Study On The Forestation Effect Of Coniferous And Broad-leaved Mixed Forests In Mountain Area Of Northern Fujian

Pure coniferous forest would cause lots of problems such as lack of available tree species, biodiversity decrease, instability of forestry ecosystem, degradation of soil fertility because of continuous plantation. The construction of coniferous and broad-leaved mixed forest was one of the effective ways to solve the problem.This thesis concentrated on coniferous and broad-leaved mixed forest where pure Chinese fir forest was planted before. That forest was planted base on orthogonal design, and tree species (Cunninghamia lanceolata,Chinese fir,Pinus massoniana, Liquidambar formosana, Liriodendron chinense, Alnus cremastogyne), density, proportion of different tree species, fertilize method and management practices were considered as main factors.Soil condition, understory plant biodiversity, litter nutrient and status of tree growth were surveyed in 2009. The results were showed as follows:(1)Soil condition: the soils were acidic in all the 22 fields, pH is mostly in the range of 3.3⁴.5. The pH was a little higher in mixed forest than that in pure Chinese fir forest.It is continuous plantation of Chinese fir that made the soil acidic.Soil nutrient quantity was low in all fields, especially N and P. Soil fertility coefficient showed that soil fertility of the mixed forest was much higher than that of pure forest. So, the construction of mixed forest contributes a lot to improve the soil condition, such as pH and soil fertility.(2)Analysis on stock, nutrient condition and water conservation ability of the litter,showed that stocks litter quantity of mixed forests are in the range of 264.75⁸71.75 kg/hm^-2, and 385.25 kg/hm^-2 in that of continuous Chinese fir plantation forest. Contents of litter nutrient were as follows: N was3.16⁷.69g·kg^-1,P was 0.24⁰.52 g·kg^-1,K was 0.26⁰.75g·kg^-1. Compared to that of the continuous Chinese fir plantation forest, only the litter stocks of Alnus cremastogyne×Cunninghamia lanceolata (1:2)and Alnus cremastogyne×Cunninghamia lanceolata (1:3) was lower than pure Chinese fir, the contents of N and P in mixed forest were slightly higher than that of pure Chinese fir.The water conservation ability of mixed forest was stronger than that of continuous Chinese fir plantation forest.So,the construction of mixed forest helped to increase litter stocks,and eventually enhanced its water conservation ability.(3)Understory plant diversity: the order of abundance indexes in every component of mixed forest was herbaceous layer>shrub layer>inter layer. Order of shannon-wienner was shrub layer>herbaceous layer>inter layer. Order of dominance evenness index was inter layer> herbaceous layer>shrub layer. Diversity of understory plant was scare, and dominant species was obvious, and the distribution was an even in pure forest. However, those factors were appear opposite in the mixed forest. The distinguish was not obvious between pure forest and mixed forest.(4)Growth condition of standing woods: Of all the five tree species, growth potential of Alnus cremastogyne was the worst, All the standing tree of Alnus cremastogyne disappeared.The growth rate of DBH and height of trees slowed down with age. The standard woods had expired the fast-growing period. However the average mass volume growth has not come to the current annual increasement, and the maximum of average growth had not achieved yet, meaning that there was still growth potential despite of the bad current growth condition in general. According to previous study, the single tree volume growth of mixed forest was lower than that of continuous Chinese fir plantation forest, however, we found that the gross standing stock was higher in the mixed forest.The difference of the average DBH and the average height was not obvious between them.(5)Evaluation of the mixing effect showed that from the result of orthogonal experiment analysis, the difference in the factors tree species, density, proportion of different tree species, fertilize method and management practice respectively were not obvious. Among those five factors, proportion of different tree species contributed the most to the gross standing stock, and the management practice ranks the second, density ranks the last. However, the best scheme could not obtained from the analysis. A regression equation (below) was established based on the gross volume stock and the five factors, which could help to express the relationshipeffectively. Y|^=57.01x₁₁+16.07x₁₂+45.96x₁₃+59.59x₁₄+9.89x₁₅-4.96x₁₆+0.00x₂₁+67.52x₂₂+45.81x₂₃+0.00x₃₁+9.12x₃₂+28.06x₃₃+0.00x₄₁-5.04x₄₂+54.76x₄₃+0.00x₅₁+65.44x₅₂+14.92x₅₃From the analysis above, the conclusion was that: compared to the continuous Chinese fir plantation forest, mixed forest showed better effect in water conservation, and had a higher volume stock. However, the effect biodiversity increase was not obvious. A regression equation was established which could help to improve the mixing method of plantation in future.