Christmas tree cultivation has shifted toward the production of higher-quality trees, increasing land quality expectations as well. Indeed, some species of tree, such as the Fraser fir, are unable to grow on low-quality, marginal farmland. Flat or gently rolling land is preferred to that with steep slopes and inclines, which is prone to erosion and fluctuations in fertility. Noticeable obstructions, such as rocks, fences or significant underbrush, are also undesirable. Like all crops and plants, Christmas trees require a specific set of nutrients to thrive. There are 16 elements crucial for growth; of those, three are obtained through air and water: hydrogen, carbon,
'The All-Species Living Tree' Project species. The tree was created by maximum likelihood analysis without bootstrap: consequently accuracy is traded off for size and many phylum level clades are not correctly resolved (such as the Firmicutes). (Eukaryotes not present in analysis). This 16S rRNA-based phylogenetic tree is based on the ARB-SILVA release LTPs 121 (June 2015) and contains all type species with validly published names. 'The All-Species Living Tree' Project 'The All-Species Living Tree' Project is a collaboration between various academic groups/institutes, such as ARB, SILVA rRNA database project, and LPSN, with the aim of assembling a database of 16S rRNA sequences of all validly