Part I
Giant sequoia trees grow in Sequoia National Park in California. Individuals of Sequoiadendron giganteum are the largest living organisms on Earth, at least by volume. Tree height can exceed 85 m, and trunk diameters of more than 8 m are documented. Giant sequoias are also among the oldest organisms. Some trees have been able to withstand all biotic and abiotic stresses for more than 3000 years, demonstrating an amazing degree of resilience. Surely they survived many extreme weather events such as strong frost, heat, drought, or storms, causing loss of branches and defoliation. Still, Sequoiadendron giganteum occurs only in scattered groves with humid climate and dry summers along the western Sierra Nevada at elevations between around 1500 and 2000 m. At this altitude winter temperatures are not too low and enough soil moisture remains available during the summer drought. Reproduction of sequoia trees is dependent on fire. Seed germination is stimulated by fire, and seedling development can only proceed in the absence of competing vegetation. Mature trees are protected from fire by a thick bark (note the fire scars on the left and right) and elevated canopy. (Photo: Stephan Clemens)