Lianas are frequently considered as light demanding plants due to their proliferation in gaps and forest edges. Since lianas are exposed to a very heterogeneous light environment they could be expected to express morphological and physiological plasticity in response to changes in the light environment as high as that found in pioneer trees. We compared the biomass allocation and photosynthetic responses of seedlings of three species of lianas and two species of pioneer trees to increased light availability. Seedlings were transferred from medium (4–5 mol m−2 d−1) to high irradiance (12–15 mol m−2 d−1) in a controlled environment. In general the three liana species allocated fewer resources to the stem in comparison with the trees. The difference in the response between irradiance regimes was similar among the species with no strong differences between trees and lianas probably due the early stage of the plants. With increase in irradiance plants accumulated more biomass allocated more resources to the roots and less to the leaves reduced the leaf area ratio (LAR) and specific leaf area (SLA). The photosynthetic rates recorded were not related to the rates of growth as measured by the increase in dry biomass (RGRm). Regardless of the life form plants under higher irradiance increased their light compensation point (Lcp) and attained light saturation (Lsp) at higher levels of irradiance while the saturated photosynthetic rate (Amax) did not show a clear pattern and dark respiration (Rd) and quantum yield (Q) were not affected by the transference. The understanding of liana and tree seedlings responses to the light environment may have important implications in the dynamics of tropical forest regeneration.