Morphology, ecophysiology, and seedling establishment for Fouquieria splendens in the northwestern Sonoran Desert

Seedling establishment for Fouquieria splendens required shading provided by a nurse plant or rock and local water accumulation; an establishment pulse apparently occurred 7 years before this study. It prefers east- or northeast-facing slopes, underscoring the importance of water availability. The mean depth for young roots was only 19 cm. Its leaves had a high mesophyll surface area per unit leaf area (64) and a moderate stomatal frequency (153 mm−2), leading to a net CO2 uptake rate that increased with light level and was up to 13 μmol m−2 s−1. The number of plants per 0.5-m height interval was fairly constant up to 5 m, with the maximum height over 6 m. Stem decay, which was accelerated by termites, removed dead plants in 5–6 years. F. splendens was highly sensitive to low temperatures, which affects its upper elevational limit, but was extremely tolerant of high temperatures, especially its stems. Although leaves were produced multiple times per year in response to rainfall, nodal extension of stems does not occur every year and was highly correlated with the number of stem rings. Based on the number of nodes along the longest stems and years with adequate rainfall, its maximal age was about 100 years, consistent with photographs taken 27 years apart.