Date Published: December 23, 2014
Publisher: Public Library of Science
Author(s): Syed Moazzam Nizami, Zhang Yiping, Sha Liqing, Wei Zhao, Xiang Zhang, Shiping Wang.
Extension of the rotation length in forest management has been highlighted in Article 3.4 of the Kyoto Protocol to help the countries in their commitments for reduction in greenhouse gas emissions. CO2FIX Model Ver.3.2 was used to examine the dynamics of carbon stocks (C stocks) in a rubber plantation in South Western China with the changing rotation lengths. To estimate the efficiency of increasing the rotation length as an Article 3.4 activity, study predicted that the rubber production and C stocks of the ecosystem increased with the increasing rotation (25, 30, 35, 40 and 45 years). While comparing the pace of growth both in economical (rubber production) and ecological (C stocks) terms in each rotation, 40 years rotation length showed maximum production and C stocks. After elongation of 40 year rotation to four consecutive cycles, it was concluded that the total C stocks of the ecosystem were 186.65 Mg ha-1. The longer rotation lengths showed comparatively increased C stocks in below ground C stock after consecutive four rotations. The pace of C input (Mg C ha-1yr-1) and rubber production indicated that 40years rotation is best suited for rubber plantation. The study has developed carbon mitigation based on four rotation scenarios. The possible stimulated increase in C stocks of the entire ecosystem after consecutive long rotations indicated that the emphasis must be paid on deciding the rotation of rubber plantation in SW China for reporting under article 3.4 of the Kyoto Protocol.
Forest plantations have been considered to measure carbon sequestered from the atmosphere and mitigate future climate change . Globally, tree plantations cover 396108 ha in 2005, and still increasing with a relatively annual expansion rate of 2%. While reforestation on the natural forest land accounts for about half of the overall increased area of tree plantations . In a meta-analysis , the forest plantation has a 28% lower C storage compared to natural wood. This led to a doubt against the replacement of natural forests by the plantations as a measure of climate change mitigation. Nevertheless, most of the plantation forests at current rotation length do not achieve their maximum biological storage yet; prolongation of the rotation period generally results in increased C sequestration . Additionally, there is also the possibility that plantation forests of very old ages would go forward to accumulate C, since recent surveys have reported that old-growth natural forests could all the same operate as a C sink , . However, over mature or old-growth plantation forests are rarely included in comparison with natural forests so far. For instance, the mean stand age of plantation forests in the synthesis of  was just 27 years. Therefore, it is fair that the reduced sequestration potential of plantation forests was merely due to their current rotations too short for C pool to regain to the pre-disturbance level. However, there is still a lack of explicit trajectories of post-harvest C stocks in tree plantations, particularly those established on the natural forest lands, which contributes to the uncertainty about the role of plantation forests in global terrestrial ecosystem C cycle .
The investigation of the economics (income) of the rubber production and the ecology (C stocking) pointed out that an increase in both income and C stocks can be achieved by changing the rotation of rubber under the light of Article 3.4 of the Kyoto Protocol. In order to cope with the environmental hazards that may result in more erosion/runoff after the clear cutting at the age of 40 years, the introduction of some economically and ecologically important species should be carried out in between the rubber trees according to the suitability (mono culture or agroforestry) from the age of 35 years. These species may include Coffea arabica, Theobroma cacao, Myristica yunnanensis, Bennettiodendron leprosipes, Gmelina arborea, Mesua ferrea, Erythrophleum fordii, Podocarpus fleuryi, Shorea chinensis, Dipterocarpus tubinatus.