Alien plant species have been essential for farming and agro-forestry
systems and for their supply of food, fiber, tannins, resins or wood from antiquity to
the present. They also contributed to supporting functions and regulating services
(water, soil, biodiversity) and to the design of landscapes with high cultural and
scenic value. Some of those species were intentionally introduced, others arrived
accidentally, and a small proportion escaped, naturalized and became invasive in
natural ecosystems—these are known as invasive alien species (IAS). Here, invasive means that these species have some significant negative impact, either by
spreading from human-controlled environments (e.g. fields, gardens) to natural
ecosystems, where they can cause problems to native species, or to other production
systems or urban areas, impacting on agricultural, forestry activities or human
health. Socio-environmental impacts associated with plant invasions have been
increasingly recognized worldwide and are expected to increase considerably under
changing climate or land use. Early detection tools are key to anticipate IAS and to
prevent and control their impacts. In this chapter, we focus on crop and non-crop
alien plant species for which there is evidence or prediction of invasive behaviour
and impacts. We provide insights on their history, patterns, risks, early detection,
forecasting and management under climate change. Specifically, we start by providing
a general overview on the history of alien plant species in agricultural and
agroforestry systems worldwide (Sect. 1). Then, we assess patterns, risks and
impacts resulting from alien plants originally cultivated and that became invasive
outside cultivation areas (Sect. 2). Afterwards, we provide several considerations
for managing the spread of invasive plant species in the landscape (Sect. 3). Finally,
we discuss challenges of alien plant invasions for agricultural and agroforest systems,
in the light of climate change (Sect. 4).