Plant diversity and tree responses following contrasting disturbances in boreal forest

doi:10.1016/S0378-1127(99)00130-9

Forest Ecology and Management

Volume 127, Issues 1–3, 1 March 2000, Pages 191-203

https://doi.org/10.1016/S0378-1127(99)00130-9 Get rights and content

Abstract

We determined the abundance and diversity of vascular plants in seven types of disturbance in mixed-wood boreal forest. Disturbance treatments included wildfire, natural regeneration after harvest and several methods of silvicultural site preparation. Relative to undisturbed forest, all disturbance treatments increased plant diversity to about the same extent. The abundance of plant growth-forms differed significantly between disturbance treatments. Silvicultural treatments involving soil disturbance (disk-trenching, drum-chopping and blading) had higher cover of grasses and annual forbs; naturally regenerated and Bräcke-cultivated treatments contained more perennial forbs and shrubs. Thus, different post-disturbance plant communities established following contrasting types of disturbance. Plant community biomass and tree growth varied among disturbance treatments. Shoot mass of aspen (Populus tremuloides Michx.) and the root mass of all species declined significantly with increasing soil disturbance intensity. Aspen and white spruce (Picea glauca (Moench) Voss) differed in their response to disturbance. Aspen growth was similar among disturbance treatments. In contrast, aspen density was significantly lower in disk-trenched and bladed treatments than in burned or naturally regenerated treatments, and aspen basal area was significantly lower only in drum-chopped treatments. White spruce grew fastest in drum-chopped sites. Burned treatments had the highest recruitment of volunteer spruce seedlings (up to 3200 ha⁻¹), but not significantly higher than in other disturbance treatments. Taken together these results suggest that the most intensive silvicultural treatments had the expected effects of reducing aspen abundance and increasing the growth of spruce, but also contained more grasses and forbs and had lower total root mass than burned or naturally regenerating sites. Further work is needed to examine long-term productivity and the persistence of both native and persistent weedy species following contrasting types of disturbance.

Introduction

The relationship between disturbance and diversity has received increasing attention from ecologists and natural resource managers in recent years (Grubb, 1977; Connell, 1978; Grime, 1979; Huston, 1979; Oliver, 1981; Miller, 1982; Rykiel, 1985; Petraitis et al., 1989; Pickett et al., 1989; Ehrlich and Wilson, 1991; Hansen et al., 1991; Roberts and Gilliam, 1995). Species diversity is often greatest at intermediate levels of disturbance intensity or frequency (Connell, 1978; Huston, 1979; Petraitis et al., 1989).

Natural disturbances influence species abundance, the outcome of succession, and biodiversity in many communities including forests, coral reefs and grasslands (Connell, 1978; White, 1979; Denslow, 1980, Denslow, 1985; Sousa, 1984; Huston, 1994; Tilman and Downing, 1994). Large-scale disturbances such as fire and insect outbreaks occur frequently in the boreal forest (Larsen, 1980; Suffling et al., 1988; Bonan and Shugart, 1989; Johnson and Larsen, 1991; Payette, 1992). For this reason forests contain many species that may be resilient to disturbance (Larsen, 1980).

Silvicultural practices also create disturbances on a wide range of spatial scales and intensities. Many studies have examined the effects of silvicultural disturbances of harvesting or post-harvest site preparation on nutrient conservation, hydrology, plant and animal diversity, soil structure, primary productivity and succession (Vitousek et al., 1979; Ezell and Arbour, 1985; Dickinson and Kirkpatrick, 1987; Halpern, 1988, Halpern, 1989; Morris and Lowery, 1988; Prévost, 1992; Paré et al., 1993; Attiwill, 1994; Halpern and Spies, 1995). Although natural and silvicultural disturbances have been examined in many systems, few comparisons of the effects of different disturbance-types on diversity within the same system have been made; exceptions include comparisons between fire and harvesting in Oregon (Halpern, 1988; Halpern and Spies, 1995) and in Ontario forests (Brumelis and Carleton, 1988; Brumelis and Carleton, 1989).

We examined the influence of disturbance intensity on plant diversity in boreal forest. To accomplish this, we used a comparative approach to study the effects of several silvicultural practices and fire on plant diversity at the stand level. Undisturbed forest communities are compared to those produced by various site preparation techniques and wildfire.

We expected to find increased plant diversity with intermediate levels of disturbance intensity in accordance with the intermediate disturbance hypothesis (Connell, 1978; Grime, 1979; Huston, 1994; Collins et al., 1995). Further, we predicted that fire would influence the species composition differently from mechanical disturbances in silvicultural treatments due to the extent of soil disturbance (Smith, 1986). We predict that herbaceous and weedy species will make an increased contribution to community diversity with increasing soil disturbance intensity.

In view of the fact that the main management goals of silvicultural treatments in this system are to decrease the abundance of trembling aspen (Populus tremuloides Michx.), and increase the growth of commercially valuable species such as white spruce (Picea glauca (Moench) Voss) (Peterson and Peterson, 1992), we also determined the abundance and growth of trees (aspen and spruce). We predict that if silvicultural treatments after harvesting are effective, they should reduce the abundance and growth of aspen while increasing the growth of spruce relative to naturally regenerating forest.

Section snippets

Study area

The study was conducted in the southern boreal forest near Prince Albert National Park in central Saskatchewan, Canada (53° 43′N, 105° 50′W). Forests in the region are dominated by white spruce and trembling aspen, and jack pine (Pinus banksiana Lamb.) in sandy areas. The understory is dominated by bryophytes and low shrubs, including bearberry (Arctostaphylos uva-ursi (L.) Spreng), twinflower (Linnea borealis L.), lingonberry (Vaccinium vitis-idaea L.), and bunchberry (Cornus canadensis L.).

Diversity and community structure

Undisturbed forest (C) contained fewer species than disturbed sites (Fig. 2(A)). Naturally regenerating (N) and straight-bladed (SB) treatments contained an average of about five more species than other disturbance treatments (Fig. 2(A)); however, this difference was not significant (ANOVA:F_6,14 = 2.47, p = 0.076). Species evenness and diversity were significantly higher in disturbed sites than in undisturbed forest (Fig. 2(B, C)). Burned (F) and drum-chopped (DC) sites had significantly higher

Diversity and community structure

No differences in species richness, evenness or diversity were observed between burned and naturally regenerated sites after harvest (Fig. 2). Both, burned and harvested treatments had significantly higher species evenness and diversity than unharvested forest (Fig. 2). The significant increase in diversity probably represents only a short-term response of the system to disturbance. For example, diversity increased until about eight years after fire and declined afterwards in northern Ontario

Conclusions

Burned and naturally regenerated sites had significantly higher plant species evenness and diversity than undisturbed forest (Fig. 2(B and C)), but not more than silvicultural disturbances (BC, DT, DC, SB). Increasing intensity of silvicultural disturbances did not change plant diversity, but more intense disturbances (DC and SB) tended to have higher cover of forbs and grasses (Table 2). Thus, different post-disturbance communities established after contrasting types of disturbance. On burned

Acknowledgements

We thank L. Ambrose, J. Bakker, J. Christian and H. Kleb for field and technical assistance, and P. Burton and an anonymous reviewer for helpful comments on earlier drafts of this paper. This work was supported by the Prince Albert Model Forest Association, the Canada–Saskatchewan Agreement in Forestry, and the Natural Sciences and Engineering Research Council of Canada.

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¹: Current address: Great Lakes Lab for Fisheries and Aquatic Sciences, Department of Fisheries and Oceans, Burlington, Ontario, L7R 4A6, Canada.

²: Current address: Saskatchewan Conservation Data Centre, 326-3211 Albert St., Regina, Saskatchewan, S4S 5W6, Canada.

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Plant diversity and tree responses following contrasting disturbances in boreal forest

Abstract

Introduction

Section snippets

Study area

Diversity and community structure

Diversity and community structure

Conclusions

Acknowledgements

For. Ecol. Manage.

J. Theor. Biol.

For. Ecol. Manage.

Biological integrity versus biological diversity as policy directives

BioSci.

Buried viable propagules as a factor in postfire regeneration in northern Saskatchewan

Can. J. Bot.

Environmental factors and ecological processes in boreal forests

Ann. Rev. Ecol. Syst.

The vegetation of postlogged black spruce lowlands in central Canada. I. Trees and tall shrubs

Can. J. For. Res.

The vegetation of post-logged black spruce lowlands in central Canada. II. Understorey vegetation

J. Appl. Ecol.

The value of managing for biodiversity

For. Chron.

Woody vegetation responses to fire versus clear-cutting logging: a comparative survey in the central Canadian boreal forest

Écosci.

Experimental analysis of intermediate disturbance and initial floristic composition: decoupling cause and effect

Ecology

Diversity in tropical rain forests and coral reefs

Science

The value of the world's ecosystem services and natural capital

Nature

Canopy-coverage method of vegetational analysis

Northwest Sci.

Patterns of plant species diversity during succession under different disturbance regimes

Oecol.

The short-term effects of clearfelling and slash-burning on the richness, diversity and relative abundance of higher plant species in two types of eucalypt forest on Dolerite in Tasmania

Aus. J. Bot.

Biodiversity studies: science and policy

Science

Effect of vegetative competition on regeneration of white spruce

Can. J. For. Res.

Long-term effects of scalping on organic matter content of sandy forest soils

Tree Planters' Notes

The maintenance of species-richness in plant communities: the importance of the regeneration niche

Biol. Rev.

Early successional pathways and the resistance and resilience of forest communities

Ecology

Early successional patterns of forest species: interactions of life history traits and disturbance

Ecology

Plant species diversity in natural and managed forests of the Pacific Northwest

Ecol. Appl.

Conserving biodiversity in managed forests

BioSci.

Patterns and causes of resistance to tree invasion in rights-of-way

Ecol. Appl.

Disturbance, diversity, and invasion: implications for conservation

Cons. Biol.

A general hypothesis of species diversity

Am. Nat.

Short-term effects of three mechanical site preparation methods on species diversity

Tree Planters' Notes

Climatically induced change in fire frequency in the southern Rocky Mountains

Ecology