Study

Factors affecting the natural regeneration of Quercus in Scottish oakwoods .1. Competition from Pteridium aquilinum

  • Published source details Humphrey J.W. & Swaine M.D. (1997) Factors affecting the natural regeneration of Quercus in Scottish oakwoods .1. Competition from Pteridium aquilinum. Journal of Applied Ecology, 34, 577-584.

Summary

In Scottish upland, semi-natural oakwoods, natural regeneration of pedunculate oak Quercus petraea and sessile oak Q.robur is frequently lacking, often due to underplanting with conifers or overgrazing by deer and livestock. This threatens the long-term survival of these remnant woodland habitats. In the absence of excessive grazing, large openings in the woodland canopy can provide suitable sites for regeneration, but these are often dominated by dense stands of bracken Pteridium aquilinum, which is thought to impact on natural regeneration.

In this study experiments were carried out in a semi-natural oakwood in north-eastern Scotland, which investigated whether shading by a bracken canopy in summer and smothering by their dying fronds in winter exerted a detrimental effect on the growth of oak seedlings.

Study site: The experiments were undertaken in Dinnet Oakwood National Nature Reserve (altitude 150-200 m) near the city of Aberdeen in north-east Scotland.
Two types of bracken stand (three of each) within the woodland were selected: i) more dense, growing in relatively large gaps in the oak canopy, ii) less dense growing in smaller gaps.

Treatments: In large gaps, three treatments were used:

Treatment 1 – oak seedlings planted after bracken cut in spring and fronds cut and removed each month all year round

Treatment 2 - oak seedlings planted under bracken fronds which were cut in winter (late October) only

Treatment 3 - oak seedlings planted under bracken fronds left uncut all year

In the small gaps only the first and second treatments were used. The oak seedlings planted (derived from Dinnet acorns) were all considered to be Q.petraea x Q.robur hybrids.


At the end of the two growing seasons (1990-1991), seedlings were harvested to take biomass and leaf area measurements.

Photosynthetically active radiation: The effects of the bracken canopy on photosynthetically active radiation (PAR) during the growing season were also measured fortnightly (1990 ; August – October; 1991 April-June).

Effect of bracken treatment on oak seedlig growth: Over the two growing seasons, significant reductions in accumulated oak seedling biomass were recorded in both large and small canopy gaps in plots subject to winter cutting (large gaps: 1.12; small gaps: 1.05 g) or no cutting (large gaps only: 0.79 g), compared to continuous cutting (large gaps: 3.52 g; small gaps: 2.24 g). Significant increases in specific leaf area, leaf area ratio, and a decrease in root:shoot ratio were also recorded in the continuously cut plots

Smothering by dying bracken fronds in winter significantly reduced seedling biomass (by 28.5%), but had induce changes in leaf morphology or a shift of resource allocations between growth organs (roots, shoots, leaves).

The effect of bracken on light: The presence of a bracken canopy during the growing season reduced PAR to 5.9% of full sunlight in the larger canopy gaps, and to 11.4% in the small gaps

Conclusions: These results suggest that effective control of dense bracken stands is necessary to promote the successful regeneration of the two native oak species at Dinnet Oakwood NNR. Bracken is a widespread and often invasive, but native, species in the UK, and bracken control is therefore applicable to other similar woodland sites with a bracken understorey if oak regeneration is to be encouraged.


Note: If using or referring to this published study, please read and quote the original paper, this can be viewed at: http://links.jstor.org/sici?sici=0021-8901%28199706%2934%3A3%3C577%3AFATNRO%3E2.0.CO%3B2-U

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