We compared patterns of understorey vegetation and abiotic factors in old-growth forests with low management intensity and young forests with high management intensity. CCA showed that disturbance gradient was the main axis of community variation, while local light availability (ISF, indirect site factor) and soil conditions (nitrate content) were also of some importance. Young stands demonstrated a significantly higher heterogeneity of vegetation with increased pattern diversity (1 − Jaccard similarity among 1 m × 1 m plots, also called beta diversity), variation in species richness and variation in the cover of both vascular plants and bryophytes. Young stands also showed a higher variation of soil nitrate content and lower average vascular plant cover. We concluded that the understorey vegetation in young stands with high intensity management is, contrary to our literature-based expectation, more heterogeneous in space than that in old stands with low management intensity. The relationship between environmental heterogeneity and diversity has been discussed extensively, but there is a scarcity of quantitative relationships documented in natural vegetation. We found that species richness in 4 m × 4 m plots was positively dependent on the variability of light availability (ISF) within plot. Pattern diversity was positively dependent on the variation of microtopography and the availability of direct radiation (DSF, direct site factor).