Natural regeneration of Pinus canariensis Chr. Sm. Ex DC in Buch in forest plantations after thinning
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Thinning is indispensable for the sustainable development and naturalization of forest plantations. In order to reveal the effect of different thinning intensities on the natural regeneration of a plantation of Pinus canariensis, we followed for two years the density of seedlings, saplings of 1 year, saplings of 1-2 years and saplings of > 2 years in plots at different thinning intensities (control, 20 and 50%). Our analysis revealed that seedling density and density of saplings > 2 years were higher in plots thinned by 50% of their total basal area, whereas the other categories were significantly more abundant in control plots. These results suggest an important impact of light in the germination of seedlings, while a more covered canopy will increase the probability of establishment of saplings 1 and 1-2 years old. However, for saplings > 2 years, the lack of space found in control plots largely determined their low abundance. We suggest that canopy openness should be much larger than is provided by the currently applied treatments, offering at least a 40-50% open canopy for a few years (it should ensure that trees around the gap are unable to close the canopy with their branches). As our results show, germination in 50% thinned plots is high, but high mortality is also expected, with probably no more than 5% of the individuals remaining after 3 years.