【Objective】Leaves are the fundamental biological organs for photosynthesis，serving as the central hub for plant energy acquisition and material exchange. Their functional traits provide key，measurable indicators of a plant’s ecological strategy and its inherent capability to adapt to various environmental constraints. This is particularly true for pioneer tree species in the Karst region，whose leaf traits provide critical insights into their response and adaptation to regional environmental changes. To thrive in the unique Karst environment，characterized by drought-prone，thin soils，pioneer species have developed distinct leaf functional traits. These include variations in leaf size，thickness，stomatal density，and biochemical composition，which directly influence photosynthetic efficiency，water regulation，and stress tolerance. Systematically analyzing the variation and patterning of these functional traits of pioneer species across various environmental conditions in the Karst region can reveal their specific ecological strategies for survival and growth under severe environmental stress. Furthermore，studying these leaf functional traits provides a valuable tool for monitoring ongoing environmental changes within the Karst area.【Method】In this study，we focused on Pyracantha fortuneana，a crucial pioneer tree species widely distributed throughout the Karst region of Guizhou Province. A comprehensive dataset of 8 120 leaves was collected from 406 P. fortuneana individuals across 93 representative field sample sites. Six specific morphological functional traits were measured and calculated for each： leaf dry weight（LDW），leaf length-to-width ratio（LLW），thickness（LT），leaf area（LA），specific leaf area（SLA）and leaf dry matter content（LDMC）. Concurrently with plant sampling，environmental data were collected. Soil samples from the 93 sites were analyzed to measure soil organic carbon（SOC），total nitrogen（TN），and total phosphorus（TP）contents. Meteorological factors collated included annual mean temperature（MAT），annual average precipitation（MAP），and annual average sunshine hours（ANS）. To explore the characteristics of trait variation and their specific environmental regional，the gathered data were subjected to advanced statistical analysis，including Pearson correlation analysis，linear regression modeling along environmental gradients，and variance partitioning（VP）analysis（hierarchical segmentation analysis）.【Result】The results of this study revealed four main findings regarding the leaf functional traits of P. fortuneana on a regional scale：（1）The coefficient of variation（CV）for the six morphological leaf functional traits ranged from 10.04% to 30.16%. Specifically，leaf dry weight（LDW）showed the largest variation（30.16%），while leaf dry matter content（LDMC）showed the smallest（10.04%）. This overall small degree of variation indicates the high stability and strong inherent adaptability of P. fortuneana to the Karst environment.（2）Significant and often inverse correlations were found among the functional traits. Specifically，LDW was found to be highly positively correlated with LT，LA and LDMC（P < 0.001），but highly negatively correlated with leaf length-to-width ratio（LLW）and SLA（P < 0.001）. Similarly，LT exhibited a significant positive correlation with LA and LDMC（P < 0.001），and a negative correlation with LLW and SLA（P < 0.001）. Indicating that there are different correlations and trade-offs between functional traits of P. fortuneana leaves.（3）Clear trends were identified in response to the major geographic variable，altitude. As altitude increased and annual mean temperature decreased，P. fortuneana adapted by increasing its leaf aspect ratio（LLW）and specific leaf area（SLA），while concurrently reducing its leaf dry weight（LDW），leaf thickness（LT），and leaf dry matter content（LDMC）.（4）Variance partitioning analysis determined that altitude was the primary influencing factor driving the regional variation in leaf functional traits，with the explanation rate for the observed trait variation rate for the observed trait variation being consistently higher than 35%.【Conclusion】The evolution of a sophisticated suite of leaf functional traits in P. fortuneana represents a key survival strategy against the typical intermittent drought of Karst areas，with these coordinated morphological and physiological adjustments significantly improving water-use efficiency and resource conservation. Furthermore，the strong influence of altitude on these trait patterns demonstrates the critical role of environmental gradients in shaping the phenotypic plasticity and evolutionary adaptation of this pioneer species within the complex Karst ecosystem. Our results reveal the adaptive characteristics of the functional traits of the leaves of the pioneer species P. fortuneana to Karst habitats at a relatively large scale，which is helpful for understanding the impact of regional scale environmental changes on plant variation and providing a reference for plant selection in karst vegetation restoration.