introduction - Ecologia Mediterranea

INFLUENCE OF IVY (HEDERA HELIX L.) ON THE GROWTH OF DOWNY OAK (QUERCUS PUBESCENS s.l.) u
the start of the liana climbing form (see fig. 5a). This is
consistent with hypotheses that ivy litter improves soil fertility
(Trémolières et al., 1988; Badre et al., 1998). In our
study, however, such an effect did not appear to be permanent.
As reported above, after a period of comparable
growth rate (fig. 5a, phase C), the growth of non-host
trees became faster than that of host trees (fig. 5a,
phase D).This prompt the idea that, after an initial cooperative
phase, an increasing competition by ivy to the detriment
of host oaks finally arose.
This suggestion agrees with the general belief that lianas
have deleterious effects on forest tree species through
direct physical suppression by shading or root antagonism
(Schnitzer & Bongers, 2002). It must be pointed
out, however, that the explicit mechanisms by which lianas
affect trees are rather unclear. Very little is presently
known about the relative contributions of above- and
below-ground competition between lianas and their hosts
(Schnitzer & Bongers, 2002). Only a few studies (e.g.
Whigham, 1984; Dillenburg et al., 1993) assert that the
predominant effect of above-ground competition can be
only apparent, while below-ground competition plays a
much greater role. In particular, antagonism for soil nitrogen,
rather than above-ground competition for light can
be responsible for the drastically reduced growth rates of
trees. Competition for soil water remains a matter of
controversial opinions (Schnitzer & Bongers, 2002.
However, when ivy reaches the canopy, its transpiration
rate probably increases, implying greater water requirements
than during the sterile understorey form which
grows in shaded conditions and in a more tempered
microclimate. Nevertheless, our data concerning the relationships
between ivy and oak crown development indicate
that an additional and significant competition for light
is established by the climbing liana.
In conclusion, it can be assumed that, after a cooperative
phase, the subsequent development of ivy involves
light and/or root competition to the detriment of host
trees, whose survival in the most severe cases can even be
threatened. According to these results, changes in the traditional
use of resources in the Monte Carcaci Nature
Reserve have given rise to new situations that must be
accurately considered in the future forest management,
especially in protected areas. The definition of control
measures is nonetheless quite problematic. Undoubtedly,
it would be quite simplistic to consider the current ivy
diffusion at Monte Carcaci as a menace for forest ecosystem
equilibrium. Moreover, cursory removal by cutting
away ivy may be inappropriate since, once establi-
ecologia mediterranea, tome 29, fascicule 1, 2003, p. 5-14
shed, woody lianas are extremely resistant to eradication
due to the strong capacity for reiteration (Oldeman, 1990).
Nevertheless, experimentations involving ivy suppression
on highly invaded trees could be carried out with the aims
of observing the liana re-growth patterns as well as to
investigate the consequences of suppression on possible
subsequent growth release of the host oaks. A continuous
monitoring of forest dynamics should indeed be necessary
to better understand the place and the role of lianas
in both forest dynamics and biodiversity, so to optimise
intervention procedures within the future forest management.
ACKNOWLEDGEMENTS
We are grateful to the General Direction of the Forest
Property Administration of the Sicilian Region (AFDRS),
and in particular to Dr. Luciano Saporito, for allowing
this research to be conducted. Appreciation is due to the
Forest Administration woodcutters for their assistance in
collecting sample data and material in the field. We are
also indebted to Dr. Vittorio Garfì, Dr. Salvo Pasta and
to an anonymous referee for their useful comments on
earlier versions of the manuscript.
References
BADRE B., NOBELIS P. & TRÉMOLIÈRES M., 1998. Quantitative
study and modelling of the litter decomposition in a European
alluvial forest. Is there an influence of overstorey tree species
on the decomposition of ivy litter (Hedera helix L.)? Acta
Oecol., 19: 491-500.
BEEKMAN F., 1984. La dynamique d’une forêt alluviale rhénane
et le rôle des lianes. Colloques phytosociol., IX, Les forêts alluviales,
Strasbourg, 1980 : 475-501.
BORING L.R., MONK C.D. & SWANK W.T., 1981. Early vegetation
of a clear-cut southern Appalachian forest. Ecology, 62:
1244-1253.
BRULLO S., SCELSI F., SIRAGUSA G. & SPAMPINATO G., 1996.
Caratteristiche bioclimatiche della Sicilia. Giorn. Bot. Ital.,
130: 177-185.
DILLENBURG L.R.,WHIGHAM D.F.,TERAMURA A.H. & FORSETH
I.N., 1993. Effects of vine competition on availability of light,
water, and nitrogen to a tree host (Liquidambar styraciflua).
Am. J. Bot., 80: 244-252.
FIEROTTI G., 1988. Carta dei suoli della Sicilia – scala 1:250 000.
Regione Siciliana, Assessorato Territorio e Ambiente, Palermo.
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