A review on decline of Pinus halepensis Mill., (1768) in urban and semi-urban areas of Quetta: Preconditions and signs

Abstract

Pinus halepensis Mill., (Aleppo or Jerusalem pine) is a drought-tolerant tree native to the Mediterranean region and widely introduced in arid and semi-arid habitats, including Quetta, Pakistan. This study investigates the ecological adaptability, morpho-physiological responses, and current decline in the urban and peri-urban landscapes of Quetta. The species shows strong resilience through various characteristics such as deep rooting, serotinous cones, and physiological plasticity, while key factors responsible for its decline include irregular rainfall, extreme heat, prolonged drought conditions, urban heat island effects, soil compaction, pest infestations, secondary pathogen invasion, and limited forest management. Visible morpho-physiological signs, such as chlorosis, premature needle fall, dieback, discoloration of needles, and reduced growth, are observed in urban Aleppo pine trees of Quetta, and the lack of research on the species further intensifies the problem. A structured narrative review was conducted using systematic search and screening procedures, following PRISMA-inspired guidelines to ensure transparency, reproducibility, and thematic synthesis of 130 selected studies. This review recommends monitoring and management practices based on scientific procedures such as chlorophyll content and fluorescence, biochemical assays of proline, dendrometric investigation, deep watering irrigation, the use of biofertilizers, and integrated pest management, and also emphasizes the need for multi-stakeholder collaboration in ensuring and implementing effective urban forestry planning. The introduction of targeted conservation scientific strategies and sustainable urban forestry policies can significantly enhance the resilience and long-term health of Aleppo pine during the ongoing climate crisis and global warming.