Responses of 20 native tree species to reforestation strategies for 6 abandoned farmland in Panama

Deforestation in the tropics often leads to unproductive agriculture, and results in 1 abandoned, degraded grasslands that tree species re-colonize poorly. To evaluate why forests do 2 not regenerate naturally, and to identify potential species for use in reforestation of degraded 3 areas, we planted 15,000 seeds of twenty native tree species varying in seed size and shade4 tolerance, in abandoned Panamanian farmland dominated by the exotic grass, Saccharum 5 spontaneum. To determine the effects of aboveand below-ground constraints on tree seedling 6 germination, survival, and growth, we utilized four mowing and shading treatments of the 7 Saccharum. Shading the Saccharum effectively eliminated it, whereas mowing led to increased 8 light above-ground, but did not reduce Saccharum growth rate. Germination, survival, and 9 growth of tree seedlings approximately doubled in shade treatments, compared to the unshaded 10 control, but were lowest when the Saccharum was mown three times. Fire significantly 11 decreased germination and survival. 12 Some species did not follow these general trends, though, and we identified four species 13 groups that varied in their response to Saccharum competition. Very small-seeded, light 14 demanding species performed poorly, and we do not recommend their use in reforestation 15 because they tolerate neither abovenor below-ground constraints imposed by the Saccharum. 16 Light-demanding species with large seeds were limited by above-ground constraints, namely 17 shading. Small-seeded, shade-tolerant species were limited by below-ground constraints imposed 18 by the Saccharum. Large-seeded, moderately to highly shade-tolerant species performed well in 19 the Saccharum; we recommend a reforestation strategy which includes planting this last group. 20