The effects of soil compaction and fertility on a threatened endemic palm species in a global conservation hotspot

Butia eriospatha (Mart. ex Drude) Becc. is a subtropical endemic palm tree that occurs in the Southern Brazilian Highlands. A vast area of its natural habitat has been lost by land-use changes, placing the species at high risk of extinction. Here, we investigated how environmental variables impact the structure of B. eriospatha populations. We randomly allocated 14,100 × 100 m plots, where all palms had the diameter at breast height (dbh) and the total height (th) measured. In the same plots, we collected data on edaphic, topographic, and land-use variables. The data were analysed by frequency histograms, factor analysis of mixed data, and regression trees. B. eriospatha’s size class frequencies tended towards a normal distribution, with few small individuals. We found that plots with flatter terrain had more compacted soils. The structure and biometrics traits of B. eriospatha’s populations were affected by the interaction between soil compaction and fertility. We conclude that sites with lower fertility and more compacted soils showed populations with lower abundance and basal area, and smaller individuals. Sustainable practices of soil management are required to prevent the species from becoming locally extinct.