Authors: Pietro Piussi, Maurizio Teobaldelli (Partner 1)
The effects of water salinity and coastal erosion on function and growth of pine forests in the Maremma Regional Park was analysed. Starting from previous studies reporting the presence of a reduced health status in the pinewood of Alberese, they analysed the problem of the stability and primary productivity of coastal pine forests.
The questions were: What are the environmental parameters which drive such functional responses? Possible candidates have been: coastal erosion, altitude, water table depth, water table salinity, management and stand age. What is the impact of human activities on these environmental variables? What is the state of vegetation?
Primary productivity was analysed using as descriptors: LAI and light interception, and leaf structural characteristics. Environmental factors were analysed using a meteorological station, monitoring of water table (salinity and depth), soil analyses (organic matter, salinity, etc.), and GIS analysis (coastal erosion, DEM). Function and growth of pine forests were studied using GIS (vegetation map, NDVI), dendroecological analysis and needle length analysis. Water use by the plants was monitored through Relative Water Content, Oxygen Isotopic analysis, Sap flow measurement. Seven transect have been positioned using a GPS, 23 wells of 2 m depth, have been installed on transects 1 to 6 orthogonal to the coast-line and transect n. 7 parallel to the Monti dell’Uccellina. In each transect the following measures were taken: length of around 100-200 needles of Pinus pinea collected in the ground on July 2003, Water- table depth on May and July 2003, Water Table Electric Conductibility on July 2003, and the percentage of salt in the soil from 0 to 200 cm depth. In transect 1, 2, 4 and 7 measures were taken of: the percentage of Organic Carbon in the soil from 0 to 200 cm depth, Relative Water Content of wood core, and Pinus pinea wood-cores yearly increments. The environmental analysis showed : 1) Sandy soils, 2) High permanent water table level, 3) High concentrations of sea salts in water table, 4) Maximum Electric Conductibility values in summer. GIS were used to show water table depth and water table conductibility, spatial change in different seasons and coastline change over time, compared with the vegetation map of the different pine tree species (Pinus pinea and Pinus pinaster ). Normalized difference vegetation index was analysed using SPOT satellite image. A dendroecological analysis has been developed to determine the relationships between climate (temperature and precipitation) and radial growth, separately for earlywood and latewood; 128 wood cores were taken from 64 trees. Three series were identified: 1) TOT= total annual increment, 2) EAR= earlywood and 3) LAT= latewood. For the dendrocronological analysis a Controlled Computer Tree Ring Measuring Device was used (Aniol, 1987 + software CATRAS); the Dendroclimatological analysis used Arma techniques, Response Functions and Bootstrap methods. The comparison between transects gave following results: Maximum Electric Condictibility values (33 dS/m) had been measured on transect n.1 near the Ombrone mouth; Some inland plots showed high value of Electric Conductibility. This is due presumably to the dune and inter-dune morfology and/or to the lower altitude on the sea level. The transect 6 and 7 showed lower values of Electric Conductibility due to lateral rainfall drainage from the hills. A generally increase of needles length was observed moving from the mouth of Ombrone river (high value of Electric Conductibility) to the inland. There is a good correlation with the altitude on sea-level of the plot rather than with the Electric Conductibility value. The analysis of relative water content made during May and July 2003 on Plots 2, 4 and 7 did not show statistical differences in relation with the distance to the sea or to the Monti dell’Uccellina. This is due presumably to variable water availability related to different root-system and soil condition. However, higher relative water content values have been measured along the transect 7 located near the Monti dell’Uccellina were pine trees receive lateral rainfall drainage from the hills. Stable oxygen isotopes have been used to detect soil water origin and the depth at which plants roots extract this water. In this study the stable isotopes of oxygen are used as natural indicators of the water present in the ecosystem (foliage, soil moisture, xylematic water) and of the water that penetrates, or could penetrate, the ecosystem (precipitation, sea, river).
Summarising, this study has analysed the influence of changes of the coastline, the salinity of the water table and the irregular rainfall regime on the growth conditions of the pine wood in three study sites located at different distances from the sea.
The results have shown that in the innermost area of the pinewood the groundwater table contains fresh water which represents a supply capable of satisfying the plant communities’ needs even during the dry season. In this site pine’s radial growth is not affected by precipitation, and is only slightly affected by temperature. In the area closest to the beach, the layer of rainwater which floats on the salty groundwater table does not dry up during the summer. The bad vegetative conditions of this stand are not, therefore, due to water stress, but to direct exposure to marine aerosols. The dendroecological analysis showed a weak response of radial growth to climatic agents which is typical of suffering trees. In the intermediate area, during the dry season the unsaturated parts of the soil undergo an increasing salinisation caused by the ebbing of the rain water in the soil and the capillary rising of the permanently salty ground water table. The vegetation doesn’t use salty water and therefore absorbs primarily fresh water from the thin layer of soil above the capillary fringe. The dendroecological analysis highlighted the positive influence of late summer and autumn rains on the production of latewood during the same vegetative season, and during the following season for the production of earlywood. It has been observed that both earlywood and latewood are influenced by climate; the latewood, however, is affected by the climate during the formation period, whereas earlywood is affected primarily by the precipitation taking place during the months preceding the start of the vegetative season. Pine transpiration greatly declined in the summer in correspondence with increases in surface salinity of the water table. Pines mainly used the fresh water stored at the top of the water table during the previous winter. When fresh water supplies were depleted, the pines drew from the underlying salty water with clear seasonal differences. Re-establishing of water availability, after a summer rainfall, allows the pines in both sites to show greater sap flow fluxes.