Community Ecology Processes, Models, and Applications

counteracting and mitigating impacts of exotic spe-
cies requires insight into how these species are con-
trolled in their native range and how these species
have evolved during their history of introduction.
On the other hand, local changes, varying from
changed agriculture or industrial discharge to
trade or climate conventions, can have wide and
remote implications.

7.3 Community interactions and land use change

7.3.1 Land use change, predictability and major drivers of secondary succession

Land use changes are often driven by external factors,
for example overproduction at the world market, or
opening up of trade barriers, which lead to land
abandonment when prices drop, or to (intensified)
cultivation when prices rise. Land use changes often
go along with altered physical–chemical inputs, such
as soil tillage, fertilization and hydrology measures.
These sudden land use changes can have enormous
impact on species, community interactions and eco-
system processes. Whereas there is extensive experi-
ence with how to bring land into cultivation,
ecosystem restoration is of a much more recalcitrant
nature. Restoration is a long-term process that often
starts with land abandonment and restoring former
hydrology and nutrient cycles. Simple steering para-
meters that enable switching from one state to the
other (Sudinget al. 2004) probably do not exist. One

question is whether ecosystems can be restored at all,

because they may have become unalterably influ-

enced by their history. The soil plays a crucial role

as the main sourceof historical legacy effects that may

constrain restoration efforts (Fig. 7.1). Soil legacy

effects cause a major difference between secondary

succession, which concerns the transformation from

one ecosystem into another (Holtkampet al. 2008),

and primary succession, where ecosystems develop

from bare soil (Neutelet al. 2007).

One of the main explanations for many examples

of unsuccessful ecological restoration is the deple-

tion of the soil seed bank and dispersal limitation of

plant species from reference sites (Bakker and Be-

rendse 1999). If plant propagules are unlimited,

land conversion requires a switch from competition

for light to competition for soil resources (Tilman

1982). According to the standard view, highest

plant diversity is obtained at intermediate soil fer-

tility (Al Muftiet al. 1977). This view, albeit devel-

oped by surveying across ecosystems, has provided

the major rationale for restoration in industrialized

countries, where restoration takes place on relative-

ly nutrient-enriched soils (Marrs 1993). Mowing on

wet soils or grazing on relatively dry productive

soils may help to reduce nutrient availability (Olff

and Ritchie 1998). Selective grazing of the dominant

forbs and grasses, which have the highest quality,

provides indirect advantage for the rarer, slow-

growing and poorly competitive plant species. In-

troducing aboveground herbivores at mild stocking

rates is a practice that is often applied in nature

Nature Agriculture

Plant roots

Exudates and detritus

Root pathway

Bacterial decomposition

Fungal decomposition

Root pathway

Bacterial decomposition

Fungal decomposition

Figure 7.1Energy transformation in three belowground pathways: the root–root feeder pathway, the detritus–
bacteria–bacterivores pathway and the detritus–fungi–fungivores pathway in agricultural soil and a natural soil.
Conversion of land use from agricultural to post-agricultural involves reorganization of the energy channels in the soil
food web according to arrow thickness: the thicker the arrow, the larger the energy flow.

APPLICATIONS OF COMMUNITY ECOLOGY APPROACHES 87