An Introduction to the Cape d'Aguilar Marine Reserve, Hong Kong

THE VEGETATION OF THE PENINSULA

THE฀VE฀ GETATION฀OF฀THE฀PENINSULA฀ 22฀ Cape d'Aguilar has a rich flora. Of particular interes t are th e grasses , shrub s an d creeper s whic h inhabi t th e coastal margin (Plates 12 and 13) . A recent student survey recorded over eighty species of plants from around the Cape d'Aguilar Marin e Reserv e during a period i n January an d February. Over th e entir e yea r ther e ar e almos t certainl y many more present . The coastal margin is a difficult zon e for higher plants to colonize . Plant s whic h attemp t t o gro w her e hav e t o cope wit h exposur e t o intens e sola r radiatio n an d stron g winds, thi n soil s an d sea-blow n salt . As w e have shown , Cape d'Aguilar i s very exposed to wind and wave and such conditions caus e win d damag e an d increas e evaporativ e water loss. Most of the plants living on the margins of the marine reserve simply cannot withstand the most exposed areas living, rather, in more sheltered regions. Those plants which d o liv e i n th e mor e expose d part s ar e characteristically stunted, for example Scaevola sericea and Pluchea indica, compared t o their conspecifics i n sheltere d sites. Creeper s whic h hu g th e groun d closely , suc h a s Clerodendrum inerme, Asparagus cochinchinensis, Synostemon bacciformis and Canavalia maritima als o do well i n th e ar eas o f high exposure , a s do grasses , such a s the commo n saltmeadow grass , Zoysia sinica, with thei r long , slender , flexible leaves . There are many grasses at Cape d'Aguilar . The mos t commo n one s includ e Cynodon dactylon, Ischaemum aristatum, Panicum repens an d Paspalum Plate 12 . Plant s o f th e Cape d'Aguila r shores . A , Paspalum vaginatum (Photo : Chong Dee Hwa); B, Lysimachia mauritiana (Photo: E. Harper); C, Synostemon bacciformis (Photo : Chong Dee Hwa); D, Ischaemum aristatum (Photo: Chong Dee Hwa). ;฀ V-" >. 23 I D 24฀ Plate 13 . Plants of the Cape d'Aguilar shores. A, Ipomoea pes-caprae (Photo: B. Morton); B, Canavalia maritima (Photo: Chong Dee Hwa); C, Vitex rotundifolia (Photo: B. Morton); D, Scaevola sericea (Photo: Chong Dee Hwa). vaginatum. Sand y beache s a t Cape d'Aguila r ar e invade d by the Railroad vine, Ipomoeapes-caprae, with purple trumpet -shaped flowers . Vitex rotundifolia everywher e spread s downwards over cobble beaches . On the most extreme edge of the land, however, there is much bare rock and very little soil. Yet, even here, plants may ancho r themselve s i n th e joint s withi n th e rhyolit e and granodiorite. Their presence expands the availabilit y of this niche for, as they grow, the pressure exerted by th e roots enlarges th e joint s an d a combination o f their ow n decay and the effect of the humic acids they produce acting on the rocks, thereby manufactures more medium in which other plants may eventually becom e established . Salt is a large problem because of the osmotic stresses placed upo n th e plan t tissue s an d thei r physiologica l processes. Ther e are , however , adaptation s displaye d b y coastal plant s whic h hav e allowe d the m t o exploi t hig h salinity regions. One suc h adaptation i s the developmen t of thic k succulen t leaves , a s see n i n Pandanus tectorius, Scaevola sericea, Synostemon bacciformis, Vitex rotundifolia, Lysimachia mauritania and Pluchea indica. This has the effec t of decreasing th e surfac e are a :volum e o f th e leave s an d thus reduces water loss. Other anti-desiccatory adaptation s are seen in the Cape d'Aguilar plants, such as an ability to roll the leaves in S. sericea which reduces the surface are a over whic h wate r ca n b e lost , th e possessio n o f thic k cuticles in S. sericea and S. bacciformis and the development of cuticula r hair s i n Ischaemum aristatum an d Passiflora foetida, whic h creat e a laye r...