Spatial distribution and association of seedlings and saplings in a spruce-fir forest in the Changbai Mountains area of northeastern China

ObjectiveSpatial distribution of seedlings and saplings is an important factor affecting the dynamic changes of forest communities. Spatial distribution of Picea jezoensis and Abies nephrolepis seedlings at different height levels was analyzed, and spatial association between their seedlings and surrounding small and large trees was studied in this paper to explore the spatial changes in a Picea jezoensis and Abies nephrolepis forest and to find the impact of spatial structure on Picea jezoensis and Abies nephrolepis seedlings. The measures were proposed for promoting natural regeneration, and theoretical basis was provided for the management plans in a Picea jezoensis and Abies nephrolepis forest.

MethodA sample plot of typical coniferous and broadleaved mixed forest with the area of 0.36 ha was set up in Jingouling Forest Farm, Jilin of northeastern China in August 2017. The SADIE spatial analysis method was used to analyze the spatial distribution of seedlings at different height levels.

ResultWithin the forest stand, the diameter distribution showed an inverted “J” curve, the diameters of the Acer mono and Abies nephrolepis showed growth distribution pattern, and the diameter distribution of Picea jezoensis and Korean pine showed multi-peak fluctuation curves. The diameters of small trees in the forest stand showed an aggregate distribution with the aggregation index of I_a > 1 and randomization test probability of P_a < 0.025. The diameters of large trees were randomly distributed with P_a value between 0.025 and 0.975. The spatial distribution of forest stands changed from aggregation to randomization with the growth and development of forest trees. Since the Abies nephrolepis was one of the main tree species, its spatial distribution was similar to the overall spatial distribution in the forest stand. The diameters of Picea jezoensis had a random distribution. The locations of Abies nephrolepis seedlings had obvious spatial association with the locations of large Abies nephrolepis trees, and they were positively spatial associated with locations of all Picea jezoensis trees. Abies nephrolepis seedlings had good shade tolerance. The locations of Picea jezoensis seedlings generally showed spatial segregation or spatial irrelevance, which was only positively correlated with the locations of Abies nephrolepis trees, so Picea jezoensis and Abies nephrolepis are good companion species. The locations of Abies nephrolepis seedlings at Ⅰ to Ⅲ height levels had similar spatial associations, the locations of Abies nephrolepis seedlings at Ⅳ and Ⅴ height levels had similar spatial associations, and the locations of Picea jezoensis seedlings at Ⅰ and Ⅱ height levels had similar spatial associations.

ConclusionWithin the forest stand, the number of Abies nephrolepis seedlings is more than Picea jezoensis seedlings. Abies nephrolepis seedlings are positively spatial associated with the trees, which is beneficial to the regeneration of Abies nephrolepis. The quality of Picea jezoensis wood is good. As the main target species, the number of Picea jezoensis and its seedlings is small, and seedlings and saplings of Picea jezoensis show a separated spatial distribution with small trees and large trees. The regeneration status of Picea jezoensis under the forest is poor. As a result, appropriate shelter measures should be adopted for Picea jezoensis at the seedling stage, and management measures like cutting in the sapling period may be proposed to promote the growth of Picea jezoensis seedlings. In addition, the spatial structure of the stand could be adjusted for releasing the growth space of Picea jezoensis by appropriate controlled number of Abies nephrolepis in order to increase the number of Picea jezoensis mother trees. Then, seed production capacity will be improved, and the regeneration of Picea jezoensis will be promoted.