introduction - Ecologia Mediterranea

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INFLUENCE OF IVY (HEDERA HELIX L.) ON THE GROWTH OF DOWNY OAK (QUERCUS PUBESCENS s.l.) u ecologia mediterranea, tome 29, fascicule 1, 2003, p. 5-14 Figure 4. Biomass of woody parts (a) and foliage (b) of the sampled trees. Figure 5. Master tree ring chronologies (a) and height growth variation through time (b) of the investigated populations. In (a) symbols above curves indicate statistical significance for difference of means between oak chronologies: P < 0.05, m P < 0.1 11
12 u G. GARFÌ, S.FICARROTTA other liana species could be promoted in disturbed sites (e.g. road border strips or logged areas), owing to their remarkable ability to repair damages and the tremendous capacity to resprout after mechanical injury (Oldeman, 1990). Moreover, as there is more light reaching the forest floor in these zones, ivy might be able to grow at a faster rate and thus cover larger areas than in the lower layers of the forest. Dendrochronological features Preliminary evaluation of ring data quality allows some observations. The rather low mean sensitivity and crossdating coefficients, combined with high and moderate auto-correlation for oak populations and ivy, respectively, made these species not quite suitable for dendroclimatological investigations. Moreover, especially for oak, a variability in individual behaviour was found as reflected by high standard deviation and coefficient of variation values. Relative differences in synchronisation between the two species can reveal a certain diversity in ecological requirements, though human disturbances (e.g. coppicing) might have had a major role in determining ring width variability (Fritts, 1976). In fact, a better match between the arboreal and liana species curves was observed from the end of the 1970s, when coppicing had definitively ceased. Consistently, in the case of oak, fluctuations in the radial and height growth centred around the second half of the 1960s (fig. 5), can probably be attributed to a coppicing event. On the contrary, decrease in ring width, which begun in the second half of the 1980s, is not to be ascribed to coppicing, but most likely could reflect regional-scale climate factors, as similar trends were also detected in downy oak and hackberry (Celtis australis L.) populations from south-eastern Sicily (Garfì, 2000). An additional factor that could have contributed to improve the agreement between ivy and oak curves in phase D could be the liana position in the forest structure. Ivy has a very particular life cycle involving two distinct growth forms: creeping chamephyte and climbing phanerophyte. In the creeping, juvenile phase, ivy is well adapted to the low light levels of the forest floor and, being sterile, spreads vegetatively. Ivy maintain this creeping state in the undergrowth of the forest, until a gap in the canopy promotes differentiation into a very fast-growing, woody stem. Anchored by adventitious roots, many individuals of ivy begin to climb up the closest trunks (Trémolières et al., 1988; Oldeman, 1990; Schnitzler, 1995). From that time forward it starts the phanerophyte, adult, fertile phase, which demands higher light levels. In the present study, during phase D, being largely develo- ped at the top of the canopy, ivy was exposed to direct climatic variations, whereas in the forest floor these conditions were more tempered.This fact could imply that the radial growth patterns of the ivy would tend to match that of the host oak. Ivy-oak interactions Several facts implicate an important influence of ivy on the oak trees at Monte Carcaci. Evidence was undoubtedly revealed by the smaller foliage biomass of host oaks compared to non-host oaks. The difference was not statistically significant, but its meaning can not be disregarded, especially when we consider the remarkable luxuriance of the liana foliage compared to the respective host trees. This would lead to notable suppression of oak sprouts which, suffering for light competition, would consequently be affected in either overall growth or fructification (Stevens, 1987; Schnitzer & Bongers, 2002). However, the actual action of the liana on host treering growth appears more complex. In both QP1 and QP0 we observed that the degree of ivy invasion usually increased according to the increasing Dbh of host trees (table 2) and this could account for the minimum host size which is required for the liana to climb (Beekman, 1984). Hence the smaller lianas could be just those who begun to climb later, when a suitable size support was available. However, ivy could actually have a beneficial effect on host tree growth depending on the amount of litter that the larger plants can produce. Trémolières et al. (1988) and Badre et al. (1998) reported that in the alluvial hardwood Rhine forest the litter of the ivy phanerophyte form plays an important role in nutrient turn-over, which in contrast to the chamephyte form decomposes rapidly in late spring, enriching the substrate nutrient content when the other forest tree species are in full growth. Likewise, being lacking of tannins, common microbiological inhibitors, ivy litter also promotes the release from the overall litter of mineral nutrients and water-soluble organic compounds. Nola (1997), based on the results of a research on ivybeech interactions, agreed with the assumption of a localised fertilising role of ivy litter. As discussed below, the detailed analysis of tree-ring series seemed to some extent to corroborate this. The periodical changes in ring growth rate between host and non-host trees probably reflect the influence of liana; significant t-values for ring width differences, obtained for several years, support such a statement. Actually, the faster growth of host trees from the end of the 1950s to the late 1970s (phase B) just occurred some years after ecologia mediterranea, tome 29, fascicule 1, 2003
Page 1 and 2: Tome 29 Fascicule 1, 2003 ISSN 0153
Page 3 and 4: Rédacteur en chef • Managing edi
Page 5 and 6: Ce fascicule a bénéficié du sout
Page 7 and 8: 6 u G. GARFÌ, S.FICARROTTA INTRODU
Page 9 and 10: 8 u G. GARFÌ, S.FICARROTTA The inv
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Page 15 and 16: 14 u G. GARFÌ, S.FICARROTTA FRITTS
Page 17 and 18: 16 u T. LA MANTIA, S.CULLOTTA & G.
Page 28 and 29: Caractérisation climatique et bioc
Page 30 and 31: CARACTÉRISATION CLIMATIQUE ET BIOC
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Attrait trophique de Damaeus flagel
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MATÉRIEL ET MÉTHODES Matériel Si
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(ANOVA à 1 facteur, F = 31.28, P
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ATTRAIT TROPHIQUE DE L’ACARIEN DA
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ATTRAIT TROPHIQUE DE L’ACARIEN DA
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88 u MOHAMED FENNANE INTRODUCTION L
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90 u MOHAMED FENNANE * Tetraclino a
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92 u MOHAMED FENNANE Barbéro, Bena
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94 u MOHAMED FENNANE 4. Pelouses, p
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96 u MOHAMED FENNANE Au Moyen Atlas
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98 u MOHAMED FENNANE * Frankenio la
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100 u MOHAMED FENNANE * Spartinetum
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102 u MOHAMED FENNANE précisées.
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104 u MOHAMED FENNANE KAABECHE M.,
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106 u MOHAMED FENNANE TÜXEN R. & E
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108 u FAITS DE CONSERVATION EN MÉD
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116 Perspectives pour une géobiolo
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118 u ANALYSES D’OUVRAGES recensa
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120 Ecologia Mediterranea publishes
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