Scrub, a major upland system, occurs on approximately 1,600 hectares (ha) of KSC. This xeromorphic shrub community occurs on infertile, well-drained, sandy soils and is dominated by clonal, evergreen oaks. Ericads and S. repens (saw palmetto) also are prevalent species in Florida scrub. This system is pyrogenic and adapted to high-intensity, stand-replacing fires. The soils supporting scrub vegetation are excessively to moderately well-drained sand and are extremely nutrient-poor.

Four types of scrub communities are present on KSC: sand pine scrub, oak and oak-saw palmetto scrub, scrubby flatwoods, and coastal strand and scrub. Oak and oak-saw palmetto scrub are the most abundant community type (909.2 ha), occurring mainly in the inland portion of Merritt Island on well-drained, acidic soils that are low in nutrients and dominated by shrub species that resprout after fire. This typically includes three evergreen oaks (Quercus chapmanii, Q. geminata, and Q. myrtifolia), S. repens, and ericads (Lyonia ferrigenea, L. fruticosa, L. lucida, and Vaccinium myrsinites). Herbaceous species are not a major component of oak-saw palmetto scrub on Merritt Island.

Oak-saw palmetto scrub was subject to at least 20 years of fire suppression on KSC until prescribed burning was initiated in 1981. Active restoration of scrub habitat was begun in 1992. This restoration includes prescribed burning and, on the more overgrown sites, mechanical treatment followed by prescribed burns. Scrub at KSC and the Merritt Island National Wildlife Reserve (MINWR) is managed for structural characteristics that benefit the threatened Florida scrub-jay (Aphelocoma coerulescens), which include keeping the height around 1.7 meters and maintaining sandy openings. Scrub at KSC/MINWR was found to grow more quickly than at other locations, and the number and size of openings greatly decrease by 3 years postburn. Therefore, the fire return interval for scrub at KSC/MINWR needs to be no longer than 10 years.

Long-term studies to determine how management regime affects species composition and structure of scrub are continuing. However, this was the first study to examine whether a species physiological response was altered by management regime (prescribed burning, mechanical treatment, and fire suppression). Ten physiological parameters were measured on three individuals of eleven scrub species at three prescribed-burn plots, three mechanically treated plots, and three fire-suppressed plots.

Management regime did not affect a species physiological response (figure 1). Similar relationships were found among all management regimes. Species responses did not vary among the three management regimes. For example, the carbon-to-nitrogen (C:N) ratio for Galactia elliottii and Smilax auriculata remained low (20 to 30) regardless of management regime, while the oaks and S. repens maintained C:N in the range of 30 to 40. This does not mean that management regime has no impact on the scrub system – ecosystem function (e.g., water exchange with the atmosphere) is determined by both the physiology of the different species or groups of species and the ecosystem composition of those species along with the total amount of transpiring leaf area. Although physiological responses of a particular species remain the same among the management regimes, species composition does not. Compositional changes with altered management are not unusual because management regime often acts as a disturbance on the system, and disturbance may be associated with a change in composition. Therefore, management regime has possible implications on ecosystem functioning in terms of carbon and nitrogen in water:

• In mechanically treated scrub, S. repens returns to only about 50 percent of its preburn cover, whereas the regrowth of trees and shrubs is similar to that of burned scrub.
  - S. repens is unique among the scrub species in its physiological response.
  - Loss of a large percentage of S. repens may lower the amount of carbon gained per water lost for the system, particularly if the loss of S. repens is not associated with a change in cover of the other functional groups.