Calciphyllous Plant

Eastern redcedars are often considered calciphyllous, or lime-loving, because of their appearance as virgin stands in the limestone-derived soils of the cedar glades of Tennessee and the limestone outcrops of the Arkansas Ozarks. Other junipers, as those in the calcareous soils of the Cedar Brakes of the Texas Hill Country, also suggest this ecological relationship.

While calcareous, or high pH, soils influence the occurrence of redcedar, the species also influences the pH of the soil. The tree does not necessarily prefer limestone-derived soils, even though there is a direct relationship between the occurrence of the species and such sites. Often redcedar is the earliest invader in acidic old fields where soils are so devoid of alkaline minerals that the pH is as low as 4.7. In those soils the trees grow well. Grasses may provide the ground cover where limestone underlies a thin soil mantle. Surrounding these grassy openings, and on less-calcareous soils, redcedars occur.

Figure 3.9 Ashe juniper in the Texas Hill Country at the western edge of the southern forest (some may chart the zone as the eastern periphery of the western forest). Older stands (left) in the high-pH soil provided fence posts, charcoal, and cabinet lumber for pioneer settlers. Naturally regenerated "brakes" (right) followed post-World War II exploitation of vast areas for fencing material exported beyond the region. Larger stems are exploited for the fragrant oil that is marketed for perfume in France.

Figure 3.9 Ashe juniper in the Texas Hill Country at the western edge of the southern forest (some may chart the zone as the eastern periphery of the western forest). Older stands (left) in the high-pH soil provided fence posts, charcoal, and cabinet lumber for pioneer settlers. Naturally regenerated "brakes" (right) followed post-World War II exploitation of vast areas for fencing material exported beyond the region. Larger stems are exploited for the fragrant oil that is marketed for perfume in France.

Presence of the juniper raises the pH by as much as one unit, due to the leaching of calcium oxide from the fallen and decaying redcedar foliage. Assuming complete decomposition of litter, the acid-neutralizing power of redcedar foliage is twice that of a legume cover and five times that of loblolly pine. Throughout the South, sampled soils under redcedar crowns and just beyond the crowns note this difference in soil pH.

Theorizing the pH was not dissimilar prior to the germination of the conifer seeds, the roots of the redcedar "forage" for calcium at considerable depths and well beyond a tree's crown. The roots absorb calcium, the tree concentrates it in the foliage and, upon needle fall and decay, includes the element in the inventory of cations in the soil. Continual adsorption and recycling further concentrate the element and raise the pH of the soil's surface horizon higher.

The species also favorably affects soil physical properties, probably because of the attraction of earthworms and other macro- and microfauna to the nutrient-rich soil. Activity by these animals alters soil structure. This enhances water infiltration and percolation by increasing soil pore volume (air and water space) about threefold and permeability 20 times that of pine sites adjacent to redcedar stands. Organic matter in the soil doubles, amounting to a difference of three tons of litter per acre. Thus, this species influences the site by increasing available calcium in the soil for the use of plants, as well as by raising the pH.

The presence of junipers also increases soil porosity, thereby improving aeration and water retention in the ground. Infiltration of rainfall improves as soil volume-weight diminishes. (Volume-weight is the weight of the mineral and organic matter in a specific volume of soil.30 )

The lower weight for a given volume of soil occurs because the ground contains a greater amount of organic matter. Aeration consequently improves and cation-exchange capacity increases. This suggests that the greatest use of forests of redcedar may be to protect watersheds. The land's capacity to store rainwater or snowmelt and, thus, reduce runoff and soil loss is enhanced.31

The ability of redcedar to survive and grow under droughty conditions involves a relationship between root development and transpiration—transpiration, and hence water consumption, increases as the ratio of root surface to leaf surface increases. Consequently, greater root growth compared with foliage growth causes sites to seem more xeric than they actually are. Tree mortality overcomes this situation, enabling increasing amounts of moisture to accommodate transpiration demands for the lesser amount of foliage. Gradual mortality maintains this shade-intolerant species in pure stands on most sites.

While these conifers may exist in pure stands, they often mix with broadleaf species, and sometimes the hardwoods capture the site to the exclusion in the biome of the coniferous species. Thus, we now consider these competing deciduous trees.

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