Colonization, Survival and Competition of Young Trees

Introduction I

Annual plants: Life span: one growing seasonHave to germinate, grow and bloom fast to produce seeds before the end of growing season

Perennial plants:Life span: two to more yearsPlenty of resources: rapid growthFew resources: efficient and low-loss growth

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Introduction II

Seasonal Adaptation of annual plants:Alternation of growing season and dormant season

Preparations for dormant season:Shedding the frost-sensitive partsFrost-hardening persistent partsForming buds for the following seasonStoring energy for winter and budding in spring

-> Seasonal changes are controlled by hormonal changesAbscisin acid: Supresses budding in dormant seasonGibberelin acid: Stimulates budding in growing seasonDonnerstag, 20. April 2023 3Ökologie A&T

Picture 1: Life cycle of perennial plants

Introduction III

Plant growth in areas with only 1-3% light irradiation (Mittelland) depends on different factors:

Carbon balance has to be positive over the yearRoot formation has to be sufficient for water and nutrient intakeFrost-hardy has to be persistent enough before winterBudding and formation of leaves in spring has to be ensured

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Introduction IV

Dynamics in forest gaps:Light irradiation changes due to fires, storms or cultivationSmall gaps: 5-15% light, large gaps: 20-60% lightPlants grow faster and light-requiring species colonize gapsCompetition for light and nutrients -> selection for fast growing plants

Colonisation of gaps by:Seeds capable of flightGerm buds in the soil from previous seasons

Dominance of certain species dependent on:Number of seedsRate of germinationRate of vertical growth

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Introduction V

Most abundant trees in the Swiss Mittelland:

Shady areas:Fagus sylvaticus (Rotbuche): very shade tolerant, survives with less than 5% light

Cold, humid and disturbed areas (many storms, avalanches)Acer pseudoplatanus (Bergahorn)Fraxinus excelsior (Esche)

Assumption: Ash and Acer colonise areas with light faster than Beech. Beech recaptures once the conditions are in its favour.

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Method I

The length grow during over one year were measured in six plants

Only Beech and Ash were examined

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Pictures:

2 Left: Fagus sylvatica

3 Right: Fraxinus excelsior

Method II

Measuring length growth of one year by examining cicatrices (Narben) on terminal buds on six plants

Noting if there is browsing (Verbiss) of the main shoot

Determination of age of other plants

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Picture 4:Terminal bud of Fraxinus excelsior

Method II

Documentation: One mark per plant and year

Results I

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What type of age distribution do the pouplations have?

Total plants in gap:

Beech (blue) 59

Ash (red) 112

Results II

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Age Distribution of a Gap in 2012

2012 2011 2010 2009 2008 2007 2006 2005 2004 2003 20020

5

10

15

20

25

30

35

Age structure of young trees in a woodland gap (March 2012)

EscheAhorn

Year of germination

Number of trees (per 4 m2)

Beech

Results III

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Growth of Seedlings over Time

0 20 40 60 80 100 120 140 160 180 2000

5

10

15

20

25

30

35

40

45

50

R_ = 0.45

R_ = 0.6

Tree height versus shoot growth in 2012 (ash - red; beech - blue)

Height (cm)

Shoor growth in 2012

Ash

Beech

Results IV

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Browsing:

Mean: Beech: 0.72

Ash: 1.65

Interpretation I

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Ash populates a newly formed gap faster due to high germination rates and faster growth, even though it is browsed more often.

Beech is better adapted to sites with low light and will probably recapture the area.

Sources

Picture 2: Fagus sylvaticahttp://flora.nhm-wien.ac.at/Seiten-Arten/Fagus-sylvatica.htm last vistited on 26.5.2013.

Picture 3: Fraxinus excelsiorhttp://www.botanik.de/bild/fraxinus-excelsior-gemeine-esche.html , last visited on 26.5.2013.

Picture 4: Terminal bud of Fraxinus excelsiorhttp://www.uni-graz.at/walter.obermayer/plants-of-styria/images/fraxinus-excelsior.html