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Providing evidence to improve practice

Action: Use prescribed fire: effects on young trees Forest Conservation

Key messages

  • Five of 15 studies (including four replicated, randomized, controlled studies) from Canada, France and the USA found that prescribed fire increased the density and biomass of young trees. Two studies found that fire decreased new tree density. Eight found no effect or mixed effects depending on the tree species, location and fire frequency.
  • Two of the above studies found mixed effects of prescribed fire on species diversity of young trees depending on the location.
  • Two replicated, controlled studies from the USA found mixed effects of prescribed fire on the survival of young trees.

 

Supporting evidence from individual studies

1 

A replicated, randomized, controlled study in 1995-1996 in temperate broadleaf forest in Virginia USA (Brose & Van Lear 1998) found that prescribed burning reduced densities of new trees of all hardwood species. Declines in density were greater following summer burns than spring or winter burns and smallest in unburned plots for hickory Carya spp. (summer burn: 1,105; spring burn: 662; winter burn: 643; unburned: 76 trees/ha) and oak Quercus spp. (summer burn: 1,124; spring burn: 543; winter burn: 531; unburned: 79). Declines in density were higher in summer and spring burn than in winter burn and the lowest in control of red maple Acer rubrum (summer burn: 1,475; spring burn: 1,425; winter burn: 541; unburned: 82/ha) and yellow-poplar Liriodendron tulipifera (summer burn: 4,231; spring burn: 4,169; winter burn: 2,801; unburned: 70) were. In 1995, four 2-5 ha areas were randomly assigned to one of four burn treatments: winter (February), spring (April) and summer (August) fires and unburned, in each of three forest sections. Each section had been shelterwood harvested. Monitoring was carried out in the autumn of 1994 (before treatments), 1995 and 1996 (after treatments) in 15 plots (20 m2) in each treatment.

 

2 

A before-and-after trial in 1994-1995 in temperate mixed forest in North Carolina, USA (Elliott et al. 1999) found that prescribed fire had mixed effects on the density and diversity of young trees in three study sites. In a site located on top of the ridge density of young trees <5 cm diameter at breast height decreased after burning (before: 12,178; after: 409/ha) while their diversity remained similar (Shannon’s index before: 1.24; after: 1.27. In a second site located in middle of the slope density of young trees increased (before: 851; after: 1,556/ha) while diversity decreased (Shannon’s index before: 1.52; after: 0.54). In a third site located close to the stream density (before: 2,153; after: 2,652/ha) and diversity (Shannon’s index before: 2.15; after: 2.40) remained similar after burning. Data was collected before (1994) and after prescribed-burning (1995) in six plots (15 × 15 m) at one location (top of the ridge) and in three similar plots at two other locations (middle of the slope and close to the stream) and in additional 20 plots (10 × 10 m) after burning.

 

3 

A replicated, controlled study in 1995-1998 in temperate mixed forest in Florida, USA (Provencher et al. 2001) found that prescribed burning increased the density of oak Quercus spp. but not of longleaf pine Pinus palustris juveniles. Numbers of oak juveniles was higher in burned (2.0/m2) than unburned plots (1.5/m2), while numbers of longleaf pine juveniles was similar in burned (90/200 m2) and unburned plots (75/200 m2). One burned (prescribed burned in spring 1995) and one unburned control plots (81 ha) were established in 1995 in each of six blocks. Data were collected in 1998 in 32 subplots (40 × 10 m) in each plot.

 

4 

A replicated, controlled study in 2001-2003 in temperate mixed forest in Georgia and Tennessee, USA (Elliott & Vose 2005) found that prescribed burning increased the density of trees <5 cm diameter at breast height but not of larger trees and did not affect species richness of new trees. Density of trees <5 cm diameter at breast height was higher in burned sites (burned: 122,660; unburned: 63,560 stems/ha). However, density of trees >5 cm diameter at breast height was similar in burned (1,150) and unburned sites (870). The number of species of trees did not differ between treatments for those <5 cm diameter at breast height (burned: 29.8; unburned: 27.0) and those >5 cm diameter at breast height (burned: 15.8; unburned: 15.0). Data was collected in 2002 in five 10 × 20 m plots in each of four burned (prescribed burned in March 2001) and two control (unburned) sites (total of 30 plots).

 

5 

A replicated, controlled study in 1994-2002 in temperate oak forest in Ohio, USA (Hutchinson, Sutherland & Yaussy 2005) found that two consecutive annual burnings decreased the number of small trees compared with no burning or four annual burnings; both two and four annual burnings decreased the density of saplings. The density of small trees was lower in burned×2 (130 individuals/ha) than unburned (190) and burned×4 plots (170). The density of large and small saplings was higher in unburned (600 and 1,100 respectively) than in burned×4 plots (200 and 100-250 respectively). Three treatment units (25 ha) were replicated in four sites: burned×4 (burned annually 1996-1999), burned×2 (burned in 1996 and 1999) and unburned. Data were collected in 2002 in nine plots (0.125 ha) within each treatment unit.

 

6 

A replicated, controlled study in 1999-2003 in temperate broadleaf forest in South Carolina, USA (Wang van Lear & Bauerle 2005) found that prescribed fire increased the biomass  and density of white oak Quercus alba seedlings. Numbers of seedlings (burned: 0.03-1.5; unburned: 0.02-0.15/ha) and average seedling biomass (burned: 0.68 g; unburned: 0.43 g) were higher in burned plots. Three forest units were divided into burned (prescribed fires in 1999 and 2000) and control (unburned) treatments (>1 ha). Data were collected in 2003 under six to eight white oak trees in each forest unit.

 

7 

A replicated, controlled study in 2001-2005 in second-growth oak forests in southern Ohio, USA (Albrecht & McCarthy 2006) found that prescribed fire reduced total large sapling density and increased large seedlings density, but not seedlings of oaks Quercus spp. A single prescribed fire reduced large sapling (3-10 cm diameter at breast height) density from 600 to 300 saplings/ha and increased large seedlings (40-150 cm tall) density from 2,000 to 6,000 seedlings/ha. Prescribed fire had no effect on the densities of small seedlings <50 cm tall (control: 135,000; fire: 140,000 seedlings/ha) and small saplings <3 cm diameter at breast height (control: 1,000; fire: 1,050 saplings/ha). A single prescribed fire did not affect densities of oak seedlings. Three forest areas were divided into treatment units (each approximately 30 ha): control and prescribed fire. Treatments were applied in the inactive season of 2001. New tree growth was sampled in ten 0.1 ha plots/treatment (a total of 40 plots/site) in summer 2004.

 

8 

A replicated, controlled study in 2002-2007 in temperate oak forest in Kentucky, USA (Alexander et al. 2008) found that prescribed fire and fire frequency had mixed effects on seedling survival depending on tree species. White oak Leucobalanus spp. seedling survival decreased to 50% in single-burn and to 40% in repeated-burn plots, compared with 70% in unburned plots. Red oaks Erythrobalanus spp. seedling survival decreased to 65% in repeated-burn compared with 75% in unburned plots. Red maple Acer rubrum seedling survival decreased to 40% in single-burn and in repeated-burn plots compared with 80% in unburned plots. Sassafras Sassafras albidum seedling survival was not affected by burning. Three study sites (200-300 ha) were subdivided into three burn treatments (58–116 ha): an unburned control, single burn (spring 2003) and repeated burning (spring 2003, 2004 and 2006). Approximately 3,000 seedlings were tagged in June 2002 and survival monitored annually from 2002 to 2007 in 8–12 plots (10 x 40 m) within each treatment.

 

9 

A site comparison study in 2002-2003 in temperate coniferous forest in Nevada USA (Allen, Chambers & Novak 2008) found no effect of burning on the number of emerged seedlings. Numbers of seedlings was similar in burned (743 seedlings/m2) and unburned plots (635 seedlings/m2). .Three 15 × 25 m plots were located in each of adjacent burned (prescribed fire in May 2002) and unburned areas. Seeds were sampled in thirty 0.1 × 0.1 × 0.05 m soil samples in each plot. Sampling was one week before burning and two growing seasons after.

 

10 

A replicated, controlled study in 2000-2005 in temperate broadleaf forest in Ohio, USA (Lombardo & McCarthy 2008) found no effect of prescribed fire on the number of chestnut oak Quercus prinus and black oak Quercus velutina acorns. Density was similar between treatments for both chestnut oak (burned: 300,000-350,000; unburned: 250,000-300,000 acorns/ha) and black oak (100,000-400,000 in both). Data were collected in 2005 in nine burned (prescribed fire in 2001 and 2005) and nine unburned plots (0.1 ha) in at each of two forest sites (40 ha).

 

11 

A replicated, randomized, controlled study in 2000-2005 in temperate forest in California, USA (Moghaddas, York & Stephens 2008) found that prescribed fire increased conifer seedling and decreased oak seedling densities. Combined conifer and California black oak Quercus kelloggii seedling density was higher in burned (14.0/m2) than unburned plots (1.5/m2) while density of California black oak was higher in unburned plots (burned: 0.10; unburned: 0.45/m2). Data were collected in 2006 in 10 sets of four plots (1 m2) in each of three unburned control and three burned (October-November 2002) treatment units (14-29 ha).

 

12 

A replicated, randomized, controlled study in 2004-2008 in Mediterranean Aleppo pine Pinus halepensis woodland in France (Prévosto & Ripert 2008) found that prescribed burning increased Aleppo pine seedling density where woody debris was left but not where it was removed. Density of seedlings in plots with woody debris was higher when burned (2.1 seedlings/m2) than unburned plots (<0.1). Where woody debris had been removed, density was similar between treatments (unburned: 0.1; burned: 0.4). Data were collected in January 2008 in 16 plots (14 × 14 m): eight control plots with no fire and eight that had a prescribed fire in 2005. Four control and four burn plots had woody debris and four of each treatment plots had the woody debris manually removed. All plots were thinned in 2004 (from 410 to 210 trees/ha).

 

13 

A controlled study in 2004-2006 in temperate mixed forest in North Carolina and Georgia, USA (Elliott & Vose 2010) found that prescribed fire had mixed effects on density and diversity of young trees depending on site. At one site density of young trees <5 cm diameter at breast height was lower in burned plots (burned: 7,000; unburned: 31,000/ha), while their diversity was similar between treatments (Shannon's index burned: 0.90; unburned: 1.00). At a second site density of young trees was similar between treatments (burned: 9,000; unburned: 14,000) while their diversity was lower in burned plots (burned: 0.87; unburned: 1.44). At a third site, the density of young trees (burned: 3,500; unburned: 1,200) and their diversity (burned: 0.57; unburned: 0.27) were similar between treatments. Data was collected in 2006 in 10-12 plots (10 × 20 m) in a burned area (in 2004) and in 4-6 plots in an adjacent unburned area (control) in each of three sites.

 

14 

A replicated, randomized, controlled study in 2001-2005 in temperate coniferous forest in Montana, USA (Fiedler, Metlen & Dodson 2010) found that prescribed fire decreased tree saplings density. The density of saplings between 0.1 to 10 cm diameter at breast height was lower in burned plots (burned: 6,550; control: 11,483/ha). Data were collected in 2003 in ten 0.1 ha plots in each of three replicates of burned (prescribed broadcast burning in spring 2002) and unburned treatments.

 

15 

A replicated, controlled study in 2002-2008 in temperate broadleaf forest in Kentucky, USA (Royse et al. 2010) found that frequent prescribed fires decreased and single fires increased the height of white oak Quercus alba seedlings and decreased their mortality rate. Fire did not affect chestnut oak Quercus prinus seedling size and mortality rate. The height of white oak seedlings was different between treatments (unburned: 12; single fire: 16; three fires: 10 cm), while their diameters were higher in single than three fire plots (unburned: 2.3; single fire: 1.8; three fires: 1.7 mm). Cumulative percent mortality for white oak seedlings was lower in single fire (65%) than unburned plots (85%). For chestnut oak seedling height (unburned: 15; single fire: 16; three fires: 13 cm) and diameter (unburned: 2.3; single-fire: 2.5; three-fires: 2.6 mm) were similar between treatments, and mortality rate was similar between unburned and single fire plots (55% in both). Data were collected in May 2006 to August 2008 in 8-12 plots (10 × 40 m) in each of three treatment areas: control (unburned), single fire (prescribed fire in 2003) and three fires (prescribed fires in 2003, 2004, and 2006). Treatment areas were established in 2002 at each of three sites (200-300 ha).

 

16 

A site comparison study in 1994-2007 in subarctic boreal forest in Yukon Territory, Canada (Brown & Johnstone 2012) found that prescribed burning with long intervals between burns increased the density of black spruce Picea mariana seedlings. The density of seedlings was higher following burns with long intervals between (8.3 seedlings/m2) than with short intervals between burns and mature forest sites (0.6 seedlings/m2 in both). Eight 30 × 30 m plots were established within each of three fire history sites: mature forest (previous fire about 77 years ago); long interval between burns (fire in 2005) and short intervals between burns (fire in both 1990/91 and 2005).  Seedlings were counted in ten 0.25 m2 subplots in each plot in 2008, 2009 and 2010.

 

17 

A before-and-after study in 2003-2005 in temperate coniferous forest in California, USA (Walker et al. 2012) found no effect of prescribed fire on the density of conifer seedlings and saplings. The changes (after minus before) in density were similar between treatments for both seedlings <1.4 m tall (burned: -735; control: -2,303 individuals/ha) and saplings >1.4 m tall and <10 cm diameter at breast height (burned: -222; control: 74). Data were collected in 2003 (before) and 2005 (after) in five plots (0.04 ha) in each of two burned (in 2004) and two control (unburned) treatment units (~1 ha).

 

Referenced papers

Please cite as:

Agra H., Schowanek S., Carmel Y., Smith R.K. & Ne’eman G. (2018) Forest Conservation. Pages 285-328 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2018. Open Book Publishers, Cambridge, UK.