Effects of Bauxite Mine Restoration Operations on Topsoil Seed Reserves in the Jarrah Forest of Western Australia

Abstract

We studied the effects of soil handling operations during bauxite mining and restoration on the numbers and depth distribution of seed stored in the surface soil of the jarrah forest. Germinable seed stores were determined in four sites of undisturbed forest, these same sites after clearing and burning of forest residues, in the soil immediately following the construction of topsoil stockpiles, in the respread topsoil and then after deep ripping of the respread topsoil. Average density of germinable seed at four sites prior to disturbance was 352 m−2. After clearing and burning, the seed store had decreased to a mean 74% of the original forest soil seed store density. When the top‐soil was stockpiled prior to respreading, the seed content was further reduced to 31% in freshly constructed stockpiles and had declined to 13% after 10 months in the stockpiles. After ripping of the respread topsoil the seed content was 16% of the original forest seed store density. In one site where the topsoil was directly stripped and respread with no period of stockpiling but with a period of fallow, the seed store was 32% after respreading and then increased to 53% of the original forest store after ripping. This increase may have been caused by an underestimate of the reserves due to insufficient heating of the samples to break dormancy in fire‐requiring species. In the forest topsoils seed was concentrated in the upper few centimeters of the soil profile, whereas after the mining and restoration operations seed was evenly distributed throughout the returned soil profile to a depth of 20 cm. Small‐seeded annual species, which were common in the forest seed store, were more sensitive to the soil handing operations and declined to very low numbers, whereas hard‐seeded plant species such as Acacia spp. were less affected by the soil handling operations. Implications for bauxite mine revegetation operations include the recommendation that direct return of topsoil should be carried out wherever possible with a minimum delay between clearing, stripping, respreading, and ripping.

Forest restoration following surface mining disturbance: challenges and solutions

“…Oil sands sites reclaimed using forest floor material (vs. peat-mineral mix) had higher cover of trees, shrubs, and forbs, and the soil microbial community composition was converging more quickly towards that of natural upland forest (Hahn and Quideau 2013). Plant propagules in forest floor material lose their viability quickly if the material is stockpiled prior to placement but direct placement of forest floor material can overcome this problem and has shown promise in trials in several different locations (Holmes 2001;Iverson and Wali 1982;Koch et al 1996;Rokich et al 2000;Tacey and Glossop 1980). For example, direct placement of forest floor material on a coal mine reclamation site in Alberta resulted in rapid (B3 year) establishment of 65 native species, 30 of which were characteristic of mature, closed boreal forest (Macdonald et al 2015).…”

Restoring a Jarrah Forest Understorey Vegetation after Bauxite Mining in Western Australia

“…For bauxite mine restoration the soil seed bank can contribute more than 70% of the plant species richness (Koch & Ward 1994; Ward et al 1996) and hence is an important resource for the restoration process. Studies have quantified the seasonal changes in the seed bank (Table 4; Ward et al 1997), the depth distribution of the seeds (Koch et al 1996), the ability of germinating plants to emerge from various levels of burial (Grant et al 1996), and the effects of different soil handling procedures on the seed bank during bauxite mining (Koch et al 1996; Ward et al 1996). These research findings have led to the following recommendations to maximize the contribution of the topsoil seed bank for restoration:…”

Smoke, Mulch, and Seed Broadcasting Effects on Woodland Restoration in Western Australia

“…As a routine part of the restoration process the company removes the woodland topsoil, which contains soil‐stored seeds, and returns the topsoil into areas to be restored. The value of fresh topsoil for increasing plant diversity in mine‐site restoration is well documented (Tacey & Glossop 1980; Koch et al 1996). For those species that do not store their seeds in the soil seedbank, replacement of species is achieved by use of broadcast seeds or through planting of green stock into restored sites.…”