Do soil properties constrain species richness? Insights from boundary line analysis across several biomes in south western Africa

Relationships between species richness per plant life form and the soil properties: infiltrability, clay plus silt content, salinity, and pH were investigated at eighteen study sites located in western South Africa and Namibia. Plant species data were categorized into five life forms: phanerophytes, chamaephytes, hemicryptophytes, therophytes, and geophytes. A boundary line approach was used to determine ranges of soil properties across which plant richness was constrained or potentially maximal. Ranges of soil properties at which richness was potentially maximal differed between life forms as follows: total plant richness (∼50–200 mm h −1 infiltrability, ∼5–20% clay & silt,