| Abstract: | Studies on soil patterning on a small scale in arid and semi-arid regions have rarely been conducted. Many papers implicitly
assume that plant distribution is controlled by some soil variables acting at small scales. We have directly tackled the relationships
between soil and some biotic variables including plant distribution at small scales in an Iberian semi-arid gypsum environment.
This has been carried out by means of Canonical Correspondence Analysis as a hypothesis-testing tool. CCA models show that
the spatial data matrix is able to explain a relevant fraction of the soil data set (P < 0.001). The most important variable,
as firstly selected in the CCA stepwise selection procedure, suggests the existence of a vegetation-elevation gradient in
relation to soil physical properties; the rest of selected variables indicates the existence of other spatial trends which
may be related to certain microgeomorphological features. On the other hand, only the cover of annuals and the cover of litter
are selected in the case of the biotic data set as constraining matrix, but not the cover of any perennial plant. Partial
CCA models indicated that the remaining information explained by the spatial data set after adjusting the biotic set as covariables
is also significant (p < 0.001). This variability is not related to the existence of vegetation bands as shown by the two
selected variables in the case of the partial CCA models. The primary source of spatial soil variation is related to the existence
of three community bands and these differences are able to explain even the change of plant life forms in vegetated band.
The soil parameters controlling the changes are mainly related to texture and surface features. However, we detected other
sources of spatial soil variation out of this primary model. This hierarchical spatial pattern seems to be related to some
geomorphological traits of the landscape, such as soil crust strength, presence of gypsum crystals or bare zones, and not
to the presence of mature gypsophytes (at least the five most frequent) which might ameliorate the soil environment. Furthermore,
the biotic data set is not able to explain any new fraction of soil variability out of that already explained by the spatial
data set.
This revised version was published online in June 2006 with corrections to the Cover Date. |
