Environmental Engineering Reference
In-Depth Information
to a restoration site (Krautzer et al . 2010 ). Long - term
supplementary management of restoration efforts is
costly and problematic. In some countries, there is also
a confl ict between laws related to seed. Use of com-
mercial non - site - specifi c seed material, as well as the
use of cover crop seeds, can also have negative impact
on spontaneous succession of plant communities
with native species. Plant nutrients will be bound up
by these plants and only be released slowly to the soil.
At the same time, surface litter can prevent site-specifi c
seeds from germinating (Cargill & Chapin 1987; Dens-
more & Holmes 1987). In subarctic, low-Arctic, sub-
alpine and alpine zones, restoration using cover seeds
is only recommended where it is needed for erosion
control (Partl 2006). At other sites, revegetation will
occur faster without use of cover seeds. Furthermore,
effects of sowing new species or ecotypes into local
plant communities are often unpredictable and may
even displace the extant vegetation or lead to undesir-
able hybridization with locally adapted ecotypes (Sack-
ville Hamilton 2001; Malaval et al .
nitely of importance. One should avoid the use of seed
material from more distant biogeographical areas.
A widely used method is the mowing of suitable
donor sites at the time when most of the desired species
are at an optimum stage of seed maturity (June-
August). To avoid excessive seed losses, the material is
cut preferably early in the morning when it is moist
with dew and then immediately taken to the restora-
tion area (receptor site) and spread there. Another pos-
sibility is to dry the mowed material and to use it later
for restoration. Nevertheless, this method requires
increased manipulation and therefore higher costs. In
addition, a large part of the seed material may be lost.
The method of meadow threshing (Kirmer & Tischew
2006 ; Jongepierova et al . 2007 ) collects site - specifi c
seeds from suitable donor sites. To obtain the greatest
possible number of mature seeds from the preferred
species particular attention has to be paid to harvest-
ing time. Seed mixtures with highest species diversity
are generally achieved by consecutive harvesting of
donor sites according to species-specifi c seed matura-
tion rates and schedules. In the Alps, seed yields are
usually between 50 and 200 kg ha − 1 . The relationship
of donor area to restoration area thus varies from
approximately 1:1 to 1:4. If application of threshed
seed material is not possible immediately after harvest,
it must be dried and stored in a dry location.
The hay - fl ower seeding method uses seed-rich
remains from threshing fl oors in hay barns, which
often keeps suffi cient seed quantities and qualities
(ÖAG 2000). In general, seed material should be
regained from hay no more than 2 years old. To acquire
an appropriately high amount of pure seeds, sieving is
helpful. Hay fl owers are recommended to be sown in
quantities of 0.5 - 2.0 kg m − 2 and with their stalks to a
maximum depth of 2 cm. To minimize loss through
scattering by wind, seeding should only take place on
wet soil, or if prompt watering of seeded areas is feasi-
ble. If germination capacity of available hay fl owers is
defi cient, site - specifi c seeds can be purchased and sown
as a supplement.
A good method that is currently practised in several
countries is the nursery or large-area production of
seed of suitable species with the aid of agricultural
techniques. Above all, species used often and in large
amounts can be produced at comparatively reasonable
costs and implemented on appropriately large project
areas. This method has been used successfully in the
United States, Austria and Switzerland for restoration
projects above the tree line (Richards et al .
2009 ;
Vander
Mijnsbrugge et al . 2010 ).
In contrast, plants arising from site-specifi c seeds
generate relatively little standing biomass but can
rapidly develop extensive, self-maintaining stands with
high resistance to subsequent uses for tourism and
agriculture (Krautzer et al . 1993 ; Peratoner 1993 ).
When site - specifi c seed mixtures are used, sowing
quantities can be drastically reduced from 200-500 kg
ha − 1 , such as are commonly used for conventional
seed mixtures, to 80 - 160 kg ha − 1 (Holaus 1997 ).
Unfortunately, as mentioned already, commercially
produced site - specifi c seed material may be diffi cult to
obtain for most of the Arctic-alpine regions, though
recently there have been signifi cant efforts in several
countries to close this gap (e.g. Rausch & Kershaw
2007; NTW seed project and ECONODA - see the
appendix at the end of this chapter). Alternative ways
of obtaining site-specifi c seed material for restoration
purposes are the use of vegetative cuttings from the
nearby areas, meadow threshings and the hay-fl ower
seeding method (Kiehl et al . 2010), all of which will
be described in the 'Sources for site-specifi c
seeds '
subsection.
Sources for s ite - s pecifi c s eeds
The availability of a donor area, which provides ripe
seed material for direct use in restoration or for the
further multiplication of suitable seed material, is defi -
1997 ;
Search WWH ::




Custom Search