Action: Fence to prevent grazing after tree planting
Key messagesRead our guidance on Key messages before continuing
- Four of five studies (including two replicated, randomized, controlled studies) in Australia, Canada , Finland and the USA found that using fences to exclude grazing increased the survival, size and cover of planted trees. Two studies found no effect on tree survival rate and one found mixed effects on planted tree size depending on the structure of the fence.
Grazing by large herbivore can significantly damage new planted trees. Excluding large herbivores from restored forest areas by creating exclosures using wire fences can help the establishment of the planted trees.
Supporting evidence from individual studies
A replicated, randomized, controlled study in 1998-2003 in boreal forest in British Columbia, Canada (Krzic et al. 2006) found that cattle exclusion in rehabilitated forest areas increased the cover of planted lodgepole pine Pinus contorta and one of four non-native forage species alsike clover Trifolium hybridum, but not of any native species. Cover of lodgepole pine (ungrazed: 4.5%; grazed: 2%) and alsike clover (ungrazed: 4%; grazed: 2.5%) was higher in ungrazed plots. In contrast, cover of the other three common non-native forage species (1-19%), of the three common native species (0-5%) and of the invasive weed oxeye daisy Leucanthemum vulgare (15-27%) was similar between treatments. Data were collected in 2003 in 0.1 ha ungrazed area (fenced with 1.5 m high wire) and 0.2 ha grazed area (230 cow-calf pairs and 20 bulls in May-June and August-September since 1999). Three forest areas were created in mid 1970s and failed to naturally regenerate, planted with 2,450 lodgepole pine seedlings/ha in May 1999.
A replicated, controlled study in 2001-2002 in eucalypt forest in Australia (Parsons et al. 2006) found that kangaroo exclusion increased planted seedlings biomass and survival rate. Seedling biomass (excluded 41; control: 27 g dry mass/plot) and survival (excluded: 13/18 plants; control: 10/18 plants) were higher in exclusion plots. Data were collected in winter 2002 in 16 replicates (each planted with a different species) of four exclusion (2.1 m fence in May-June 2001) and four control plots (1.3 × 1.3 m). Each plot was planted with nine plants in August 2001, at each of two rehabilitated bauxite-mine sites.
A replicated, controlled study in 2001-2008 in boreal forest in Finland (Den Herder, Kouki & Ruusila 2009) found that exclusion of moose Alces alces and hares Lepus spp. had mixed effects on the height of different tree species, but no effect on their mortality. The height of Eurasian aspen Populus tremula was higher in moose and hare exclusion plots (60 cm) than in moose exclusion and control plots (40 cm). Eurasian aspen mortality was similar in all treatments (17-33%). Height (50-70 cm) and mortality (45-75%) of silver birch Betula pendula were similar in all treatments as were the height (45-60 cm) and mortality (0-15%) of rowan Sorbus aucuparia. Ten seedlings of each species were planted in 2002-2003 in each of three treatment plots (10 ×15 m): control, moose exclusion (fence mesh size 15 cm) and moose and hare exclusion (fence mesh size 5 cm), replicated in three sites. Treatments were applied in 2002. Data were collected in 2002-2008.
A replicated, controlled study in 1996-2000 in boreal forest in Saskatchewan, Canada (Milakovsky et al. 2011) found that herbivore exclusion increase the growth rate but not the survival rate of planted white spruce Picea glauca seedlings. Height increase was greater in two large mammal and large and medium mammal exclusion treatments (25-26 cm) compared to control plots (20 cm). Seedling survival was similar between treatments (75-78%). In 1996, fifteen plots (4 × 8 m) of large mammal exclusion (prevent browsing by moose Alces alces, elk and deer), all mammal exclusion (also prevent browsing by snowshoe hares Lepus americanus) and control (no exclusion) treatments were established in each of eight blocks. Data were collected in 2000 in four subplots (2 × 2 m) planted with white spruce in June 1996. All plots were harvested (trees >2 m height removed by a feller-buncher) before treatments.
A replicated, randomized, controlled study in 2004-2009 in temperate broadleaf forest in Pennsylvania, USA (Long, Brose & Horsley 2012) found that deer exclusion increased the size of planted northern red oak Quercus rubra seedlings. Seedling height (fenced: 33 cm; unfenced: 16 cm) and root-collar diameter (fenced: 9.5 mm; unfenced: 6.5) were higher in fenced plots. Data were collected in 2009 in four fenced (2.4 m tall wire to exclude deer in 2002-2004) and four unfenced plots (12.5 × 8.5 m) at each of five sites. All plots were partially thinned (shelterwood harvest) within the past 12 years and were planted with northern red oak seedlings in Apr 2004.
- Krzic M., Newman R., Trethewey C., Bulmer C. & Chapman B. (2006) Cattle grazing effects on plant species composition and soil compaction on rehabilitated forest landings in central interior British Columbia. Journal of soil and water conservation, 61, 137-144
- Parsons M.H., Koch J., Lamont B.B., Vlahos S. & Fairbanks M.M. (2006) Planting density effects and selective herbivory by kangaroos on species used in restoring forest communities. Forest ecology and management, 229, 39-49
- Den Herder M., Kouki J. & Ruusila V. (2009) The effects of timber harvest, forest fire, and herbivores on regeneration of deciduous trees in boreal pine-dominated forests. Canadian Journal of Forest Research, 39, 712-722
- Milakovsky B., Frey B.R., Ashton M.S., Larson B.C. & Schmitz O.J. (2011) Influences of gap position, vegetation management and herbivore control on survival and growth of white spruce (Picea glauca (Moench) Voss) seedlings. Forest ecology and management, 261, 440-446
- Long R.P., Brose P.H. & Horsley S.B. (2012) Responses of northern red oak seedlings to lime and deer exclosure fencing in Pennsylvania. Canadian Journal of Forest Research, 42, 698-709