Investigating potential altitudinal-environmental variation on recruitment, regeneration and re-establishment of Juniperus seravschanica in Northern Oman

Juniperus seravschanica is a keystone species within the northern mountains of Oman. The species appears to be declining in the area, particularly at lower altitudes, with little regeneration being recorded. Alterations in temperature and moisture availability due to climate change could be main responsible for this decline. The main aim of this research is to identify causes of decline and suggest viable conservation strategies that may have wider application for tree conservation in this region. Surveys indicate considerable foliar dieback of trees at lower altitudes (< 2500 m) with healthy trees limited to cooler (high altitude) or high moisture sites (wadis and depressions). A lack of juvenile trees indicates inadequate recruitment and highlights conservation concerns. Trees growing at low altitude had low growth rates compared to mid-altitude trees. Trees at low altitude produce fewer seeds and these have a lower proportion of viable, embryo intact seed (9%) with a low germination capacity. In controlled conditions, reducing irrigation below optimum reduced growth, even under optimal temperature. In field studies, seeds and young trees, 2 and 5-year-old, were planted at selected altitudes, Low (2220 m), Mid (2300 m) and High (2560 m); the planted trees were maintained under differential irrigation regimes. Planting young trees were more successful than seed sowing when re-establishing plants in the wild. Age of transplant was important with 5-year-old trees showing greater survival (> 97%) than younger stock. Younger stock only succeeded when planted at high altitude or provided with regular artificial irrigation at low altitude. The availability of high soil moisture was important in maintaining tree viability at low altitude; however, in some locations heat stress too may be limiting plant viability and growth. Practical conservation that includes selecting genotypes with greater drought/heat tolerance and augmenting natural habitat with more mature nursery-grown trees is strongly recommended to avoid further loss of this species.