Biological Conservation 158 (2013) 271–279
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Biological Conservation
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Review Rediscovering traditional vegetation management in preserves: Trading experiences between cultures and continents ⇑ Beth A. Middleton
U.S. Geological Survey, National Wetlands Research Center, 700 Cajundome Boulevard, Lafayette, LA 70506, USA article info abstract
Article history: Land managers are grappling with massive changes in vegetation structure, particularly in protected Received 23 June 2012 areas formerly subjected to fire and grazing. The objective of this review was to compare notes on the Received in revised form 4 October 2012 historical and current management of ecosystems around the world (especially in wet to dry grasslands Accepted 8 October 2012 in the Americas, Australia, Africa, Europe and Asia) with respect to the usage of fire, grazing and cutting to Available online 29 November 2012 reduce dominance and support the biodiversity of rare species. This review suggests that former distur- bances, which are now often lost, may have once kept tall vegetation from pushing out rarer subdomi- Keywords: nant species. In cases where prehistoric biodiversity depended on fire or large ungulate grazing, Cattle/bison grazing traditional agricultural and indigenous practices may have carried biodiversity forward to historical Fire management Farm abandonment times by mimicking pre-cultural disturbances (e.g., lightning fire and bison grazing). Ironically, biodiver- Landscape biodiversity sity related to species richness, landscape heterogeneity and function may decline in preserves, especially Land use change if traditional management once maintained this biodiversity. Managers can benefit from a cross-conti- Natural disturbance nental comparison of the full arsenal of management techniques used to control encroaching vegetation. Protected area management Ó 2012 Elsevier Ltd. All rights reserved.
Contents
1. Introduction ...... 271 2. Disturbance and biodiversity maintenance: theoretical underpinnings ...... 272 3. Abandonment of traditional management ...... 273 4. Reintroducing disturbances into natural ecosystems...... 274 5. Research needs ...... 276 Acknowledgments ...... 277 Appendix A. Supplementary material...... 277 References ...... 277
1. Introduction lendorf and Engle, 2004; Öckinger et al., 2006). These days, some preserves may not be receiving the appropriate disturbances to Exclusion of human activities in nature preserves is a common maintain these landscape attributes (Russell-Smith et al., 1997; practice. Nevertheless, natural disturbances, traditional agricul- Berkes et al., 2000). Certain traditional land management practices tural and indigenous land management were once important com- (e.g., haying, cattle grazing, wood cutting, fire) may have resem- ponents of maintaining worldwide landscapes including certain bled pre-historical disturbances (large mammal grazing, lightning grasslands, wetlands, and even some types of forests (Russell- fire; following Svenning, 2002; Rey Benayas et al., 2007), creating Smith et al., 1997; Middleton, 1999; Kimmerer and Lake, 2001; an argument to use some of these traditional land management Raisch et al., 2005; Anderson, 2006; Gellrich et al., 2007; Rey Bena- practices to mimic pre-historical disturbances. yas et al., 2007). Disturbance is an important component of species A cross-continent exploration of techniques to recreate natural richness, heterogeneity and/or function in these landscapes (Fuh- disturbances could be helpful in designing management strategies for conservation biodiversity. The objective of this paper was to examine approaches used in various parts of the world to manage ⇑ Tel.: +1 337 266 8618; fax: +1 337 266 8586. E-mail address: [email protected] vegetation before and after nature preserve designation, and to
0006-3207/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biocon.2012.10.003 272 B.A. Middleton / Biological Conservation 158 (2013) 271–279 what extent grazing and fire was currently used to support biodi- on levels of disturbance (van der Valk, 1981; Hobbs and Huenneke, versity. The methods of this review paper were to consider a com- 1992, respectively). More recent models predict high biodiversity prehensive set of research articles on this topic, particularly those with intermediate disturbance as long as other parameters are published since 2005. Using this approach, comparisons were constant (e.g., rainfall; Oba et al., 2001). Also, the dynamic equilib- made on how successful particular methods were in reducing veg- rium model explains that low to moderate levels of cattle grazing etation encroachment and in maintaining species in various eco- promote abundant butterfly and moth populations in semi-natural systems of the world. grasslands in Europe (Pöyry et al., 2004). Beyond the scope of this paper is any consideration of the role Biodiversity response to cattle grazing largely follows the inter- of disturbance in support of biodiversity in tropical ecosystems, be- mediate disturbance hypothesis in many ecosystems, but the effect cause human activities in the tropics may be simultaneously acted of grazing level depends on ecosystem type. In high levels of graz- on by intense logging, agricultural intensification, and/or cattle ing, species richness decreases (e.g., in Ponderosa pine, sagebrush grazing (following Flamenco-Sandoval et al., 2007; Dent and desert and mountain canyons) (Rummel, 1951; Reynolds and Trost, Wright, 2009; DeClerck et al., 2010; Norris et al., 2010; Tabarelli 1980; Cottam and Evans, 1945, respectively). A high diversity of et al., 2010). Also excluded are areas that have had extensive agri- native plant species can be maintained in grassy woodlands in Aus- cultural intensification related to planted pastures, e.g., the cerrado tralia using low levels of cattle grazing (Dorrough et al., 2006). Sim- of Brazil (Ratter et al., 1997). ilarly, moderate and low levels of grazing can support high plant While natural landscapes change naturally with or without dis- species richness in tallgrass prairie (Hickman et al., 2004) but little turbance (Middleton, 1999), a lack of contemporary grazing, burn- information is available on the effects of heavy grazing in this sys- ing and cutting has resulted in the loss of biodiversity (Rey Benayas tem (Symstad and Jonas, 2011). In short grass prairie, most studies et al., 2007). Loss of endangered or Red Listed subdominant species suggest either neutral or negative effects with either moderate or can occur with the proliferation of taller species, which can be re- heavy grazing (Symstad and Jonas, 2011). Some effects of cattle duced by disturbance (see especially Scanga and Leopold, 2012; grazing may take some time to manifest themselves; after cattle Schuch et al., 2012). Appropriate management may be more are removed from pastures, shrubs may increase (Winegar, 1977; important than climate change to the long-term maintenance of Schulz and Leininger, 1990). Disturbance also can promote the rare species in some ecosystems (Bucharová et al., 2012). invasion of non-native species in ecosystems (e.g., Hobbs and A crisis emerges for land managers if tall vegetation proliferates Huenneke, 1992). For example, livestock grazing may promote in formerly grazed nature preserves designated to protect small the invasion of Kentucky bluegrass (Poa pratensis) in wet meadows rare species. Eventually, the shorter species may be extirpated un- (Middleton, 2002a,b; Valles Caldera Trust, 2009). Even though low der the shade of tall species (Galvánek and Lepsˆ, 2008; Ruprecht levels of cattle grazing could introduce disturbance to help main- et al., 2010). After some time, sites may become too wooded for tain biodiversity, high intensities of cattle grazing would be unac- restoration, if permanent thresholds have been crossed (Grant ceptable in many ecosystems. and Murphy, 2005). Before the regenerative capabilities of rare Many studies examine the role of cattle grazing in the mainte- species are lost, traditional practices could stall these thresholds nance of habitat features for various types of species. High insect by opening the vegetation by grazing, fire, haying, and mechanical biodiversity has been linked to the role of cattle grazing in creating cutting. environmental heterogeneity (Rickert et al., 2012). Certain rare Overgrowth of tall species is not purely a natural outcome of plant species benefit from selective grazing by low densities of succession following the lack of fire and grazing/cutting related sheep, e.g., Gentianella and Gentianopsis in nutrient-poor calcareous to pre-historical disturbances or traditional vegetation manage- grasslands (Oostermeijer et al., 2002). Landscapes with a mixture ment. These days, many landscapes have little exposure to what of traditionally kept or recently abandoned hay meadows, mature may be necessary levels of fire and grazing acting in concert (Mur- abandoned grasslands or uncut grassland within hayfields could phy and Bowman, 2007; Fuhlendorf et al., 2008). Native animal help maintain habitat heterogeneity (Baur et al., 2006; Humbert species are no longer present in many contemporary natural pre- et al., 2012). Habitat heterogeneity may be of benefit to insects be- serves, but these have been key elements for maintaining biodiver- cause such features support the full gamut of life stages sity in natural ecosystems, e.g., marsupials in Australia (Williams, (Schwarzwälder et al., 1997). A lack of heterogeneity in habitats 2000; Yibarbuk et al., 2001; Vigilante et al., 2009), elephants in from the combined suppression of natural disturbances and tradi- Africa (Laws, 1970; Smart et al., 1985), and European or North tional management may be reducing biodiversity in natural areas American bison (Bachelet et al., 2000; Kuemmerle et al., 2010). (Pykälä, 2001; Galvánek and Lepsˆ, 2008). For a list of large mammals by region and their degree of persis- While the practices of traditional agriculturalists likely sup- tence since AD 1500, see Morrison et al. (2007). Along with native ported biodiversity by reducing dominant vegetation, the herding animals, fire was an important disturbance in certain grasslands of domestic animals may have dispersed seeds in ways that resem- and open woodlands, and these were ignited by both indigenous bled earlier pre-historical grazing systems. At the same time, na- people and lightning (Yibarbuk et al., 2001; Anderson, 2006; Vigi- tive grazers can no longer move freely in most modern lante et al., 2009; Pivello, 2011). Fires set by traditional agricultu- landscapes, so that the earlier avenues of long-distance seed dis- ralists decreased greatly after WWII in midwestern North America persal disappeared along with herds of North American and Euro- (Middleton et al., 2006a,b). Much natural land has ceded to public pean bison (Rosas et al., 2008; Jaroszewicz et al., 2008). agencies during the past century (Appendix 1), and managers could Nevertheless, cattle still move the seeds across landscapes through benefit from the knowledge of cross-cultural, continental and his- ingestion and defecation (Middleton and Mason, 1992; Mt. Pleas- torical management approaches. ant and Schlather, 1994; Bruun and Fritzbøger, 2002), but the movement of cattle is becoming much more limited with modern agricultural approaches. Traditional patterns of long-distance 2. Disturbance and biodiversity maintenance: theoretical movement of livestock by traditional agriculturalists and transhu- underpinnings mant herders (Ruiz and Ruiz, 1986; Manzano and Malo, 2006; Mid- dleton, 2002a; Nyssen et al., 2009; Huband et al., 2010; Middleton Disturbance plays an important role in the maintenance of spe- et al., 2006c) may have once moved seeds of natural ecosystems cies in ecosystems by reducing competitive exclusion by dominant long distances. At least a few studies have documented long-dis- species (Connell, 1978). Vegetation composition shifts depending tance seed dispersal by transhumant sheep herding (Manzano B.A. Middleton / Biological Conservation 158 (2013) 271–279 273
Fig. 1. Generalized model of the physiognomy of grassy ecosystems (e.g., fen, sedge meadow, grassland, prairie) with disturbances including pre-cultural large mammal and fire, restricted management with no (little) fire or grazing, and traditional cattle management including light grazing of cows, sheep (and other species), fire and mowing or hand cutting. and Malo, 2006), machines (e.g., hay bailing machines), and live- usage of agrochemicals, fertilization and other practices, which stock grazing (Matjková et al., 2003; Pärtel et al., 2005). Lack of dis- can destroy native vegetation seed banks and the capacity for spe- persal may have additional conservation implications because of cies to be restored (Middleton, 1999). These larger societal issues reduced genetic exchange between fragmented populations (Hon- may be reflected in a loss of traditional vegetation management, nay et al., 2006). which has become a rarity in various parts of the world as farm populations age (e.g., satoyama: Katoh et al., 2009). 3. Abandonment of traditional management Agricultural abandonment has occurred many times through- out history and in many regions of the world (Appendix 1), but Many contemporary preserves were originally used for pas- the most recent episode has occurred with land-use changes in tures, wood gathering or hunting areas, but such activities on these the twentieth century. Similar to marginal farmland worldwide, lands generally ceased as traditional farming disappeared (e.g., some of the less productive land has been abandoned in the United after World War II; see citations in Appendix 1), or as land ceded States and Europe (Kauppi et al., 2006; US: Rhemtulla et al., 2007, from indigenous peoples (Yibarbuk et al., 2001; Vigilante et al., Europe: MacDonald et al., 2000). The collapse of the former Soviet 2009). Traditional agriculturalists were often family land holders Union in 1989 led to the abandonment of state-owned farmland, pursuing low to moderate yielding farm production without the e.g., in the Carpathian Mountains of Poland, Slovakia and the Uk- high input and effort required to maximize yield (Loomis, 1984), raine, although the outcome of these changes depended on geo- and managed natural ecosystems either as private or common pas- graphical and socio-economic realities (Kuemmerle et al., 2008; tures, or natural hay fields (Middleton, 2002a). Their traditional Baumann et al., 2011). In most cases, agricultural policies underlie land management techniques may have mimicked pre-historical the pattern of land abandonment, because these policies often natural disturbances (Fig. 1), which in many cases supplied the encourage the intensive use of fertile land and the abandonment necessary conditions to maintain biodiversity (Svenning, 2002; of less productive land (MacDonald et al., 2000). At the same time, Rey Benayas et al., 2007). these policies have had environmental repercussions for the natu- The loss of traditional agriculturalists and their land manage- ral landscapes surrounding abandoned farmland (Stoate et al., ment practices belie the linkage between agricultural land use pol- 2009). icy and ecosystem dynamics (Bürgi and Turner, 2002; Peters et al., Public agencies often inherit the management problems of nat- 2007; Fonderflick et al., 2010; Baumann et al., 2011). Over all, agri- ural landscapes as usage in surrounding ag land is either aban- cultural abandonment is driven largely by socio-economic factors, doned or intensified (see Section 5). The new managers can and can lead to biodiversity loss in adjacent natural ecosystems witness the alarming regrowth of vegetation in these landscapes. (Sikor, 2003; O’Rourke, 2006; Rey Benayas et al., 2007). The prac- Woody species encroachment is occurring in worldwide grasslands tices of traditional agriculturalists on marginal farmland has been (Muller et al., 1998; Archer et al., 2000; van Auken, 2000, 2009; abandoned in many parts of the world (see Appendix 1), as agricul- Clark and Wilson, 2001; Bond and Parr, 2010), sedge meadows ture has intensified on more productive lands in recent times. Con- and fens (Bowles et al., 1996; Middleton, 2002a,b). Macrophytes temporary agriculture has included more intensive cultivation, proliferated after cattle were excluded in new national parks in 274 B.A. Middleton / Biological Conservation 158 (2013) 271–279 monsoonal wetlands in India and Costa Rica (van der Valk et al., would be more likely create a pulse disturbance (Bengtsson 1993 and McCoy and Rodriguez, 1994, respectively). After the de- et al., 2003). cline of cattle herding in the western European mountains (trans- A number of studies examine faunal characteristics of ecosys- humance), an overgrowth of woody species and loss of rare species tems with respect to cattle grazing. In floodplain wetlands of the occurred (MacDonald et al., 2000). Abandonment of grazing has Murray-Darling Basin of Australia, frog diversity decreased with caused hedgerows to become scrubby in the Mediterranean region heavy grazing (Jansen and Healey, 2003), but amphibians recov- as moderate levels of cultural disturbance have disappeared (e.g., ered rapidly in secondary forests developed from abandoned pas- cattle grazing; Schmitz et al., 2007). Similarly, the lack of vegeta- tures in northeastern Costa Rica (Hilje and Aide, 2012). Also, tion cutting by traditional agriculturalists (e.g., haying, hand cut- cattle grazing decreased the densities of molluscs and rare snails ting) can be directly linked to biodiversity loss (Dumortier et al., in Phragmites-dominated fens in the UK (Ausden et al., 2005). In 1996; Middleton, 2002a; Questad et al., 2011). continuously grazed grasslands in Europe, small spiders, carabids and ants (Myrmica spp.) were more common (Lenoir and Lennarts- son, 2008). At the same time, if grazing intensities were too high, 4. Reintroducing disturbances into natural ecosystems other rare species declined, e.g., the abundance of bog fritillary but- terflies in Europe decreased because of damaged grass tussocks Following the North American pre-settlement ideal, vegetation (for sun basking), and also perhaps because cattle damaged non- removal by native ungulate grazing may be an important mode of mobile young eggs, caterpillars and pupae (Schtickzelle et al., disturbance to reintroduce into natural ecosystems (e.g., bison; 2007). Truett et al., 2001). At the same time, both herbivores and fire The usage of livestock grazing and other traditional manage- may have intermingled to regulate the dynamics of many natural ment techniques to create suitable disturbances in nature pre- landscapes (Archer et al., 2000; Bachelet et al., 2000; Fuhlendorf serves is likely to be controversial for certain applications in and Engle, 2004; Murphy and Bowman, 2007; O’Connor et al., North America, despite the fact that cattle grazing already is used 2007; Fuhlendorf et al., 2008). While the reintroduction of fire or in nature conservation management in Europe (Middleton et al., herbivores may be important for maintaining biodiversity in nat- 2006a,b; Wesche et al., 2012; Scanga and Leopold, 2012). The ure preserves, the reintroduction of these disturbances bear threat of damage by livestock in natural ecosystems requires seri- lengthy consideration. ous consideration, and the negative impacts of heavy cattle grazing There may be suitable large nature preserves in the Great Plains on vegetation composition, structure and function are well docu- of North America to reintroduce American bison or elk (Allred mented (Fleischner, 1994). The greatest negative impact of cattle et al., 2011), where these could be maintained successfully (e.g., is in very dry or very humid environments (Asner et al., 2004). High using extra-strong fences for bison; Plumb and Dodd, 1993). Simi- densities of cattle can compact soil, reduce infiltration, and in- larly, European bison might be reintroduced into expanses of aban- crease runoff and sediment erosion (Trimble and Mendel, 1995). doned farm and grazing land in the Carpathian Mountains because Particularly in riparian settings, cattle can damage water quality of declining human populations there (Kuemmerle et al., 2010; and stream bank integrity because cattle seek shade, water and Ziółkowska et al., 2012). Note that the reintroduction of large na- desirable vegetation along the edges of waterways (Belsky et al., tive grazers (as well as fire) may be best suited to temperate and 1999). Riparian vegetation is affected by soil compaction, plant re- subtropical systems. In addition, certain parts of tropical America moval, and physical damage by cattle rubbing, trampling, browsing may not have had any large native herbivores for more than and removing terminal buds (Kauffman and Krueger, 1984; Szaro, 10,000 years (Janzen and Martin, 1982). 1989). After heavy grazing in western riparian systems, some dam- The conceptual utility of native bison for grassland manage- aged areas can recover only after a long period of cattle exclusion ment is not questioned, noting that according to some research, (Belsky et al., 1999). For traditional livestock management to be the measurable differences in tall grass prairies grazed by bison useful for conservation, livestock damage could be carefully man- versus cattle are relatively minor in North America (Towne et al., aged by fencing sensitive areas such as waterways (e.g., Valles Cal- 2005). Fenced cattle could also create grazing disturbances, but dera Trust, 2009). cattle are likely to be more objectionable than bison from the per- Cattle grazing may have less potential for managing biodiver- spective of the North American presettlement concept. Specific sity in forests than in some other ecosystem types. Cattle may dis- procedures might be developed to utilize cattle for creating distur- rupt tree regeneration in forests, e.g., Draceana cinnabari in Socotra, bance in preserves to maintain biodiversity, particularly because Yemen (Attore et al., 2007), Araucaria araucana in Chile (Zamorano- cattle may be easier than bison to handle for natural ecosystem Elgueta et al., 2012), Eucalyptus in Australia (Dorrough and management. Moxham, 2005; Weinberg et al., 2011), and Nothofagus dombeyi/ While the re-introduction of appropriate native grazing and fire Austrocedrus chilensis in northern Patagonia, Argentina (Blackhall cycles would be an ideal solution to the problem of vegetation et al., 2008). At the same time, the regeneration of some tree encroachment in nature preserves, using these disturbances in nat- species is little affected by cattle grazing, e.g., Betula regenerates ural areas near large human populations may pose difficulties despite low levels of sheep grazing in woodlands in Scotland (Knapp et al., 1999; Radeloff et al., 2005). As an alternative ap- (Pollock et al., 2005). proach to the re-introduction of unfeasible natural disturbances, Despite the fact that cattle grazing generally reduces tree regen- livestock grazing and/or controlled prescribed burning could eration in forests, cattle grazing has been implicated in the woody staunch woody encroachment. Managers have used patch-burn invasion of grassland (Fig. 2b and c), savanna and other ecosystem grazing to focus livestock grazing on burned areas to encourage types depending on the livestock species, intensity of grazing, and high plant biodiversity (Helzer and Steuter, 2005) and habitat qual- interactions with other disturbances. Shrub encroachment may oc- ity for rare Greater and Lesser Prairie Chickens in North American cur after heavy cattle grazing because of the reduced abundance of grasslands (Hart, 2006). Domestic cattle and North American bison herbaceous species and lack of fuel for fire (Asner et al., 2003). Past have very similar impacts on grassland vegetation (Fig. 2a) (Plumb heavy grazing also can be the culprit in woody proliferation be- and Dodd, 1993), although cattle spend more time in woody vege- cause damaged grassland may allow aggressive woody species to tation (Allred et al., 2011). Without specific management rotations, establish and spread (van Auken, 2000). Cattle hoof prints can fenced cattle may differ in their grazing pattern from bison in that sometimes create openings for woody invasion in otherwise thick cattle typically create a press disturbance, while unfenced bison graminoid vegetation. While the cattle graze, invaded woody seed- B.A. Middleton / Biological Conservation 158 (2013) 271–279 275
Fig. 2. Traditional agricultural management often included cattle grazing of natural areas. (a) Cattle grazing near the edge of open peatlands of Xingkai Lake, northeast China. (b) Shrubs at front of invasion in formerly grazed peatland near the Changbai Mountains, northeast China. (c) Shrub and tree cover in formerly open peatland about 30 years after cattle grazing stopped, Lodi Marsh Natural Area, Wisconsin, USA. Photos by Beth Middleton, U.S. Geological Survey, National Wetlands Research Center. lings may be eaten and barely noticeable (Glinski, 1977; Middle- their effects; in open hill habitats in Scotland, sheep and cattle ton, 2002a,b). After cattle are removed from a pasture, invaded had higher impacts than wild herbivores (red deer, rabbits, moun- woody seedlings may grow aggressively and mature into tall tain hares and red grouse) (Albon et al., 2007). Grazer type may shrubs or trees, which shade shorter herbaceous and graminoid influence vegetation and habitat characteristics, although type species (Middleton, 2002a,b). After drought, woody species may may be less important than the size of the cattle (Rook et al., proliferate when rains resumed as was the case in semi-desert in 2004). In addition, sheep in low stock densities have helped to re- Texas in the 1950s (Buffington and Herbel, 1965). store dwarf shrubs on moorland in Europe (Pakeman et al., 2003). An alternative explanation for woody encroachment is that lit- Livestock already have been incorporated into conservation man- ter accumulates after cattle grazing stops, thus increasing the agement strategies of certain natural areas (e.g., Valles Caldera Na- intensity and frequency of fire disturbance. Fire itself may favor tional Preserve, New Mexico) (Valles Caldera Trust, 2009; Wesche woody species (Bachelet et al., 2000). Fire intensity may have in- et al., 2012). Nature conservation approaches including both graz- creased with the extirpation of bison and subsequent build-up of ing and mowing have been successful in maintaining biodiversity fuel in the northern Great Plains of North America (Umbanhower, in agricultural grasslands in Central Europe over many decades 1996). Beyond land use change, there is also evidence that woody (Wesche et al., 2012) including the maintenance of threatened spe- plant proliferation can be attributed to global increases in atmo- cies such as Cnidium dubium (Karsten Wesche, personal spheric CO2 level (Archer et al., 2000; van Auken, 2000, 2009; Bond communication). and Parr, 2010), deposition of nitrogen (Wigley et al., 2010), rain- Beyond cattle grazing, traditional agriculturalists also managed fall, fire regimes (Bowman et al., 2010), and/or chronic high levels vegetation in natural grasslands with haying (Questad et al., 2011; of grazing (van Auken, 2000, 2009). Global changes may override Wesche et al., 2012). Agriculturalists cut native hay as forage for any effects related to agricultural abandonment. For example, in livestock, which reduced the dominance of grasses and increased South Africa, woody species have expanded in conservation areas, biodiversity (Questad et al., 2011), while livestock grazing favored as well as in communal lands where land use related to grazing, grasses and small herbs (Stammel et al., 2003). Sometimes in small fire and woody gathering practices have not changed in recent wetland conservation areas in Europe, vegetation is cut by hand to times (Wigley et al., 2010). The potential reasons for woody maintain the biodiversity of Red Listed species (Middleton et al., encroachment of grasslands are complex and overlapping, but do 2006a,b). Mowing can reduce dominance of vegetation in wet- not overshadow the urgency to manage the problem. lands, even though grazing may be more effective in creating open- If a site is deemed suitable for biodiversity management by live- ings in wetland vegetation (Hobbs and Huenneke, 1992). stock grazing, then there are worldwide studies that could inform Reintroduction of traditional agricultural practices such as mowing guidelines (e.g., livestock number, type, timing). Temporary intro- and grazing has been recommended to stem the continued loss of ductions of various herbivores could be considered for conserva- orchid species in wet grasslands, calcareous grasslands and wood- tion management, particularly species that browse woody lands in Europe (Kull and Huchings, 2006). Similarly in North vegetation, e.g., cattle and goats. It is important to keep in mind America, experimental cutting in forested fens has been successful that various herbivores at different grazing intensities differ in in promoting openings to support rare species such as Trollius laxus 276 B.A. Middleton / Biological Conservation 158 (2013) 271–279
(Scanga and Leopold, 2012). At the same time, mowing may be less scribed fire, grazing or cutting to promote biodiversity is certainly useful than grazing to promote rare bryophytes in calcareous in need of more research. Keep in mind that underlying any debate grasslands (Vanderpoorten et al., 2004). In an activity similar to in North America is the sheer force of the pre-settlement perspec- mowing, cattail (Typha domingensis) has been crushed with modi- tive, which may be blocking the consideration of traditional vege- fied tractor wheels to reduce overgrowth in tropical seasonal wet- tation management. There is some growing acceptance of the lands in Palo Verde National Park, Costa Rica (Osland et al., 2011). usage of cattle grazing and fire in nature preserves in the US to Traditional agricultural practices are not always useful in manage- maintain habitats for some rare species (e.g., prairie chickens; Hart, ment, for example, there was no benefit to grazing or mowing for a 2006). While cattle grazing is sometimes used in nature preserves rare orchid species in Eucalyptus woodland in Australia (Prasophyl- in Europe (Wesche et al., 2012), prescribed fire is not as widely lum correctum; Coates et al., 2006). used there as in North America or Australia (Middleton et al., Invertebrates sometimes benefit from traditional management. 2006b). So, more worldwide research needs to be focused on In grasslands, butterfly abundance is highest after mowing (Skórka comparisons of the realized outcomes of vegetation management et al., 2007), burning (cool season: Panzer and Schwartz, 2000), with fire, large mammals and cutting with a view toward likely and/or grazing (Vogel et al., 2007), although bird and invertebrate ecosystem conditions during prehistoric, indigenous, traditional biodiversity decreases if cutting is too intensive in Phragmites aus- agriculturalist and contemporary times. Research needs to be con- tralis stands (Valkama et al., 2008). Similar responses occur to ducted on how desired outcomes might be realized in a world wood cutting; for example, in cork oak forests (Quercus suber)in setting much changed from its prehistorical context. In this way, Portugal, butterfly richness and abundance was highest after cop- managers could consider the worldwide arsenal of tools (e.g., na- picing (Verdasca et al., 2012). In oak forests in Sweden, beetle rich- tive ungulate grazing, fire regimes, livestock grazing, mechanical ness increased when secondary tree species were cut from Quercus harvesting, and disturbance interactions), to ascertain which meth- forests (Franc and Götmark, 2008). ods might be acceptable for vegetation management within spe- The value of traditional approaches to stimulate rare species cific contexts. should not be underestimated. Both burning and cutting have been Traditional management practices by agriculturalists and indig- successful in both North American and European fens (Middleton enous groups may be the best choice to tackle vegetation et al., 2006b; Scanga and Leopold, 2012) but there may be time encroachment especially in urban preserves; these techniques limits to re-instigate this procedure. In Europe, 20 years after the have been used to manage natural vegetation for millennia abandonment of traditional management, mowing was less effec- (Russell-Smith et al., 1997; Berkes et al., 2000; Williams, 2000; tive in reestablishing biodiversity in mountain grasslands (Gal- Bengtsson et al., 2003; Bowman and Prior, 2004). Procedures for vánek and Lepsˆ, 2008); however, after 40 years of agricultural the removal of encroaching vegetation could be augmented with abandonment, mowing and/or grazing still revived some rare tar- research on the traditional management approaches of agricultur- get species in steppe grassland (Ruprecht et al., 2010). Natural alist and indigenous groups. Combinations of strategies to manage prairies with an annual hay harvest had the highest species rich- vegetation encroachment with grazing, fire, and/or cutting could ness level including federally endangered species in the United help maintain endangered species (Berkes et al., 2000; Questad States, while protected and little grazed prairies had lower levels et al., 2011), and encourage a shifting mosaic of habitats for conser- of species richness (northeastern Kansas; Questad et al., 2011). vation (Fuhlendorf and Engle, 2001, 2004). Conservation Reserve Program lands in the United States are not Gaps in knowledge exist to approach specific problems regard- managed with haying, grazing or native grassland species restora- ing vegetation management. From the perspective of land aban- tion, but such practices might increase their biodiversity potential donment after agricultural intensification, nutrient addition to (Questad et al., 2011). improve forage for cattle has increased non-native species (tropical Fire is an important disturbance in grasslands and other ecosys- grasslands: Boughton et al., 2011), and decreased forbs (temperate tems. Prescribed burning can reduce woody material (Clark and floodplain: Wesche et al., 2012). Vegetation removal to reduce the Wilson, 2001), and has been used routinely by traditional agricult- level of nutrients in soil has been attempted (Oelmann et al., 2009), uralists to maintain pasturelands (Middleton, 2002a,b). While fire but research is fairly scant in this area. Nevertheless, one study is not commonly used in Europe, fire is widely used for the man- showed that reducing fertilization levels did not increase biodiver- agement of many ecosystems in North America, Australia (Middle- sity unless the seed bank still harbored rare species (Muller et al., ton et al., 2006b), and South Africa (van Wilgen et al., 2004). 1998). Nevertheless, mowing fertilized pastures revived perennial Prescribed fire is not always effective in promoting biodiversity, native forbs, e.g., in coastal prairie (Maron and Jefferies, 2001). e.g., winter burns may not be hot enough to reduce shrubs in Reduction of nitrogen fertilization (Maurer et al., 2006) and low northern sedge meadows (Middleton, 2002b). Burning is related cattle stocking densities helped maintain biodiversity in European to changes in species composition in calcareous grasslands in Eur- grasslands (Klimek et al., 2007). ope (Kahmen et al., 2002) and certain species of butterflies are neg- Shrub encroachment is a particularly intractable problem in for- atively affected by fire for 3–5 years after prescribed burning mer pastures damaged by heavy grazing, and research is needed to (Swengel, 1996). As is the case with the reintroduction of mammal determine how to reduce shrub overgrowth after it establishes. grazing, the reintroduction of fire cannot always be accomplished Subsequent to shrub clearing, cattle grazing has been used to re- in regions with large human populations. store xeric natural grasslands, e.g., in Tuscany, Italy (Maccherini and Santi, 2012). Cattle could be particularly useful for the man- agement of certain types of shrub thickets that do not burn readily. 5. Research needs Scottish highland cattle reduced shrubs such as Rubus spp., while fire reduced Ribes missouriensis in formerly grazed oak woodland What constitutes a natural disturbance, and how important are savanna in the Midwest of the United States (Harrington and these in maintaining biodiversity in worldwide ecosystem types? Kathol, 2008). After heavy cattle grazing in the Midwest, red cedar While natural disturbances such as fire and large herbivore grazing infested tall grass prairie, so that moderate cattle stocking and fire are no doubt important in many grasslands, the necessity of these was useful for controlling red cedar (Morton et al., 2010). The com- disturbances becomes more debatable in forests, especially fire- bined forces of fire and temporary cattle grazing could be a shrewd sensitive tropical rainforests and Atlantic forests (Pivello, 2011). way to stimulate prairie vegetation some years after shrub thickets Whether or not natural disturbances can be mimicked with pre- have established (Harrington and Kathol, 2008). B.A. Middleton / Biological Conservation 158 (2013) 271–279 277
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