Large ecosystem-scale effects of restoration fail to mitigate impacts of land-use legacies

Ecological restoration is a global priority, with potential to reverse
biodiversity declines and promote ecosystem functioning. Yet, successful
restoration is challenged by lingering legacies of past land-use
activities, which are pervasive on lands available for restoration.
Although legacies can persist for centuries following cessation of human
land uses such as agriculture, we currently lack understanding of how
land-use legacies affect entire ecosystems, how they influence restoration
outcomes, or whether restoration can mitigate legacy effects. Using a
large-scale experiment, we evaluated how restoration by tree thinning and
land-use legacies from prior cultivation and subsequent conversion to pine
plantations affect fire-suppressed longleaf pine savannas. We evaluated 45
ecological properties across four categories: 1) abiotic attributes, 2)
organism abundances, 3) species diversity, and 4) species interactions.
The effects of restoration and land-use legacies were pervasive, shaping
all categories of properties, with restoration effects roughly twice the
magnitude of legacy effects. Restoration effects were of comparable
magnitude in savannas with and without a history of intensive human land
use; however, restoration did not mitigate numerous legacy effects present
prior to restoration. As a result, savannas with a history of intensive
human land use supported altered properties, especially related to soils,
even after restoration. The signature of past human land-use activities
can be remarkably persistent in the face of intensive restoration,
influencing the outcome of restoration across diverse ecological
properties. Understanding and mitigating land-use legacies will maximize
the potential to restore degraded ecosystems.