Are seed dispersal and seedling establishment distance- and/or density-dependent in naturally regenerating larch patches? A within-patch scale analysis using an eigenvector spatial filtering approach

Abstract

The success of natural regeneration in silviculture depends on the complex interactions between interventions of stand structure, the natural seed-dispersal processes, and seedling development. Particularly, the spatial patterns of seed dispersal, seedling establishment and growth, and microenvironmental factors are closely interrelated, controlling the outcomes of natural regeneration practices. wWe performed a within-patch scale spatial analysis and modeling for seed dispersal and seedling development on four different natural regeneration patches (seed tree, grouped seed tree, reserved seed tree, and strip clear-cut methods) of Japanese larch (Larix kaempferi) using an eigenvector spatial filtering (ESF) approach. Our spatial analysis allowed us to determine whether seed fall, seedling establishment, and seedling growth are distance- rather than density-dependent, corresponding to the Janzen–Connell hypothesis. The ESF model revealed that gentle slope, moderate soil moisture, and low crown closure were essential in achieving potential seedling establishment and growth. In addition, the ESF based spatially varying coefficient (ESF-SVC) model provided the difference in impacts of those environmental factors across the regeneration patches. The strategy of planting a large number of evenly distributed remnant seed trees in the regeneration patch of the reserved seed trees was effective in improving seed dispersal, while no remnant seed tree in the regeneration patch of the strip clear-cut method contributed to seedling growth. These findings indicate that ESF-based approaches may represent a feasible way of natural regeneration modeling with more reliable statistical estimations and interpretations by accounting for spatial autocorrelation and heterogeneity.