Two models of the relationship between stand dynamics and stand structure were proposed for Western Carpathian subalpine spruce stands. In the first one, severe stand-replacing disturbances hit forests over a large area, resulting in low variability of the age and size of trees recruited synchronously over extensive areas. In the second model, gap-phase dynamics produce spruce stands composed of distinct age cohorts of trees that originated over extensive areas.

Rare events of massive plant reproductive investment lead to long-term density-dependent reproductive success. Strong negative density-dependent effects on rowan reproduction were found in only a few of the 16 studied years. Such processes operated mainly during large-crop years and at relatively small spatial scales. These years of large reproductive investment had a decisive influence on the overall spatial pattern of the fruit crop.

Studying the changes in the spatial distribution of adult trees that died attacked by bark beetles (Ips typographus) in this Carpathian subalpine spruce forest, we found that the density of snags originating during 10 years was positively correlated spatially with the density of snags from the previous decade, indicating that trees attacked by I. typographus appeared mostly in the same places during two consecutive decades. This suggests that existing gaps expand more often than new ones are created.

Considering the microsite-specific survival of spruce saplings, we found two factors relevant to the survival of young spruces: the share of canopy gap area in their vicinity, and substrate type. The highest 20-year rate of sapling survival was recorded on windthrow mounds, and the lowest on decaying logs. Sapling height and gap area in their vicinity did not impact the survival rate significantly. Although coarse woody debris is more favorable for the establishment of spruces, they survive better on the forest floor, on windthrow mounds in particular.

Herbivore pressure on palatable young rowan trees can be limited by coarse woody debris and hiking trails. In subalpine spruce forest, which is under strong herbivore pressure, rowans can leave the seedling bank and succeed to higher forest strata in places that have an abundance of logs lying on the forest floor and in places close to hiking trails. The presence of logs seems to be a sufficient barrier to deer activity, protecting the young trees; also, deer are likely to be startled near trails and may learn to avoid them, reducing their pressure on rowan sapling growth.

We found negative density dependence of mortality among spruce saplings: that is, conspecific facilitation among niche competitors. Tree debarking caused by antler rubbing by red deer (Cervus elaphus) was the main identified cause of sapling mortality and showed a strong density- and distance-dependent pattern. The deer killed young trees, choosing isolated trees for antler rubbing more frequently than they chose trees growing in aggregations.

© 2016-2018 by Magdalena Żywiec

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