Spatial distribution patterns and intra-specific competition of pine (Pinus yunnanensis) in abandoned farmland under the Sloping Land Conservation Program

The Sloping Land Conversion Program is also known as the ‘Returning Farmland to Forest Program’ intent to gradually recreate farmlands back to the original forested state. Providing cognition on the effects of the policy on the distribution of dominant species is important to better understand plant community structures, development dynamics, regeneration conditions, and possible underlying ecological mechanisms. The purport of this study is to inspect the population structure of Pinus yunnanensis in a 2500 m2 area of abandoned farmland where restituted to forest in 2004. The results showed that the population structure of P. yunnanensis settled on tree age formed an inverted J-distribution (20.1% seedlings, 34.2% young trees, 38.5% middle-aged trees, and 7.1% adult trees) since 2009, whereas seedlings, young trees, and middle-aged trees showed clustered distribution. Seedlings showed the highest aggregation degree (g(r) = 6.4), followed by young trees (g(r) = 2.3) and middle-aged trees (g(r) = 1.7), but a random distribution showed in adults throughout the research area. The spatial relationships among seedlings, young trees, middle-aged trees, and adults indicated that the aggregation consequences increased with the decreasing difference in the diameter at breast height. Furthermore, the correlation of canopy height and diameter at breast height decreased with the increasing competition among the individuals signified that seedlings and young trees growing in the same area might use fewer resources than needed. Generally, the study illustrated that intra-specific competition due to environmental resources is a rarely occurring event.