Three replicated, controlled studies in Sweden and the USA found that shelterwood harvesting resulted in higher plant diversity, lower grass cover and higher density of tree species compared with clearcutting.
Shelterwood harvesting is a management technique designed to obtain even-aged trees without clearcutting. It involves harvesting trees in a series of partial cuts, with trees removed uniformly over the plot. This allows new seedlings to grow from seeds dispersed by older trees. This can help in maintaining distinctive forest species and increase structural diversity of stands.
A replicated study in 1985-1993 in temperate coniferous forest in Sweden (Hannerz & Hånell 1997) found that shelterwood harvesting increased plant diversity compared with clearcutting. Plant diversity was higher in shelterwood (Simpson index: 0.48) than in clearcut areas (0.37). Species richness, average height and total cover of plants were similar between shelterwood (species: 5.3/0.25 m2; height: 33 cm; cover: 75%) and clearcut areas (species: 4.2/0.25 m2: height: 34 cm: cover: 65%). In 1985, 2-4 clearcut (all trees removed) plots (40 × 25 m) and 4-8 shelterwood (140-200 trees/ha retained) plots (20 × 25 m) were established in each of four sites. Monitoring was undertaken in 1993 in 24-160 subplots/treatment in each site. Each subplot was 0.5 × 0.5 m.
A replicated, controlled study in 1974-1992 in temperate coniferous forest in Montana, USA (Shearer & Schmidt 1999) found that shelterwood harvesting increased the density of conifers compared with clearcutting. Density (trees/ha) of conifers >30 cm tall (shelterwood: 19,895; clearcut: 6,834) and total conifer density (shelterwood: 31,389; clearcut: 8,741) were the highest in shelterwood. Three blocks of each treatment, shelterwood and clearcutting, were duplicated in two sites in 1974. Data were collected in 1992 in 80 plots (0.004 ha) in each treatment block.
A replicated, study in 1993-2000 in temperate forest in Sweden (Karlsson & Nilsson 2005) found that shelterwood harvesting increased the density of some tree species and decreased the cover of grasses compared with clearcutting. Density (seedlings/ha) of Scots pine Pinus sylvestris (shelterwood: 18,500-23,000; clearcut: 3,000-6,500) and Norway spruce Picea abies (shelterwood: 17,000-20,000; clearcut: 2,500-3,000) was higher in shelterwood while density of birch Downy birch Betula pubescens and Silver birch B. pendula was similar between treatments (3,500-8,500 seedlings/ha). Cover of grasses (shelterwood: 19-20%; clearcut: 32-35%) was lower in shelterwood while cover of herbs (5-11%) and dwarf-shrubs (12-18%) was similar. In 1993-1995 two shelterwood (cutting 40% of volume) and two clearcut treatment plots (0.4 ha) were established in each of eight sites. Data were collected in 2000.