Changes in Edaphic Gradients across Forest-Land Use Margins in an Isolated Rainforest Remnant in the Knuckles Range, Sri Lanka

Abstract

Forest fragmentation is been identified as one of the factors that initiate forest degradation.The size of the forest patch and its bordering landscape decide the severity of disturbances tothese forest patches. Moraella forest, a lowland rainforest remnant located in the KnucklesRange, is bordered by many landuse types. The present study was aimed at investigating theedaphic gradients across the forest edge bordered by different forest-landuse types viz., Pinus,grassland, tea plantation and a scrubland. Seven linear quadrates (3 m x 12 m) were laid in 3transects totaling 21 quadrates per forest-landuse category. The quadrates were positionedparallel to the forest-landuse edge and at different distances away from the edge (0, 10 and 30m towards the forest interior; 10, 30 and 50 m towards the bordering landuse type). Soilsamples (up to a depth of 5 cm) were collected from each quadrate and were bulked togetherto make a representative sample for each distance and per transect. The samples wereanalysed for available cations (Ca, Mg and K), available P, total C and N, pH using standardmethods. Data was analysed using General Linear Model (GLM) taking distance as a fixedfactor in Minitab 14.1.

The results showed that soil Mg and available P showed significant differences betweendistances in forest-landuse transects while Ca and Mg concentrations showed significantdifferences between landuse types. Pair-wise comparisons revealed that the soil Mg in theforest interior was higher than that of the bordering landuse, irrespective of the type of thelanduse. Available soil P also showed a similar increase towards the forest interior. This ispossibly due to higher mycorrhizal-dependent tree species found in the forest than that in thebordering landuse types. Other chemical parameters did not show any significant differencesalong these transects. Soil Ca in the scrubland and small-holder tea plantation showedsignificantly higher concentrations compared to Pinus and it was evident in both in the forestinterior as well as in the open landuse. Higher Ca levels in the small-holder tea plantationmay be due to the use of lime to reduce soil acidity. The forest-scrubland soils showedsignificantly higher Mg levels than that of other three landuse categories. However, soil C, Nand pH showed no significant differences across these forest-landuse transects. The presentresults suggest that edaphic gradients do exist across forest-landuse transects, but with somesoil parameters. The bordering landuse type and its management practices may have someimpacts on creating such gradients.