Protection Management, Nurse Plants, and Diversity of Companion Species Influence Natural Regeneration of Pinus gerardiana in the Western Himalayan Pine Forests

ABSTRACT

Protection strategies, nurse plants, and abiotic factors affect the natural regeneration of tree seedlings. However, their interactions have been less considered in restoration and management programs. We assessed the impacts of nurse plants, diversity of companion species, and soil factors on the density of Pinus gerardiana seedlings under different protection levels in the alpine pine forests of the western Himalayas in Afghanistan. We selected three sites with different protection strategy levels (low protection (LP), medium protection (MP), and high protection (HP)). Three macro‐plots were established in each site; then, 10 × 10 m ² quadrats were established within the macro‐plots to quantify woody species. Then, three 1 × 1 m ² quadrats were established within 10 × 10 m ² quadrats to measure herbaceous species. Soil factors were collected within the quadrats. In each site, some dominant woody species were selected as nurse species, and the area beneath their canopies was sampled using 0.5 × 0.5 m ² quadrats and the same number of quadrats in open areas to assess the density of pine species without the effects of woody species. Linear mixed‐effect models and variation partitioning analysis were performed to assess the effects of the predictors on pine density. The density of pine exhibited a direct relationship with the presence of nurse species, particularly in HP and MP sites. A negative correlation was found between the diversity of companion species and pine density in LP and MP sites, whereas a positive effect of such diversity was found on pine density in the HP site. Phosphorus and sulfur were identified as primary soil factors influencing pine density in HP and MP sites, while organic carbon and pH were important to explain pine density in the LP site. Overall, the diversity of companion species, nurse plants, and soil parameters significantly affected the density of pine. However, their effects were overshadowed by management strategies.