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

doi:10.1016/j.foreco.2007.03.022

Forest Ecology and Management

Volume 250, Issues 1–2, 15 October 2007, Pages 17-24

https://doi.org/10.1016/j.foreco.2007.03.022 Get rights and content

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.

Introduction

Windthrow is an important driver of gap dynamics in European temperate and boreal forest ecosystems (Ulanova, 2000). The consequences of wind disturbance can be quite varied, depending on forest structure and composition and the characteristics of each storm (Lindemann and Baker, 2001). One of these characteristics, disturbance severity, may however provide a way to organize such daunting variation among disturbances. Indeed, in at least two recent conceptual models of forest disturbance and recovery, those of Frelich (2002) and Roberts (2004), severity is one of the primary axes for differentiating disturbance effects. Disturbance severity determines which component of pre-disturbance vegetation survives or is killed. Consequently, severity can influence regeneration in two ways: (1) the physical change in light and nutrient availability; (2) the availability of seed trees, seedbanks or advance regeneration for seedling establishment.

Regeneration via seed in storm-damaged areas depends on patches suitable for germination, establishment, and survival (Ulanova, 2000, Ruel and Pineau, 2002). Environmental conditions within the gap vary greatly, and can positively or negatively influence each of these stages. Light availability, for example, increases most north of gap center (in the northern hemisphere, De Chantal et al., 2003), which could alter the community structure (Hytteborn and Packham, 1987, Dyer and Baird, 1997, Drobyshev, 2001). Uprooted trees increase environmental heterogeneity because of the creation of a pit–mound microtopography by the relocated root systems and because of the freed space on the forest floor (Greenberg and McNab, 1998, Ulanova, 2000). Pits, defined as the areas where mineral soil has become exposed; mounds, defined as the rootplates that have turned into a vertical position; intact, forest floor and decaying logs provide areas with very different microclimates and conditions (Peterson et al., 1990, Bazzaz, 1996, DeLong et al., 1997, Clinton and Baker, 2000, Peterson and Pickett, 2000, Ulanova, 2000, Ruel and Pineau, 2002), which in turn may increase biodiversity at the stand level (Lässig and Močalov, 2000, McAlister et al., 2000).

An important management question after windstorms is whether to leave or harvest the windthrown trees. General forestry practice prescribes salvage harvesting after heavy storm damage because of the fear of insect outbreaks and fire hazard. Both natural and artificial regeneration has also been thought to establish more efficiently on cleared sites (Karr et al., 2004, Beschta et al., 2004). However, the validity of such assumptions has recently been questioned in North America (Lindenmayer et al., 2004, Donato et al., 2006), generating much controversy.

Our objective in this study was to find out how disturbance severity and management influence recovery. The following hypotheses were formulated: (1) in accordance with the site heterogeneity, recruitment tree species diversity is greater in uncleared areas; (2) small-seeded species germinate better in exposed mineral soil (pits and mounds), large-seeded species need a more stable environment (intact soil); (3) pioneer species establish and grow better in more severely damaged areas, cleared areas, on mounds and to a certain extent in pits, while shade-tolerant species prefer uncleared, partly damaged areas and vegetated intact forest floor; (4) because of soil instability, seedlings on mounds will show the highest mortality figures; (5) in addition to soil stability, seedling survival depends on the individual's height and seedling densities.

Section snippets

Material and methods

The study areas are situated in Tudu (59°11′N, 26°52′E) and Halliku Forest Districts (58°43′N, 26°55′E) in Eastern Estonia. Thunderstorms occurred in Tudu in July 2001 and Halliku in July 2002, the amounts of dead wood reaching over 600 m³ per hectare (Ilisson et al., 2005a). In both areas Norway spruce (Picea abies (L.) Karst.) dominates in mixed forests. Accompanying tree species are silver and downy birch ((Betula pendula Roth. and Betula pubescens Ehrh.), European aspen (Populus tremula L.)

Results

Species composition of seedlings differed in areas with different damage severity and among microsites (Table 3). The Shannon diversity was highest in areas with moderate damage, followed by heavily damaged areas. The least diversity and eveness were found in harvested plots, where birch strongly dominated (Fig. 2). Pits showed the highest diversity among microsites. Species were also more evenly distributed in pits.

The damage severity had significant influence on pooled total seedling density

Discussion

The recovery of a stand in the uncleared areas may be influenced by the very heterogeneous microtopography. The pits, mounds and intact forest floor can vary greatly in nutrient level, soil moisture, light and temperature (Peterson et al., 1990, Bazzaz, 1996, DeLong et al., 1997, Carlton and Bazzaz, 1998, Clinton and Baker, 2000, Peterson and Pickett, 2000, Ulanova, 2000, Ruel and Pineau, 2002), which implies greater species diversity in uncleared areas, as confirmed in our study.

The harvested

Conclusions

The recovery of windthrow areas may be strongly influenced by the cumulative severity of natural and anthropogenic disturbances. This study has shown that extent of canopy destruction and logging activities influence regeneration patterns. Such findings agree with the predictions of recent conceptual models (Frelich, 2002, Roberts, 2004) that high severity is likely to produce major changes in species composition. Post-windthrow harvesting increases disturbance severity, and the results

Acknowledgements

The authors wish to thank two anonymous reviewers for linguistic revision of the manuscript and suggestions for adaptations to text structure and statistics. This study was supported by a grant from the Estonian Environmental Investment Fund, the Estonian Science Foundation (Grant no. 6087) and the Metsämiesten Säätiö. Dr Roderick McConchie, University of Helsinki, corrected the English.

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Wind is a natural disturbance factor in boreal and temperate forests having large ecological and economic consequences. We investigated recovery processes in forests severely damaged by windthrow, by conducting a systematic quantitative literature review of 34 case studies. We addressed three questions on forest ecosystem recovery: (1) Which forest regeneration processes dominate forest recovery after windthrow? (2) Which structures and processes enhance or impede forest recovery after windthrow? (3) Does salvage logging after windthrow influence forest recovery? Our analyses showed that the main focus of the reviewed studies was on post storm seedling regeneration and survival. Advanced regeneration from suppressed seedlings or saplings also played an important role in the studies, especially for shade tolerant species and in the boreal biome. Pits and mounds and coarse woody debris played an important role for the establishment of Picea sp., especially in the studies from the boreal biome, whereas in the temperate biome game interference and competition from ground vegetation seemed to be the most important influencing processes. Salvage logging mostly acted as a subsequent disturbance after the windthrow, pushing the forest ecosystem towards an earlier successional stage, hereby impeding recovery. In none of the studies however, did the windthrow nor the consequent salvaging halt recovery completely, confirming the resilience of forests as the dominant vegetation type in these biomes. Based on our results forest management implications are discussed.
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It seems that in open areas, seedling establishment may better develop in less extreme sites which may already be overgrown by ground vegetation, but succeeding developmental stages are retarded by its competition. Dominant and planted sapling survival was also positively related with sapling height and negatively related to excessive ungulate browsing, both of which have often been reported in studies (Belli et al., 1999; Kupferschmid and Bugmann 2005; Cunningham et al., 2006; Ilisson et al., 2007; Rammig et al., 2007). As reported in other studies (Hanssen, 2003; Mansourian et al., 2005; Van Couwenberghe et al., 2010; Rozman et al., 2015), micro-sites near the forest edge are often associated with better conditions for regeneration due to the proximity of seed trees and the special transitional microclimate between the forest interior and open areas.
We studied regeneration dynamics in forests disturbed by three different windthrow events in 2008 in Slovenia to assess the success of natural regeneration vs planting and subsequent silvicultural treatments. Fifty-three plots with planted saplings of Norway spruce and sycamore maple and 50 plots with dominant naturally regenerated saplings were selected in a randomly stratified manner. Sapling characteristics (height, height increment, root collar diameter, free-to-grow score, browsing and micro-site) were assessed in 2012 and 2014. Herbs and seedling establishment were studied in two subplots within each plot. Average seedling density was 13,074 and 14,674 ha⁻¹ four and six years after the windthrows, respectively. Seedlings were irregularly distributed, which suggests micro-site differences in regeneration dynamics. The results indicated lower seedling success on sites that were southerly exposed, farther from the forest edge and seed trees, on undisturbed micro-sites and at higher altitudes. On such sites planting was justified. While seedling density indicated a positive relation to herb coverage, sapling survival was negatively associated with it as well as with browsing. Initial sapling height was the strongest predictor of survival. Spruce saplings had the lowest mortality, while shade-tolerant silver fir and beech experienced high mortality. The study indicated a high density and species diversity of naturally regenerated seedlings within windthrow areas, which was reduced by planting, mowing of competing vegetation and protection measures favouring planted saplings. Recommendations for the improvement of silvicultural operations for post windthrow restoration are given.

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

Abstract

Introduction

Section snippets

Material and methods

Results

Discussion

Conclusions

Acknowledgements

Forest Ecol. Manage.

Forest Ecol. Manage.

Forest Ecol. Manage.

Forest Ecol. Manage.

Forest Ecol. Manage.

Adv. Ecol. Res.

Forest Ecol. Manage.

Forest Ecol. Manage.

Forest Ecol. Manage.

Forest Ecol. Manage.

Forest Ecol. Manage.

Forest Ecol. Manage.

Plants in Changing Environments. Linking Physiological, Population, and Community Ecology

Postfire management on forested public lands of the western United States

Conserv. Biol.

Pattern and Process in a Forested Ecosystem

Resource congruence and forest regeneration following an experimental hurricane blowdown

Ecology

Comparing the importance of seedbed and canopy type in the restoration of upland Thuja occidentalis forests of Northern Minnesota

Rest. Ecol.

Microsite effects on first-year establishment and overwinter survival of white spruce in aspen-dominated boreal mixed woods

Can. J. Forest Res.

Wind disturbance in remnant forest stands along the prairie-forest ecotone, Minnesota, USA

Plant Ecol.

Forest Dynamics and Disturbance Regimes: Studies from Temperate Evergreen-Deciduous Forests

Microsite controls on tree seedling establishment in conifer forest canopy gaps

Ecology

Guidelines for Measurements of Woody Detritus in Forest Ecosystems. U.S. Long Term Ecological Research (LTER) Network

Structure and regeneration patterns in a virgin Picea Abies forest in Northern Sweden

J. Veg. Sci.

Left to nature: forest structure and regeneration in Fiby Urskog, Central Sweden

Arboric. J.