Orchid abundance in hemiboreal forests: standscale effects of clear-cutting, green-tree retention, and artificial drainage

The current knowledge on the impact of forest management on plant species of conservation concern is poor. We asked how three basic silvicultural techniques (clear-cutting, green-tree retention, and artificial drainage) affect the abundance of terrestrial orchid species and their communities in Estonia, hemiboreal Europe. Fixed-area, fixed-effort surveys (4 h per 2 ha plot) were used in 29 plot clusters representing five site types, with each cluster including plots of four treatments (old growth, mature managed forest, and cutover with and without live retention trees). Altogether 11 species of orchids were recorded in those 116 plots, with the most complete sets of species in artificially drained plots and mature stands. Five species were widely distributed among treatments and site types, but most site types also hosted shade-tolerant orchids (six species) that characteristically disappeared after timber harvesting. Cutover areas (3-7 years after harvest) hosted no species absent from uncut forest stands, and retention of solitary trees had no effect on orchid abundance over clear-cuts. Modern Estonian forest landscapes appear to support viable populations of many orchids, with rotation ages sufficient for population development of the majority of shade-tolerant species.