The management of the light ambient in multipurpose agroforestry systemsConsidering the great diversity of native tree species and the modest advances of silviculture on these when in productive systems, this study aimed to verify the responses of different native species to the variation of the light environment. For this, the eucalyptus stands were thinned systematically and progressively, providing gradual differences in the canopy cover. The experiment with four non-randomized blocks consisted of five treatments with different levels of forest density, T100 -100% of eucalyptus, T75 -75% of eucalyptus, T50 -50% of eucalyptus, T33 -33% of eucalyptus and T0 -without eucalyptus/full sun, and three sub-treatments, S1 -Pioneer (PIO), S2 -Non-pioneer (NPIO) and S3 -Mixed planting (MIX). For the eucalyptus crop, the average annual increment and the basal area were characterized as results of the differential thinning in each treatment. The T33 treatment, due to the reduction in competition, provided the highest diametric gains, 2.2 cm/year/tree, but presented the lowest basal area given the lower forest density. The monitoring of the eucalyptus canopy was performed using hemispherical photographs. Higher intensities of thinning provided larger spaces for the canopy growth, resulting in more significant gains in the canopy coverage index. With light sensors arranged under different conditions of vegetation cover, the light conditions present in the understory of each treatment were measured. The available light in the treatments ranged from 41.01-to 91.50% of the maximum possible luminosity at the beginning of the experiment and from 35.35% to 83.41% at the end of the observations. The forty species of Brazilian native trees (20 pioneer species and 20 nonpioneer species) implanted in the system, which were submitted to different radiation conditions, were evaluated in a census for mortality, height growth, increase in diameter at root collar, and observation of responses plastic. For mortality, a continuum of responses was observed, with trends of higher mortality in the opposite extreme conditions of radiation found in treatments T0 (full sun) and T100 (more shaded environment). The group of pioneer species showed the highest plasticity for growth in height; the response known as "shadow avoidance syndrome" was driven by treatments T75 and T50. The highest diametric gains for all sub-treatments (PIO, NPIO, MIX) were provided by full sun conditions (T0). The species Schinus terebinthifolius (Aroeira pimenteira) and Peltophorum dubium (Canafístula) were individually analyzed. Due to their different uses and economic potential, which are optimized by different light conditions, it is recommended that S. terebinthifolius be cultivated in full sun and P. dubium in the shade (approximately 45% of available solar radiation).
