Elsevier

Forest Ecology and Management

Volume 289, 1 February 2013, Pages 69-77
Forest Ecology and Management

Prescribed burning and browsing to control tree encroachment in southern European heathlands

https://doi.org/10.1016/j.foreco.2012.09.041Get rights and content

Abstract

Land abandonment and the cessation of traditional management practices is favouring scrubland and forest expansion throughout Europe, reducing the extent of many semi-natural open habitats of a high ecological value. Tree encroachment is threatening several Calluna vulgaris (L.) Hull heathlands. The objective of this study was to analyze vegetation dynamics resulting from an experiment designed to test management options aiming at controlling the encroachment of Populus tremula (aspen) and favouring heathland recovery. The research was conducted at Vauda Heath, North-western Italy, from 2005 till 2009. We studied prescribed burning and goat browsing, both alone or in combination, assessing their effects on structure and density of encroaching trees, as well as on heathland main species, C. vulgaris and Molinia arundinacea. Treatments were applied to 42 experimental units (300–650 m2 each), with each treatment combination replicated from six to twelve times (including untreated controls).

Prescribed burning and browsing showed complementary effects on post-fire vegetation development. Both back and head fire behaviors were effective in inducing stem mortality of aspen and rejuvenating the heathland, but in the absence of measures to control post-fire suckering, aspen tended to recover the pre-treatment stand structure. A higher fire frequency (annual winter fire) controlled tree encroachment, but hindered Calluna recovery, whilst favouring competing grass species. Goat browsing alone was initially able to reduce tree growth and slow down woodland expansion, until aspen individuals reached an escape size of 1.5 m in height. Prescribed burning followed by yearly goat browsing effectively contained tree encroachment while maximizing post-fire heathland regeneration. This integrated approach thus proved its efficacy also at the southern limits of Calluna distributional area.

Highlights

► We test prescribed fire and browsing to control aspen in southern European heaths. ► Treated units (n. 42) were monitored from 2004 to 2009 at Vauda heath, NW Italy. ► One-off burns within prescription rejuvenate heaths, but do not restrict tree recovery. ► Browsing after fire limits tree competition effects on heathland regeneration. ► Planning pastoral fire use and pasturing is necessary to maintain open heathlands.

Introduction

Anthropogenic disturbance has been a major factor affecting European landscapes and ecosystems for thousands of years mostly through fire, pastoral and agricultural activities (Antrop, 2005, Plieninger et al., 2006, Moreira and Russo, 2007). Since the middle of the XIXth century, land abandonment has favored scrubland and forest expansion, resulting in a strong decrease of many semi-natural open habitats (Chauchard et al., 2007, Garbarino et al., 2011). In Europe, given the tight integration among biodiversity and traditional human activities (Farina et al., 2003, Foster et al., 2003), the reforestation of formerly open lands can be a main cause of habitat loss (Dullinger et al., 2003, Falcucci et al., 2007). Calluna vulgaris (L.) Hull heathlands are a major cultural landscape in Europe (Gimingham, 1972). Given their conservation importance there is interest in reducing the decline they are experiencing mainly because of the abandonment of traditional management (Pywell et al., 2011). A significant amount of research has been studying practices which maintain open heathlands such as burning, cutting, grazing (e.g., Hobbs and Gimingham, 1987, Sedláková and Chytrý, 1999, Bokdam and Gleichman, 2000, Vandvik et al., 2005, Newton et al., 2009, Davies et al., 2010). Research has been focused on the response of Calluna to management in presence of competitors such as grasses and ferns (e.g., Miles, 1981, Mugion, 1996, Brys et al., 2005, Mohamed et al., 2006). Fewer studies have addressed heathland restoration in presence of advanced tree encroachment (Marrs, 1987, Hester et al., 1991, Bokdam and Gleichman, 2000, Manning et al., 2004), particularly at the southern limits of Calluna distributional area (Bartolomé et al., 2005). Transition toward woodlands in southern heathlands is favored by several factors: (i) limiting conditions (e.g., drought; poorly drained soils) which reduce Calluna competitiveness (Gimingham, 1972); (ii) no thick acidic organic layer (Pavari, 1927) which could inhibit tree establishment (Rode, 1999); (iii) heathland fragments surrounded by forests (Bartolomé et al., 2005). European aspen (Populus tremula L.) and birch (Betula pendula Roth) are the primary tree species that out-compete lowland heathlands on stream terraces which border southern European Alps (Mugion, 1996, Sindaco et al., 2008, Borghesio, 2009). In this region heathlands covered large areas since the late Middle Age and there are evidences they were maintained by anthropogenic disturbance in the form of pastoral burning and pasturing (Pavari, 1927, Sulli, 1985). Nevertheless, very few formal knowledge about traditional management practices (e.g., type of pasturing; fire regime) is available (Ascoli et al., 2009). During the last two centuries several agro-forestry programs converted these lands to forest plantations or intensive agriculture (Sulli, 1985). In addition, urbanization in last decades constrained heathlands to isolated patches, which have been recently included in nature reserves. Despite protection policies, remnant heathlands are rapidly converting to aspen-birch woodlands (Sindaco et al., 2008) and restoration programs need to be implemented (Borghesio, 2009).

Prescribed burning is one of the main management tools to maintain heathlands (Mohamed et al., 2006, Davies et al., 2010, Måren et al., 2010, Harris et al., 2011), inducing stem mortality of trees and rejuvenating Calluna before it degenerates (sensu Watt, 1955). Nevertheless, Calluna regeneration after fire may be modified by local environment (Vandvik et al., 2005) and interactions with encroaching trees (Manning et al., 2004). Previous studies suggest that fire provides sites for aspen and birch seed germination (Chantal et al., 2005, Borghesio, 2009), and promotes seedling establishment by removing the vegetation cover and depleting allelophatic soil compounds (Mugion, 1996). In addition, aspen post-fire stem mortality induces root suckering over sizeable areas, consequently encroaching stands enlarge at each fire event until they merge and out-compete the heathland (Ascoli and Bovio, 2010). Borghesio (2009) underlies that burning alone is insufficient to stop woodland expansion, and that subsequent, prolonged grazing, might be essential. Few studies have addressed P. tremula control by domestic ruminants (Gudmundsson, 1986). Moreover, most of the research on the management of Populus tremuloides Michx., the vicariant species in North America (Chantal et al., 2005), is carried out through grazers such as cattle and sheep (DeByle, 1985; Bailey et al., 1990). Browsers (e.g., goats) are expected to result in a minor impact on Calluna than grazers (Hancock et al., 2010) and in a higher tree selection than other animal species (Celaya et al. 2010; Van Soest, 1994).

The aim of this study is to investigate the effects of prescribed burning and browsing on tree control in heathlands at the southern limits of their distribution area by testing the following hypotheses: (1) prescribed burning followed by browsing maximizes tree control and Calluna regeneration; (2) heathland regeneration and tree encroachment are affected by fire frequency and behavior; and (3) heathland regeneration is affected by tree competition despite management.

Section snippets

Study site

A heathland conservation experiment started in 2005 at the Nature Reserve of Vauda (Ascoli et al., 2009), northwest Italy (7°41′17″E, 45°13′13″N). The Vauda is located on a stream terrace at 240 and 480 m a.s.l. It is characterized by ancient and leached soils, with a fairly low pH (4.8), rich in clay and with a thin organic layer (Borghesio, 2009). Annual precipitation is 1130 mm, 40% of which fall during the growing season (May–September). The driest period is in winter from late December to

Vegetation response to treatments

Before treatments, average (±SE) tree density and basal area were 22,722 ± 1518 stems ha−1 and 3.1 ± 0.4 m2 ha−1, respectively. Aspen root collar diameter ranged from 0.5 to 7 cm and accounted for 86% of the total density and 69% of basal area (birch accounted for the rest). Mean species abundance of Calluna and Molinia were 42% ± 2 and 47% ± 3, respectively. After fire treatments in winter 2005, the percentage of fire-killed stems was 100% for aspen and 96% for birch, with a consequent strong reduction in

Discussion

Prescribed burning, browsing and their combinations affected differently the tree layer, the heathland and their competition dynamics. Prescribed burning followed by yearly goat browsing effectively contained tree encroachment while maximizing post-fire heathland regeneration. Fire significantly reduced tree competition on a short term by inducing a high tree stem mortality. Similar results have been reported for P. tremuloides (Brown and De Byle, 1987, Bailey et al., 1990, Wang, 2003) whose

Acknowledgements

We thank the Vauda managers (Aschieri A, Maccioni A) for technical support, the State Forestry Corp (Noveri D), the Regione Piemonte Fire Fighting Volunteers for logistic support in prescribed burning, Sacco D and Garbarino M for statistical analysis suggestions and Ceccato R, Cugno D, Gorlier A, Mello N, Zerbini M, for fieldwork assistance. We also thank three anonymous reviewers and the open review of Marrs RH. The work was in part financed by the Regione Piemonte and in part carried out

References (65)

  • R.J. Pakeman et al.

    Rehabilitation of degraded dry heather [Calluna vulgaris (L.) Hull] moorland by controlled sheep grazing

    Biol. Conserv.

    (2003)
  • T. Plieninger et al.

    Traditional land-use and nature conservation in European rural landscapes

    Environ. Sci. Policy

    (2006)
  • R.F. Pywell et al.

    Long-term heathland restoration on former grassland: the results of a 17-year experiment

    Biol. Conserv.

    (2011)
  • F. Quetier et al.

    Farmers’ management strategies and land use in an agropastoral landscape, Roquefort cheese production rules as a driver of change

    Agric. Syst.

    (2005)
  • G. Rein et al.

    The severity of smouldering peat fires and damage to the forest soil

    Catena

    (2008)
  • M.W. Rode

    Influence of forest growth on former heathland on nutrient input and its consequences for nutrition and management of heath and forest

    Forest Ecol. Manage.

    (1999)
  • N.H. Abu-Hamdeh et al.

    Soil thermal conductivity, effects of density, moisture, salt concentration, and organic matter

    Soil Sci. Soc. Am. J.

    (2000)
  • S. Aguilar et al.

    The challenge of applying governance and sustainable development to wildland fire management in Southern Europe

    J. Forestry Res.

    (2011)
  • D. Ascoli et al.

    Tree encroachment dynamics in heathlands of North-west Italy the fire regime hypothesis

    iForest

    (2010)
  • D. Ascoli et al.

    Developing an adaptive management approach to prescribed burning, a longterm heathland conservation experiment in North-west Italy

    Int. J. Wildland Fire

    (2009)
  • A.W. Bailey et al.

    Regeneration of woody species following burning and grazing in Aspen Parkland

    J. Range Manage.

    (1990)
  • J. Bokdam et al.

    Effects of grazing by free-ranging cattle on vegetation dynamics in a continental North-west European heathland

    J. Appl. Ecol.

    (2000)
  • L. Borghesio

    Biodiversity erosion in the Vauda Nature Reserve (Turin, Piedmont, NW Italy)

    Riv. Piem. St. Nat.

    (2004)
  • L. Borghesio

    Effects of fire on the vegetation of a lowland heathland in North-western Italy

    Plant Ecol.

    (2009)
  • R.J. Brown et al.

    Fire damage, mortality, and suckering in aspen

    Can. J. Forest Res.

    (1987)
  • G.M. Byram

    Combustion of forest fuels

  • M. Chantal et al.

    Early regeneration of Populus tremula from seed after forest restoration with fire

    Scand J. Forest Res.

    (2005)
  • S. Chauchard et al.

    Patterns of land-use abandonment control tree recruitment and forest dynamics in Mediterranean mountains

    Ecosystems

    (2007)
  • R. Celaya et al.

    Changes in heathland vegetation under goat grazing: effects of breed and stocking rate

    Appl. Veg. Science

    (2010)
  • P. Daget et al.

    Une métode d’analyse phytologique des prairies

    Ann. Agron.

    (1971)
  • G.M. Davies et al.

    Fire intensity, fire severity and ecosystem response in heathlands, factors affecting the regeneration of Calluna vulgaris

    J. Appl. Ecol.

    (2010)
  • DeByle, N.V., 1985. Animal impacts, in: DeByle, N.V., Winokur, R.P. (Eds.), Aspen, Ecology and Management in the...
  • Cited by (45)

    • Does intensive cutting regime maintain lowland dry heathlands habitat? The case study of Milano Malpensa airport (Northern Italy)

      2022, Urban Forestry and Urban Greening
      Citation Excerpt :

      Therefore, a recurrent management practice that halts succession is needed (Olmeda et al., 2020) since natural (pre-human) disturbances that kept the heathlands open (such as natural large herbivores) are not present anymore. Among others management practices, such as grazing and prescribed burning, sward cutting has been successfully implemented as a conservation measure for dry heathlands, promoting periodical renewal of heather and contrasting shrub and tree encroaching (Ascoli et al., 2013). Cutting regimes can broadly vary depending on conservation objectives and local environmental conditions.

    • To graze or not to graze: A core question for conservation and sustainable use of grassy ecosystems in Brazil

      2021, Perspectives in Ecology and Conservation
      Citation Excerpt :

      A specific challenge in grassy ecosystems is woody encroachment control. Woody encroachment can be avoided or even reversed by management strategies using different domestic and wild herbivores (grazers and browsers) (Augustine et al., 2011), controlling the intensity of herbivory by browsers (Pontes et al., 2012) and combining herbivory by browsers and controlled fire (Ascoli et al., 2013). It seems, thus, that in ecosystems where shrub encroachment threatens biodiversity and productivity, mixed grazing by sheep, cattle, buffaloes and goats could be used as a management option to improve biomass consumption and encroachment control due to their complementary grazing behaviour (Osoro et al., 2013).

    View all citing articles on Scopus
    View full text