In the worst areas on our site no native trees have been able to grow, but ferns can invade and dominate. Can they eventually improve conditions for trees?
Do weedy ferns that invade the worst soils help improve those soils?
Tropical soils that are too poor for anything else to grow are often invaded by several species of ferns. In fact, ferns can indicate areas with especially degraded conditions.
The worst conditions on our site are exposed bedrock, landslides, and high ridge-tops. No plantings of native tree seedlings have established here, only the non-native pine. However, after a decade or so, ferns invaded and took over many of these areas. The photo at right shows a vining fern that climbs over the terrain and sapling trees.
We tested the possibility that after a few years ferns might change the soils in ways that could later lead to better tree seedling growth once the ferns are removed. For example, their roots, called “rhizomes”, might break up compacted clayey soils, and dead fronds might create humus, improving texture and nutrient availability.
We planted three tree species in plots of land cleared of fern (below, left) and in adjacent plots without fern as controls (below, right). Escaped cattle destroyed our control plots, so we need to
repeat this experiment. However, by eye and by feel it is clear that the soil is a better texture and color in the plots that we cleared of ferns. This is an important possibility that should be pursued.