Wang H, Hall CAS, Cornell JD, Hall MHP.
2002. Spatial dependence and the relationship
of soil organic carbon and soil moisture in Luquillo experimental forest. Landsc.
We used geo-spatial statistical techniques to examine the spatial variation and relationship of soil organic carbon
(SOC) and soil moisture (SM) in the Luquillo Experimental Forest (LEF), Puerto Rico, in order to test the hypothesis
that mountainous terrain introduces spatial autocorrelation and crosscorrelation in ecosystem and soil
properties. Soil samples (n = 100) were collected from the LEF in the summer of 1998 and analyzed for SOC,
SM, and bulk density (BD). A global positioning system was used to georeference the location of each sampling
site. At each site, elevation, slope and aspect were recorded. We calculated the isotropic and anisotropic semivariograms
of soil and topographic properties, as well as the cross-variograms between SOC and SM, and between
SOC and elevation. Then we used four models (random, linear, spherical and wave/hole) to test the semivariances
of SOC, SM, BD, elevation, slope and aspect for spatial dependence. Our results indicate that all the
studied properties except slope angle exhibit spatial dependence within the scale of sampling (200 – 1000 m
sampling interval). The spatially structured variance (the variance due to the location of sampling sites) accounted
for a large proportion of the sample variance for elevation (99%), BD (90%), SOC (68%), aspect (56%) and SM
(44%). The ranges of spatial dependence (the distances within which parameters are spatially dependent) for
aspect, SOC, elevation, SM, and BD were 9810 m, 3070 m, 1120 m, 930 m and 430 m, respectively. Cross
correlograms indicate that SOC varies closely with elevation and SM depending on the distances between
samples. The correlation can shift from positive to negative as the separation distance increases. Larger ranges of
spatial dependence of SOC, aspect and elevation indicate that the distribution of SOC in the LEF is determined
by a combination of biotic (e.g., litterfall) and abiotic factors (e.g., microclimate and topographic features) related
to elevation and aspect. This demonstrates the importance of both elevation and topographic gradients in
controlling climate, vegetation distribution and soil properties as well as the associated biogeochemical processes
in the LEF.