Welcome to this second issue of Botany News!
- A note from the editor
- Plants grown in northern gardens: Woolly Willow
- The growth and survival of introduced Holcus
lanatus in grassland patches
- Wetlands of Iceland
- Submit your Botany News article!
- The flower box
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A note from the editor
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Plants grown in northern gardens: Woolly Willow
Woolly Willow (Salix lanata) is an evergreen
creeping or upright woody plant with strong branches and
thick annual shoots. In Iceland, Woolly Willow may reach
2m in cultivation. The leaves are broad, pointed and
covered with greyish hair. The catkins are thick and
Woolly willow grows well in gardens where it maybe be
grown as a hedge. Woolly willow is tolerant of arid
conditions whether in gardens or in the wild. Woolly
willow is a dominant species of many heaths and sandy
habitats in Iceland and its sand-binding properties are
The species is usually low-growing or absent if grazing
animals are present, while recovering rapidly following
protection of land. Woolly Willow is common at northern
latitudes and forms scrublands in Iceland, northern
Scandinavia and parts of Siberia. This species is also a
rare native of Scotland.
The growth and survival of introduced Holcus lanatus
in grassland patches. - Botany News. June 2005. By
A mown grassland in Wales was chosen as the study
site because of its relatively homogeneous structure and
absence of large grazers such as sheep and cattle. A
closely mown sward is ideal for experimental studies as
it is easy to create patches of a well defined size. A
large field experiment was carried out and important
findings of the study were reported by Arnthorsdottir
(1994). Patches of Holcus lanatus were created in
the field to examine the effect of invasion by
neighbours. The introduced patches of Holcus are
referred to here as Holcus stands. This paper
adds to an understanding of the effect of the size of a
Holcus stand and plant position within it on
plant performance and survival.
In early spring, each Holcus stand was planted
into disturbance patches from which all vegetation had
been cleared. The performance of Holcus in the
patches is a strong indicator of the resources available
to the plants. Holcus commonly forms dense
aggregations in Welsh grasslands and is a dominant
species in the mown grassland of the present study.
The major recordings on Holcus in the patches
involved measures of the change in the overall density
of Holcus as well as detailed recordings of the
performance and survival of individual plants in
relation to patch parameters. The results reflect the
effect of the patch size, position of a plant within the
patch and the relative importance of intra- and
interspecific interactions of Holcus and its
neighbours. Importantly, the experiment allows a
comparison of the growth and survival of Holcus
to be made at the same density. The Holcus plants
were planted into the stands. The effect of excluding
neighbours from the Holcus stands was also
The survival of Holcus plants clearly depends on
the size of a Holcus stand. While the Holcus
plants were originally introduced at the same density,
they survived best in the largest Holcus stands.
Interestingly, position within a Holcus stand was
important for plant survival. In general, the plants
grew best in the larger Holcus stands and in the
centres where there was less invasion of neighbours.
The production of adventitious roots differed with the
type of Holcus stand and position of plants. The
greatest differences were between edges of large
Holcus stands, with or without invasion. Some of the
Holcus plants formed adventitious roots in the
smaller Holcus stands and the direction of
running tended to be into the Holcus stand.
Edge invaders had little effect on the formation of
runners by the resident Holcus.
Resources, in particular nutrients, are
likely to be enhanced per area and per individual
Holcus plant in the larger Holcus stands.
This likely explains the enhanced survival and performance
of Holcus plants with an increased size of a
Holcus stand. Larger Holcus stands
probably contain more nutrients per unit area, while
moisture may be reduced and temperature fluctuations
greater. However, light levels are likely not very
limiting in the tightly mown sward of the current study.
Selfthinning occurs in the centres of those Holcus
stands where neighbours are excluded. Survival is higher
in the larger Holcus stands. The difference
between Holcus stands with and without invasion
is most pronounced in patch centres. Holcus
stands with natural invasion from the edge have a higher
survival of plants in the centre. The results indicate
an increased intraspecific competition in the centres of
Holcus stands, especially were invaders from the
surrounding sward were kept out. Selfthinning is likely
to be occurring in centres of Holcus stands where
fewer individuals survive to grow larger.
Arnthorsdottir, S. 1994. Colonization of experimental
patches in mown grassland. Oikos 70:73-79.
Wetlands of Iceland
In the wetlands, you commonly find a mixture of sedges,
cottongrass and moss. Wetlands in Iceland may be divided
into wetter and drier types, the wetter fens and the
drier marshes. Fens are very wet and remain submerged in
shallow water during at least a part of the year. Fens
are characterized by cottongrasses, especially, Common
Cottongrass (Eriophorum angustifolium) and sedges
such as Lyngbye’s Sedge (Carex lyngbyei), Common
Sedge (Carex nigra), Beaked Sedge (Carex
rostrata) and String Sedge (Carex chordorrhiza).
A marsh is the drier type of wetland, where the
vegetation is seldom submerged and often has better
drainage due to a slight inclination of the land.
Marshes are common in all parts of Iceland including
montane areas, where Bigelow's Sedge (Carex bigelowii)
and willows predominate. Wetland patches with rushes are
also common. The diversity of species in marshes
surpasses that of fen vegetation.
While sedges, horsetails, grasses and shrubs thrive in
marshes, the flowers of herbs such as the Grass of
Parnassus (Parnassia palustris) and Marsh Violet
(Viola palustris) add to the beauty of the
vegetation. Lush wetlands also exist in the central
highlands close to major rivers. Here productive wetland
oasis are dominated by graminoids, sedges, deciduous
willows and the evergreen Bog Bilberry (Vaccinium
uliginosum) shrubs among patches of wetland mosses
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The Flower Box
The plan is to organize several botanical tours in
Iceland in the summer of 2006. A first announcement for
the "Customized Botanical Tours" is now available on our
Botany in Iceland.
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contact us well in advance.
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June 4, 2005 -- Botany News, Issue #002