Soil

In the course of studying the fuelwood benefits of shellac forests, investigations were also conducted on the impact of these forests on soil fertility. The findings indicate that implementing intercropping with grain in shellac fuelwood forests on long-abandoned fallow lands can restore and enhance soil fertility in a relatively short period, with a more pronounced fertilization effect compared to monoculture shellac forests. Although monoculture shellac forests can also improve soil fertility, they require a longer duration to do so.

In 1986, an intercropping system with grain was implemented in a shellac fuelwood forest on abandoned land in the rear mountains of Jinfan storage in Jingdong County, Yunnan. Two years later, investigations showed that the organic matter content in the topsoil layer (0-40cm) increased from 1% (before afforestation, i.e., the control) to nearly 2%; total nitrogen content rose from 0.05% to 0.10%. In addition, the content of phosphorus and potassium in the soil also increased.

The reasons for the increase in soil nutrient content are as follows: Firstly, the application of fertilizers, such as farmyard manure, cow and horse dung, urea, and other inorganic fertilizers, as well as foliar fertilizers. These fertilizers not only meet the current year's needs of the trees and intercropped crops but also contribute the remainder to the soil, becoming a potential source of fertility. Secondly, the stems and leaves left in the field after crop harvest become another important source of soil organic matter and other nutrients.

Observations from soil profile excavations indicate that after establishing shellac host forests on suitable barren slopes, the growth of host tree root systems, which are broader, deeper, and more robust than those of herbaceous plants and have a greater biomass, results in the formation of numerous water-retaining cavities and channels in the deeper soil layers upon their death. Furthermore, the interception by the canopy and ground cover allows rainwater ample time to infiltrate deep into the soil, reducing the likelihood of surface runoff and thereby improving the soil's moisture conditions.

Soil sample analyses have shown that during the rainy season, the moisture content of the surface soil on barren slopes is at its highest, while the moisture content of the subsoil layer (25-75cm) decreases progressively with depth. However, moisture content increases again in the bedrock layer. In shellac host forests, as the canopy density increases, the moisture content of the surface soil gradually decreases, whereas the moisture content of the subsoil layer increases, and the moisture content in the bedrock layer relatively decreases. This suggests that the establishment of host trees improves the moisture conditions in the middle and deep soil layers, where plant root systems are primarily distributed, thereby enhancing the effective utilization of soil moisture.

Moisture is one of the primary factors of soil fertility in forest lands. The condition of soil moisture directly affects the growth of host plant roots and their distribution throughout the soil profile. If the soil moisture condition in the forest land is favorable and evenly distributed across different parts and vertical layers of the plot, then the plant root system will grow well and tend to distribute evenly throughout the soil profile. Investigations of the root systems in the soil profiles inside and outside the shellac host forests at the Green Spring experimental site indicate that, compared to barren slopes, the moisture content in various parts of the soil profile in shellac forest lands is extremely uneven. From the topsoil layer to the bedrock layer, soil moisture content gradually decreases, and a similar trend is observed in the distribution of root systems. However, within the shellac host forests, plant root systems are well-developed, and the distribution of roots in the soil profile is relatively even, with minor variations in soil moisture. This suggests that the establishment of shellac host forests has led to an improvement in the soil fertility of the local barren slopes.