnon reduced by 12.9 percent within a 17-year period, from 1990 to 2007, according to a study presented Thursday at the Bukidnon Watershed and River Basin Forum in this city.

From 1,645,690.24 tons in 1990, the carbon stocks or the quantity of carbon “sequestered” at the watershed decreased to 1,433,250.7 tons in 2007 based on an assessment within the three sub-watersheds of Alanib, Maagnao and Kulasihan, according to Myrna Decipulo, of the Environmental Research and Development Services of the Department of Environment and Natural Resources.

Alanib, Maagnao and Kulasihan are the major rivers in Lantapan whose headwaters are in the Mount Kitanglad Range.

Decipulo, a senior scientist at ERD who headed the assessment, attributed the finding to the decrease in the area’s natural as well as manmade forest covers. She said that in 1990, natural old growth forests accounted for 6,737.4 hectares of the watershed. In 2002, it decreased to 6,454.44 hectares and shrank further to 6,305.22 hectares in 2007.

Decipulo added that aside from declining natural forest cover there was also a decrease in the size of areas for agroforestry farms. She said that in 1990, agroforestry farms covered 7,459.65 hectares of the Manupali watershed. The figure increased to 7,665.93 hectares in 2002, but went down to 5,287.14 hectares in 2007.

Scientists have confirmed that trees play a significant role in controlling the release of carbon into the atmosphere. Huge emissions of carbon into the atmosphere in the past several decades have been blamed for the phenomenon called global warming which in turn has caused drastic changes in climatic conditions worldwide.

The highest increase in terms of land area is sugar cane plantation which shot up from 218.88 hectares in 1990 to 863.91 hectares in 2007, Decipulo said.

“This may be due to the ready market for sugar cane with the presence of two sugar mills in Bukidnon,” she said.

The assessment also found out that “densely populated manmade forest plantation can stock carbon higher than the natural old growth forest in terms of above ground biomass but in terms of litters and necromass, the old growth natural forest yielded the highest.”

Biomass refers to the stems, total height and diameter of live trees and under storey or vegetation growing beneath bigger trees.

Necromass includes dead trunks, standing dead trees, litter in the form of leaves, stem, twigs, flowers, fruits, and other residues, Decipulo explained.

Necromass in agroforestry farm is negligible, she added. “Agro forestry farms are dominated by fruit trees and coffee which normally do not grow as big as forest trees, thus lesser carbon stock.”

The assessment proved that trees have more carbon stocks compared to herbaceous vegetations per unit area, Decipulo said.

Among the herbaceous plants that were assessed, grassland and shrub lands with natural regrowth exhibited the lowest carbon stock in terms of above ground biomass with 2.27 tons per hectare only.

“However, it does not differ significantly from corn and banana plantations that yielded almost the same stock with 2.58 and 2.53 tons per hectare, respectively,” Decipulo said.

The dense population of sugarcane yielded a high carbon stock of 12.85 tons per hectare, she said.

The study covered 28 trees with 30-centimeter diameter at breast height and above within a 20m x 100m plot, and 32 trees of smaller diameter within a 5m x 40m plot.

Decipulo said the carbon content for each tree above 30cm dbh was computed to range from 117 to 4,436 kg, while those less than 30cm dbh has a carbon content of 1.7 to 61.8 kg per tree.

Jose Hermis Patricio, chair of Central Mindanao University’s Environment Science Department, said the assessment done at the Manupali watershed should have included soil and root biomass as carbon sink. He said carbon in soil has the longest “residence time”.

Patricio also recommended a province-wide carbon stock assessment to measure the carbon sequestration capability of lesser known indigenous tree species.

He lamented that unlike other Asian countries, the Philippines has no equipment that can measure carbon stocks in real time. (H. Marcos C. Mordeno / MindaNews)