High densities of wild deer can undermine the contributions of trees and woodlands to tackling the climate and biodiversity crises. Herbivory of young trees, saplings and understorey plants can stunt tree growth, inhibit regeneration altogether, and tip forest ecosystems toward alternative states. In addition, deer inflict major economic losses to forestry and agriculture, and can threaten public health via road traffic accidents and Lyme disease. At the same time, deer provide benefits through their intrinsic, aesthetic, and cultural value, while also generating significant income from hunting and tourism. For decades, landowners, hunters, conservationists, and government officials have been unable to reach consensus over what constitutes successful deer management in different contexts.
Managing deer populations and their impacts on woodlands is extremely challenging. Management actions that influence the degree to which deer damage woodlands can be classified into direct efforts to control deer population size e.g., via culling (henceforth ‘deer management’), and forestry/landscape decisions that influence deer behaviour, such as the siting/location, tree species composition and density of new and existing woodlands, and, the provision of features such as alternative forage, non-lethal repellents and fencing (henceforth ‘woodland management decisions’). While actions are implemented locally -with rights to shoot or create woodlands resting with landowners- live deer are res nullius, owned by no-one, and are highly mobile animals that cross jurisdictions and boundaries. Consequently, local management actions can elicit effects that cascade across entire landscapes, influencing outcomes elsewhere. For example, fencing might displace deer to neighbouring farmland, or tree planting will alter woodland cover and configuration at the landscape scale, influencing deer movement and impacts elsewhere. Project iDeer contends that these landscape-scale effects of deer and woodland management decisions must be explicitly considered in environmental land management plans, in order to effectively expand and safeguard woodlands, mitigate trade-offs among objectives, and prevent conflicts among stakeholders.