Impacts of disturbance initiated by road construction in a subtropical cloud forest in the Luquillo Experimental Forest, Puerto Rico

Abstract

The impacts of road construction and the spread of exotic vegetation, which are common threats to upper elevation tropical forests, were evaluated in the subtropical cloud forests of Puerto Rico. The vegetation, soil and microclimate of 6-month-old roadfills, 35-year-old roadfills and mature forest with and without grass understories were compared. Recent roadfills had higher light levels, soil temperatures, bulk densities, larger pools of exchangeable soil nutrients and higher soil oxygen concentrations; but lower soil moisture, soil organic matter and total soil N than the mature forest. On the 35-year-old roadfills, bulk density, soil pH and P pools were statistically similar to the mature 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 was non-woody. Seedling density, tree density and total woody biomass were 12, 28 and 2% of mature forest sites, respectively. In these areas, where soils were disturbed during construction, accumulation of biomass is the slowest known for the LEF. It may take 200–300 years for biomass to attain mature forest levels. In areas that were not directly disturbed during construction, the road has had little effect on the vegetative 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 roadside, they were generally absent from the mature forest and only abundant in habitats of anthropogenic origin.