Ecological factors controlling the abundance of non-native invasive black cherry (Prunus serotina) in deciduous forest understory in Belgium

The relation between invasion success of Prunus serotina and type of recipient habitat was studied in a large forest in central Belgium. The major emphasis in this study was the determination of factors controlling the abundance of P. serotina in understory strata. Environmental variables measured in 34 sample plots were slope, aspect, litter depth, soil type, pH, soil compaction, soil moisture, air humidity, soil temperature and light intensity in spring and late summer. Site conditions were also expressed indirectly for 210 sample plots using Ellenberg indicator values (soil nutrients, acidity, moisture, light conditions). Plots with P. serotina had lower mean indicator values for soil moisture, reaction (pH) and nitrogen, compared to plots without P. serotina. Twenty indicator species were identified for plots in which P. serotina occurs. The species richness of the herb layer was negatively correlated with the percentage cover of black cherry in the shrub layer. The percentage cover of P. serotina saplings in different overstory types was ranked as follows: Quercus > Pinus > Fagus > logging areas. Only three variables explained significant amounts of variation in Prunus abundance: slope, light intensity at 120 cm in April and light intensity at ground level in September. We found a positive response of black cherry seedlings to light intensity between 58 and 80% of full light (April measurements at 120 cm), while saplings showed a negative response within this range. Between 21 and 47% of full light (April measurements at 120 cm), seedlings were poorly represented whereas saplings showed a quite high cover. Between 0.3 and 1.8% light (September measurements at ground level), seedlings were almost absent while saplings maintained a high abundance. The results suggest that P. serotina shows a differential response to light intensity in relation to its development stage, i.e. the species is heliophilous at the seedling stage and becomes a shade plant at the sapling stage.