The use of prescribed burning to encourage oak Quercus seedling regeneration for oak forest restoration, Cleveland Metroparks Brecksville Reservation, Ohio, USA
The Cleveland Metroparks, founded in 1917, form a semicircle of woodland patches around the city of Cleveland, northern USA. One of these parks, Brecksville Reservation, was formerly oak woodland but cleared for agriculture. In 1921 cultivation ceased and tree regeneration was allowed to occur. However, a survey of the woodland in 1990 revealed that in comparison to natural oak woodland, there were: i) too many trees with large basal areas and few canopy openings; ii) the understorey and herbaceous species exhibited early dormancy, low flowering and fruiting; iii) there was poor establishment of oak seedlings and iv) there was a dense understory of non-oak forest species, mostly sugar maple Acer saccharum, American beech Fagus grandifolia, with some exotics, e.g. honeysuckle Lonicera spp. In order to try and reinstate an oak forest more like that which originally occurred, restoration was attempted by using managed burns and canopy and understory vegetation removal by thinning. It was hoped that the thinning and burning of non-oak woody species would mimic the natural processes of fire and help enhance native oak forest species regeneration.
Study site: The oak forest restoration was undertaken in Brecksville Reservation located about 16 km to the south of the industrial city of Cleveland, Ohio, northern USA.
Forest restoration treatments: Oak forest restoration attempts were initiated 1990, using thinning and burning to hopefully encourage regeneration of oak forest species. Treatment plots (81 in total) were selectively thinned from 1991 to 1994, and burned from 1991 to 1995; 15 plots where no management took place were established as controls.
Monitoring: In 96 quadrats (81 treatment and 15 control), understory woody species weremonitored from 1992 to 2002, and canopy opening was quantified.
Six years into the study, the area was heavily invaded white-tailed deer Odocoileus virginianus and gypsy moths Lymantria dispar, their herbivory complicating the assessment of the results of the restoration efforts.
The 11 study period could be divided into three distinct phases:
1 - 1992–1994 treatment effects; oak forest and non-oak forest species both increased in the treatment area compared with the control area. Burning encouraged oak seedlings, and thinning reduced competition from non-oak woody species, suggesting a temporarily successful restoration attempt.
2 - 1995–1999 period of invasion by deer and gypsy moths; intense herbivory by gypsy moth larvae reduced the number of oak seedlings, created conditions more favorable to non-oak woody species, and the quantity and diversity of seedlings increased as the canopy was opened. In summer 1999, gypsy moth larvae consumed nearly every leaf on every conifer and deciduous tree in treatment and control areas. Deer browsed most species (oak and non-oak). Many trees died over the study period due to the stress from continuous defoliation and inadequate rainfall.
Gypsy moth infestation and deer browse were considered analogous to thinning and burning, so no further treatment was undertaken in this 5-year period.
Deer culling began in 1999, as a result of which their numbers gradually declined; the effects of this may be reflected in future seedling recruitment.
3 - 2000–2002 post-invasion; original treatment effects may have been continuing however, additional years of study would be needed to elucidate this.
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