Study on Pinus elliottii Plantations in Pengchang Forest Farm of Jingmen City

Pengfei XU Maochang LIANG Zhenjun WU Lidan FANG Yongjun FEI Die HU

Abstract ［Objectives］This study was conducted to improve the ecological and economic benefits of Pinus elliottii plantations in Pengchang Forest Farm, Jingmen City.

［Methods］ P. elliottii plantations in Pengchang Forest Farm in Jingmen City were selected as the research object, and the appearance and quantitative characteristics of P. elliottii community were studied and analyzed by a sampling method.

［Results］ Phanerophytes were the most in the P. elliottii community, accounting for 50%. In the community, except P. elliottii, the importance values of native plants were higher. The order of species diversity of P. elliottii community in Pengchang Forest Farm was herb layer, tree layer and shrub layer. The stress resistance of the community was weak, and strong intraspecific competition existed in P. elliottii. It is recommended to thin P. elliottii trees with insufficient lighting, poor growth potential and severely damaged tree body, and interplant Phoebe zhennan after thinning the P. elliottii plantations, so as to create a coniferous and broad-leaved evergreen mixed forest.

［Conclusions］ This study provides scientific support for thinning, tending, and forest management of P. elliottii plantations.

Key words Pinus elliottii; Plantation; Community science; Tending thinning

Received: June 23, 2022  Accepted: August 25, 2022

Pengfei XU (1998-), male, P. R. China, master candidate, devoted to research about garden plants.

*Corresponding author. Die HU (1985-), female, P. R. China, doctoral candidate, lecturer, devoted to systematic and evolutionary botany research.

Pinus elliottii is an evergreen tree species of the genus Pinus in the family Pinaceae, which is native to warm and humid low-altitude areas of the southeastern United States. It has been introduced and cultivated in Hubei, Jiangxi, Jiangsu, Anhui, Guangdong, Taiwan and other places in China［1］. P. elliottii is resistant to barrenness, and has fast growth rate, good adaptability, tall and straight tree shape, excellent texture, and few pests and diseases［2］. In most areas south of the Yangtze River in China, it can become a better tree species for landscaping and ecological afforestation. Pengchang Forest Farm in Jingmen City, as a national base for improved varieties of P. elliottii, undertakes the monitoring and maintenance of P. elliottii plantations. The forest farm has a history of nearly 60 years of introduction and cultivation of P. elliottii, and certain achievements have been made in the scientific research and promotion of P. elliottii and the approval of improved varieties.

The current research on P. elliottii forests includes disease resistance research［3］, shelterbelt afforestation［4］, understory vegetation diversity, etc. In this study, ecological research was carried out on the P. elliottii plantations in Pengchang Forest Farm, and ecological investigations were carried out on the species under the P. elliottii forest, and the growth status of the P. elliottii forest was analyzed as well, aiming to provide scientific support for thinning, tending, and forest management of the P. elliottii forest.

Materials and Methods

General situation of the investigation area

The improved P. elliottii seed base of Jingmen City is located in Shilipu Town, Shayang County. Shayang County is adjacent to Jianghan Plain in the south and Jingshan Mountain in the northwest. It is located in the lake area and hilly area, the terrain is high in the north and low in the south［5］. It has a northern subtropical humid continental monsoon climate, with four distinct seasons, the same period of rain and heat, a long frost-free period, an annual average temperature of 16.1 ℃, and an annual average precipitation of 1 010.8 mm［6］. Pengchang Forest Farm in Jingmen City［7］ was identified as a national base for improved varieties of P. elliottii in 2009. The forest farm was established in 1973, with an operating area of 12 km2, including 9.7 km2 of pure P. elliottii forest, 0.85 km2 of P. elliottii seed garden, and 1.33 km2 of landscaping nursery.

Methods

In July 2020, the ecological method［8］ was adopted to investigate the P. elliottii plantation community in Pengchang Forest Farm of Jingmen City. Representative plantations with less artificial disturbance were elected as sample plots, and quadrats with a size of 20 m × 20 m were selected in each plot, and five sub-quadrats of 4 m × 4 m were selected in each quadrat. The latitude and longitude coordinates, altitude, slope and slope aspect of the investigated plots were recorded using GPS instruments and other equipment; the coverage and canopy closure were visually observed; environmental factors such as terrain and soil were recorded; the associated species of the herb layer, shrub layer and tree layer in the plots were recorded; and the "single-tree tally survey method" was used to record the diameter at breast height, ground diameter, crown width, plant height, row spacing, plant spacing, etc.

Plant life forms can express community appearance characteristics and vertical structure, and community appearance characteristics are one of the important indicators of community classification［9］. According to the Raunkiaer life-form system［10］, the life forms of the understory species in the P. elliottii forest were determined, and the life-form spectra were made by classifying them.

All species in the surveyed quadrats were recorded and comprehensive statistics were made. According to Mr. Wu Zhengyi’s Distribution Area Types of Spermatophyta Genera in China［11］ and World Spermatophyta Family Distribution Area Type System［12］ and his revised division standards, the distribution area types of species families and genera were statistically divided.

Data processing and analysis

The quantitative characteristics of a community can reflect the overall structural characteristics of the community. Formulas for quantitative characteristics and dominance analysis calculation were as follows: Density=Number of a species in the community/Plot area; Frequency=Number of quadrats where a species appears/Total number of quadrats; Dominance=Bottom area or total coverage area/Sample plot area. The calculation methods of species importance values adopted Song’s method［13］:

Relative density=Ratio of the density of a species/Total density of all species×100%;

Relative dominance=Ratio of the dominance of a species/Total dominance of all species×100%;

Relative frequency=Ratio of the frequency of a species/Total frequency of all species×100%;

Importance value of tree=(Relative density + Relative frequency + Relative dominance)/3;

Important value of shrub/herb= (Relative density + Relative frequency + Relative dominance)/3.

Species diversity indexes included Margalef richness index, Simpson diversity index, Shannon-wiener diversity index and Pielou evenness index［14］, and the calculation methods were as follows［15］:

Margalef richness index ( DM=S-1lnN);

Simpson diversity index ( DS=1-∑si=1P2i);

Shannon-wiener diversity index ( H=-∑si=1Pilog1Pi);

Pielou evenness index (J=HlnS).

In the equations, S is the number of all species in the plot; N is the total number of individuals in the community; and Pi is the ratio of the number of individuals of species i to the total individuals in the community.

Results and Analysis

Life forms of P. elliottii community

According to Table 2, it can be seen that the number of life forms in the community from high to low were phanerophytes, chamaephytes, lianas, epiphytes, hemicryptophytes, geophytes and therophytes. Specifically, there were 29 species of phanerophytes, accounting for 50%, 19 species of chamaephytes, accounting for 32.76%, 5 species of lianas, accounting for 8.62%, 2 species of epiphytes, accounting for 3.45%, and hemicryptophytes, geophytes and therophytes all included one species, accounting for 1.72%.

Floristic analysis of plant genera in P. elliottii community

It can be seen from Table 3 that the plants of 53 genera in the P. elliottii plantations of Pengchang Forest Farm could be divided into 11 distribution types. Except for the world distribution, the pan-tropical distribution type accounted for the highest proportion, accounting for 19.56%, and the north temperate zone distribution type and the East Asia distribution type had obvious advantages, accounting for 15.22%, which was in line with the geographical environment of Pengchang Forest Farm. The cumulative tropical distribution (including pantropical distribution, tropical Asia and tropical America discontinuous distribution, old world tropical distribution, tropical Asia to tropical Oceania distribution, and tropical Asia distribution) accounted for 52.17% of the total genera, and the temperate distribution accounted for 17.39%. Based on this, it could be seen that in the floristic distribution of the plant genera in the P. elliottii plantation community, the tropical component had a greater dominance.

Analysis of important values of main vegetation under the forest

It can be seen from Table 4 that among the dominant species in the arbor layer of the P. elliottii forest, the important value of the main species, P. elliottii, reached 0.275. Except for P. elliottii, the important values of Cinnamomum camphora and Melia azedarach in the arbor layer species reached 0.082 and 0.062, respectively. In the survey area, Koelreuteria paniculata were mostly small trees, and showed an important value of 0.060; and Quercus aliena had a high frequency, but the individuals were small and the dominance was low, and the important value was 0.057. Among the plants in the shrub layer, the important value of Rubus parvifolius reached 0.079, which was higher than that of other plants in the shrub layer; the important value of Solanum pseudocapsicum was 0.067; and the important value of Rosa multiflora was 0.063. Among herbaceous plants, Chrysanthemum indicum had the highest important value at 0.050, followed by Asparagus cochinchinensis at 0.041.

Agricultural Biotechnology2022

Community species diversity

According to Table 5, it can be seen that the Margalef richness index of the herb layer was the highest, indicating that the species richness of the herb layer was higher. The species richness of the tree layer was the second, and that of the shrub layer was the lowest. The Simpson index of the arbor layer was the highest, indicating that the probability of randomly collecting the same species in the arbor layer was the highest, followed by the herb layer, and it was the smallest in the shrub layer. The Shannon-wiener index of the herb layer was the highest, indicating that the herb layer had the highest degree of complexity and contained the largest amount of information, followed by the tree layer, and the shrub layer, which was the lowest. The Pielou evenness index of the herb layer was the highest, indicating that the distribution of species in the herb layer was relatively uniform, while the distribution of species in the shrub layer and tree layer was relatively random. According to the species diversity analysis of the tree layer, shrub layer and herb layer, the species diversity of different layers of the P. elliottii community ranked as herb layer > tree layer > shrub layer.

Conclusions and Discussion

Conclusions

The P. elliottii plantations were all investigated to have yellow-brown soil, and they are located at an altitude between 50 and 70 m and had a canopy closure of 70%-80%. Phanerophytes accounted for 50% of the P. elliottii community, with 29 species, and the chamaephytes accounted for 32.76%, with 19 species. In the P. elliottii community, there were 51 species of angiosperms, belonging to 47 genera of 31 families, 6 species of pteridophytes, belonging to 5 genera of 4 families, and only 1 gymnosperm, i.e, P. elliottii. Among them, the species and genera of Leguminosae, Rosaceae and Moraceae were the most numerous. The important value of P. elliottii was 0.275, which was the highest, followed by C. camphora, M. azedarach and K. paniculata, the important values of which were 0.082, 0.062, and 0.060, respectively. The species with the highest important value in the shrub layer was Rubus parvifolius with an important value of 0.079, followed by S. pseudocapsicum with an important value of 0.067. These plants are also native to Jingmen. The herb layer showed a Margalef richness index reaching 2.686 539 754 and a Shannon-wiener index of 4.481 690 536, both of which were the highest, and the Simpson index was 0.944 638 175, which was the second highest. The herb layer had the highest species diversity, which was related to the suitable environment under the plantations.

Discussion

The survey object of this study was plantation forests, which had the characteristics of strong artificial disturbance, low species diversity, and easy occurrence of pests and diseases compared with natural forests. During the survey, we found that many shorter P. elliottii were in poor growth condition and had obvious self-thinning phenomenon. Due to insufficient lighting, the branches at the lower part of the plants had all died.

P. elliottii trees have high requirements for lighting, therefore, plants with poor lighting and poor growth potential can be thinned in areas with small plant spacing, and other trees can be interplanted to increase species richness, thereby increasing community productivity［16］. Traditional forest management is to promote the rapid growth of reserved trees according to the characteristics and cultivation goals of forest stands, and according to the principles of removing the small and keeping the big, removing the dense and keeping the thin, removing the inferior and keeping the excellent［17］, which is a management measure to improve the efficiency of forest stands. Previous studies have shown that the growth of Phoebe zhennan and Chinese fir in mixed forest of Chinese fir and P. zhennan is higher than that of pure P. zhennan and Chinese fir［18］. Therefore, it is suggested that interplanting P. zhennan after thinning of P. elliottii plantations can not only improve species diversity and community stress resistance, but also improve economic benefits.

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