Evaluation of potential evaporation as a means to infer loblolly pine seedling physiological response to a given microclimate

Foresters understand that there is no single correct way to treat every forest stand to produce optimum results, and that poor treatment can produce adverse effects on most sites. An example of this problem concerns areas that produce poor environmental conditions for regeneration upon clearcutting. Valigura and Messina (Journal of Environmental Management, 1994) found that loblolly shelterwoods substantially influence the temperature, radiation humidity and windspeed of the seedling-level microclimate relative to those in a clearcut, but they could not predict the effects of these modified understory conditions on seedling performance. The primary question addressed in this study is: on harsh sites, what advantages/disadvantages does a partial overstory impose on seedlings growing underneath relative to seedlings grown in a clearcut? The objective was to evaluate the combination equation for potential evaporation as a relative means to infer the amount of stress imposed on loblolly pine seedlings in a shelterwood or clearcut environment, subsequently inferring the effect of a partial overstory on seedling performance. It was shown that although PE statistically explained some of the variance measured in seedling physiological variables, it was not possible to use PE estimates to infer seedling performance to microclimate, on these sites, during the relatively wet period of 1990/1991. This study qualitatively confirmed the ability of a shelterwood to favorably influence the seedling microclimate relative to a clearcut microclimate. However, there is still a need to explore and develop an inferential technique to evaluate the effect of different environments on seedling performance.