Background information and definitions
Some forests are the most complex terrestrial habitats, with countless species interacting. Restoring such complexity is difficult, but there is an ever-increasing amount of research and investment into the area. For example, insurance firms and shipping companies are financing a 25-year project to restore forest ecosystems along the Panama Canal (TEEB 2008); whilst mining companies in Australia are increasingly able to reconstruct the forests they destroyed after they have finished mining at a site (Nichols & Grant 2007).
Trees grow slowly and therefore the effects of forest restoration may not be evident for decades or even longer after restoration begins. Care must therefore be taken when interpreting the results of these studies.
Some studies below describe the effects of riparian forest and buffer strip creation as a habitat type. The effects of riparian buffer strips as a pollution-reducing intervention are discussed in ‘Threat: Pollution – Provide buffer strips along rivers and streams’.
Nichols, O.G. & Grant, C.D. (2007) Vertebrate fauna recolonization of restored bauxite mines-key findings from almost 30 years of monitoring and research. Restoration Ecology, 15, S116-S126.
The Economics of Ecosystems and Biodiversity (2008) An interim report, Banson, Cambridge.
Supporting evidence from individual studies
A replicated study in 1979-1981 in jarrah Eucalyptus marginata forests in Western Australia, Australia (Nichols & Watkins 1984), found that approximately 84% of jarrah forest bird species (56 of 67) used 19 areas of forest restored after open-cut mining for bauxite for feeding, resting or breeding. Sixteen species (none jarrah specialists) were only present in low numbers, compared to on three forest plots. Some revegetated areas as young as 4-5 years age, supported similar bird species numbers, densities and diversities as undisturbed forest. Techniques were improved over time, from planting eastern Australian eucalypt species (chosen for timber quality and resistance to jarrah dieback disease and resulting in plantation-like vegetation with a sparse mid- and under-storey, and few ground species) to using a eucalypt mix comprising at least 50% native species, and seeding with native understorey plants. Application of fresh topsoil promoted a higher diversity of understorey plants which in turn benefited birds. Plots planted with the same eucalypt species but without understorey planting or fresh topsoil addition had fewer bird species and lower densities.Study and other actions tested
A replicated, controlled study from 1989-1993 in four restoration sites (all established in 1989-1990; all 3-5 ha) and one natural site (16 ha) of riparian forest habitat in California, USA (Kus 1998) found that least Bell’s vireos Vireo bellii pusillus were slow to colonise restored sites and did so at lower abundances (9 pairs/site for restored sites vs. 41 for natural site) but exhibited similar reproductive output to natural areas when they did (56% nest success and 1.6 fledglings/nest for restored sites vs. 46% and 1.3 for natural sites). Vireos foraged in restored sites from the first growing season but they did not establish territories until small patches of vegetation became characteristic of natural nesting areas (colonisation rate was also correlated with the presence of adjacent mature riparian habitat).Study and other actions tested
On Bangka Island, Indonesia, a replicated, controlled before-and-after trial in 1992-1995 (Passell 2000) found that bird species richness and diversity increased over time in eight 4 ha restored former strip mine sites, whilst it remained low in four 4 ha unrestored sites (13 species recorded in restored plots vs. nine in unrestored). After three years, species richness remained lower than in secondary forest (16 species), but many of the species present were forest specialists (absent from unrestored plots). Bird abundance also appeared to increase over time but this result was less certain. Black wattle Acacia mangium was planted for restoration in 1992-1994 (400 seedlings/ha) with some trees reaching 3-4 m tall by 1995.Study and other actions tested
A replicated, controlled study from May-June in 1989-1994 in riparian forest in California, USA (Larison et al. 2001) found that song sparrow Melospiza melodia nesting success, clutch size and density were lower in three restored sites, compared to four natural, mature sites (controls) and one naturally regenerating site (average of 1.5 pairs/ha for regenerating forest vs. 4 pairs/ha for mature forest and 12 pairs/ha for the naturally regenerating site). No differences in nestling mass or fledgling rate were found among stands.Study and other actions tested
A controlled study from July 1996 until January 1997 in Western Australia, Australia (Comer & Wooller 2002), found that bird assemblages were similar, but not identical in a former 300 ha mineral sands mine site, planted with native vegetation in 1977-83 and in a nearby Banksia woodland-mixed heath reserve. A total of 603 birds (36 species) were recorded in two areas (9 and 10 ha) of the reserve and 533 (33 species) in two areas (8 ha and 5 ha) of the mine site (28 species common to both). The same common insectivores were present in both areas and at similar abundance. The same species of honeyeaters occurred in both areas but at the mine site larger nectarivores were far more numerous (e.g. two commonest species: 102 vs. 29 in the reserve) whilst small spinebills much less common (e.g. western spinebill Acanthorhynchus superciliosus, 7 vs. 61). This was in part due to vegetation differences, but also as nectar-providing shrubs and trees in the restoration area had been planted in clumps, thus allowing the larger honeyeaters to dominate these nectar sources.Study and other actions tested
A replicated study in the summers of 1996-1997 at 20 restored bottomland forest sites in the Mississippi floodplain in Mississippi and Louisiana, USA (Twedt et al. 2002), found that birds used young (less than ten year-old) restored cottonwood Populus deltoides forests more than similarly aged restored oak Quercus spp. forests (average of 380-449 territories/100 ha, 14-20 species/plot and Shannon index of 2.0-2.5 for 13 cottonwood stands vs. 257 territories/100 ha, 8 species/plot and Shannon index of 1.5 for seven oak stands). Conservation value (calculated as density multiplied by a conservation priority score) was highest for 5-9 year-old cottonwood stands but did not differ between oak stands and younger (2-4 year-old) cottonwood. Nest survival and predation rates did not differ between forest types, but brood parasitism was higher on 5-9 year-old cottonwood (23% of 580 nests) than young cottonwood (3% of 93 nests) or oak (1% of 152 nests) stands. The slower-growing oak stands were used more by open-country species.Study and other actions tested
A controlled, replicated study at the same sites as studied in Nichols & Watkins (1984), from Feburary-March and July-August in 1992, 1995 and 1998 in jarrah forests in southwestern Australia (Nichols & Nichols (2003) found that bird species richness and diversity was comparable between four mined and restored, and four intact sites, eight years after rehabilitation. Of 70 bird species inhabiting intact jarrah forest, 95% were recorded in the rehabilitated sites at some point in the succession. Community dissimilarity (between mined and intact sites) decreased over time. Bird recolonisation was significantly correlated with vegetation growth. The four rehabilitated sites were established in June-July 1990 by re-contouring the mining pit to natural conditions, ripping the pit floor to reduce compaction, and replacing the topsoil. Local trees and understory species were directly seeded and covered with fertiliser.Study and other actions tested
A replicated and controlled study between April 2000 and June 2001 in northeast New South Wales, Australia (Martin et al. 2004), found that eight 1 ha plots of restored eucalyptus forest contained more bird species (average of 19-31 species/plot for eight plots) than cleared plots (8 species/plot for two plots), but not as many as remnant forest patches (43 species/plot for two plots). The number of species found increased with the age of the restored forest, from 19 species/plot in two plots planted in 1998 to 31 species/plot in two restored in the 1950s. Five locally declining species were recorded restoration plots; five others were only recorded in remnant woodland.Study and other actions tested
A study in October-November 1996-1998 and May 1997 in the Atherton Tablelands, Queensland, Australia (Jansen 2005), found that whilst rainforest specialists were absent, ten species of ‘mainly-rainforest’ birds were recorded in a corridor of restored rainforest, only two or three years after planting. Counts of these species increased from 1 bird/count in 1996 to 4 birds/count in 1998. Community structure in the restored forest became more similar to rainforest and remnant vegetation sites over time, and the number of fruit-eaters (potentially important for increasing seed dispersal) recorded increased from 2 birds/count in 1996 to 4 birds/count in 1998.Study and other actions tested
A replicated site comparison trial in 1993-2003 on ten sites along the Sacramento River, California, USA (Gardali et al. 2006), found that 13 of 20 bird species were increasing on plots revegetated as part of riparian reforestation, although abundances did not reach that of plots of remnant forest. Nine of these were also increasing on the remnant plots, with a further three only increasing in remnants. Three species were stable on both plot types and one, lazuli bunting Passerina amoena, declined on both (mirroring a regional trend). Restoration focused on revegetating with native trees, shrubs and understory plants, and restoring natural river processes.Study and other actions tested
A replicated, controlled study from March-May 2001-2 in two riparian oak forest sites in Missouri, USA (Furey & Burhans 2006), found that red-winged blackbird Agelaius phoeniceus territory area and density were similar between four blocks planted with oak seedlings and two control (unplanted) blocks (1,657-1,852 m2/territory and 0.6.territories/ha for planted blocks vs. 1,540 m2 and 0.2). Differences between blocks seeded with redtop grass Agrostis gigantean and those not seeded are discussed in ‘Grassland restoration and creation’.Study and other actions tested
A study at Rawcliffe Bridge farm, East Yorkshire, UK (Bryson et al. 2007), recorded 14 bird species in a 3 ha patch of woodland, 10-12 years after planting, including linnet Carduelis cannabina and willow warbler Phylloscopus trochilus. Three hectares of native broad-leaved woodland, berry-bearing shrubs and Corsican pine were planted on the farm in 1993-1994. Birds on the farm were monitored five times each year from 2003 to 2005, by walking the field boundaries. The number of breeding pairs/ha was estimated from clusters of sightings.Study and other actions tested
A 2007 study (Nichols & Grant 2007) reports on longer-term studies of the jarrah areas described in Nichols & Watkins (1984). In some restored plots, avian communities were becoming very similar to that of native (undisturbed) forest sites (with 95% of species recorded) within 10 years of restoration.Study and other actions tested
A replicated, controlled study from 1999-2005 in eight restored corridor sites (average width 60 m) and five natural sites (3 sites 2-5 ha; 2 sites 260-490 ha) of riparian forest in Queensland, Australia (Freeman et al. 2009) found that restored and natural sites contained comparable numbers of species and community similarity increased over time. Overall, fewer species were found in natural than restored sites (60 vs. 71): 19 species were found only in natural sites; 30 species were found only in restored sites; 41 species were recorded in both sites. Over the study, 55% of the rainforest specialist species were recorded in restored sites. After 4-7 years, communities in restored sites were more similar to natural sites than younger restored sites (0-3 years old). Restoring habitat connectivity between remnant forest patches began in 1998 (50 000 trees planted by 2006) with 1-2 ha re-vegetated each year.Study and other actions tested
A controlled study in the summers of 1969-2007 in New York State, USA (Brooks & Bonter 2010), found that species richness increased on a 9.3 ha forest site restored from an agricultural field (17 species increased and nine declined) and on a 10.7 ha site maintained at an early successional stage (an actively managed Christmas tree farm), but stayed constant at a 16.6 ha forest site. Total territory density declined on the restored site (from 96 territories in 1969-1973 to 57 in 1999-2003), although Neotropical migrant territories increased from zero to 30 and woodland species also increased. Territory density increased significantly in the managed plot (breeding pair density increased for 11 species and declined for three). The forest plot exhibited no significant difference in territory density or species richness over time.
A study in a restored koa Acacia koa forest in northern Hawaii, USA (Camp et al. 2010), found that three native birds showed long term population increases, with populations of the common ‘amakihi Hemignathus virens, the ‘i’iwi Vestiaria coccinea and the apapane Mimatione sanguinea all at least doubling between 1987 and 2007. Densities of ‘amakihi were similar to those in closed forest (lower than in open forest), densities of i\'iwi and apapane were much lower than in the forests. Three native, endangered species (‘akiapola’au H. munroi, Hawaii creeper Oreomystis bairdi and Hawaii akepa Loxopus coccineus) were not seen in enough numbers to be analysed. This study also investigates the impact of grazer exclusion and removal from native vegetation, discussed in ‘Threat: Invasive and other problematic species - Reduce adverse habitat alterations by excluding problematic species’.Study and other actions tested