Action: Use patch retention harvesting instead of clearcutting
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- One before-and-after study of two from the USA found that areas under patch retention harvesting contained more birds of more species than clearcut areas, retaining similar numbers to unharvested areas.
- Two studies from the USA found that forest specialist species were found with greater frequency in patch retention plots than other management types. One found that habitat generalists increased on other management types, relative to patch retention areas.
In forests in which trees are commercially exploited for timber, a system known as patch retention harvesting may be used as an alternative to a total clear-cut. Typically, around 10% of mature and/or immature trees are retained in patches within an otherwise, clear-cut harvest compartment, with ‘prompt reforestation’ subsequent to timber extraction in the other 90%. These retained patches could help maintain characteristic forest species and act as reservoirs for re-colonisation by forest dependant species.
Supporting evidence from individual studies
In McDonald-Dunn Forest, Oregon, USA, a replicated, controlled study (Chambers et al. 1999) found that patch-group-harvested stands (33% of tree volume removed in 0.2 ha patches) retained an old forest-associated bird composition more similar to that of control (unharvested, old-growth Douglas-fir Pseudotsuga menziesii) stands, compared to two-story (66% of wood removed) and modified clearcut (1.2 trees retained/ha) stands. Of ten abundant forest species in patch group stands, five restricted-range species declined in modified clear-cut and two-story harvested stands, whilst nine mostly habitat generalists species increased in these two treatments. Seven to 11 stands of each treatment were studied, with birds surveyed in the breeding season prior to, and in the two years after, timber harvest (1989-1993).
A controlled before-and-after study in May-June 1999-2001 in bottomland hardwood forest in South Carolina, USA (Harrison & Kilgo 2004), found that a small increase in species richness in the short-term in an area with patch-retention harvesting and a control area, whilst richness decreased in an area with clearcutting (patch retention area: 21 species in 1999, 15 in 2000, 25 in 2001; clear cut area: 25, nine, five; control area: 18 in 1999 and 30 in 2001). Species lost from the clearcut plot were mostly forest specialists. Estimated bird density in the patch-retention area fell from c.3.5 pairs/ha in 1999 to 17 in 2000, recovering to around 34 in 2001. In the clear-cut area, it fell from 3.3 pairs/ha before harvest to around three in 2000 and 14 in 2001. Densities in the control remained relatively constant (c.3.2 pairs/ha). Estimated bird density in the patch-retention area fell from 3.5 pairs/ha in 1999 to 1.7 in 2000, recovering to around 3.4 in 2001. In the clear-cut area, it fell from 3.3 pairs/ha before harvest to around 0.3 in 2000 and 1.4 in 2001. Densities in the control remained relatively constant (3.2 pairs/ha).
- Chambers C.L., McComb W.C. & Tappeiner II J.C. (1999) Breeding bird responses to three silvicultural treatments in the Oregon Coast Range. Ecological Applications, 9, 171-185
- Harrison C.A. & Kilgo J.C. (2004) Short-term breeding bird response to two harvest practices in a bottomland hardwood forest. Wilson Bulletin, 116, 314-323