Altitudinal and slope gradients as key determinants of Robinia pseudoacacia growth.

Abstract

Robinia pseudoacacia is a major plantation species in northern China, yet quantitative assessments of its growth across topographic gradients remain limited. This study investigated the growth performance of R. pseudoacacia in relation to landform types (plains, hills, low mountains) and key topographic factors (altitude, slope) in Weifang, Shandong Province. Field surveys were conducted across 67 pure‑stand sample plots. One‑way ANOVA revealed that trees on plains had significantly greater mean diameter at breast height (DBH) and tree height than those on hills and low mountains. Linear regression showed significant negative correlations: DBH and height decreased by approximately 0.58 cm and 0.47 m per 100 m increase in altitude, and by 0.76 cm and 0.57 m per 10° increase in slope. Altitude explained slightly more variation (R² = 10.1-10.6%) than slope (R² = 5.5-6.8%). Allometric analysis indicated stable height-DBH scaling across landforms (ANCOVA, P = 0.776), with scaling exponents (b) of 0.59 (low mountain), 0.48 (hill), and 0.68 (plain). Our results quantitatively delineate growth patterns of R. pseudoacacia across topographic gradients, highlighting the strong association between gentle, low‑lying terrains and superior growth. These findings provide an empirical basis for site selection in afforestation projects, suggesting a preference for plain areas to enhance plantation productivity. Future studies should incorporate soil and microclimatic data to elucidate underlying mechanisms.