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

摘要

The impacts of road construction and the spread of exotic vegetation, which are common threats to upper altitude tropical forests, were evaluated in the subtropical cloud forests of Puerto Rico. The vegetation, soil and microclimate of 6-month-old and 35-yr-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-yr-old roadfills, bulk density, soil pH and P pools were statistically similar to those of the mature forest while soil moisture, total N and base cations weredifferent. The total above-ground biomass of 6-month-old roadfills was about 2 Mg/ha and dominated by a variety of monocotyledonous and herbaceous species. The 35-yr-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 Luquillo Experimental Forest, and itmay take 200-300 yr 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 monocotyledons, one of which had been planted along the road 35 yr earlier, were copious along the disturbed roadside, they were generally absent from the mature forest and only abundant in habitats of anthropogenic origin.