Rodent-mediated seed dispersal of Juglans mandshurica regulated by gap size and within-gap position in larch plantations: Implication for converting pure larch plantations into larch-walnut mixed forests

Abstract

Abstract Larch (Larix spp.) is planted extensively after clear-cut of secondary forests in Northeast China to satisfy the enormous timber demands. However, some serious problems arise in larch plantations (LPs) due to mono-species composition, such as a decline in soil fertility and acidification of surface runoff. Converting pure LPs into larch-broadleaf mixed forests would resolve these issues. Since larch-walnut mixed forests are mutually beneficial, it is crucial to promote the regeneration of Juglans mandshurica in LPs. Rodent-mediated seed dispersal of J. mandshurica determines the regeneration success or failure and is closely related to stand structure. Forest gaps are formed by an uneven thinning that changes stand structure in plantation management; the gap size and within-gap position are two key characteristics that affect tree regeneration by changing the micro-environment. We hypothesized that rodent-mediated walnut seed dispersal were strongly influenced by these two key factors. The field trial was conducted by releasing tagged J. mandshurica seeds in two sizes of artificial gaps in LPs (small and medium gaps) and at four positions (south, north, east and west) of the gap edges. The seed releases were conducted at three stages of seed rain (early, middle and final stages) during two continuous growing seasons. Our results showed that only the seed removal rate was significantly affected by gap size and within-gap position; the rate in medium gaps was significantly higher than that in small gaps (Wald = 24.57, df = 1, P