Western Carpathian mountain spruce forest after a windthrow: Natural regeneration in cleared and uncleared areas

Abstract

A catastrophic windstorm called “bora” occurred in The Tatra National Park in Slovakia in 2004 and destroyed an extensive area of mountain spruce forests. Part of the windthrow area was left uncleared for natural development, but most of the area was cleared. We analyzed natural regeneration in cleared and uncleared windthrows, and in reference closed canopy forest in 2007 and 2008 with the aim of assessing the regeneration capability of the windthrown forests and proposing the best method for their restoration. The species composition and quantity of natural regeneration reflected the influence of the windthrow and tree extraction. The highest recruitment density was found in the reference area in closed canopy forest for both years (67,500 and 38,000 indiv./ha), while the lowest density was in cleared windthrow (3380 and 1210 indiv./ha). There were 8835 and 7225 indiv./ha in uncleared windthrow. Spruce was the predominant species in natural regeneration in both years in the reference forest and cleared windthrow. Larch, which forms an admixture in these forests, was found only rarely, and so we cannot make any conclusions regarding its regeneration. Pioneer species such as birch and willow became the most numerous in uncleared windthrow in 2008. There was a natural decrease of numbers of young spruce seedlings in all the plots and natural decrease of their numbers can still be expected in windthrown areas distant from seed sources. In uncleared windthrow, spruce was replaced by newly established birch and willow in areas that are still without vegetation and so suitable for seedling establishment. Birch and willow were rare in cleared windthrow, which was already covered by dense vegetation. If the total numbers in cleared windthrow will still decrease, then there will probably not be sufficient trees for forest regeneration and some management measures, such as planting or seeding, may be necessary. The numbers in uncleared windthrow are undoubtedly sufficient for successful regeneration of the forest. Moreover, future stands in uncleared windthrow will be more diverse and probably more resistant against disturbances. For these reasons, we recommend leaving the windthrown stands in the protected area without clearing as the best option for forest restoration.