Field germination and establishment characteristics of redberry juniper



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Texas Tech University


Field establishment of Pinchot juniper (Juniperuspinchotii Sudw.; Cupressaceae) was assessed for seed produced by a west central Rolling Plains population in 1997. To test the hypotheses that Pinchot juniper establishment is either episodic or continuous and requires either high or low light intensities and precipitation, seeds were planted at the surface of native soils then treated with or without shade and water supplementation. Seed fill was found to be 44% with 100% embryo viability at the time of planting. After a two year period in native soil with water and shade manipulations, less than 1% of the seeds planted had germinated and established. Seeds that were planted but did not produce seedlings were recovered and it was found that none had germinated, seed fill was 14.8%, and embryo viability was 72%). These findings do not assist in understanding the increases in density and distribution of Rolling Plains Pinchot juniper populations that is believed to have occurred in some areas since the 1940's decade. However, low seed germination can be partly explained by low seed fill and decreasing viability.

Two techniques were evaluated for their efficacy to unconditionally determine the fill status of Pinchot juniper seeds collected from a west central Rolling Plains population. Seeds were placed in water and separated into groups that sank and floated. The fill status of the two groups was determined by opening and visually inspecting the contents of 1000 seeds from each group and by viewing x-ray films of 1935 seeds that sank. Though more filled seeds sank than floated (x^2 = 313.72, p<0.05) and the number of filled seeds observed in opened versus x-rayed seeds did not differ (x^2 = 1.2281, p> 0.05) approximately 30% of seeds that sank were not filled. This error can be attributed to the thickened coats of empty seeds that sank. X-ray of seeds that sank resulted in unequivocal identification of filled seed. Using this combined technique, the seed fill status of three Pinchot juniper populations of the Rolling Plains and one of the Trans- Pecos was assessed. The findings were used to support the hypothesis that Pinchot juniper as a taxon produces empty seeds.

Pinchot juniper seeds and seed cones were exposed to grass fires in groups simulating naturally occurring surface and subsurface seed banks. Seed survivorship was documented and numbers of seedlings produced from surviving seed compared to those produced from untreated seed. Naked seed survivorship was 42% for surface banks and 75%) for subsurface banks. Fifty-four percent of seed cone banks survived and there were no differences in the numbers of seedlings produced from them and untreated seed. Significantly more seedlings were produced from seed cone, subsurface, and untreated seed banks than from surface naked seed banks. More seedlings were produced from subsurface banks than from untreated seed suggesting that heat shock, combustion products, or both may stimulate germination of Pinchot juniper seed.

Pinchot juniper sprout rooting ability was evaluated following their mechanical dislodgement from the shrub basilar meristematic tissues of a random sample of a west central Rolling Plains population. The objectives of the evaluation were to determine if dislodged sprouts are capable of producing adventitious roots and establishing as individual plants. Twenty-five sprouting shrubs were slashed then top removed with chain saw cuts and random samples often dislodged sprouts from each shrub were placed on gravel and soil and watered monthly on a single bench in the greenhouse. All of the sprouts placed on gravel died within six months after dislodgement. Ninety-eight of the sprouts placed on soil survived and of them 22 produced adventitious roots and established as independent plants. It appears that mechanical manipulation of shrubs can result in sprout dislodgement and if dislodged sprouts are dispersed to a microsite with access to soil and water they can establish as independent plants. Best management practices would suggest that mechanical manipulation of Pinchot juniper be deferred or followed by pyric treatment within one year of slashing or top removal to kill dislodged sprouts.

Pollen DNA of four populations, three representing the northern most to southern most distribution of Pinchot juniper in the Rolling Plains and one from the Trans-Pecos, Texas, were used to evaluate the feasibility of using random amplified polymorphic display (RAPD) to distinguish populations. The PCR products of five universal random 10-mer primers were documented and scored. Though it cannot be ascertained with the data obtained in this study what the polymorphisms detected are responsible for in terms of life history, metabolism, or reproductive efforts, having knowledge that they exist suggests that treating all populations of Pinchot juniper similarly in control efforts may be inappropriate. Until polymorphism data can be converted to genetic marker data, it may be provident to treat different populations differently by testing treatments and assessing response before instituting large scale manipulations.