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Critical Factors During the First Years of Life of the Saguaro (Cereus Giganteus) at Saguaro National Monument, Arizona
Author(s) -
Steenbergh Warren F.,
Lowe Charles H.
Publication year - 1969
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.2307/1933696
Subject(s) - seedling , germination , biology , habitat , ecology , agronomy , cactus
Germination and establishment of the saguaro giant cactus were studied by periodic observations on natural seedling populations, seedling distribution within rocky, rolling hill, and flat terrain habitats, and field—germination experiments in the Sonoran Desert. As a result of bird, mammal, and insect activity, a very small percentage of seeds (<1 x 10 — 3 of the seed crop) remains on the ground until suitable conditions for germination occur during the summer monsoon. Germination begins after the start of summer rains in July and continues in August and September. The principal apical stem growth of seedlings takes place during these months, with a few plants exhibiting slight growth during favorable late winter and early spring months. Establishment of seedlings is limited primarily by frost, drought, rodents, and insects, which affect the differential survival associated with seedling size, microhabitat, and season. Initial high rates of seedling mortality drop sharply after the first year and are lowest for plants associated with microenvironments among rock outcrops. The large number of seeds germinated in the alluvial soils of the flat terrain habitats is offset by a higher seedling mortality there. In the rocky habitats more seedlings survive from fewer germinations. The significant difference is attributed primarily to the effect of the microhabitat upon the operation of the critical controlling factors listed above.