Home  Forest Genetics Jan-Erik Nilsson Project page
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Jan-Erik Nilsson Project page |
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Adaptation
of forest trees in northern latitudes
General on adaptation
Forest tree populations have reached certain degrees of adaptation,
over many generations, to local climate and photoperiod conditions.
In northern latitudes the adaptation is strongly related to
survival and reproduction under conditions with long, cold
winters and short summers. In these areas, early cold acclimation
rhythms are usually the most critical factor for survival.
Contact Info |
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PI: Jan-Erik Nilsson
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General on adaptation
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| Variation in autumn cold acclimation among Scots
pine seedlings is indicated by injury after artificial
freeze testing. |
Forest tree populations have reached certain degrees of adaptation,
over many generations, to local climate and photoperiod conditions.
In northern latitudes the adaptation is strongly related to
survival and reproduction under conditions with long, cold
winters and short summers. In these areas, early cold acclimation
rhythms are usually the most critical factor for survival.
The cold acclimation is initiated by elongation of the nights
in late summer, and northern populations are adapted to initiate
cold acclimation at shorter night lengths than more southern
populations. For Pinus sylvestris strong clinal covariation
of survival and phenological traits with the latitude of origin
has been verified in numerous provenance studies under field,
climate chamber and greenhouse conditions. However, the adaptation
to the present climate is usually far from perfect because
of factors such as the variability of climate/weather conditions
over time and the continuous geographic distribution of the
species, which allows gene exchange between populations by
long distance pollen transfer. As a consequence of this non-optimal
adaptation, provenance selection (usually involving southern
transfer of seeds) and breeding for adaptation increases survival
and volume production compared to regeneration with local
seeds.
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Genetic variation and natural pollen clouds of Pinus
sylvestris
In our projects we are studying:
- the genetic variation in traits related to cold acclimation
of P. sylvestris,
- the importance (and duration) of physiologi cal after-effects
of maternal growth environment in:
a) progeny testing and
b) selection for northern latitudes,
- the influence of long distance pollen tranfer on
a) the adaptation of natural forests
b) tree hardiness, and
c) geographical utilization of seeds from Swedish seed orchards.
Basic methods being applied in the studies are:
- artificial freeze testing under controlled conditions simulating
natural conditions
- phenological observations in short term experiments in climate
chamber, greenhouse, nursery and field experiments.
Isolation of female flowers allows fertilization
with pollen from selected parents
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| Isolation of female flowers allows fertilization
with pollen from selected parents. |
Freeze testing of whole plants and repeated freeze testing
of detached needles (non-destructive for the tested plants)
is used to study genetic variation and changes in cold hardiness
over the year. The use of artificial freeze testing during
late summer and autumn to assess climate adaptation is justified
by the high correlations found between injuries during freeze
testing of one- and two- year old plants and mortality due
to weather and climatic factors in 10-20 year old field trials
of provenances and families. Forest trees produce enormous
amounts of pollen that can carry genes over long distances
if winds and other weather conditions are favourable. In Sweden
southerly winds often prevail during the flowering period,
carrying ”unhardy” southern genes to fertilize
northern populations. However, wind directions vary both within
and among years, probably causing pollen of different geographical
origins and genetic characteristics to fertilize trees at
various localities, and for similar variations to occur at
the same locality on different days and in different years.
In this project we are studying whether differences in hardiness
and geographical origin of the background pollen can be estimated
by comparing progenies from open pollination and progenies
from controlled crossing of the same mother trees with pollen
from different latitudes. The close relationship between autumn
frost hardiness and latitude of origin will then be exploited
to estimate the latitudinal origin of natural pollen clouds.
For this purpose, seventeen clone archives, including grafts
of ten Scots pine clones (selected for poor pollen production)
were planted in central and northern Sweden. They will act
as mother trees for the background pollen and were therefore
planted in areas with few natural Scots pine trees. We also
are studying whether mobile grafts can be used as pollen receivers
at any locality without loss of precision of the pollen population
estimates obtained from progeny testings caused by physiological
after-effects of the graft treatment.
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Research
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