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The Irregular Shelterwood System: Review, Classification, and Potential Application to Affected by Partial Disturbances

Patricia Raymond, Steve Be´dard, Vincent Roy, Catherine Larouche, and Ste´phane Tremblay

Structurally different from even-aged and balanced uneven-aged stands, irregular stands are an integral that silvicultural practices must emulate eco- part of forested landscapes in northeastern North America. The maintenance or restoration of irregular logical processes and interactions if compo- stand structure may be desirable, especially in areas under ecosystem-based management. This can be sition, structure, and ecosystem function are achieved at the stand level through the implementation of irregular shelterwood systems. The objectives to be maintained within their limits of nat- of this synthesis are to assemble the existing knowledge about the system, clarify the terminology in ural variability (Kaufmann et al. 1994, Sey- use, and discuss its place in silviculture in northeastern North America. Irregular shelterwood is mour et al. 2002, Gauthier et al. 2008) at compared with other methods and we propose a classification based on three variants. This multiple spatial and temporal scales (Ga- silvicultural system is compatible with ecosystem-based management in types driven by partial lindo-Leal and Bunnell 1995). At the stand stand mortality and gap dynamics and provides opportunities for maintaining old-growth forest scale, the growing interest in ecosystem-

ABSTRACT attributes. However, it presents important challenges, especially with regards to planning, growth and based management brings into question cur- yield prediction, and operational application. rent silvicultural practices and how they can contribute to maintaining ecological values Keywords: ecosystem-based management, irregular uneven-aged silviculture, multiaged stand, (Guldin 1996, Puettmann and Ammer irregular shelterwood variants, regeneration methods 2007). This article focuses on the silviculture of irregular stands. In American n many North America jurisdictions, (Kohm and Franklin 1997). In a managed textbooks, even-aged stands are clearly dis- the management of public forestlands territory, applying principles of ecosystem- tinguished from uneven-aged stands (Smith I has gradually shifted from timber pro- based management is a way of achieving sus- et al. 1997, Nyland 2002). Even-aged stands duction to ecosystem-based management, tainable objectives (Ga- are composed of in the same age class, with a focus on late-successional habitat lindo-Leal and Bunnell 1995). This implies with the oldest and youngest trees differing

Received November 24, 2008; accepted May 20, 2009. Patricia Raymond ([email protected]), Steve Be´dard ([email protected]), Vincent Roy ([email protected]), Catherine Larouche ([email protected]), and Ste´phane Tremblay ([email protected]) are research scientists in silviculture, Direction de la recherche forestie`re, Ministe`re des Ressources naturelles et de la Faune, Gouvernement du Que´bec, Que´bec, Canada. The authors thank Paul Bouliane and Louis Be´langer for being a source of inspiration with the development of the irregular shelterwood system at Foreˆt Montmorency Experimental Forest (Universite´ Laval) and give special thanks to Jean Noe¨l and Maripierre Jalbert for their help with the figures, Debra Christiansen-Stowe for the linguistic revision, and Lucie Jobin for assistance with the literature review. The authors also thank Daniel Dumais, Jean-Claude Ruel, Yan Boucher, Jean-Pierre Saucier, Robert S. Seymour, and two anonymous reviewers for their helpful comments on earlier versions of this article. Copyright © 2009 by the Society of American .

Journal of Forestry • December 2009 405 in age by no more than 20% of the rotation matic subdomains, is 24 and 45%, respec- cation of irregular shelterwood in northeast- length. Uneven-aged stands contain an inti- tively (Boucher et al. 2003). A historical ern North American silviculture. mate association of at least three age classes study, recently conducted at the boundary growing in the same area (Smith et al. 1997, between the balsam fir–yellow birch (Betula The Irregular Shelterwood Nyland 2002). Although the debate around alleghaniensis Britton) and sugar maple (Acer System and Its Variants the binary classification of stand age struc- saccharum Marsh.)–yellow birch bioclimatic As early as the 19th century, practicing ture (even-aged versus uneven-aged) has domains, showed the predominance of ma- foresters in several European locations began been going on for decades, it has long been ture stands with an irregular structure in pre- expressing their displeasure with the scarcity acknowledged that intermediate structures industrial landscapes (Barrette and Be´langer of mixed stands and forest homogenization exist (Silvy-Leligois 1953). For instance, 2007). The importance of irregular stands in generated by the use of even-aged systems two-aged stands have two distinctly differ- natural forests was also recognized elsewhere such as regular shelterwood and ent ages classes (Smith et al. 1997, Nyland in northeastern North America (Lorimer with planting (Fourchy 1952, Silvy-Leligois 2002). Furthermore, authors such as Smith 1977, Lorimer and Frelich 1994, Seymour 1953, Spurr 1956). They developed new re- et al. (1997) distinguish “balanced” from and Kenefic 1998, Lorimer and White generation methods in response to specific “irregular” uneven-aged stands. In balanced 2003). local ecological and economical conditions uneven-aged stands, age classes occupy ap- Given the ecological significance of ir- (Puettmann et al. 2008). This development proximately equal areas that function as self- regular stands in unmanaged forests, main- triggered an important switch from manag- contained, sustained yield units, whereas ir- taining these structures on a proportion of ing regeneration at the stand level to more regular uneven-aged stands (hereafter called the area might be desirable, e.g., to meet ec- flexible applications adapted to conditions irregular stands) are unbalanced and do not osystem-based objectives. However, current at smaller spatial scales (Puettmann et al. contain the age-class distribution necessary management practices do not always permit 2008). Gayer first described the concept of to produce a constant yield of mature trees at the specificity of irregular stands to be main- the irregular shelterwood method (Femel- short intervals indefinitely. tained. Generally, the aim is to regulate schlag) and recommended that foresters In northeastern North America, irregu- stand structure, which results in a simplifi- should seek their inspiration from natural lar stands used to be an important landscape cation of stand attributes (Franklin et al. stand dynamics when implementing silvi- component, given the predominance of late- 2007). A good example is the generalized use cultural prescriptions (Gayer 1880 in Silvy- successional forests (Lorimer 1977, Bou- of clearcutting and its variants in coniferous- Leligois 1953). Gayer’s objectives were to chard et al. 2008, Boucher et al. 2009). Ir- dominated stands of Canadian boreal and promote the establishment of natural regen- regular stands typically develop as a result of mixedwood forests (Bergeron et al. 1999, eration and the creation of mixed species episodic partial stand mortality occurring in Groot 2002). Using even-aged silvicultural stands. Shelterwood methods share the com- the absence of whole stand-replacing distur- systems in irregular stands sacrifices vigorous bances (Fajvan and Seymour 1993, Fraver small merchantable stems and simplifies mon objective of establishing regeneration and White 2005, Bouchard et al. 2006, stand structure (McCarthy and Weetman under the overhead or side shelter of forest Bergeron et al. 2007). Various old-growth 2006). This may have an impact on biodi- cover (Matthews 1989). Irregular shelter- attributes, cited in Bauhus et al. (2009), can versity (Aplet 1994, Desponts et al. 2002). differs from regular shelterwood and be found in irregular stands: multiple can- Although balanced uneven-aged silvicul- its variants in that the forest cover is retained opy layers, high variation in sizes, pres- tural systems may conserve several irregular during a long period of time to accommo- ence of several cohorts (e.g., group of trees stand attributes, especially those related to date special management objectives (Han- developing after a single [Helms vertical structure, the maintenance of an ir- nah 1988, Nyland 2002). The method was 1998]), high spatial heterogeneity of tree regular structure over the long term is not first investigated by von Huber in Bavaria distribution, irregular gap size and distribu- the objective (Smith et al. 1997, Angers et al. (Spurr 1956). Initially, stand irregularity re- tion, and high variation in branch systems 2005). ferred to vertical variation in tree height, but and crown structure, as well as the presence Maintaining the structure of irregular the concept has evolved to include horizon- of advance regeneration. It is generally ac- stands without converting them to even- tal variation as well (Schu¨tz 2002). The knowledged that structurally complex aged or balanced uneven-aged stands re- commonality of the first irregular shelter- stands provide a wide variety of habitats for quires an appropriate silvicultural system. wood systems (Bavarian, Swiss) was to re- animal and plant species (Hansen et al. The irregular shelterwood system, defined as generate the stand by harvesting irregularly 1991, McComb et al. 1993). a system of successive cuttings with a long or spaced small groups of trees (Fourchy 1952). In Quebec (Canada), several studies indefinite regeneration period, offers the Many Femelschlag deviated from the initial have quantified the historical importance of flexibility of generating spatial and vertical form, and today Femelschlag refers to a vari- irregular stands at the landscape scale. In the heterogeneity in stands (Matthews 1989). ety of silvicultural systems that differ among easternbalsamfir(Abiesbalsamea[L.]Mill.)– However, in practice, the use of this system countries and forest managers (Matthews white birch ( Marsh) biocli- is rather limited in North America (Seymour 1989). matic subdomain, e.g., irregular stands used 1992, 1995). While conducting our litera- In the scientific literature, descriptions to occupy 39% of the virgin forest (Leblanc ture review, we realized that there is some- of irregular shelterwood systems vary as well. and Be´langer 2000). The percentage of un- times confusion in the terminology used. In However, the common objective is to estab- managed stands presenting an irregular this article, we review the existing knowl- lish, at each entry, a new cohort composed of structure in the western and eastern black edge about this system, clarify the current desirable midtolerant or tolerant tree spe- ( [Mill.])–moss biocli- terminology, and discuss the potential appli- cies, with a longer regeneration period than a

406 • December 2009 Table 1. Variants of the irregular shelterwood system.

Variant Expanding-gap irregular shelterwood Continuous cover irregular shelterwood Extended irregular shelterwood

Other names Bayerischer Femelschlag Badischer Femelschlag Slow or delayed regeneration Acadian Femelschlag Swiss or Baden shelterwood Extended shelterwood Irregular group shelterwood Coupe progressive irrégulière à couvert Coupe progressive irrégulière à régénération Bavarian shelterwood permanent lente Coupe progressive irrégulière par trouées agrandies Period of regeneration Ͼ20% rotation length Ͼ20% rotation length Ͼ20% rotation length Harvesting pattern Group gradually expanded Free, single tree, and group Single tree, group, or strip Final removal Optional No Optional Arrangement of cohorts Juxtaposed cohorts Stratified cohorts Two cohorts during Ͼ20% of rotation New cohort established besides the previous New cohort established on the same area than Only one new cohort established during the one the previous one rotation Vertical structure Regular at small scale Irregular Regular or irregular Single layer Multiple layers Single or two layers Horizontal structure Irregular Irregular Variable according to harvesting pattern Mosaic of cohorts Mix of cohorts References Fourchy 1952 Fourchy 1952 Smith 1986 Spurr 1956 Spurr 1956 Hannah 1988 Lanier 1994 Seymour 1992, 1995 Schütz 2002 Lanier 1994 Saunders and Wagner 2005 Smith et al. 1997 Seymour 2005 Nyland 2002 regular system (more than 20% of rotation or stratified cohorts (continuous cover and clude conserving specific animal habitats length; Smith 1986, Hannah 1988, Lanier extended) during portions or all of its rota- (e.g., caribou [Rangifer tarandus 1994). We propose a classification based on tion length and therefore maintains a more caribou]; Daintith et al. 2005, Stone et al. three variants (Table 1). These variants dif- or less regular vertical and horizontal struc- 2008), protecting the regeneration of species fer in their spatio-temporal applications, ture. All variants may include the retention sensitive to abiotic damage such as which are in line with their specific objec- of legacy trees (Smith 1986, Franklin et al. and frost (e.g., red spruce [ tives. The first variant, expanding-gap irreg- 2007). The choice of variant should be Sarg.]; Dumais and Pre´vost 2007), insect ular shelterwood, aims to regenerate new co- based on the autecology of desired species, damage (e.g., white weevil [Pissodes horts in groups that are gradually enlarged management objectives, and natural stand strobi Peck.]; Hannah 1988) and weed com- until the stand is totally removed (Spurr dynamics. In the example (Figure 1), the petition (e.g., red [Quercus rubra L.]; 1956). With this variant, regeneration and choice of variant for a particular stand may Hannah 1988). Of course, while other silvi- harvesting are closely integrated to achieve a be influenced by different reasons. The con- cultural systems may also be appropriate, the spatial order, which brings the stand to- tinuous variant appears to be the most ap- objective here is to describe situations when gether into a managed unit (Matthews propriate if there is a need to maintain a irregular shelterwood could be a relevant 1989). In the second variant, continuous continuous forest cover, as is the case for tool. cover irregular shelterwood, the sequence of sensitive landscapes, side roads, recreational, Once irregular shelterwood is identified cuttings is applied more freely in space and and riparian areas. The two others variants as a potential tool, a few basic requirements time, which permits maintenance of a mul- may be simpler to apply and economically must be verified to ensure that the system is ticohort structure and a continuous forest more advantageous, but they create less het- applicable, and then, the general decision cover (Fourchy 1952). The silviculturist erogeneity in the stand. The expanding-gap key may help to choose a suitable variant works more with the material in place and variant causes less damage to regeneration (Figure 2). First, desired species must have adjusts the frequency and intensity of inter- because the harvesting sequence is organized high or moderate shade tolerances (Schu¨tz ventions to the autecology of the species and in such way that there is usually no return to 2002). Second, unless enrichment with arti- local site characteristics (Fourchy 1952). the regenerating areas (Matthews 1989). ficial regeneration is planned, the dominant The third variant, extended irregular shelter- The extended variant is the least intensive cover must contain an adequate quantity wood, aims to regenerate the whole stand and is applied similarly to regular shelter- and favorable distribution of trees of the while keeping a more regular structure. Un- wood systems (Nyland 2002). This variant desired species, taking into consideration der this variant, two cohorts are maintained is useful for establishing and protecting a seed dispersion distances, and the frequency, for at least 20% of the rotation length, be- layer of high regeneration over a period of and abundance of seed . Seed trees cause of a delay of the final removal (Smith several decades (Seymour 1992). must be old enough to produce in 1986, Nyland 2002). Silviculturists may opt for the imple- abundance (Malcolm et al. 2001). Third, Figure 1 illustrates the sequence of cut- mentation of irregular shelterwood as part of the stand must contain sufficient acceptable tings for each of the three variants in a hy- a management plan that is governed by ex- growing stock and be relatively wind firm to pothetical mixed-species irregular stand. ternal factors, such as social (e.g., aesthetical, minimize the risk of during the Depending on the variant used, the resulting recreational, and social acceptability) or eco- regeneration period (Malcolm et al. 2001). stand may have juxtaposed (expanding-gap) logical objectives. These objectives may in- Finally, age structure, number of cohorts,

Journal of Forestry • December 2009 407 regular structure” category that better re- flects this range (Table 2). The recognition of three categories is necessary because the most defining feature of a silvicultural sys- tem is the age structure of a stand (Seymour and Hunter 1999, Nyland 2002). The range of variants associated with an irregular shel- terwood system can then be used to manage the array of structures within the irregular category. Both regular and irregular shelterwood methods have the same objective to induce the establishment of multispecies cohorts by adapting openings to the light re- quirements of desired species (Smith et al. 1997, Kneeshaw and Bergeron 1998, Mc- Carthy 2001). However, the irregular shel- terwood method allows more flexibility for growing mixed stands that are composed of species with different longevities and levels of . This is especially true of the continuous cover variant. The timing of cutting and the selection of harvested trees can be adjusted to the species’ lifespans. Long-lived species such as yellow birch, sugar maple, red spruce, white spruce ( (Moench Voss), northern white-ce- dar (Thuja occidentalis L.), and white pine ( L.) can be maintained in the stand over a longer period of time, while short-lived species like balsam fir and red maple (Acer rubrum L.) can be harvested on shorter cutting cycles. Other principles common to shelter- wood methods, such as using the partial cover to ensure a constant seed supply, and sheltering the new cohort from adverse mi- croclimatic conditions and undesirable fast- growing species, are prolonged with the ir- regular system since the regeneration period is lengthened (Nyland 2002). Overtopped may also experience slower growth with the irregular method (Smith et al. 1997, Miller et al. 2006, Moores et al. 2007). Shelterwood systems differ from Figure 1. Example of silvicultural scenarios illustrating three variants of the irregular shelter- systems, because the re- wood system in a fictive mixed balsam fir–yellow birch stand over a 90-year period. Red bars tained trees in the latter do not promote re- before cutting, generation through shelter (Mitchell and ؍ indicate marked trees. Numbers represent number of years since beginning. a ,paper birch. Beese 2002). In variable retention systems ؍ yellow birch, and PB ؍ balsam fir, YB ؍ red spruce, BF ؍ after cutting, RS ؍ b long-term structural diversity is assured by and the principal structural objective (mainte- place within the family of regeneration trees that are left standing for at least one nance or transformation) will be taken into methods? We think that regener- rotation without periodic entry in the stand, consideration when selecting the most appro- ation methods should be classified according leading to one regeneration cohort. priate variant for a given stand (Figure 2). to three age structure categories (Table 2). In The expanding-gap and the continuous fact, a range of intermediate age structures cover variants may appear to be similar to Irregular Shelterwood among exists between even-aged and balanced un- systems. However, the Other Silvicultural Systems even-aged structures. We propose expansion main difference is that there is no objective Because irregular shelterwood has sim- of the recognized two-aged structure (Smith to balance the different age classes of the ilarities with other systems, what is its real et al. 1997, Nyland 2002) to a broader “ir- stand by single tree removal or by establish-

408 Journal of Forestry • December 2009 Figure 2. General decision key for choosing the appropriate variant of irregular shelterwood, according to the age arrangement and the structural objective. ment of groups on a restricted area or spe- uous cover irregular shelterwood, the objec- and Sendak 2002, Neuendorff et al. 2007, cific spatial arrangement, which is character- tive of a selection system is to maintain a Webster and Jensen 2007). Furthermore, istic of selection systems (Fourchy 1952, balanced structure and to achieve a constant windstorms are episodic events that occur in Matthews 1989). The expanding-gap vari- periodic yield over cutting cycles. In fact, the northern stands (Canham and ant may look similar to group-selection cut- idea of balance is an economic concept that Loucks 1984, Frelich and Lorimer 1991) ting after the first cutting, but it differs allows more straightforward harvest plan- and generate additional structural heteroge- thereafter because future cuttings will en- ning and a continuous timber supply (Smith neity in late-successional forests (Lorimer large the gaps, whereas, the next group-selec- et al. 1997). and Frelich 1994). With the perspective of tion cuttings will create new gaps at each diversifying silvicultural practices, irregular entry, thus creating a balanced age-class dis- Justification and Potential shelterwood could be an alternative to a reg- tribution over the area (Leak 1999, Nyland Application in the Northeast ular shelterwood system and might help to 2002). In the continuous cover variant, the increase heterogeneity in these forests. It also The renewal of northern hardwood for- least rigid of the approaches (Fourchy offers more possibilities than a group-selec- ests is characterized by a small-scale distur- 1952), the major goal is to obtain stands tion system for promoting the regeneration bance regime of gap dynamics (Frelich and with the highest production value possible of less shade-tolerant species. in terms of quality and quantity. Thus, the Lorimer 1991) and selection cutting is a Stands impoverished by repeated selec- concept of cutting cycle becomes blurred. commonly used system in this forest type. tive (diameter limit) cuttings are common in Compared with selection methods, the Although this system emulates some features North America (Pre´vost et al. 2003, Kenefic length of cutting cycles and regeneration pe- of natural dynamics in late-successional et al. 2005). They often contain poor quality riods are not fixed, while silvicultural inter- stands (Crow et al. 2002, Seymour et al. trees and regeneration and, because of highly ventions are adjusted to species autecology, 2002), it generally creates small openings variable harvest intensity, have a rather irreg- site characteristics, and needs that are more favorable to shade-tolerant ular structure (Robitaille and Boivin 1987, (Fourchy 1952). Therefore, when compared species (Leak and Wilson 1958, Crow and Nyland 2002). These stands are difficult to with selection cutting systems, this variant Metzger 1987, Majcen et al. 2005). In the manage under selection cutting systems be- offers greater flexibility (Fourchy 1952, long run, application of single-tree selection cause of their poor growing stock (Leak et al. Smith et al. 1997) at the expense of consis- cutting can decrease the abundance of mid- 1987). In stands with a minimum quantity tency of volume production. Unlike contin- tolerant species such as yellow birch (Leak of acceptable growing stock, an irregular

Journal of Forestry • December 2009 409 Table 2. General characteristics of regeneration methods used in natural high forests (after Matthews 1989, Smith et al. 1997, Helms 1998, and Nyland 2002).

Age arrangement Stand structure (cohorts) Regeneration method Silvicultural objectives and description

Even-aged Single cohort Clearcutting To regenerate the stand with natural seedlings or by planting shortly after complete overstory removal. Seed-tree To regenerate the stand with natural seedlings from widely spaced trees left in the stand until the natural regeneration is established. Regular shelterwood To regenerate the stand under partial shade of mature trees left in the stand by successive fellings until the new cohort of natural regeneration is established. Regeneration period Ͻ20% of rotation length. Irregular uneven-aged Two cohort Extended irregular shelterwood To regenerate the stand and maintain a partial cover for an extended period of time; the stand is composed of an upper and a lower story of trees of seedlings originating from seed, growing in intimate mixture on the same site. Irregular multicohort Expanding-gap irregular shelterwood To regenerate and maintain an unbalanced Continuous cover irregular shelterwood multiaged stand for a long and indefinite period of time by successive regeneration fellings. Balanced uneven-aged Balanced multicohort Selection cutting To regenerate and maintain a balanced multiaged stand by removing trees in all size classes either singly or in groups throughout the stand in order to sustain yield of mature trees at short intervals indefinitely. shelterwood system could be used as a resto- plement the three variants of irregular shel- ceptable or prohibited (e.g., MRN 1994). As ration tool instead of even-aged systems such terwood in this forest type. with other regeneration methods, site prep- as regular shelterwood. Irregular shelter- In temperate mixedwood and boreal aration may be required to reduce competi- wood may help to maintain the irregular forests, where balsam fir is abundant, spruce tion from undesired vegetation and create structure by retaining cohorts of acceptable budworm (Choristoneura fumiferana [Clem.]) suitable seedbeds for regeneration of species growing stock, while creating gaps through epidemics result not only in whole stand such as yellow birch, white pine, white the removal of the poorest growing stock. mortality, but in partial mortality as well spruce, and northern white-cedar (Ray- Some key elements of mature stands, such as (Kneeshaw and Bergeron 1999, Bouchard et mond et al. 2000, Pre´vost 2008). Finally, shade-tolerant saplings and seed trees, may al. 2007, Kneeshaw et al. 2008). When where the frequency of irregular stands de- be conserved as part of new stands (Smith stands are composed of tree species that are creased in boreal and mixedwood forests 1986) to help restore the attributes of irreg- less vulnerable to spruce budworm or other (e.g., Leblanc and Be´langer 2000), irregular ular stands lost during previous harvests insects, partial mortality may be generated shelterwood may be used for converting (Fourchy 1952). Regenerated cohorts of de- by senescence or windthrow. This was doc- stands from even-aged to irregular uneven- sired species can be maintained and site umented for pure black spruce stands by aged structures (Spurr 1956, Schu¨tz 2001). preparation will promote natural regenera- Harper et al. (2002). These types of distur- Although irregular shelterwood man- tion in unproductive openings invaded by bances could be emulated with an irregular agement (extended variant) is occasionally undesired vegetation. Also, high-graded, shelterwood system by allowing the estab- used by private landowners in North Amer- hardwood-dominated stands could be grad- lishment of a new cohort after each entry ican -dominated stands, there is no ually restored with irregular shelterwood and keeping structural heterogeneity, old- consensus on its application or guidelines and later converted to a selection system. growth attributes, and (Gunn (Seymour 1992). There are only a few ongo- To our knowledge, only variants of the and Hagan 2000, De´ry and Leblanc 2005). ing empirical and controlled trials of irregu- regular shelterwood system have been docu- For example, irregular shelterwood could be lar shelterwood systems, but literature is mented in northern (e.g., Tubbs useful in addressing issues such as red and scarce on their effects. The expanding-gap and Metzger 1969, Ray et al. 1999, Nyland white spruce rarefaction (Seymour 1992, variant is currently being studied at Penob- et al. 2000), while effects of irregular shelter- Barrette and Be´langer 2007, Dumais and scot Experimental Forest (Maine), emulat- wood are still poorly known. However, re- Pre´vost 2007). Moreover, as with other con- ing the 1% natural disturbance frequency sults from studies in hardwood forests, in- tinuous cover systems, irregular shelterwood that is common in the Acadian forest (Saun- cluding group- and patch selection (Leak is well suited to integrated vegetation man- ders and Wagner 2005, Seymour 2005). In and Filip 1977, Leak and Gottsaker 1985, agement strategies focusing on “preventive Quebec (Canada), the continuous cover Leak 1999) and reserved shelterwood (e.g., silviculture” (Roy et al. 2003), especially in variant has been implemented operationally Smith et al. 1989, Miller and Schuler 1995, forest types prone to severe competition and for more than 10 years in the balsam fir– Miller et al. 1997), could be gleaned to im- where the use of is socially unac- white birch forest at Foreˆt Montmorency, as

410 Journal of Forestry • December 2009 an alternative to clearcutting in sensitive ar- windy locations (Ruel 1995). The use of BARRETTE, M., AND L. BE´LANGER. 2007. Recon- eas requiring a continuous forest cover careful also plays a role in reducing stitution historique du paysage pre´industriel (Bouliane and Dubois 2003). To expand damage to mature reserve trees and to de la re´gion e´cologique des hautes collines du Bas-Saint-Maurice. Can. J. For. Res. 37:1147– our knowledge about the effects of irregular younger trees during the initial and fol- 1160. shelterwood in Quebec, le Ministe`re des low-up cuttings (Nyland 2002). BAUHUS, J., K. PUETTMANN, AND C. MESSIER. Ressources naturelles et de la Faune initiated Moreover, the flexibility of irregular 2009. Silviculture for old-growth attributes. a comprehensive project across three repre- shelterwood may present some risks, because For. Ecol. Manag. 258:525–537. sentative stands of the boreal, temperate misapplication of the system may result in BERGERON, Y., B. HARVEY,A.LEDUC, AND S. GAUTHIER. 1999. Forest management guide- mixedwood, and northern hardwood forest . To avoid this, quality stan- lines based on natural disturbance dynamics: zones (MRNF 2009). The goal is to com- dards for tree marking and harvesting should Stand and forest-level considerations. For. pare the effects of irregular shelterwood with be established. When choosing the reserve Chron. 75:49–54. other silvicultural systems with respect to trees, it is necessary to consider tree vigour, BERGERON, Y., P. DRAPEAU,S.GAUTHIER, AND N. stand structure, quality, yield, composition, quality for factory , and mortality LECOMTE. 2007. Using knowledge of natural risk. It is important that the trees remain disturbances to support sustainable forest and old-growth forest attributes, in a context management in the northern Clay Belt. For. of ecosystem-based management. alive and hold or increase their value during Chron. 83:326–337. the extended regeneration period (Nyland BOUCHARD, M., D.D. KNEESHAW, AND Y. Challenges of Operational 2002). Protocols for retention of legacy trees BERGERON. 2006. Tree recruitment pulses and Implementation and snags might also be required to address long-term species coexistence in mixed forests specific biodiversity issues. of western Que´bec. Ecoscience 13:82–88. Implementing an irregular shelterwood BOUCHARD, M., D.D. KNEESHAW, AND C. MESS- system presents important challenges. Simi- IER. 2007. following spruce lar to other regeneration methods, advance Conclusion budworm outbreaks in the northern and regeneration may be damaged by cutting The recent shift in management objec- southern mixedwoods of central Quebec. Can. (Hannah 1988). Planning and prediction of tives from timber production to the valori- J. For. Res. 37:763–772. BOUCHARD, M., D. POTHIER, AND S. GAUTHIER. growth and yield in irregular shelterwood zation of multiple forest resources provides opportunities for diversifying silvicultural 2008. Fire return intervals and tree species suc- systems is more complex than in even-aged cession in the North Shore region of eastern interventions. Irregular stands were once an or balanced uneven-aged systems. The main Canada. Can. J. For. Res. 38:1621–1633. challenges are related to the spatial and tem- important component of our preindustrial BOUCHER, D., L. DE GRANDPRE´, AND S. GAU- poral arrangements of the cohorts. The har- landscape. The flexibility of applying the ir- THIER. 2003. De´veloppement d’un outil de vesting program must be arranged to pro- regular shelterwood system, as illustrated by classification de la structure des peuplements et comparaison de deux territoires de la pessie`re a` vide a sustained yield at the forest scale the three variants described in this article, establishes its potential for achieving ecosys- mousses du Que´bec. For. Chron. 79:318–328. (Matthews 1989, Smith et al. 1997). As for BOUCHER, Y., D. ARSENEAULT,L.SIROIS, AND L. tem-based management objectives in several other systems involving partial harvesting, BLAIS. 2009. Logging pattern and landscape irregular shelterwood has operational diffi- northeastern North American forest types. changes over the last century at the boreal and culties resulting from stand variability and The irregular shelterwood system may be a in Eastern Canada. valuable tool for maintaining or restoring ir- Landsc. Ecol. 24:171–184. complexity, and it may increase harvesting regular uneven-aged stands while diversify- BOULIANE, P., AND J. DUBOIS. 2003. Bilan des cost. However, greater individual stem vol- ing silviculture in boreal, mixedwood, and coupes progressives irre´gulie`res re´alise´es a` la Foreˆt ume, increased lumber yield, and product Montmorency de 1986 a` 2002 et´tablissement e northern hardwood forest zones. However, value may compensate for these higher costs d’un dispositif permanent. Univ. Laval, De´pt. of it is not a panacea and should be used wisely. (Ruel et al. 2007). The residual density Sci. Bois Foreˆt, Que´bec, Canada. 48 p. With such a complex silvicultural system, it CANHAM, C.D., AND O.L. LOUCKS. 1984. Cata- should be managed to protect the residual is important to define benchmarks to ensure strophic windthrow in the presettlement for- canopy trees that may die as a result of the that management objectives are achieved in ests of Winsconsin. 65:803–809. sudden exposure (Nyland 2002) or decrease CROW, T.R., AND F.T. METZGER. 1987. Regen- practice. As with any in quality (e.g., epicormic branches in hard- eration under selection cutting. P. 81–94 in process, it will be essential to adjust practices ; Godman and Books 1971, Erdmann Proc. of a Silvucltural symp. on Managing north- as we gain more knowledge under North ern hardwoods, Nyland, R.D (ed.). Tech. Publ. and Peterson 1972, Trimble and Seegrist American conditions. The study of this sys- 13 (ESF 87-002 and Soc. Am. For. Publ. 87- 1973). 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