Roles of plant species diversity on carbon and nutrient storages in lower montane forest at Doi Suthep-Pui National Park, Chiang Mai Province

Abstract

The study on roles of plant species diversity on carbon and nutrient storages in the lower montane forest at the Doi Suthep-Pui National Park, Chiang Mai province, was investigated by the method of plant community analysis for studying plant community structures, species diversity, biomass production, soil characteristics, carbon and macronutrients. Fifteen sampling plots were arranged in the lower montane forest by a stratified random sampling technique. Each plot had 40 x 40 m2 in size, and dividing into 16, 10 x 10 m2 , subplots. Data collection included measuring stem girths at breast height (1.3 m above ground), tree heights of tree species with height over >1.5. All plots were located using GPS. As a result, a total of 171 species (129 genera and 70 families) was existed in the forest. These included 49 big trees, 38 medium-sized trees, 44 small trees, 18 shrubs and 14 climbers

Plant communities: The quantitative characteristics of plant species in the forest were investigated. Four species had the highest frequency value (100%); Castanopsis acuminatissima, Phoebe paniculata, Symplocos sp. and Diospyros glandulosa. Average density of all species was 4,031 trees/ha. The species with the highest density, dominance and important value index was Castanopsis acuminatissima; 650 trees/ha, 27.23% and 15.06%, respectively. The SWI as indicating plant species diversity was different among 15 plots, 3.72 to 5.16 (4.52+0.43 on average), indicating the high species diversity whereas the FCI were 13.48 to 30.52 (21.72 on average).

Biomass production: Amounts of plant biomass in the LMF varied between 236.86 to 827.02 Mg/ha (438.78 Mg/ha on average). The biomass amounts in stem, branch, leaf and root were calculated in the following order: 153.42 to 541.37, 47.35 to 196.59, 4.09 to 7.33 and 31.93 to 81.73 Mg/ha. Castanopsis acuminatissima contained the highest biomass amount (124.90 Mg/ha) or 28.47% all of species.

Carbon storage in plant biomass: Amounts of carbon stored in plant biomass varied between 117.0 to 408.75 Mg/ha (216.81 Mg/ha on average). The biomass amounts in stem, branch, leaf and root were calculated in the following order: 76.60 to 270.14, 23.06 to 95.74, 1.97 to 3.54 and 15.38 to 39.31 kg/ha. Castanopsis acuminatissima contained the highest carbon amount (61.72 Mg/ha).

Macronutrients storage in plant biomass: Amounts of N nitrogen stored in plant biomass varied between 1,070.01 and 3,666.06 kg/ha (1,959.81 kg/ha on average). Amounts of P varied between 126.38 and 453.81 kg/ha (237.56 kg/ha on average). Amounts of K varied between 530.56 and 1,821.94 kg/ha (972.82 kg/ha on average). Amounts of Ca calcium varied between 2,101.19 and 7,357.75 kg/ha (3,895.56 kg/ha on average). Amounts of Mg varied between 314.44 and 1,096.69 kg/ha (580.69 kg/ha on average). Castanopsis acuminatissima contained the highest amounts of carbon and nutrients among all species in the forest.

Soil characteristics: The LMF soil varied widely with sites in the forest. It varied from a deep to very deep soil (up to more than two meters) with well-developed horizons. The surface soil (Oi/A) was dark brown to dark reddish brown with clay loam to clay. Soil reaction was strongly acid to moderately acid. The soil profile included many horizons: A/Bt1/Bt2/Bt3/Bt4/Bt5/BCr/Cr. Soil textures were sandy loam, sandy clay loam and clay. Soils in all 5 pits were classified in to Order Ultisols.

Carbon and nutrient storages in ecosystem: The amounts of C, N, P, K, Ca and Mg storages in plant biomass were 216.81 Mg/ha 1,959.81, 237.56, 972.81, 3,895.56 and 580.69 kg/ha, respectively. It was estimated that the average amount of organic matter on the forest floor (Ao layers) was 37.48 Mg/ha. According to the average contents of C, N, P, K, Ca and Mg in Ao layers as 34.65%, 1.70%, 0.097%, 0.39%, 1.29% and 0.177%, respectively. Amounts of C, N, available P, extractable K, Ca and Mg in Ao layers were estimated at 12.99 Mg/ha, 637.16 kg/ha, 36.37 kg/ha, 146.17 kg/ha, 483.49 kg/ha and 66.34 kg/ha, respectively while the average amounts in soil of five pits were 452.84 Mg/ha 2,948.01, 74.29, 5,204.31, 5,024.33 and 373.11 kg/ha. The total ecosystem storages were determined in the order of 682.64 Mg/ha 5,544.98, 348.22, 6323.29, 9,403.38 and 1,020.14 kg/ha.

The lower montane forest inside the Doi Sutep-Pui national park had been disturbed through shifting cultivation and selective tree cutting before establishing the park in 1959. The forest recovery has been appeared according to the park regulations and laws, and the forest community develops progressively by natural succession and reforestation. People in villages inside and surrounding the national park have the good cooperation of forest conservation. After 60 years the forest become to be the good condition with high plant species diversity and can store the high amounts of carbon and macronutrients.