Action: Cut large trees/shrubs to maintain or restore disturbance
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- Two studies evaluated the effects, on peatland vegetation, of cutting large trees/shrubs to maintain or restore disturbance. One study was in a forested fen and one was in an open fen. N.B. Cutting large trees/shrubs in peatlands with no history of disturbance is considered as a separate action.
- Plant community composition (1 study): One before-and-after, site comparison study in a fen in Poland found that in an area where shrubs were removed (along with other interventions), the plant community composition became more like a target fen meadow.
- Characteristic plants (1 study): One before-and-after, site comparison study in a fen in Poland found that in an area where shrubs were removed (along with other interventions), the abundance of fen meadow plant species increased.
- Vegetation cover (1 study): One replicated, paired, controlled study in forested fen in the USA found that cutting and removing trees increased herb cover, but had no effect on shrub cover.
- Vegetation structure (1 study): One replicated, paired, controlled study in a peat swamp in the USA found that cutting and removing trees increased herb biomass and height.
Regular disturbance may maintain vegetation in a desirable, semi-natural state – particularly in fen meadows and some fens (Middleton 2012). In particular, disturbance can clear shrubs and trees that would otherwise become dominant. To control woody vegetation, conservationists may sometimes want to restore or compensate for a disturbance that has been lost. Initially, large trees and shrubs may need to be managed by cutting them close to the ground. Afterwards, a traditional mowing or grazing regime may be resumed to keep regrowth of trees or shrubs in check, and manage the vegetation as a whole.
Caution: Tree/shrub removal may be desirable on a subset of peatlands e.g. open bogs, fens and fen meadows. Tree thinning may be desirable on some naturally forested peatlands - but tree removal is more typically a threat here.
Related actions: cutting/mowing herbaceous plants and small woody plants, to maintain or restore disturbance or control problematic plants whose growth is not attributed to loss of traditional management.
Middleton B.A. (2012) Rediscovering traditional vegetation management in preserves: trading experiences between cultures and continents. Biological Conservation, 158, 750–760.
Supporting evidence from individual studies
A replicated, paired, controlled study in 2002–2007 in a forested fen in New York State, USA (Scanga & Leopold 2012) found that in areas where trees were felled and removed, herb cover, height and biomass were greater than in adjacent forested areas, whilst shrub cover was similar. After 4–5 years, cleared areas had greater cover than adjacent forested areas of forbs (66 vs 44%) and sedges (9 vs 3%). There was a similar, but non-significant, trend for cover of grass-like plants overall (cleared: 50%; forested: 34%) and ferns (cleared: 17%; forested: 9%). Shrub cover did not significantly differ between areas (cleared: 9%; forested: 10%). In cleared areas, herbs were taller overall (cleared: 44; forested: 25 cm) and produced more biomass (cleared: 68; forested: 21 g/0.25 m2). In spring 2002 and 2003, all trees were cut and removed from 11 circular areas (5 m radius) in a forested fen. This mimicked historical human disturbance. For each cleared area, a forested area <40 m away provided a control. In August 2007, vegetation was surveyed in each area within nine 0.25 m2 quadrats.
A before-and-after, site comparison study in 2004–2009 in a degraded fen in Poland (Kotowski et al. 2013) found that in an area cleared of shrubs (then rewetted and mown), the plant community composition changed in favour of fen meadow and wet meadow species. Over five years, the overall plant community composition in the managed area became more similar to a target fen meadow vegetation (data reported as a graphical analysis; change not tested for statistical significance). The abundance of fen meadow and wet meadow species, including sedges Carex spp., increased in the managed area but did not change in the target area (data reported as an abundance index). In 2004, willow Salix cinerea shrubs were cleared from 0.7 ha of drained, overgrown fen. The area was then mown annually and rewetted. The study does not distinguish between the effects of these interventions. The managed area was compared to 0.9 ha of target, shrub-free, fen meadow vegetation (retained in depressions during the drained period, but also affected by the rewetting and mown every other year). Annually between 2004 (before shrub clearance) and 2009, cover of every plant species was estimated in 18–22 plots/area. Plots were 20 x 20 m.
- Scanga S.E. & Leopold D.J. (2012) Managing wetland plant populations: lessons learned in Europe may apply to North American fens. Biological Conservation, 148, 69-78
- Kotowski W., Dzierża P., Czerwiński M., Kozub Ł. & Śnieg S. (2013) Shrub removal facilitates recovery of wetland species in a rewetted fen. Journal for Nature Conservation, 21, 294-308