Forest and fynbos are alternative states on the same nutrient poor geological substrate

• We compared adjacent forest and fynbos to test whether forest and fynbos soils had different nutrient status
• Plant traits were measured to test whether differences in soil nutrient status were reflected in vegetation
• Forest had higher soil nutrient status than fynbos but relative to other systems, both are relatively nutrient-poor
• Measured traits of the dominant vegetation are not strongly associated with soil characteristics
• Both forest and fynbos species seem to have traits that confer conservative resource strategies

We ask two questions concerning the creation and maintenance of boundaries between forest and fynbos biomes in the southern Cape, South Africa: 1) is the presence of forest vegetation constrained to nutrient-rich soils? and 2) do plant traits (specific leaf area, leaf area, leaf dry matter content, leaf nutrients) reflect underlying soil nutrient status? At seven paired sites where forest and fynbos occur adjacent to each other with identical geology and position in the landscape, we tested whether forest soils had a different nutrient status to that of fynbos soils. At three of these sites we measured a suite of plant traits and tested whether these traits were correlated with soil characteristics. The paired site comparisons found that forest soils had a higher nutrient status and higher soil C:N ratios than the fynbos soils. Nonetheless, when compared across sites many forest soils had a nutrient status that was equivalent or lower than some fynbos soils. In addition, the forest soils at our study sites are still relatively nutrient-poor when compared to those of other temperate ecosystems. Although fynbos vegetation had traits that confer higher nutrient use efficiency than forest, both forest and fynbos species seem to have traits that confer conservative resource strategies (e.g., low leaf N and high leaf dry matter content). We suggest that both fynbos and afrotemperate forest are dominated by communities that are adapted to nutrient-poor conditions, and that the increase in nutrient status observed in forest soils is driven by niche construction.