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Canopy ManagementAfter selecting a site, the first restoration step is to thin the number of trees per acre, or basal area, to the desired target number. Basal area is used to describe the average amount of an area (usually an acre) occupied by tree stems, typically expressed as square feet per acre. Although there are no exact criteria for savannahs and woodlands, suggested basal area targets for savannahs are between 30–45 ft2/ac. and for woodlands between 45–65 ft2/ac. Basal area range should be modified depending on stem diameter and crown size. Stands with numerous large diameter trees or large crowns should be thinned to the lower end of the basal range. Conversely, stands with many small diameter trees should be thinned to the higher end of basal area range. Thinning to a higher initial basal area may be beneficial to offset loss of trees from wind, insects, disease, or fire damage. Leave trees, or the trees remaining after thinning, should be vigorous, large canopied trees of fire-tolerant species. It is recommended to retain fire-tolerant white and red oak types, hickories, and black gum. Fire-intolerant species, such as maple, yellow poplar, and white and Virginia pines are likely to be damaged by prescribed fire and are recommended for removal. Fire ManagementPrescribed fire is essential for restoring and maintaining the savannah or woodland landscape. Following thinning, especially where hardwood roots are well established, woody vegetation will regrow vigorously with the increased sunlight created by thinning the canopy (Fig. 3). If this hardwood vegetation is not suppressed with fire, it will dominate the understory within 3–5 years, depending on site quality. Therefore, it is critical to begin burning 2–3 years after thinning the site, a sufficient time frame where sprouts and woody seedlings grow large enough to be vulnerable to fire. Waiting 2–3 years also enables a small duff layer, or fine fuels, to accumulate on the forest floor and fuel a low temperature fire. Initially, leaf litter will be the primary source of fine fuels, but over time, fire-adapted grasses will become established and contribute to the fine fuel bed. Growing-season fires are highly effective at killing hardwood roots and other understory woody vegetation and should be used when possible. Fire intensity should be low enough not to damage overstory trees but intense enough to be effective in suppressing sprouts. Flame lengths of 2–3 feet with moderate rates of spread (burning less than 5 feet/ minute) are desirable. In areas that receive greater than 40 inches of annual rainfall, prescribed fire, or fire return intervals, should be every 2 years. On drier sites receiving less than 40 inches of rainfall a year, fire return interval is every 2–3 years. Less frequent intervals will result in hardwood overgrowth, which will dominate the ground layer and become difficult to control. In the early stages of restoration, this is especially critical since many hardwood sprouts are supported by large, well-established roots. Dormant-season fires may also be used, especially when weather conditions prevent growing-season burns. Ultimately, prescribed fire is critical for successful savannah and woodland restoration.
Herbicide as an Alternative to FireAlthough herbicides are not a satisfactory replacement for fire, they play an important role in restoration. Trees that are greater than 3 inches in diameter at breast height (DBH), are not likely to be controlled by fire. These trees can be treated with herbicides by several manual application methods including basal bark spray, stem injection, and cut stump. Directed foliar spray can be used on sprouts that persist following fire. Although they are labor intensive, manual herbicide treatments provide landowners a safe and effective way to control unwanted hardwoods with minimal equipment. |
