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Methodologies in forest grazing research
Forest Ecology and Management 120 (1999) 1±2
Introduction
Methodologies in forest grazing research A.T. Kuitersa,*, K.J. Kirbyb a
Institute for Forestry and Nature Research (IBN-DLO), P.O. Box 23, NL-6700 AA Wageningen, The Netherlands b English Nature, Northminster House, Peterborough PE1 1UA, UK
1. Introduction From ancient times, large herbivores have had a major impact on the structure, species composition and succession in natural forests of Europe and North America. Many ecological processes in forests, such as nutrient cycling, soil formation and gap dynamics, are profoundly affected by herbivores (Pastor et al., 1988; Hobbs, 1996). Historical ecological research suggests that the traditional view of primeval forest as closed forest should be reconsidered as forests probably were in part more like open parkland or savannah-like landscapes (Kirby and Watkins, 1998). Large herbivores, including species such as the aurochs (Bos primigenius), giant deer (Megaloceros giganteus) and wild horse (Equus ferus ferus), that became extinct probably created and maintained extensive open areas. In more recent periods in European forest history, livestock grazing with cattle and horse breeds, goats, sheep and domestic pig became established as `traditional' management system (Putman, 1986; Peterken, 1996). Foresters in most European countries are nowadays confronted with increasing wild herbivore densities (Gill, 1990), whereas traditional grazing systems with domestic stock have strongly declined over the last centuries. Recently, however, livestock has been introduced again in certain forest areas for nature conservation purposes (Kirby et al., 1994) or to restore traditional farming systems such as wood-pasture. *Corresponding author.
The main problem facing forest managers today is how grazing regimes can be used to achieve a better balance between ecological and economic objectives (Humphrey, 1998). Appropriate grazing regimes have to be de®ned with respect to management goals. Insight is needed in the ecological impact of herbivores on forest systems, in particular on forest regeneration, tree species assemblages and sustainable forestry. 2. Research methods A workshop was convened in 1997 in Edinburgh, Scotland, which focussed on methodologies applied in forest grazing research. Participants illustrated different approaches from current research and this special feature covers several of the workshop presentations. Forest managers throughout Europe are confronted with increasing population densities of wild ungulates or unpredictable population ¯uctuations. A palaecological approach, with time horizons ranging from hundreds to thousands of years, can help in placing such variations in a broader, longer-term perspective. The hypothesis that contemporary forests signi®cantly differ from their natural state, being unusually dark as a consequence of glacial extinctions of megafauna and anthropogenic activities, needs to be evaluated (Bradshaw and Mitchell, 1999 this issue). This is particularly relevant to the current trend in many European countries towards minimum-intervention or near-
0378-1127/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 9 8 ) 0 0 5 3 7 - 4
2
A.T. Kuiters, K.J. Kirby / Forest Ecology and Management 120 (1999) 1±2
natural forests and set-aside agricultural land, with the re-introduction of grazing regimes involving wild herbivores and domestic stock for nature conservation purposes. In such re-shaping of herbivore species assemblages in natural and semi-natural forests, the interspeci®c interactions between grazer- and browser-species and aspects of facilitation or competition for available resources deserve further attention (Latham, 1999 this issue) in order to develop multispecies grazing models. The need to link modelling studies with long-term surveys to gain insight into the relationships between herbivores and forest dynamics was proposed. `Scenario-studies' can suggest critical threshold grazingpressures. These are de®ned as the herbivore density at which forest development is not in¯uenced by, or at least is not affected more than an acceptable level, as de®ned by the management objectives (Kienast et al., 1999 and Jorritsma et al., 1999, this issue). Historical records of herbivore numbers and changes in vegetation composition can be used to validate these simulation models (Bradshaw and Mitchell, 1999, this issue). The impact of herbivores, i.e. fraying, browsing of leader shoot and side twigs and bark peeling, is often indicated as `damage' in the sense of a problem caused by a condition that is judged as unfavourable for forestry practice. `Damage' rates in managed woodlands can be determined by certain objective and operational assessment systems using indicators such as the current status of regeneration, total tree density, species composition and height structure (Reimoser et al., 1999, this issue). In natural and semi-natural woodlands, a different set of indicators may be needed to determine suitable grazing pressures for the maintenance of nature-conservation values.
References Bradshaw, R., Mitchell, F.J.G., 1999. The palaecological approach to reconstructing former grazing-vegetation interactions (this issue). Gill, R.M.A., 1990. Monitoring the Status of European and North American Cervids. GEMS Information Series No. 8. Global Environment Monitoring System. UN Environment Programme, Nairobi, Kenya, pp. 277. Hobbs, N.T., 1996. Modification of ecosystems by ungulates. J. Wildl. Manage. 60, 695±713. Humphrey, J.W., 1998. Grazing as a management tool: a synthesis of common research needs. In: Humphrey, J.W., Gill, R., Claridge, J. (Eds.). Grazing as a Management Tool in European Forest Ecosystems. Forestry Commission, Technical Paper 25. Edinburgh, pp. 79±90. Jorritsma, I.T.M., Van Hees, A.F.M., Mohren, G.M.J., 1999. Forest development in relation to ungulate grazing: a modelling approach (this issue). Kienast, F., Fritschi, J., Bissegger, M., Abderhalden, W., 1999. Modelling successional patterns of high-elevation forests under changing herbivore pressure ± responses at the landscape level (this issue). Kirby, K.J., Watkins, C. (Eds.), 1998. The Ecological History of European Forests. Wallingford, CAB International, pp. 373. Kirby, K.J., Mitchell, F.J., Hester, A.J., 1994. A role for large herbivores (deer and domestic stock) in nature conservation management in British semi-natural woods. Arbor. J. 18, 381± 399. Latham, J., 1999. Interspecific interactions of ungulates in European forests: an overview (this issue). Pastor, J., Nainman, R.J., Dewey, B., McInnes, P., 1988. Moose, microbes and the boreal forest. BioScience 38, 770±777. Peterken, G.F., 1996. Natural Woodland. Ecology and Conservation in Northern Temperate Regions. Cambridge University Press, pp. 522. Putman, R.J., 1986. Grazing in Temperate Ecosystems: Large Herbivores and the Ecology of the New Forest. Croom Helm± Chapman and Hall, London, pp. 210. Reimoser, F., Armstrong, H., Suchant, R., 1999. Measuring forest damage of ungulates: what should be considered (this issue).
Introduction
Methodologies in forest grazing research A.T. Kuitersa,*, K.J. Kirbyb a
Institute for Forestry and Nature Research (IBN-DLO), P.O. Box 23, NL-6700 AA Wageningen, The Netherlands b English Nature, Northminster House, Peterborough PE1 1UA, UK
1. Introduction From ancient times, large herbivores have had a major impact on the structure, species composition and succession in natural forests of Europe and North America. Many ecological processes in forests, such as nutrient cycling, soil formation and gap dynamics, are profoundly affected by herbivores (Pastor et al., 1988; Hobbs, 1996). Historical ecological research suggests that the traditional view of primeval forest as closed forest should be reconsidered as forests probably were in part more like open parkland or savannah-like landscapes (Kirby and Watkins, 1998). Large herbivores, including species such as the aurochs (Bos primigenius), giant deer (Megaloceros giganteus) and wild horse (Equus ferus ferus), that became extinct probably created and maintained extensive open areas. In more recent periods in European forest history, livestock grazing with cattle and horse breeds, goats, sheep and domestic pig became established as `traditional' management system (Putman, 1986; Peterken, 1996). Foresters in most European countries are nowadays confronted with increasing wild herbivore densities (Gill, 1990), whereas traditional grazing systems with domestic stock have strongly declined over the last centuries. Recently, however, livestock has been introduced again in certain forest areas for nature conservation purposes (Kirby et al., 1994) or to restore traditional farming systems such as wood-pasture. *Corresponding author.
The main problem facing forest managers today is how grazing regimes can be used to achieve a better balance between ecological and economic objectives (Humphrey, 1998). Appropriate grazing regimes have to be de®ned with respect to management goals. Insight is needed in the ecological impact of herbivores on forest systems, in particular on forest regeneration, tree species assemblages and sustainable forestry. 2. Research methods A workshop was convened in 1997 in Edinburgh, Scotland, which focussed on methodologies applied in forest grazing research. Participants illustrated different approaches from current research and this special feature covers several of the workshop presentations. Forest managers throughout Europe are confronted with increasing population densities of wild ungulates or unpredictable population ¯uctuations. A palaecological approach, with time horizons ranging from hundreds to thousands of years, can help in placing such variations in a broader, longer-term perspective. The hypothesis that contemporary forests signi®cantly differ from their natural state, being unusually dark as a consequence of glacial extinctions of megafauna and anthropogenic activities, needs to be evaluated (Bradshaw and Mitchell, 1999 this issue). This is particularly relevant to the current trend in many European countries towards minimum-intervention or near-
0378-1127/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 9 8 ) 0 0 5 3 7 - 4
2
A.T. Kuiters, K.J. Kirby / Forest Ecology and Management 120 (1999) 1±2
natural forests and set-aside agricultural land, with the re-introduction of grazing regimes involving wild herbivores and domestic stock for nature conservation purposes. In such re-shaping of herbivore species assemblages in natural and semi-natural forests, the interspeci®c interactions between grazer- and browser-species and aspects of facilitation or competition for available resources deserve further attention (Latham, 1999 this issue) in order to develop multispecies grazing models. The need to link modelling studies with long-term surveys to gain insight into the relationships between herbivores and forest dynamics was proposed. `Scenario-studies' can suggest critical threshold grazingpressures. These are de®ned as the herbivore density at which forest development is not in¯uenced by, or at least is not affected more than an acceptable level, as de®ned by the management objectives (Kienast et al., 1999 and Jorritsma et al., 1999, this issue). Historical records of herbivore numbers and changes in vegetation composition can be used to validate these simulation models (Bradshaw and Mitchell, 1999, this issue). The impact of herbivores, i.e. fraying, browsing of leader shoot and side twigs and bark peeling, is often indicated as `damage' in the sense of a problem caused by a condition that is judged as unfavourable for forestry practice. `Damage' rates in managed woodlands can be determined by certain objective and operational assessment systems using indicators such as the current status of regeneration, total tree density, species composition and height structure (Reimoser et al., 1999, this issue). In natural and semi-natural woodlands, a different set of indicators may be needed to determine suitable grazing pressures for the maintenance of nature-conservation values.
References Bradshaw, R., Mitchell, F.J.G., 1999. The palaecological approach to reconstructing former grazing-vegetation interactions (this issue). Gill, R.M.A., 1990. Monitoring the Status of European and North American Cervids. GEMS Information Series No. 8. Global Environment Monitoring System. UN Environment Programme, Nairobi, Kenya, pp. 277. Hobbs, N.T., 1996. Modification of ecosystems by ungulates. J. Wildl. Manage. 60, 695±713. Humphrey, J.W., 1998. Grazing as a management tool: a synthesis of common research needs. In: Humphrey, J.W., Gill, R., Claridge, J. (Eds.). Grazing as a Management Tool in European Forest Ecosystems. Forestry Commission, Technical Paper 25. Edinburgh, pp. 79±90. Jorritsma, I.T.M., Van Hees, A.F.M., Mohren, G.M.J., 1999. Forest development in relation to ungulate grazing: a modelling approach (this issue). Kienast, F., Fritschi, J., Bissegger, M., Abderhalden, W., 1999. Modelling successional patterns of high-elevation forests under changing herbivore pressure ± responses at the landscape level (this issue). Kirby, K.J., Watkins, C. (Eds.), 1998. The Ecological History of European Forests. Wallingford, CAB International, pp. 373. Kirby, K.J., Mitchell, F.J., Hester, A.J., 1994. A role for large herbivores (deer and domestic stock) in nature conservation management in British semi-natural woods. Arbor. J. 18, 381± 399. Latham, J., 1999. Interspecific interactions of ungulates in European forests: an overview (this issue). Pastor, J., Nainman, R.J., Dewey, B., McInnes, P., 1988. Moose, microbes and the boreal forest. BioScience 38, 770±777. Peterken, G.F., 1996. Natural Woodland. Ecology and Conservation in Northern Temperate Regions. Cambridge University Press, pp. 522. Putman, R.J., 1986. Grazing in Temperate Ecosystems: Large Herbivores and the Ecology of the New Forest. Croom Helm± Chapman and Hall, London, pp. 210. Reimoser, F., Armstrong, H., Suchant, R., 1999. Measuring forest damage of ungulates: what should be considered (this issue).