IMPACTS OF DISTURBANCE INITIATED BY ROAD CONSTRUCTION IN A SUBTROPICAL CLOUD FOREST IN THE LUQUILLO EXPERIMENTAL FOREST, PUERTO-RICO

The impacts of road construction and the spread of exotic vegetation, which are common threats to upper elevation tropical forests, were eva luated in the subtropical cloud forests of Puerto Rico. The vegetation , soil and microclimate of 6-month-old roadfills, 35-year-old roadfill s and mature forest with and without grass understories were compared. Recent roadfills had higher light levels, soil temperatures, bulk den sities, larger pools of exchangeable soil nutrients and higher soil ox ygen concentrations; but lower soil moisture, soil organic matter and total soil N than the mature forest. On the 35-year-old roadfills, bul k density, soil pH and P pools were statistically similar to the matur e forest while soil moisture, total N and base cations were different. The total aboveground biomass of 6-month-old roadfills was about 2 Mg /ha and dominated by a variety of monocot and herbaceous species. The 35-year-old roadfill areas had a biomass of 10.5 Mg/ha, 77% of which w as non-woody. Seedling density, tree density and total woody biomass w ere 12, 28 and 2% of mature forest sites, respectively. In these areas , where soils were disturbed during construction, accumulation of biom ass is the slowest known for the LEE It may take 200-300 years for bio mass to attain mature forest levels. In areas that were not directly d isturbed during construction, the road has had little effect on the ve getative composition beyond a 5-10 m zone immediately adjacent to the pavement. Although non-native monocots, one of which had been planted along the road 35 years earlier, were copious along the disturbed road side, they were generally absent from the mature forest and only abund ant in habitats of anthropogenic origin. (C) 1998 Elsevier Science B.V .