Archive image from page 30 of Development and evaluation of an. Development and evaluation of an even- and uneven-aged ponderosa pine/Arizona fescue stand simulator . developmentevalu267hann Year: 1980 Figure conversion from blackjack pine to yellow pine by diameter class size and site index (S) . Diameter Closs Size in Inches Recruitment The requirements for adequate natural regeneration in the southwestern ponderosa pine are the presence of large, vigorous trees well dispersed over the area, a good seed crop, adequate rainfall in two consecutive years, and low level of comp
Archive image from page 30 of Development and evaluation of an. Development and evaluation of an even- and uneven-aged ponderosa pine/Arizona fescue stand simulator . developmentevalu267hann Year: 1980 Figure conversion from blackjack pine to yellow pine by diameter class size and site index (S) . Diameter Closs Size in Inches Recruitment The requirements for adequate natural regeneration in the southwestern ponderosa pine are the presence of large, vigorous trees well dispersed over the area, a good seed crop, adequate rainfall in two consecutive years, and low level of competitive vegetation (see appendix G for details). This combination of conditions occurs at erratic invervals and, as a result, ade- quate natural regeneration is erratic. For example, the last excellent regeneration period occurred in 1918-1919 (Pearson 1950; Meagher 1950; and Schubert 1974). Cooper (1960) has concluded that erratic natural regeneration is a major reason for the 'unbalanced' size struc- ture of the ponderosa pine forests of the Southwest. Ideally, a natural regeneration model should take all of these factors into consideration as components of it (such as the one described by Leak and Graber 1976). Unfortunately, the data available in this study preclude the development of a regeneration model. This was unfortunate because the greatest distinction between even- and uneven-aged stand development is the method of regeneration. The even-aged stand usually starts as a surge of regeneration over a relatively short period of time (20 years or less). Next is a stage where little or no regeneration takes place. Finally, some regeneration may again occur (depending upon the species and site characteristics) as the stand becomes mature (or overmature) and develops a more open structure. On the other hand, the uneven-aged stand is usually characterized by a more or less continuous flow of regeneration into the stand. 23
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