Fjölrit RALA - 15.01.2001, Side 7

SUMMARY
Vegetation succession in areas colonized by the introduced Nootka lupin (Lupinus nootkatensisj in
Iceland
The effect of Nootka lupin on vegetation and soil (0-10 cm) was investigated at 15 sites in southem
and northem Iceland. Plant biomass was determined at 10 of the sites. The lupin had been at the sites
for 10-40 yrs and colonized barren eroded areas, glacial river beds, partly vegetated moss heaths and
denser dwarf-shrub heaths. Transects were laid out and a comparison made of lupin of different age
within patches and the adjacent areas outside them. A total of 27 patches was investigated and
measurements carried out in 93 plots. In the analysis CANOCO-ordination was used to analyse
sucessional trends.
In southem Iceland, where annual precipitation is 900-3400 mm, the lupin was of high stature
(80-120 cm) and formed a closed canopy. In northem Iceland, where annual precipitaion is 500-800
mm, the lupin was lower in height (40-110 cm) and did not form a closed canopy on the driest gravel
flats. There it, however, formed dense patches on dwarf shmb heaths and in coastal areas. Lupin
biomass was 300-990 g/m2 in the southem area and 80-650 g/m2 in the northem area.
At sites where the lupin formed dense, long-lasting patches it had great effect on the vegetation
development. The ordination results revealed that successional changes caused by the lupin tended to
go into the same direction irrespective of the type of land it colonized. Within the patches the
vegetation developed towards a forb-rich grassland, abundant in horsetails (Equisetum) at some of the
sites. In the south Poa pratensis was the dominant grass species at most of the sites, but Poa glauca
and Festuca richardsonii in the north. A dense mosslayer developed undemeath the lupin at most of the
sourthem sites. The effects of the lupin were generally greater in the southem area and the vegetation
of old patches was rather uniform. It was more diverse in the northem area, where the lupin had less
pronounced effects on vegetation composition at the drier sites.
Species richness was greatly reduced at most of the sites where the lupin formed dense patches.
At the southem sites 20-60 plant species were found in plots outside the patches but 5-25 species
within the oldest parts of lupin patches. At the northem sites 10-55 species were found on the outsite
but 3-62 species within the oldest parts of the patches. The greatest reduction occurred where the lupin
had colonized dwaf-shmb heathlands in northem Iceland resulting in disappearance of most of the
native species. At the drier northem sites species richness was little affected by the lupin or even
mcreased. There, most existing species survived within the open lupin patches and at some of the sites
birch (Betula pubescens) colonization occurred which was rare at other sites.
The lupin was generally densest close to the edges of patches where the plants had just reached
maturity. The lupin density tended to decrease towards the oldest center of the patches. The longevity
of the lupin varied, however, greatly between sites. At some of the southem and the drier northem sites
the lupin had degenerated in the oldest parts of patches, where it had colonized 15-25 years earlier. At
other southem and northem sites the lupin maintained a high cover and was still dominant in the oldest
parts of patches where it had been growing for 25-35 years. Most of these sites were from areas of high
annual precipitation, late snowmelt in spring or high groundwater table.
C and N content of soil increased considerably where the lupin colonized barren or partly
vegetated areas. The changes were greatest at sites from the southem area where C increased about
0,1% (-1300 kg/ha) and N 0,01% (-120 kg/ha) per year. There was about tenfold difference in the rate
of C and N accumulation in the soil between sites. At sites in the northem area where the lupin had
colonized dwarf-shmb heathland with a relatively humus rich soil there were indications of net-carbon
loss from the soil.
The Nootka lupin is a very effective plant for land reclamation in Iceland. Dense plant cover
and soil fertility can be gained within a relatively short time span, where the growth of the lupin is not
limited by droughts. The Iupín is well suited for reclamation of large, barren areas. The nitrogen
fixation of the lupin, rapid growth, size and patch formation, on the other hand, enables it to invade
mossheaths and dwarf-shmb heathlands which it will take over and displace. This calls for strict
management guidelines on the future use of the plant in the country.
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