Resolving gap patterns and dynamics from a new perspective: Ratio effects of the evergreen versus deciduous trees in broadleaved – Korean pine forests

Abstract

Clarifying gap patterns and dynamics on a regional scale is necessary to understand forest succession. However, few studies quantified the species composition influences except for geography and time effects. We examined the spatial and temporal gap patterns in an old-growth broadleaved–Korean pine (Pinus koraiensis) forest using two satellite image datasets with a ten-year interval and complementary field survey datasets. The forests were evenly divided into 121 plots with a plot size of 100 ha, and the crown projection area ratio of evergreen trees (RE/A) in each plot was quantified to represent simplified species composition (i.e., evergreen versus deciduous trees). We found that gap fraction and density reduced from 19.0% and 25.0 gaps ha-1 in 2007 to 16.8% and 17.6 gaps ha-1 in 2017, respectively, equivalent to a transformation of 213 ha from gaps to closed canopy. Generalized linear mixed models showed that the RE/A explained substantial variance in gap fraction, size, and number, much more than geography factors (slope and altitude). However, the gap size frequency distribution consistently followed a power-law distribution with weak geography, time, and species composition influences. Univariate analyses showed that the gap distribution patterns differed by gap size but tended to randomness over time, likely due to the randomness of gap formation and the differences in gap closure processes. The species composition of gap makers and fillers diverged along the RE/A gradient. In summary, our study proposed a novel factor (RE/A) to reveal the spatial and temporal gap patterns in the broadleaved–Korean pine forests, which provided insights into the necessity of refining species composition in conducting regional-scale gap studies with the development of airborne hyperspectral and LiDAR remote sensing technologies.