Publication

In this study we tested the hypothesis that related tree species within the timber tree genus Syzygium differ in their shadetolerance. We propose that difference in tolerance relate to the successional status and site affinities of each species found within the rain forests of southwest Sri Lanka. Seedlings of each of the four S yzygium species were grown for 24 months in replicated environmental treatments that simulated six different shade quality and quantities recorded from a Sri Lankan rain forest. Treatments were: (i) a deep uniform shade (DS) environment that comprised only 1% of photosynthetic photon flux density (PFD) as compared to that of the full open; (ii) a medium uniform shade (MS) environment receiving 14% of PFD as compared to the full open; (iii) a light uniform shade (LS) environment receiving 50% of PFD; (iv) the center environment of a small 200 m(2) opening (SD), receiving 18% of PFD; (v) the center environment of a large 400 m 2 canopy opening (LD), receiving 54% of PFD; and (vi) full sun (FS) receiving 100% of PFD. All species increased both above- and below-ground growth with increasing amounts of PFD. Seedling height, root collar diameter and dry mass gain were greatest in the brighter shade treatments with little discrimination shown among LD, LS, and FS. Significant differences in growth also occurred among the four species. Comparisons among species in the full sun (FS) treatment revealed S. rubicundum and S. operculatum to have greater height increments than S. makul and S. firmum. The low leaf mass ratio of S. operculatum, in particular, and S. rubicundum, suggests both to be prone to wilt during periods of desiccation. S. rubicundum also had greatest leaf and branch numbers and smallest leaves compared to the other three species. S. firmum in particular, but also S. makul, had larger, thicker leaves, with greater total dry mass in the FS treatment compared to the other two species. In the deep shade treatment (DS) S. firmum had greatest total dry mass and S. operculatum had the least. Taken together these findings reveal S. rubicundum and S. operculatum to be the most shade-intolerant of the four Syzygium species. Both appear prone to desiccation and water loss, though we speculate the small, numerous leaves and fine branches of S. rubicundum (characteristics of more drought-tolerant species) make this species less so. Both S.firmum and S. makul do best in the brighter shade treatments. Compared to the other two Syzygium spp., both are less susceptible to desiccation in high light environments because of their larger, thicker leaves and greater bulk. S. firmum appears to be the most shade-tolerant of the four Syzygium species. Findings have direct implications for forest management. To secure regeneration establishment and release or to create suitable planting environments Syzygium spp. require silvicultural treatments that account for species specific limitations of site (water availability) and shade (canopy opening size). (C) 2002 Elsevier Science B.V. All rights reserved.