Leaf physiologycal and morphological responses of seven dipterocarp seedlings to degraded forest environments in Sarawak, Malaysia: A case study of forest rehabilitation practice

Abstract

Leaf physiological and morphological responses were studied in seedlings of seven dipterocarp species planted in three degraded forest environments: grassland, logged remnant forest and secondary forest. Dryobalanops beccarii, Parashorea macrophylla, Shorea macrophylla, S. ovata, S. par vifolia, S. seminis and S. virescens were used as study species. The leaf photosynthetic rate at light saturation (A max), the dark respiration rate (R d), light compensation point (I c), leaf mass per area (LMA) and SPAD value were measured during the 38 months after planting. Water loss by detached leaves was also determined at 13 months after planting. In the grassland, LMA and A max increased from three months after planting in all species except S. ovata. The time by which 50% of total leaf water content had been lost from detached leaves was positively correlated with LMA, suggesting that species with high LMA (D. beccarii, S. ovata and S. par vifolia ) have high tolerance to desiccation in the grassland. The positive correlation found between LMA and A max indicates that LMA accelerated the photosynthetic rate, although those species with higher A max/LMA (P. macrophylla, S. macrophylla and S. seminis) had low tolerance of desiccation in the grassland. The seedlings planted in the remnant forest had lower leaf R d and higher SPAD values than in the other environments. Large increase in SPAD value and decrease of I c in P. macrophylla and S. virescens suggest that both species have acclimation ability to the remnant forest. The lowest mortality and I c in the remnant forest was in S. seminis and suggests high shade tolerance in this species. In contrast, S. ovata, which maintained the highest I c over the measurement period, may suffer greatest mortality in the remnant forest. In the secondary forest, the leaf A max, LMA and SPAD value were intermediate in value between the other two environments. We conclude that leaf ecophysiological traits in dipterocarp seedlings differ significantly between species. This is information needed for enrichment planting in degraded tropical rainforest areas in Southeast Asia.