Deep Sand 25-32 PZ

Description

The Savannah State is the reference state. The information was taken from a Range Site Description, approved 3-11-1987.
The plant community is a post oak and blackjack oak dominance with noticeable absence of little bluestem. The woody cover makes a 40 to 60 percent canopy cover. A few tallgrasses occur in the scattered open areas. Forbs, legumes, woody vines and shrubs add to the variety of the historic plant community.

Relatively frequent fires (7-12 year mean fire return interval) (Frost 1998) maintained the open areas by minimizing shrub cover that was not yet to a fire resistant height. Mature single stemmed hardwoods were long-lived and resistant to ground fires.

Fires were natural or human-induced. When fires were frequent on the savannah, most fires burned only the understory, leaving mottes of trees. Even with proper grazing and favorable climate conditions, a long time lack of fire or brush management will allow trees and shrubs to increase in canopy to reach the 60 percent level that indicates the shift to the Woodland State. This transition is not so much dependent on degradation of the herbaceous community as on the lack of some form of brush control and the reduction in fire. Once the site had dense tree cover, the site would be resistant to fires and a very resilient woodland community would develop. Grazing management alone cannot maintain the site in the Savannah State. The Savannah State always has potential for shrub dominance without fire. Mann (2004) discussed the importance of human induced fire as an important factor in maintaining open grasslands before European settlement. A major role of grazing management is to build and preserve fine fuel to carry maintenance fires.

Brush control can play a similar role that natural fires played pre-settlement. However, it is difficult to manage in an ecological and economic matter on a small scale, as this site is rapidly repopulated by shrubs and trees without fire or brush management. Brush control may be prescribed fire, mechanical, chemical or biological control, or targeted grazing (generally by goats, although some instances exist in the Central Basin where exotic wildlife species or overpopulated white-tailed deer reduce woody cover). There are examples of this site being maintained as a savannah with introduced hay meadows and mottes of trees.

Total annual production varies from 1800 - 2700 air-dry pounds per acre depending upon growing conditions.

Submodel

Description

The Woodland State is characterized by trees, a significant shrub cover, and a shortgrass- understory having over 60 percent woody plant canopy, dominated by hardwoods and shrubs.

The Woodland State loses its savannah appearance with native shrubs beginning to fill the open grassland portion of the savannah. Shade from overstory is the driving factor. This community results from the lack of effective brush control. Production of the overstory canopy has increased by a similar amount to the decrease in herbaceous production. Unpalatable woody species have increased in size and density. Without brush control, tree canopy will continue to increase until canopy cover approaches 80 percent.

Ground cover and herbaceous production beneath shrub canopies is minimal, but soil organic carbon and nitrogen levels are enhanced.


In this State, annual production is dominated by woody species. Goats and deer can find fair food value if browse plants have not been grazed excessively. Forage quantity and quality for cattle is low. Over-browsing coupled with the shading effect of the overstory will result in a visible browse line.

Intensive treatment is required to affect restoration back to the Savannah State (1.0). Prescribed burning may not be possible until the woody cover is reduced by herbicides or mechanical treatments to the point that grasses (fine fuels) can establish. Brush treatment tends to be short-lived. Observation shows that even effective treatment will require constant maintenance to suppress brush reestablishment. Without maintenance, canopy cover may exceed 30 percent in 3 to 5 years.

Description

The Converted Land State occurs when the site, either the Savannah State (1.0) or Woodland State (2.0), is cleared and plowed for planting to cropland, hayland, native grasses, tame pasture, or use as non-agricultural land. The native component is usually lost when seeding non-natives. Even when reseeding with natives, the ecological processes defining the past states of the site can be permanently changed. Agronomic practices are used typically with non-native forages. Cropland and tame pasture require repeated and continual inputs of fertilizer and weed control to maintain the Converted State.

Common introduced species include hybrid bermudagrass, Kleingrass, Wilman lovegrass, and Old World bluestems (Bothriochloa spp.). Newly seeded stands are prone to invasion by annual and perennial weeds and woody plants, so proper grazing and brush/weed management are required for their maintenance. The rate of woody plant re-establishment will depend on the brush management practice initially used to clear the site, seedbed preparation technique, proximity to undisturbed shrub stands and the rate of livestock and wildlife transporting seeds.

Stands seeded to native grasses are also susceptible to invasion by non-native, aggressive pasture grasses such as King Ranch bluestem and seeded bermudagrass. These exotic species, while providing forage and soil stability, may be very difficult to eliminate once established.

Production of these introduced forage grasses may exceed that of native grasses when fertilized. However, the extent to which introduced grasses provide better forage than native grasses is debatable, especially when their adverse effects on wildlife are taken into account. Conversion of introduced pasture back to native grassland is difficult and typically requires aggressive and costly management intervention. Given the potential adverse long-term effects of exotic grasses on native grassland flora and fauna, their use should be critically and carefully considered.