From Biophysical Suitability to Planning-Relevant Rubber Land Evaluation in Hilly Central Vietnam: Evidence from Current Land Use and Fresh Latex Yield

This study evaluated the planning relevance of biophysical land suitability for rubber plantation in a hilly landscape of Central Vietnam. A GIS-based square-root parametric method calculated a land suitability index (LSI) using elevation, slope, annual rainfall, soil depth, soil texture, and soil type. LSI values ranged from 0 to 77.67. Highly and moderately suitable land covered 38.79 ha (0.31%) and 3986.01 ha (31.83%), respectively, with soil depth and texture as important constraints. Overlay with the 2023 land-use map showed that biophysical suitability did not directly indicate practical land availability. Planted forest occupied 38.16 ha, or 98.38%, of the highly suitable class, and no existing rubber plantations occurred in this class. In contrast, 49.27% of existing rubber plantations occurred in the moderately suitable class. After excluding planted forest, paddy rice land, and existing rubber plantations from the 4024.80 ha classified as highly or moderately suitable, only 251.46 ha remained in unused land and annual cropland for further assessment. Data from 45 PB260 plantations showed a positive association between LSI and fresh latex yield after adjustment for the other variables in the multiple regression model, with an adjusted partial regression coefficient of 2.09 kg ha−1 year−1 per LSI unit (p = 0.016). Thus, suitability maps should not be used as expansion maps without considering current land use, practical land availability, and plantation performance.