Epsilon Archive for Student Projects

Abstract

To describe the historical patterns of natural disturbance regimes in European boreal
forests we conducted a dendroecological study in a primeval old-growth spruce
dominated stands and reconstructed the long-term dynamics of canopy disturbances.
We treated the radial growth releases of individual sub-canopy trees as the major
indicator of sudden openings in the forest canopy. Growth releases were detected by
using the formal approach only (strict criteria were applied). The reconstruction of
past canopy disturbances was done by GIS-based analysis of spatial information on
released trees over the study period.
The study area was located in the transitional vegetation zone of the middle and
northern taiga, on the watershed of Northern Dvina and Pinega rivers, North-Western
Russia.
Spatial and temporal characteristics of canopy disturbances were studied within the
area of 1.8 ha along the two transects, 20x450 m2 each. All trees with DBH > 6 cm
(dead and alive) and coarse woody debris (DBH > 18 cm) within transects were
mapped and described (n = 2126) and all living and recently dead trees were sampled
with an increment corer (n = 1678) at the height 40 cm above the root collar.
Stands were composed of Picea abies and Betula pendula, mean standing volume was
211 m3/ha.
Spruce was of multiple ages with pronounced regular peaks (cohorts) in trees age
distribution. At least four such cohorts were distinguished and represented peaks in
spruce regeneration.
No evidence of stand replacing events was found over the 250(300)-year period that
the study covered. The dynamics was likely driven by small and middle-size canopy
disturbances, occurring at varying frequencies. A detailed spatial disturbances
reconstruction reflecting the last 170 (160) years revealed a disturbance rate of about
4% yearly mortality. Periodic increases in disturbance rate however played a major
role in forest regeneration. Four such peaks were timed to decades 1850, 1890, 1930
(1920 – for transect 1) and 1980. Disturbance rates at peaking decades were about
60% and never exceeded 75% of the canopy area.
Surprisingly little difference in disturbance rates was found among forest types with
different soil moisture. Though forests with higher soil moisture had slightly lower
disturbance intensity and less pronounced regular peaks in disturbance rate over
considered time span.