Research on the Variation of Light Intensity Across Surfaces with Beech Seedlings Planted after the Application of the Progressive Felling Treatment

The research we have undertaken seeks to clarify some aspects concerning the specific characteristics of aforest microclimate. Spot measurements were carried out for 12 hours/day, on certain days that are typical for the period of vegetation and, respectively, for the period of vegetative rest. Measurements regarding the intensity of light were conducted across surfaces where progressive felling had been applied. The research findings about the light regime are presented below: 1. Surfaces subjected to the progressive felling treatment I - seeding fellings that create cut block sites in the mature stand canopy u. a. 74 B, UP III, Nirajul Mic, the Sovata Forestry. In these regeneration areas appear noticeable changes of the light regime, caused by the intensity of the fellings, the size of the cut block sites and the position of each cut block site sector. Thus, in clear cut block sites, having an elliptical shape of 0.5 H³ X 0.75 H*, in which seedlings have not yet been planted, the amount of light that reaches the soil surface, in relation to the open field solar radiation, is approx. ¼ - 1/3 in the eastern and southern sectors, 2/3 in the central sector and, respectively, 2/5 - ½ in the western and northern sectors. In the case of elliptical cut block sites, with diagonals of 1.0 H X 1.5 H, we have found some variations, in the sense that the eastern and the southern sectors receive, at ground surface, approx. 1/5 - 2/5 of the light from an unforested area, the central sector receives a little over 2/3, while the western and the northern sectors receive 4/5 -1/1 of the light from an unforested area, which is also the area with relatively maximum light availability. 2. Surfaces subjected to the progressive felling treatment II - fellings for expandingcut block sites UP VI, Valea Soveții, u.a 127,the Sovata Forestry. Thus, in an elliptical cut block site (1.0 H X 1.5 H) from UP VI, u.a. 127, at1 p.m.,when the sky was overcast, 50% of full light reached the eastern sector, 40% reached the southern sector, approx. 80-90% reached the center of the cut block site, and 75-85% of the amount of light from an unforested area reached the western and the northern sectors at soil surface level. Forest ecosystems are characterized by a great capacity of solar radiation absorption. As a result of selective processes of absorption, reflection and transmission, carried out at the level of the “active surface”, the light regime inside the forest presents a series of distinct features. Light intensity decreases from the top of the canopy to the ground. The decrease is accentuated in the canopy and much slower in the space underneath the canopy, all the way to the ground. Thus, while an average of 66-67% is recorded at the level of the canopy (2/3 of full light), underneath the canopy it reaches 9% (under 1/10 of full light) and only 6-7% of the light from an unforested area is recorded at ground level. Differences are found from one measurement point to another, within the same level, as a result of the foliage structure and the different thickness of the foliage mass located above the measurement point.