Reversing declines in farmland birds: how much agri-environment provision is needed at farm and landscapes scales?

1) Agri-environment schemes (AES) are the primary policy mechanism for
addressing farmland biodiversity declines across Europe. Despite previous
studies on the impacts of AES on biodiversity, there is little empirical
evidence on the scale of provision required to reverse declines. 2) Across
three regions of lowland England with contrasting farm systems (arable,
pastoral, mixed) we estimated avian Population Growth Rates (PGRs) on
farmland with high AES provision (‘higher-tier’: average bird-friendly
option cover = 7.4%), low AES provision (‘lower-tier’: 2.3%), and no
bird-friendly AES (‘no AES’). Ten-year PGRs were derived for 24 species
and three multi-species groups comprising farmland-associated species
(‘farmland birds’), species of conservation concern (‘priority birds’),
and species restricted to farmland (‘specialist birds’). We used PGRs to
simulate the proportion of the regional farmland landscape that would have
to be assigned to higher- and lower-tier agreements to stabilise or
increase populations. 3) In the arable and pastoral regions, 13/23 and
13/22 species respectively had more positive PGRs under higher-tier AES
than on no AES farmland (none had more negative PGRs), compared to 4/22
(positive) and 1/22 (negative) in the mixed region. Only 2-4 species per
region exhibited more positive PGRs under lower-tier AES compared to no
AES farmland. 4) Multi-species PGRs in the arable and pastoral regions
increased from no AES (strong decline), to lower-tier (decline or
stability) to higher-tier (moderate or strong increase). There was no
overall AES effect in the mixed region. 5) To increase regional farmland
bird populations by 10% over 10-years, 47% and 26% of the farmed landscape
would need to be devoted to higher-tier agreements in arable and pastoral
landscapes respectively. This falls to 34% and 17% when higher-tier is
targeted at localities supporting higher abundances of target species, and
to 29% and 10% when 30% of the farmed landscape is also devoted to
lower-tier. Priority and specialist birds require higher provision levels.
6) Policy implications. Where farmland bird recovery is an AES objective,
farms should prioritise higher-tier agreement delivery over lower-tier.
Farmland bird responses to AES provision are likely to vary regionally but
careful targeting will reduce the amount needed in the landscape.