Seed Dispersal of Three Framework Tree Species and Seed Predation of Manglietia garrettii Craib

ABSTRACT: Deforestation is a serious problem in northern Thailand. Framework tree species are native forest trees that help to accelerate natural forest regeneration. Planting them can, therefore, rapidly restore forest ecosystems in degraded areas. Understanding seed dispersal and predation mechanisms can help to select framework tree species and generate useful information to improve restoration techniques.

The study site of this research was evergreen forest (1000-1600m above sea level) in Doi Suthep-Pui National Park, Muang, Chiang Mai. Direct observations of animals visiting three framework tree species (Prunus cerasoides D. Don, Balakata baccata (Roxb.) Ess. and Manglietia garrettii Craib were made with binoculars. The animals were identified and their role in seed dispersal or seed predation was recorded. The observation for each tree species totaled 50 hours.

Various bird and squirrel species were the main seed dispersers of these tree species. Five bird species fed on P. cerasoides fruits; one squirrel species and 5 bird species fed on the fruits of B. baccata and one squirrel species and 6 bird species fed on M. garrettii fruits. The most common seed disperser of all 3 framework tree species was Pycnonotus jocosus, a very common resident bird. Callosciurus erythraeus, a squirrel species fed on both B. baccata and M. garrettii fruits was . Animals dispersed the seeds by swallowing the seeds or whole, fresh fruits, bringing them far from the parent trees or deliberately or accidentally dropping fresh fruits or seeds beneath the parent trees.

Seed predation in natural habitats and the effects of seed proximity to the parent tree on seed survival levels were determined for M. garrettii. The seeds were placed on the ground in circular sampling units, established along two line transects beneath each of 3 parent trees. Seven days after seeds were placed, percent removal was 100 in the first and second tree sampled, and for the third tree sampled it was 92.8. Average percent removal of M. garrettii seeds was 97.6. Seed removal of M. garrettii was density- and distance-independent. Seed removal animals observed, using sand traps to record their footprints, were Sus scrofa, pheasants and ants. Ants were secondary dispersers that induced seed germination by consuming the aril of the seeds.

Seed germination tests were conducted at the Forest Restoration Research Unit (FORRU) nursery. Percent germination of seeds without aril (65.67±4.72) was significantly higher than that of seeds that retained the aril (10.67±2.08). Median length of dormancy (MLD) of seeds without aril was significantly shorter than that of seeds that retained the aril. In natural conditions, aril is related to seeds dormancy, removing the aril can increase seed germination. Manglietia garrettii is a rare tree species with regeneration problems in natural conditions. Nursery production of seedlings and reintroduction to the natural habitat could help to conserve the species. Direct seeding is not suitable.