Driscoll et al. (1) have recently drawn attention
to the risk of new pasture plants becoming
invasive, because the same biological traits
that promote pasture productivity may also
facilitate the invasion of natural areas. The
authors indicate some aspects that could mitigate
the risk of invasion: namely, the use of
native species to develop new pasture plants,
the avoidance of new characteristics associated
with environmental weeds, and the
selection of new characteristics that limit invasion
risk. Here we describe a system that
meets the above criteria—specifically, the last
one—through the existence of a mismatch
between the environmental conditions found
in managed and in natural areas, such that
improved pasture plants face environmental
limitations in natural areas while keeping a
high performance in managed ones.
The system of sown biodiverse permanent
pastures rich in legumes (SBPPRL) has been
successfully implemented in Portugal on
farms in Mediterranean climate areas (2, 3).
SBPPRL were developed by Portuguese
agronomists, namely David Crespo, as a response
to the low levels of productivity and
feed quality obtained in seminatural pastures.
The pastures’ low performance results from
endogenous low soil fertility and historical
land use practices that depleted soil nutrients,
disrupted soil structure, and caused plant
community impoverishment, especially the
decline of legume species (4). SBPPRL consist
in mixtures of up to 20 taxa of grasses
and legumes, each mixture tailored to local
environmental conditions (e.g., precipitation
and soil texture) to best cover the available
environmental niches. Seed mixtures include
autochthonous (the majority) and exotic species
(all native to the Mediterranean basin)
selected to achieve the best performance in
soils with enhanced fertility. Legumes and
associated Rhizobium fix atmospheric nitrogen,
making the system self-sufficient in
nitrogen, but require an external input of
phosphorus (a limiting nutrient in Mediterranean
soils) and the correction of soil acidity
for optimal legume growth (5). As result, improved
cultivars are not competitive in oligotrophic
environments with acidic soils (i.e.,
natural environments) but outcompete spontaneous
pasture plants in managed systems.
This aspect not only contributes to the longterm
persistence of SBPPRL but also to reducing
their invasive risk. In fact, the older
SBPPRL are now over 30 y old, and there are
no reports of exotic pasture species establishment
outside ruderal or managed pasture
habitats (i.e., in natural ecosystems).
Moreover, SBPPRL offer an alternative for
sustainable intensification by combining
higher pasture productivity (i.e., socio-economic
benefits) with environmental benefits
that emerge as positive externalities, such as
soil carbon sequestration and soil restoration,
both associated with the absence of tillage in
SBPPRL and the accumulation of soil organic
matter (3, 4). Additionally, the use of phosphorus
fertilization is more than compensated
by the avoided impacts of using
nitrogen fertilizers (otherwise required either
to produce concentrate feed or fertilize
pastures), and potential leaching of phosphorus
is mitigated by increased soil organic
matter (4). The opportunities for society
of SBPPRL were acknowledged by the
Portuguese Carbon Fund* through the payment
of soil carbon sequestration (2009–
2014) in around 50,000 ha, in an estimated
total of 1 million tons of CO2 (2).
