Seasonal and landform effects on plant productivity and carrying capacity at Bisha Rangeland, Saudi Arabia

Arid rangelands in Saudi Arabia face major management challenges due to pronounced seasonal variability and landform-related differences in vegetation productivity, necessitating science-based grazing strategies. However, the combined effects of these factors on plant biomass and livestock carrying capacity remain poorly quantified. To address this gap, this study investigated the individual and interactive effects of season and landform on vegetation productivity and livestock carrying capacity at Bisha-1 rangeland across four survey seasons (Autumn 2023, Spring 2024, Autumn 2024, and Spring 2025) and two landforms (valleys and plains). Highly significant differences were recorded among seasons in total palatable biomass ( p  −1 in Autumn 2023 to 215.84 kg DM ha −1 in Spring 2024, representing a 2.5-fold variation. Significant differences were also recorded between landforms ( p  = 0.007), with valleys exhibiting 20% higher total palatable biomass than plains. However, the season × landform interaction was non-significant ( p  = 0.810), indicating that seasonal patterns remained consistent across landform types. Palatable tree biomass was the dominant component, accounting for 70–80% of total palatable biomass across all season–landform combinations, whereas palatable shrub biomass made a smaller but seasonally variable contribution. Based on a standardized 90-day seasonal grazing model, livestock carrying capacity varied with season, ranging from 0.48 sheep units ha -1– 90 days -1 in Autumn 2023 to 0.72 sheep units ha -1– 90 days -1 in Spring 2024, representing a 1.5-fold variation, while landform effects on carrying capacity were secondary (valleys: 0.61 sheep units ha -1– 90 days -1 ; plains: 0.53 sheep units ha -1– 90 days -1 ) across the four seasons. These findings support seasonally adjusted stocking strategies, the conservation of palatable herbaceous and shrub components during periods of forage scarcity, and consideration of precipitation variability to sustain rangeland productivity in the Aseer region. However, interpretation of the estimated carrying capacity is limited by the single-site, four-campaign design and the absence of direct measurements of forage quality and animal utilization.