1
A framework that summarizes the direct and indirect effects of past land use on forest
herb recolonization is proposed, and used to analyse the colonization patterns of forest
understorey herbaceous species in a 360-ha mixed forest, grassland and arable landscape
in the Dijle river valley (central Belgium).
2
Fine-scale distribution maps were constructed for 14 species. The species were
mapped in 15 946 forest plots and outside forests (along parcel margins) in 5188 plots.
Forest stands varied in age between 1 and more than 224 years. Detailed land-use history
data were combined with the species distribution maps to identify species-specific
colonization sources and to calculate colonization distances.
3
The six most frequent species were selected for more detailed statistical analysis.
4
Logistic regression models indicated that species frequency in forest parcels was a
function of secondary forest age, distance from the nearest colonization source and
their interaction. Similar age and distance effects were found within hedgerows.
5
In 199 forest stands, data about soils, canopy structure and the cover of competitive
species were collected. The relative importance of habitat quality and spatio-temporal
isolation for the colonization of the forest herb species was quantified using structural
equation modelling (SEM), within the framework proposed for the effects of past land
use.
6
The results of the SEM indicate that, except for the better colonizing species, the
measured habitat quality variables are of minor importance in explaining colonization
patterns, compared with the combination of secondary forest age and distance from colonization
sources.
7
Our results suggest the existence of a two-stage colonization process in which
diaspore availability determines the initial pattern, which is affected by environmental
sorting at later stages.
Key-words
:
Adoxa
,
Arum
, dispersal limitation, forest herbs,
Geum
, historical ecology,
Lamium
, landscape ecology,
Primula
,
Ranunculus
, secondary forest succession, structural
equation modelling
Journal of Ecology
(2003)
91
, 731–742