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Volker Hesse:

Epiphytic lichen diversity and its dependence on chemical site factors in differently elevated dieback-affected spruce stands of the Harz Mountains

2002. 191 pages, 66 figures, 49 tables, 14x23cm, 390 g
Language: English

(Dissertationes Botanicae, Band 354)

ISBN 978-3-443-64266-2, paperback, price: 42.00 €

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Keywords

FichteHarzFlechteEpiphytic lichen diversityHarz MountainPicea abies

Contents

Abstract top ↑

Epiphytic lichen distribution on trunks of Norway spruce (Picea abies) and its dependency on chemical site factors were investigated. The study was carried out in montane woodlands of the Harz Mountains in Northern Germany. For investigating the influence of forest dieback on epiphytic lichen vegetation and on chemical site conditions, two boggy stands were selected. Within both stands tree vitality ranged from healthy to dead. Differences in tree vitality are assumed to be due to small-scale differences of ground-water levels, as Norway spruce is more susceptible to pollution-caused forest dieback when water logging occurs.

In both stands, more species grew on dieback-affected trees than on healthy ones. Especially pollution-sensitive species had higher mean cover or frequency in the dieback-affected plots than in the healthy ones. Conversely, the extremely toxitolerant crustose lichen Lecanora conizaeoides covered larger areas in the healthy plots than in the dieback-affected ones. Stem flow of the dieback-affected spruce trees of both stands contained significantly less SO42-, NO3-, and NH4+ than stem flow of the intact ones. Moreover, stem flow content of PO43-, H+ and Fe and conductivity were significantly lower on the dieback-affected trees than on the healthy ones in one of both stands. The concentrations of SO42- and NO3- decreased linearly in stem flow from healthy over dieback-affected to dead trees. Therefore it is assumed that a smaller canopy surface of the dieback-affected trees, which results from needle loss, causes a reduced interception of the atmosphere, and, thus, results in smaller concentrations in stem flow especially of dryly deposited substances.

For testing the impact of the factor altitude, a stand in an altitude of 1000 m was compared with a stand in 550 m. Epiphytic lichen vegetation in the more highly elevated stand consisted of 22 species, whereas only 13 species occurred at 550 m. Significantly larger areas of bark were covered on trees at 1000 m. Moreover, mean cover of 15 species was higher in 1000 m, but differences were significant for only seven taxa. At 550 m, six species had a trend for higher mean cover. Epiphytic lichen vegetation of both stands was dominated by Lecanora conizaeoides, making up more than 50 % of the total area covered by lichens. Element content in incident precipitation did not differ significantly between the stands. However, Na content in stem flow was significantly higher in 1000 m than it was in 550 m. Stem flow content of Mn and the ratios of Mn / Ca and Mn / Mg were higher in the more lowly elevated stand. Mn content, Mn / Ca and Mn / Mg ratios were also higher in the bark of the latter stand. These high Mn concentrations are assumed to be a result of significantly higher concentrations of extractable Mn in the soil.

A comparison between only the healthy trees of both stands revealed significantly higher doses of Na, SO42- and PO43- in stem flow of the more highly elevated stand. However, SO42- concentration in stem flow was higher for the trees of the more lowly elevated stand. Amounts of stem flow were significantly higher on trees of the stand in 1000 m. Therefore, it is assumed that despite higher deposition rates at higher altitudes, stem flow concentrations of pollutants such as SO42- and NO3- might be more unfavourable to lichens at lower altitudes because of a lower dilution in these stands.

Strong correlation was found between SO42- content of stem flow and lichen cover. In both stands, cover of Hypogymnia physodes and the number of species per tree declined with increasing concentrations. Cover values of Lecanora conizaeoides showed an optimum curve.

In the low elevated stand, high Mn concentrations in stem flow are considered to have a strong impact on lichen vegetation. However, the Mn / Ca ratio of stem flow is more important, as strongest correlations occurred both with cover of Hypogymnia physodes and the number of lichen species per tree. Mn content and the Mn / Ca ratio of the bark was also correlated with a decrease in cover of Hypogymnia physodes and the total number of species per tree. Positive correlations of cover of Lecanora conizaeoides with mean NO3- content in stem flow occurred in both stands. Furthermore, in one of both stands this was the only parameter with which L. conizaeoides was correlated. Therefore, a promotional effect of NO3- content in stem flow could not be ruled out. Other correlations with stem flow and bark parameters are considered coincidental, although they cannot be ruled out, as experimental knowledge is not sufficient in many cases.

Summarizing, there is strong evidence that forest-dieback promotes epiphytic lichen abundance due to reduced concentrations of atmospheric pollutants in stem flow. This applies to SO42- in particular. Furthermore, the importance of the factor soil is highlighted. Differences in epiphytic lichen vegetation between both stands are probably a result of between-stand differences in the concentrations of extractable Mn in the soil.

Bespr.: Ber.Bayer.Bot.Ges. 73/74, 31.12.2004 top ↑

Zur Bewertung der Luftqualität nutzt man heute gerne die Indikatoreigenschaften von Flechten. Ihre von Art zu Art unterschiedliche Empfindlichkeit gegenüber bestimmten Gasen (wie Schwefeldioxid) macht eine solche Indikation möglich. Extrem empfindliche Arten (wie viele Bartflechten) stehen sehr toxitoleranten Arten (wie Lecanora conizaeoides) gegenüber. Andere Arten reihen sich bezüglich ihrer Emfpindlichkeit an unterschiedlichen Stellen der Skala zwischen diesen Extremen ein.

In vom ``Baumsterben'' betroffenen Fichtenwäldern zeigen jedoch stark geschädigte, absterbende oder schon tote Bäume überraschenderweise eine oft reichere Flechtenflora als gesunde Bäume in unmittelbarer Nachbarschaft. Dieses Phänomen konnte bisher nicht schlüssig erklärt werden und wurde kontrovers diskutiert. So glaubten einige Autoren, die Flechtenvegetation könnte an geschädigten Bäumen von dem dort höheren, durch den Nadelverlust der Bäume bewirkten, Lichteinfall und vielleicht auch von einer erhöhten Wasserspeicherkapazität der veränderten Borke gefördert sein. Andere sahen darin einen Hinweis dafür, daß diese Art der Baumschädigung nicht durch Schadstoffbelastung aus der Atmosphäre verursacht sein könne.

Der Autor der vorliegenden Arbeit überprüfte eine andere Hypothese, die kleinräumige Veränderungen chemischer Standortfaktoren als Ursache dieses Phänomens annimmt.

Das an den Baumstämmen (hier an Fichten untersucht) ablaufende Regenwasser wurde dabei chemisch auf Inhaltsstoffe (Ammonium, Sulfat, Phosphat, Nitrat, Kalium, Natrium, Magnesium, Eisen, Mangan, Zink) und seinen pH-Wert hin untersucht. Zwei in unterschiedlicher Höhenlage und über morrigem Grund stockende Fichtenwaldparzellen im Harz, die jeweils gesunde, geschädigte und absterbende Bäume enthielten, dienten als Untersuchungsgebiete. Dort fand sich die mäßig toxitolerante Hypogymnia physodes erheblich häufig an toten, als an gesunden Bäumen, während umgekehrt die viel unempfindlichere Lecanora conizaeoides an den gesunden Bäumen häufiger auftrat.

Geschädigte Bäume zeigten denn auch - mit solchem Besiedelungsverhalten in Übereinstimmung - einen signifikant geringeren Gehalt an Sulfat-, Nitrat-, Phosphat- und Ammoniumionen im Stammabfluß als gesunde Bäume.

Der Autor macht hierfür die bei geschädigten Bäumen erheblich reduzierte Nadelmasse verantwortlich, die eine verringerte Wasseraufnahme (und damit Schadstoffaufnahme) der Baumkrone zur Folge hat und dadurch das Wachstum von empfindlicheren Flechtenarten am Stamm dieser Bäume begünstigt.

Das Buch stellt sich als ausführliches, durch zahlreiche Tabellen und Graphiken übersichtlich gestaltetes, datenreiches Protokoll der vorgenommenen (und hier nur zum kleinen Teil skizzierten) Untersuchungen dar, zu deren Interpretation eine reiche Literatur (über 530 Titel im Literaturverzeichnis) herangezogen wurde.

H. Hertel

Ber.Bayer.Bot.Ges. 73/74 31.12.04

Contents top ↑

1 Introduction 7
2 Study area 9
2.1 Location of the study area 9
2.2 Geology and climate 9
2.3 History of forest management 11
2.4 History of forest dieback 12
2.5 Epiphytic lichen flora 13
3 Material and methods 15
3.1 Estimation of tree vitality 15
3.2 Sample trees 15
3.3 Mapping of epiphyte vegetation 16
3.4 Precipitation studies 16
3.4.1 Sampling of stem flow and incident precipitation 16
3.4.2 Sample preparation and chemical analyses 16
3.5 Studies of the element content in bark and in the lichen
Hypogymnia physodes 17
3.6 Soil analyses 18
3.7 Statistics 18
4 Distribution of epiphytes 19
4.1 Differences between stands W2 and W3 19
4.2 Stand vitality 21
5 Incident precipitation and its chemical composition 27
5.1 Amount of precipitation 27
5.2 Element content 27
5.3 Correlation between the parameters measured in incident
precipitation 28
6 Element concentrations in stem flow 29
6.1 Differences between stands W2 and W3 29
6.1.1 Amount of stem flow 29
6.2 Element content 29
6.3 Differences between healthy and dieback-affected trees 30
6.3.1 Amounts of stem flow 30
6.3.2 Element content 31
6.3.2.1 Stand W2 31
6.3.2.2 Stand W3 33
7 Element doses of stem flow 35
7.1 Differences between stands W2 and W3 35
7.2 Differences between healthy and dieback-affected trees 35
7.2.1 Stand W2 35
7.2.2 Stand W3 36
8 Substrate 39
8.1 Differences between the sample plots 39
8.2 Differences between healthy and dieback-affected trees 39
8.2.1 Stand W2 39
8.2.2 Stand W3 40
9 Element content of Hypogymnia physodes 41
10 Soil conditions 43
10.1 Soil types 43
10.2 Soil chemistry 43
10.2.1 Differences between stands W2 and W3 43
10.2.2 Differences in soil from the surroundings of healthy and
affected trees 44
11 Relations between chemical site factors and epiphytic lichen
vegetation 47
11.1 Stem flow 47
11.1.1 Hypogymnia physodes 47
11.1.1.1 Comparison between the stands W2 and W3 47
11.1.1.2 Comparison between healthy and dieback-affected trees 48
11.1.2 Lecanora conizaeoides 49
11.1.2.1 Comparison between stands W2 and W3 49
11.1.2.2 Comparison between healthy and dieback-affected trees 49
11.1.3 Number of lichen species per tree 50
11.1.3.1 Comparison between the sample plots 50
11.1.3.2 Comparison between healthy and dieback-affected trees 51
11.2 Effects of the substrate 52
11.2.1 Hypogymnia physodes 52
11.2.1.1 Comparison between stands W2 and W3 52
11.2.1.2 Comparison between healthy and dieback-affected trees 52
11.2.2 Lecanora conizaeoides 52
11.2.2.1 Comparison between stands W2 and W3 52
11.2.2.2 Comparison between healthy and dieback-affected trees 53
11.2.3 Number of lichen species per tree 53
11.2.3.1 Comparison between stands W2 and W3 53
11.2.3.2 Comparison between healthy and damaged trees 54
11.3 Multivariate regression analysis 54
11.3.1 Stand W2 54
11.3.1.1 Hypogymnia physodes 54
11.3.1.2 Lecanora conizaeoides 55
11.3.1.3 Number of species per tree 55
11.3.2 Stand W3 56
11.3.2.1 Hypogymnia physodes 56
11.3.2.2 Lecanora conizaeoides 56
11.3.2.3 Number of species per tree 57
11.3.3 Correlations between element content of Hypogymnia physodes and
its cover 57
12 Discussion 59
12.1 Species composition 59
12.1.1 Influence of forest dieback on epiphytic lichen abundance 59
12.1.2 Differences between the sample plots with reference to the
factor altitude 65
12.2 Element concentrations in incident precipitation 69
12.3 Different tree damage in stands W2 and W3 70
12.4 Modification of element deposition in the canopy 71
12.5 Altitude as a factor determining element deposition on the tree
trunk and concentration in stem flow 72
12.6 Influence of forest dieback on element deposition on the trunk
surface 73
12.7 Possible effects of chemical site factors on lichen vegetation in
the investigated spruce stands 75
12.7.1 Hypogymnia physodes 75
12.7.1.1 Stand W2 75
12.7.1.2 Stand W3 84
12.7.2 Lecanora conizaeoides 88
12.7.2.1 Stand W2 88
12.7.2.2 Stand W3 93
12.7.3 Number of species per tree 94
12.7.3.1 Stand W2 94
12.7.3.2 Stand W3 96
12.8 Relations between biological and geochemical diversity 97
12.9 Microclimatical aspects of small-scale lichen distribution 98
13 Abstract 103
14 Acknowledgements 105
15 References 107
16 Appendix 137