By A. R. Croft, Ranger Naturalist
AT BURRO SPRING, on the Tonto Plateau, 3500 feet below the South Rim of Grand Canyon, there is a large Pinyon Pine (Pinus edulis) that has probably not produced a single mature seed during its entire lifetime, and its age must be more than two hundred years. This tree is located a considerable distance below the natural range of its kind and probably has been able to grow to maturity in its desert habitat only because of its favorable location----in an arroyo fed by occasional showers.
The only evidence that female flowers are produced on this tree is the presence of scaly, cone-like structures which resemble the fruit of the Alder. These are modified female cones which apparently are unable to mature in a normal fashion because of adverse climatic conditions -- probably excessive heat and lack moisture.
The condition of the "Burro Spring" pine is probably not characteristic of all trees of this species at their extreme lower limit in this region. Very noticeable, however, is the fact that fruit is by no means typical under such conditions and is much reduced in quantity.
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