(Acer campeslre L.). tree of heaven (Ailanthus altissima L.), Italian alder (Alnus cordata ... European beech (Fagus sylvattea L.), manna ash (Fraxinus ornus L.),.
ANNALI DI BOTANICA
Vol. LIV
1996
Mediterranean forest tree decline in Italy: relationships between drought, pollutants and the wax structure of leaves
E.
PAOLETTI*,
F.
BUSSOTTI**, P. RADDI*
... lstituto Patologia Alberi Forestoli - CNR Bi%gia Vegetale, LaboralOrio di Botanica Forestale. Universith di Firenze o l.niwIO Pato{ogia Albed Forestall· CNR PiaUtlle delle Cascine 28, 1·50144 FIDrence Italy· Tel, +39.55.360546 Fax. +39,55.354786 - E·mail raddi@csps/m.fi.cnr.il
** Dipartimento di
ABSTRACT· After presenting the situation of forest decline in Italy and analyzing the factors that play
a contributing role, tbis paper studies the response of the epicuticular wax structures and the stomata in ten broadleaf species and one conifer to fog-like treatments with acids andlor surfactants and to severe water stress. The main results are that wax structure alterations vary in intensity in the different species studied and that the microstructural alterations observed in field conditions cannot be attributed only to severe drought. since sample trccs put through water stress simulations do nol differ significantly from controls. In the artificial surfactant treatment, a positive relationship between structural damage to tbe stomata and transpiration suggests possible synergies between the effects of drought and those of pollutants in inducing stress conditions in Mediterranean vegetation.
KEY WORDS - Forest decline, acid rain, surfactant. water stress, Mediterranean species, wax structure
INTRODUCTION
Forest decline was defined as a disease of forest ecosystems (SchUtt, 1988), which includes a simultaneous and rapid decline in the health and vigor of both coniferous and broad-leaved foresIs with symptoms classified as growthdecreasing, abnormal growth and water stress. Recently, Skelly and Innes (1994) observed that the concept of a general forest decline, as described by SchUtt and Cowling (1985), is untenable and that forest decline is a complex problem involving a range of stress factors, including pollution, and argue that no single hypothesis can explain the forest decline phenomena observed in different locations on different species. Each species decline is characterized by a specific suite of symptoms. Moreover, crown transparency, the most widely used index of forest health in surveys, was recently considered non etiologically specific (Innes, 1993). Further, in Europe the parameters of defoliation and discolouration are calibrated on Picea abies, but this seems insufficient in the Mediterranean area (Cadahia et al., 1992). Forest damage assessments need more careful diagnostics and the use
166
of all the knowledge of the fields of forest pathology, entomology, stress physiology, silviculture before reaching conclusions about forest health. It is very difficult to evaluate the vigor of a tree with the classical morphological characters utilized now in forest surveys. Because of the great debate on the evaluation methodology of tree health, since 1988 our research has examined the wax leaf structures of trees in forest and of young stressed trees. Because the symptomatology of forest decline is often non-specific and similar to a generic response to stress, especially water stress, the main goal of our research programme was to artificially reproduce the alterations of the leaf wax structures by treatments with pollutants and by water stress actions and to compare among them the alterations caused by these two treatment types and those found in forest.
STATUS OF RESEARCH IN ITALY
Table 1 shows that the percentage of damaged trees has been continuously increasing from 1985 to 1991, both in the Northern, Central and Southern Italy. An analysis of the yearly survey reports carried out between 1987 and 1991 in Tuscany (Central Italy) along a vegetational transect including coastland Mediterranean vegetation (evergreen sclerophylla), sub-Mediterranean vegetation (deciduous oakwoods) and mountain Mediterranean vegetation (beechwoods), has allowed Bussotti el al. (1995a,b,c) to ascertain the following: I. the crown status is worse in the more markedly Mediterranean areas (coastlands) because of the influence of winds and sea aerosol, as well as the presence of large urban and industrial concentrations; 2. unlike mountain conifers (Abies alba and Pinus nigra), the crown status of Mediterranean pines is worse in the younger trees, probably because their reduced root system does not allow them to withstand water stress as well; 3. crown status is affected by the meteorological trends of the previous year, especially as far as total rainfall is concerned; 4. mountain trees (especially European beech) recover very slowly even when rainfall returns to abundant levels after a period of drought; 5. Mediterranean zone trees, on the other hand, react excellently to variations in the rainfall level and (especially Quercus ilex) appear to be more sensitive to low temperatures and to winter droughts than they are to summer water stress. The stress factors which affect the status of Italian forests are many and varied. An element frequently recorded is the acidification of precipitation (Pantani el aI., 1984, Cossu el al., 1989, Udisti el al., 1990, Fuzzi el al., 1990, MA, 1992), which occurs especially in winter months, although only rarely does the acidity reach values below the damage threshold as demonstrated experimentally (acid mist at pH < 3.5, e.g. Morrison, 1984). Among the gaseous pollutants, ozone is the most widespread and is frequently found in concentrations higher than the toxicity threshold for forest trees (50 f.lg m· 3; Bergmann, 1992). Damage caused by sulphur dioxide is closely related to proximity to industrial estates (Rosini and
167 TABLE 1 PERCENTAGE OF DAMAGED TREES IN TIiE WHOLE OF ITALY AND INS OMB REGIONS WHICH CARRIED OUT mElR OWN INVENTOR1ES BETWEEN
1985
AND
1991
1985
1986
1987
1988
1989
1990
1991
Alto Adfge Nonhem Italy
Td Ed
8.3 0.9
7.5 0.8
9.7 1.8
14.6 3.3
14.6 3.5
17.1 4.6
22.8 8.6
Trenlino Northern Italy
Td Ed
38.8 10.8
21.8 3.7
44.5 14.7
42.4 16,8
46.4 15.3
43.6 13.0
47.4 12,9
Frlull Northern Italy
Td Ed
55.7 17.4
55,2 17.6
55.4 15,3
74.4 33.8
74.8 36.1
77.1 34,8
78.2 33.2
Lombardla Northern I
