Upland Hardwoods
Introduction
Upland hardwood forests cover 64 million acres and are generally either oak-hickory (Carya species) or maple (Acer species)-beech (Fagus species)-birch (Betula species) forests. Various oak species are the main resource in these areas, although they are often being replaced by aggressive red maple (Acer rubrum) and yellow poplar (Liriodendron tulipifera) because of the exclusion of low-intensity fires (Smith 1995; Hicks and others 2004). Most of the forests are second growth or result from revegetation of abandoned farms and are often, but not always, even-aged. Many have also been high-graded which has resulted in an increase in shade tolerant species. However, only 8% of these forests have, or are expected to have, any sort of intensive management such as using fertilizers or thinning (Siry 2004). Ownership and topography are often significant factors in management (see Silviculture of Degraded Hardwood Stands).
Silviculture of Upland Hardwoods
A detailed description of silviculture for this forest type is given in the section entitled Natural Upland Hardwoods. The following summary gives an overview.
The regeneration of upland hardwoods can be implemented with either even-aged or uneven-aged reproduction methods, but in practice the even-aged methods are generally easier and less costly to undertake (Smith 1995; Hicks and others 2004). Hicks and others (2004) further state that none of the shade tolerant species, favored by uneven-aged silviculture, provide viable management opportunities for these forests. Nevertheless, the forest structure and objectives of some owners may cause them to use uneven-aged methods such as group selection (Smith 1995; Johnson and others 2001).
Clearcutting, where large openings in the forest are made, promotes regeneration of faster growing intolerant species such as yellow poplar, sweetgum (Liquidambar styraciflua) and pines (Johnson and others 2001; Hicks and others 2004). It can also be used for oaks on some sites or where there is good advanced regeneration of oaks. Competing vegetation can delay regeneration. Clearcutting is less desirable aesthetically and may not be as applicable to NIPF owners.
The shelterwood method is often recommended for regenerating oak species that are usuaUpland Hardwood Forest Managementlly intermediate in shade tolerance (Loftis 1990; Johnson and others 2001). Shelterwood systems allow control of light and competition and oftern involve two or three cuts within the stand to obtain regeneration (Hicks and others 2004).
A two-aged system is also possible (Smith 1995; Hicks and others 2004). This practice involves a partial harvest and leaving some trees until the end of the next rotation (sometimes called leave-tree, irregular shelterwood or deferment cutting practice). Each age group contains >20% of the basal area. Objectives for two-aged stands include aesthetics, ensuring seed production, protecting habitat diversity, and producing large sawlogs.
Stands or groups, in the case of the group selection method, respond to light crown thinning, an operation that focuses on favoring crop trees in the upper canopy. A different version is the crop-tree management strategy (Hicks and others 2004). Other stands may benefit from cleanings or more intensive thinning. Thinning is strongly recommended on high quality sites where yellow poplar dominates (Smith 1995).
Improvement cuttings, made in stands past the sapling stage, are widely applicable to upland hardwood forests because of their age, species composition, and effects of high-grading (Hicks and others 2004). Here the focus is on removing undesirable species and poor trees, although marketing them can be difficult. If the stand has been too degraded it may be best to regenerate it, rather than using an improvement cutting.
Apart from improvement cuttings, the main recommended timber management alternatives for the widespread degraded stands are to:
- convert them to pines;
- regenerate them as hardwoods, usually by clearcutting and relying on stump sprouts; or
- where there are sparse stands of good trees, 10-14 inches in diameter, release them by removal of all other trees down to 2 inches in diameter.
Biomass Potential of Upland Hardwoods
Biomass collection could come during the regeneration phase, from improvement cuttings and more intensive thinning, or cleaning.
Clearcutting offers the best prospects for residue collection at harvesting. With the shelterwood method, care is needed not to damage the remaining stand or the new regeneration, if residual material is to be removed for bioenergy.
For degraded stands that are being regenerated to either pines or hardwoods, shearing and chipping are good options that would be facilitated by strong bioenergy markets. The resulting stands on poor quality sites are unlikely to develop into high value trees but they would be good for pulpwood or bioenergy. Medium quality sites should regenerate into stands that will produce sawlogs and chips. The highest quality sites also have good potential for producing sawlogs but will often have large numbers of culls and undesirable species that could be used for bioenergy.
Thinning and improvement cuttings are important to improve the long-term value of stands, and even if the biomass harvesting does not fully cover the cost, it still may be economically worthwhile.
Topography, which greatly influences harvesting techniques and economics, and transport, could be limiting factors that need to be considered as many of these forests are located in mountainous areas.
Encyclopedia ID: p1337
