Abstract
BackgroundRestoration of degraded forest ecosystem is crucial for regional sustainable development. To protect the country’s fragile and fragmented environment, the Chinese government initiated an ecological engineering project, the Natural Forest Protection Program, in seventeen provinces in China beginning in 1998. Fully hillside-closed forest protection (vegetation restoration naturally without any artificial disturbance) was one of vital measures of the Natural Forest Protection Program applied nation wide. Whether plant diversity, biomass and age structure of dominant tree species and soil nutrients in protected stands may become better with increase of protected period are still open problems.MethodsWe investigated community diversity, biomass of dominant tree species, age structures, and analyzed soil chemical properties of a Pinus tabulaeformis population at protected sites representing different protected ages at Huanglongshan Forest Bureau on the Loess Plateau, Shaanxi, China.ResultsPlant species richness of Pinus tabulaeformis community was significantly affected (p < 0.05) by forest protection and the effect attenuated with protection age. Shannon evenness index of plant species generally increased with protection age. Stands protected for 45 years had the highest tree biomass and considerable natural regeneration capacity. Contents of organic carbon, available phosphorus and available potassium in top soil increased in protected stands less than 45 years, however decreased significantly thereafter. Long-term forest protection also decreased the content of mineral nitrogen in top soil.DiscussionWe found that the richness of shrubs and herbs was significantly affected by forest protection, and evenness indices of tree, shrub and herb increased inconsistently with protected ages. Forest protection created more complex age structures and tree densities with increasing age of protection. Content of soil mineral nitrogen at 0–20 cm soil depth showed a decreasing trend in stands of up to 30 years. Soil available phosphorus and potassium contents were higher in stands with greater proportions of big and medium trees. Long-term protection (>45 years) of Pinus tabulaeformis stands in southeast Loess Plateau, China, may be associated with decreasing plant species richness, proportion of medium to large trees, dominant biomass of Pinus tabulaeformis and soil nutrients.
Highlights
Ecological restoration is being recognized as an international priority (Aronson & Alexander, 2013; Wortley, Hero & Howes, 2013) and it plays a crucial role in rebuilding ecological equilibrium and reversing ecosystem degradation (Ma, Lv & Li, 2013)
The objectives of this study are to address a few of these key knowledge gaps, including: (i) do the stands exhibit significant differences in plant assemblage; (ii) does soil fertility change with stand age structure; (iii) can a functional relationship be defined regarding length of stand protection and stand quality, i.e., are stands protected for longer time frames ‘‘better’’ than other stands; and (iv) based on findings of i–iii above, can a preliminary estimate regarding the optimal time span for Pinus tabulaeformis stands be recommended to the Natural Forest Protection Program?
Our results showed that long-term protection (>45 years) of Pinus tabulaeformis stands in southeast Loess Plateau, China, may be associated with decreasing plant species richness (Table 2), proportion of medium to large trees (Fig. 6), dominant tree biomass (Fig. 5) and soil nutrients (Fig. 7)
Summary
Ecological restoration is being recognized as an international priority (Aronson & Alexander, 2013; Wortley, Hero & Howes, 2013) and it plays a crucial role in rebuilding ecological equilibrium and reversing ecosystem degradation (Ma, Lv & Li, 2013). Hillside-closed forest protection (vegetation restoration naturally without any artificial disturbance) was applied nation-wide. To protect the country’s fragile and fragmented environment, the Chinese government initiated an ecological engineering project, the Natural Forest Protection Program, in seventeen provinces in China beginning in 1998. Biomass and age structure of dominant tree species and soil nutrients in protected stands may become better with increase of protected period are still open problems. Available phosphorus and available potassium in top soil increased in protected stands less than 45 years, decreased significantly thereafter. Long-term protection (>45 years) of Pinus tabulaeformis stands in southeast Loess Plateau, China, may be associated with decreasing plant species richness, proportion of medium to large trees, dominant biomass of Pinus tabulaeformis and soil nutrients
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