The vegetation status of regrowth forests in abandoned farmlands in the subtropical forest of Eastern Bhutan Himalaya

The vegetation status of regrowth forests in abandoned farmlands in the subtropical forest of Eastern Bhutan Himalaya

Many regrowth forests have occurred in abandoned farmlands all over the world. The regrowth forests of 20‒60 years old on abandoned farmlands and old-growth forests in a subtropical forest of Eastern Bhutan Himalaya are studied and their floristic and structural compositions are compared. A total of 64 and 43 plots were sampled in regrowth forests and old-growth forests respectively based on stratified random sampling method. Species richness of woody plants and predominant ground covers in regrowth forests is lower than old-growth forests though few of them show higher species richness in woody stems. Species composition of trees (≥5cm DBH) in younger regrowth forests (<30 yrs.) and older regrowth forests (>30 yrs.) show 10% and 42‒51% of Bray Curtis similarity to their adjacent old-growth forests respectively. A total of 53% of trees and 63% of large saplings/shrubs (≤4cm DBH and≥1m height) are shared species between two forest types. The top dominant species such as Betula alnoides Buch.-Ham. ex D.Don, Lithocarpus fenestratus (Roxb.) Rehder, Schima wallichi Choisy, and Itoa oreintalis Hemsl. in regrowth forests make distinct patches different from old-growth forests. Species composition of trees in regrowth forests retains the variation along the elevation gradient like old-growth forests. Land-use history of the regrowth forests has also affected the regeneration of forest. Basal area and density of trees in regrowth forests are close or even higher than old-growth forests. The regrowth forests reveal robust recovery of old-growth species and growth of unique species.