TRANSITION MATRIX ANALYSIS OF LAND-COVER CHANGE IN THE ACCRETION AREA OF THE LOWER DELTA OF THE PARANA RIVER (ARGENTINA) REVEALS TWO SUCCESSION PATHWAYS

摘要

Aerial photographs from 1978, 1990, and 1995 were used to measure historical land-cover changes in the accretion portion of the Lower Delta of the Parana River in Argentina. Six land-cover types were identified and mapped according to the dominant physiognomy: rushes, marshes, seibo forest, mixed prairies of woody and herbaceous plants, vegetated lagoons, and a human land-use category resulting from anthropomorphic intervention (willow and poplar plantations and tourist or recreational areas). The occurrence and magnitude of changes in cover were estimated through Kappa indices, and transition matrices were calculated in order to represent all possible changes that occur in the landscape. The study area had an increase in island surface of 11.75% from 1978 to 1995. Although the delta is in an active accretion phase, the results indicate that the landscape shows moderate to little changes in the time period analyzed (General Kappa: 1978-1990: 0.75, 1990-1995: 0.79). Rushes are pioneer colonizers of banks, which later give rise to marshes or woody and herbaceous prairies and forests. Marshes and forests are stable systems. The pattern of change in islands does not follow a one-way sequence; on the contrary, two main pathways were identified. In the time period analyzed, human activity increased substantially to the detriment of marshes and native forests. Quantification of landscape-change processes allowed us to construct a probability model of land-cover change and compare our results to the predictions formulated in previous vegetation studies based on plant community analysis.