Analysis of spatial distribution pattern and its influencing factors of the Tamarix chinensis population on the beach of the muddy coastal zone of Bohai Bay

To explore the spatial distribution pattern of the Tamarix chinensis population and the influencing factors in the muddy coastal zone of Bohai Bay, we studied the T. chinensis forest on the beach of the muddy area of Beihai New District, Binzhou City, Shandong Province. A combination of field investigations and laboratory-based sample analyses were used to measure and analyze the forest density, height, cover, distance from the sea, groundwater depth, soil salinity, basic soil physical properties and soil nutrients. The results showed that the coefficients of variation for the 18 soil and forest indices for T. chinensis were between 0.03 and 0.96; the coefficients of variation for forest density, soil Ca2+ and Na+ content were the greatest, followed by those for soil Mg2+, soil salt content, distance from sea, and available phosphorus, while those for soil bulk density, total phosphorus, pH and other indicators changed less. The population of T. chinensis on the beach of the coastal zone of the Yellow River Delta showed an aggregated distribution, and its aggregation intensity decreased with increasing spatial scale, and it tended to evolve into a random distribution on a larger scale. The spatial distribution of the T. chinensis population showed a certain density dependence; that is, the greater the density was, the greater the aggregation intensity. The reason for the aggregated distribution of the T. chinensis population was mainly related to the biological characteristics of the organism itself or to the interactions between its biological characteristics and environmental factors. T. chinensis forest density was significantly and negatively correlated with organic carbon, total phosphorus, Ca2+, and Na+ (P < 0.05) and very significantly and negatively correlated with available phosphorus (P < 0.01). The soil water content was significantly and positively correlated with the soil salt content, K+, and Na+ (P < 0.01) and significantly and negatively correlated with the distance from the sea and groundwater depth (P < 0.05). The soil salt content was significantly and positively correlated with K+, Na+, and nitrate nitrogen (P < 0.01) and significantly and negatively correlated with distance from the sea and groundwater depth (P < 0.05). K+ and Na+ were the main cations contributing to soil salinity in this T. chinensis forest. With an increase in the distance from the sea, the groundwater depth and forest density gradually increased, and the soil water content and soil salt content gradually decreased. Soil water content, soil salt content, K+, and Na+ content were the dominant factors affecting the spatial distribution pattern for the T. chinensis population in the coastal tidal flat of the Yellow River Delta, followed by organic carbon, ammonia nitrogen, and finally the Mg2+, SO42-, Cl- content, and distance from the sea. The population distribution pattern for T. chinensis was mainly affected by the water and salt conditions, which is a result of the long-term adaptation and evolution of the species within the coastal saline-alkaline environment. Therefore, in the planting management and protection of T. chinensis in the muddy coastal zone of Bohai Bay, we should try to maintain the aggregation growth characteristics of the population according to the adaptation mechanism and biological characteristics of different habitats and community types of T. chinensis, allowing other species to coexist with T. chinensis, and thus optimizing the habitat in the coastal zone.