Legacy of pre-disturbance spatial pattern determines early structural diversity following severe disturbance in mountain spruce forests in Czech Republic

Background Severe canopy-removing disturbances are native to many temperate forests and radically alter stand structure, but biotic legacies (surviving elements or patterns) can lend continuity to ecosystem function after such events. Poorly understood is the degree to which the structural complexity of an old-growth forest carries over to the next stand. We asked how predisturbance spatial pattern acts as a legacy to influence post-disturbance stand structure, and how this legacy influences the structural diversity within the early-seral stand. Methods Two stem-mapped one-hectare forest plots in the Czech Republic experienced a severe bark beetle outbreak, thus providing before-and-after data on spatial patterns in live and dead trees, crown projections, down logs, and herb cover. Results Post-disturbance stands were dominated by an advanced regeneration layer present before the disturbance. Both major species, Norway spruce (Picea abies) and rowan (Sorbus aucuparia), were strongly self-aggregated and also clustered to former canopy trees, predisturbance snags, stumps and logs, suggesting positive overstory to understory neighbourhood effects. Thus, although the disturbance dramatically reduced the stand’s height profile with ~100% mortality of the canopy layer, the spatial structure of post-disturbance stands still closely reflected the pre-disturbance structure. The former upper tree layer influenced advanced regeneration through microsite and light limitation. Under formerly dense canopies, regeneration density was high but relatively homogeneous in height; while in former small gaps with greater herb cover, regeneration density was lower but with greater heterogeneity in heights

Regeneration development 4-5 years after a storm in Norway spruce dominated forests, Estonia

Abstract The regeneration patterns in wind-damaged areas are largely influenced by damage severity and varied microrelief. Regeneration was studied in Picea abies dominated stands with total and partial canopy destruction and in harvested areas in Myrtillus and Filipendula site types in Estonia 4¿5 years after a storm, examining particularly the influence of microsites on regeneration establishment and growth. The seedling densities of regeneration were highest in harvested plots compared to heavily and moderately damaged areas. The seedling densities were lowest on mounds and highest in pits among microsites in heavily and moderately damaged sites. The most common tree species regenerating in pits were birch (Betula pendula Roth., Betula pubescens Ehrh.) and alder (Alnus glutinosa (L.) J. Gaertn.). Birch and alder seedlings that survived to 2005 were taller in 2004 than those that died. Trees were also taller with lower regeneration density. Spruces (Picea abies (L.) Karst.) did not prefer any particular microsite, but those growing in pits were smaller than those in other microsites. The plots harvested regenerate more rapidly with hardwood species. Keywords: Windthrow; Regeneration; Pit and mound; Wind severity; Microsit

Storm disturbance in forest ecosystems in Estonia

Several storms have damaged Estonian forests in recent years. Individual tree properties such as diameter at breast height (dbh) and tree height affect the type of damage (stem breakage or uprooting) and influence the formation of postdisturbance forest structure. The aim of this study was to analyse how the risk of uprooting and stem breakage varied with respect to tree diameter, height, species and soil conditions. The data were collected from plots located in storm-damaged forests in eastern Estonia. The probability of uprooting increased with increasing diameter for Norway spruce, European aspen and birch. Black alders with large stem diameter usually suffered stem breakage. A high proportion of stem breakage also occurred among small Norway spruce in the understorey, probably damaged by falling canopy trees. Soil conditions influenced the ratio between uprooting and stem breakage of Norway spruce, the ratio being much higher on gley soils than on podzolic soils. The root plate size of Norway spruce was only slightly correlated with dbh, tree height and volum

Recovery of forest-floor vegetation after a wildfire in a Picea mariana forest

We aimed to detect the trajectories of forest-floor vegetation recovery in a Picea mariana forest after a wildfire. Since fire severity in boreal forests is expected to increase because of climate changes, we investigated the effects of ground-surface burn severity, a surrogate for overall fire severity, on the revegetation. We annually monitored vegetation < 1.3 m high in 80 1 m x 1 m quadrats at Poker Flat Research Range (65A degrees 12'N, 147A degrees 46'W, 650 m a.s.l.) near Fairbanks, interior Alaska, where a large wildfire occurred in the summer of 2004, from 2005 to 2009. Sphagnum mosses were predominant on the unburned ground surface. In total, 66 % of the ground surface was burned completely by the wildfire. Total plant cover increased from 48 % in 2005 to 83 % in 2009. The increase was derived mostly by the vegetative reproduction of shrubs on the unburned surface and by the immigration of non-Sphagnum mosses and deciduous trees on the burned surface. Deciduous trees, which had not been established before the wildfire, colonized only on the burned surface and grew faster than P. mariana. Although species richness decreased with increasing slope gradient, these deciduous trees became established even on steep slopes. The wildfire that completely burned the ground surface distorted the revegetation, particularly on steep slopes. The restoration of the Sphagnum surface was a prerequisite after the severe wildfire occurred, although the Sphagnum cover had difficulty returning to predominance in the short term