Abstract
Aim of the study: We analysed the effects of thinning intensity and canopy type on Scots pine growth and stand dynamics in a mixed Scots pine-beech forest. Area of the study: Western Pyrenees. Material and methods: Three thinning intensities were applied in 1999 (0, 20 and 30% basal area removed) and 2009 (0, 20 and 40%) on 9 plots. Within each plot, pure pine and mixed pine-beech patches are distinguished. All pine trees were inventoried in 1999, 2009 and 2014. The effects of treatments on the tree and stand structure variables (density, basal area, stand and tree volume), on the periodic annual increment in basal area and stand and tree volume, and on mortality rates, were analysed using linear mixed effects models. Main Results: The enhancement of tree growth was mainly noticeable after the second thinning. Growth rates following thinning were similar or higher in the moderate than in the severe thinning. Periodic stand volume annual increments were higher in the thinned than in the unthinned plots, but no differences were observed between the thinned treatments. We observed an increase in the differences of the Tree volume annual increment between canopy types (mixed < pure) over time in the unthinned plots, as beech crowns developed. Research highlights: Moderate thinning is suggested as an appropriate forest practice at early pine age in these mixed forests, since it produced higher tree growth rates than the severe thinning and it counteracted the negative effect of beech on pine growth observed in the unthinned plots.Keywords: competition; Fagus sylvatica L.; Pinus sylvestris L.; forest management; mortality; Mediterranean forest.
Highlights
Pure coniferous forests have been historically favoured in the European temperate zone for management reasons (Spiecker, 2003), and because of a higher volume growth expectation (Pretzsch, 2005)
Tree volume decreased with increasing thinning intensity at the beginning of the study, but in 2014, it was highest in the M plots (P < 0.001, Table 3, Figure 2a)
Differences between canopy types for pine density decreased over time (PC > MC, P = 0.09, Figure 2b), except for tree volume, which was similar between canopy types at the beginning of the experiment, but it was higher in PC than in MC at the end of the study (P < 0.05, Figure 2b)
Summary
Pure coniferous forests have been historically favoured in the European temperate zone for management reasons (Spiecker, 2003), and because of a higher volume growth expectation (Pretzsch, 2005). Conversion to near-natural and often, mixed broadleaved-coniferous forests is being considered (Spiecker, 2003), due to the multiple benefits that mixed woodlands may provide, such as greater diversity, protection from. Spiecker (2003) suggested that the structure of mixed stands may be maintained and improved by management practices like thinning, which has been recommended as a necessary first step in the conversion process from pure Scots pine plantation to mixed broadleaved forests (Crecente-Campo et al, 2009). Several studies have been focused on the effects of thinning on tree growth in Scots pine pure stands Several studies have been focused on the effects of thinning on tree growth in Scots pine pure stands (e.g. Montero et al, 2001; Mäkinen & Isomäki, 2004; Mäkinen et al, 2005; Río et al, 2008; Crecente-Campo et al, 2009; Novak et al, 2011), but just few studies have tackled the same issue in mixed woodlands (e.g. Primicia et al, 2013)
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