The influence of herbaceous vegetation on the colonization of native and invasive trees: consequences for semiarid forest restoration

We evaluated the influence of herbaceous vegetation on the colonization of an invasive and two native tree species in a degraded area located at the Caatinga semiarid forest in Northeastern Brazil. Seedlings of the native trees Anadenanthera colubrina and Astronium urundeuva were planted in nine paired blocks with intact and removed herbaceous vegetation. In addition, seeds of the invasive tree species Leucaena leucocephala were sown in the same paired plots. Growth, germination, establishment, and survival of the tree species were monitored for 8 months. The results showed that herbaceous vegetation hampered native seedling growth in respect to leaf number, leaf size, height, and stem diameter. Conversely, herbaceous vegetation had a neutral effect on the germination, establishment, and growth of the invasive species L. leucocephala. Dominant ruderal herbaceous species strongly prevent the natural succession of native trees in this semiarid forest, while not affecting the establishment of an invasive tree. Management of herbaceous vegetation cover in degraded areas might be a key step for successful restoration in this dryland.