Individual study: Restoration of native plant communities on degraded and reclaimed land by fertiliser addition at Holar Farm, southern Iceland
Elmarsdottir A., Aradottir A.L. & Trlica M.J. (2003) Microsite availability and establishment of native species on degraded and reclaimed sites. Journal of Applied Ecology, 41, 815-823
In Iceland, as a result of over-grazing and wood gathering large areas of native birch Betula woodland have been destroyed. Subsequent erosion has led to poor soils and barren areas. Objectives of this study were to identify microsites conducive to establishment of native plants on degraded and reclaimed sites, and determine the effects of attempts to enhance reclamation through, for example, application of fertilisers.
Study sites: The study was undertaken in an eroded area (c. 50 ha) of land at Holar Farm, southern Iceland. Four study sites were selected. The first was an unreclaimed site ('the control') with a vascular plant cover of about 10% and moss cover of less than 10%. Vegetation consisted mostly of wild thyme Thymus praecox, moss campion Silene acaulis, common sorrel Rumex acetosa, bedstraw Galium normanii and two grasses, Festuca richardsonii and creeping bent Agrostis stolonifera. Common mosses were Racomitrium ericoides, Bryoerythrophyllum recurvirostrum, Pogonatum urnigerum and Schistidium papillosum and the lichens Peltigera leucophlebia, P.canina, Stereocaulon alpinum and S.rivulorum.
The other three sites were reclamation areas that had undergone 2, 5 or 11 years of reclamation effort with 50%, 77% and 75% vascular plant cover respectively, with less than 10% moss cover on the youngest site and 55% on the oldest. Lichen cover was less than 3% on all sites.
Treatments: A 1-2 cm thick manure layer was spread, followed by about 150 kg/ha of inorganic NPK (20:12:8) fertiliser applied in the second year. Inorganic fertiliser was then applied to each site every second or third year thereafter. Approximately 350 sheep grazed the area during mid-June to mid-July, 60 during the late summer and 200 during autumn (late September to early November).
Monitoring: Within each site, four plots (10 x 10 m) were chosen to representative of vegetation present. Within each plot, 10 quadrats were randomly placed. Data were collected in July and August 2000. All seedlings from the current growing season were identified and microsite cover (nine categories, below) recorded:
1) Biological soil crusts - layer of cyanobacteria, fungi, algae, mosses, lichens and organic materials, ≤ 1 cm thick mosses
2) Mosses - mosses greater than 1 cm thick
3) Lichens - all lichens
6) Sand - sand ≤ 0.2cm diameter on the surface
7) Small stones - stones 0.2-2 cm diameter on the surface
8) Large stones - stones greater than 2 cm diameter on the surface
9) Litter - litter, humus and dung
Microsite types: Cover of biological soil crusts, mosses, grasses and forbs increased with age of the reclamation. The cover of small stones was 39% on the non-reclaimed control site compared with 1% on the oldest reclamation site. Cover of biological soil crusts was less than 1% on the control compared with 48% on the oldest reclamation site.
Seedling density: Seedling density was about 100% greater on the 2 year-old site compared with the control. However, on the 5 and 11-year old sites seedling density was not significantly different from the control. Overall, 4,053 seedlings were counted on all plots representing 14 species or genera of forbs, grasses and sedges. The number of seedling taxa was greatest on the control site (13) and smallest on the oldest reclamation site (9).
Seedling preference for microsite types: Cerastium spp. (i.e. C.alpinum and/or C.fontanum), T.praecox, R.acetosa, Euphrasia frigida and G.normanii were the most common species of seedling in the study area and accounted for 22%, 21%, 17%, 16% and 11% respectively of the total seedling number.
More seedlings were found adjacent to small stones in the control (51%) and 2 year-old reclamation site (57%) than would be expected from random occurrence. In contrast fewer seedlings than would be expected were found in sand (16%) in the control site and in sand (24%), large stones (9%), litter (2%) and forbs (less than 1%) in the 2 year-old reclamation site.
More seedlings were found in biological soil crust than expected from random occurrence in the 5 (69%) and 11 year-old (81%) reclamation sites, and fewer seedlings in the grass (13%), large stone (less than about 2%) and forb (less than 1%) microsite types. There were also fewer seedlings than expected from random occurrence in the moss microsite type (3%) at the 11 year-old reclamation site. No seedlings were observed in the lichen microsite type. Individual analysis of the five most commonly occurring taxa (Cerastium spp. T.praecox, R.acetosa, E.frigida and G.normanii) showed the same general pattern.
Conclusions: Application of fertiliser without additional seeding proved to be a simple reclamation approach that enhanced the establishment of native species and subsequently allowed vegetation cover to expand.
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