Resource availability and heterogeneity are recognized as two essential environmental aspects to determine species diversity and community abundance. However, how resource availability and heterogeneity determine species diversity and community abundance in highly heterogeneous and most fragile karst landscapes is largely unknown. We examined the effects of resource availability and heterogeneity on plant community composition and quantified their relative contribution by variation partitioning. Then, a structural equation model (SEM) was used to further disentangle the multiple direct and indirect effects of resource availability on plant community composition. Species diversity was significantly influenced by the resource availability in shrubland and woodland but not by the heterogeneity in woodland. Abundance was significantly affected by both resource availability and heterogeneity, whereas variation partitioning results showed that resource availability explained the majority of the variance in abundance, and the contribution of resource heterogeneity was marginal. These results indicated that resource availability plays a more important role in determining karst plant community composition than resource heterogeneity. Our SEMs further found that the multiple direct and indirect processes of resource availability in determining karst species diversity and abundance were different in different vegetation types. Resource availability and heterogeneity both played a certain role in determining karst plant community composition, while the importance of resource availability far exceeded resource heterogeneity. We propose that steering community restoration and reconstruction should be highly dependent on resource availability, and multiple direct and indirect pathways of resource availability for structuring karst plant communities need to be taken into account.