| Pinus massoniana is not only the main commercial tree species but also the pioneer species for forestations in southern China, which has important economic value and ecological service function. Pinus massoniana plantation is one of the most widely distributed artificial forests, next to Cunninghamia Lanceolata and Populus plantation, whose areas reached335.85hm2, accounting for8.40%of the total. With the speed of constructing artificial forest accelerating, the areas increase rapidly. Successive planting of pure forests is common with decreased biodiversities and serious soil degradations. This paper designed forest-green manure plant, forest-medical plant, forest-agriculture and forest-herb modes to restore vegetation in the second generation of successive planting of the pure forest of Pinus massoniana that had apparent degraded characteristics from the view of vegetation, and then analyzed effect of different modes on growth of forests, micro-ecosystem effect and the improvement of community structures. The main results:1. The construction of undergrowth vegetation restoration modes in Pinus massoniana plantation. By investigating key community structure characteristics of Pinus massoniana plantation, there were117species belonging to96genera and57families in the sampling plot, of which Rosaceae, Gramineae, Fagaceae and Rubiaceae were frequently seen. In the young forest, the Importance Values (Ⅳ) of Lespedeza davidii, Loropetalum chinensis, Quercus fabric, Syzygium buxifolium, Rhododendron simsii were all over25.00in the shrub layer; the IV of Miscanthus was the highest in the herb layer, reaching80.38. In middle-age forest, the IVs of Clerodendrum trichotomum and Gardenia jasminoides were the highest in the shrub layer, the IVs of Loropetalum chinensis, Rubus tsangorum and Rhododendron simsii were relatively high. In the herb layer, both Lophatherum gracile and Rumex japonicus were characteristic species, Phytolacca americana, Polygonum flaccidum, Polygonum perfoliatum, Semiaguilegia adoxoides, Miscanthus and Artemisia argyi were all common species. I constructed two forest-green manure plant modes, namely Amorpha fruticosa+Triolium repens and Lespedeza davidii+Triolium repens in the young forest, the forest-medical plant mode, namely Gardenia jasminoides+ Clerodendrum trichotomum+Lophatherum gracile, and the forest-agriculture mode, namely Camellia sinensis, in the middle-age forest.2. The effect of undergrowth restoration on growth of Pinus massoniana plantation. In the young forest, compared with the check plot, the growth rates of plant height in the forest-green manure plant mode1and2increased by42.16%and59.80%respectively, mean growth rates of ground diameter increased by88.52%and124.59%respectively. In the middle age forest, the forest-medical plant mode was the best, whose plant height, breast diameter and tree volume increased by78.79%,83.33%and31.90%respectively, reaching0.59m,1.54m and4.1257m3/hm2respectively.3. The micro-ecosystem effect of soil of undergrowth restoration. In the young forest, the forest-green manure plant mode2was slightly superior to the mode1on the whole. In the forest-green manure plant mode2, the soil bacteria quantity and the activity of urease increased by865%(reaching4.30X106cfu/g) and17.28%respectively, soil porosity and bulk density reached48.54%and1.36g/cm3respectively. In the middle age forest, the forest-medicinal plant mode was obviously superior to the others in terms of bacteria quantity, the activity of the soil enzymes and the improvement of physical and chemical properties of soil.4. The improvement of community structure after undergrowth restoration. In the young forest, Lespedeza davidii showed good adaptability as native tree species. In middle age forest, it was rich in species in the shrub layer of forest-medical plant mode with the best community structure. Although competition was violent between species, the original species did not decline in initial stage of undergrowth restoration. On the contrary, the growth of original individuals can be promoted by the undergrowth restoration to some extent.According to these results, In Zijinshan natural forest of Hengshan county, Lespedeza davidii was suggested first to restore vegetation in young forest of successive planting Pinus massoniana plantation, Amorpha fruticosa can be selected as a candidate. The forest-medical plant mode (Gardenia jasminoides+Clerodendrum trichotomum+Lophatherum gracile) was suggested first to restore vegetation in middle age forest. The forest-agriculture had a common effect, in which Camellia sinensis, however, can regulate micro climate in forests. The forest-agriculture mode with the combination of forestry and agriculture can be further studied. |
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