The changing role of ornamental horticulture in alien plant invasions

Abstract

The number of alien plants escaping from cultivation into native ecosystems is increasing steadily. We provide an overview of the historical, contemporary and potential future roles of ornamental horticulture in plant invasions. We show that currently at least 75% and 93% of the global naturalised alien flora is grown in domestic and botanical gardens, respectively. Species grown in gardens also have a larger naturalised range than those that are not. After the Middle Ages, particularly in the 18th and 19th centuries, a global trade network in plants emerged. Since then, cultivated alien species also started to appear in the wild more frequently than non-cultivated aliens globally, particularly during the 19th century. Horticulture still plays a prominent role in current plant introduction, and the monetary value of live-plant imports in different parts of the world is steadily increasing. Historically, botanical gardens - an important component of horticulture - played a major role in displaying, cultivating and distributing new plant discoveries. While the role of botanical gardens in the horticultural supply chain has declined, they are still a significant link, with one-third of institutions involved in retail-plant sales and horticultural research. However, botanical gardens have also become more dependent on commercial nurseries as plant sources, particularly in North America. Plants selected for ornamental purposes are not a random selection of the global flora, and some of the plant characteristics promoted through horticulture, such as fast growth, also promote invasion. Efforts to breed non-invasive plant cultivars are still rare. Socio-economical, technological, and environmental changes will lead to novel patterns of plant introductions and invasion opportunities for the species that are already cultivated. We describe the role that horticulture could play in mediating these changes. We identify current research challenges, and call for more research efforts on the past and current role of horticulture in plant invasions. This is required to develop science-based regulatory frameworks to prevent further plant invasions.

Domestic gardens play a dominant role in selecting alien species with adaptive strategies that facilitate naturalization

“…spreading rapidly over large areas and often causing negative environmental or societal impacts; Pyšek, Jarošík, & Pergl, ), a much greater proportion of naturalized plants is introduced intentionally for human uses including ornamental horticulture (Dehnen‐Schmutz, Touza, Perrings, & Williamson, ; Hulme et al, ; Lambdon et al, ; Pyšek et al, ; Reichard & White, ). Botanic gardens have played a key role in introducing ornamental alien plants and, globally, they hold > 150,000 plant species in their collections (Hulme, ; van Kleunen et al, ; Mounce, Smith, & Brockington, ). Thus, although botanic gardens currently play a vital role in conserving plant diversity and preventing extinction (van Kleunen et al, ; Mounce et al, ; Sharrock, ), they also cultivate many species with invasion potential (Hulme, ).…”

“…Botanic gardens have played a key role in introducing ornamental alien plants and, globally, they hold > 150,000 plant species in their collections (Hulme, ; van Kleunen et al, ; Mounce, Smith, & Brockington, ). Thus, although botanic gardens currently play a vital role in conserving plant diversity and preventing extinction (van Kleunen et al, ; Mounce et al, ; Sharrock, ), they also cultivate many species with invasion potential (Hulme, ). Similarly, domestic gardens also constitute an important source of potential alien invaders (Dehnen‐Schmutz, Touza, Perrings, & Williamson, ; Hulme, ; Hulme et al, ; van Kleunen et al, ; Pergl et al, ).…”

Nitrogen acquisition of Central European herbaceous plants that differ in their global naturalization success

“…Human activities have resulted in the introduction of many plant species to new regions, where they are not native (van Kleunen, Essl et al, ). More than 13,000 of these alien plants have been able to establish self‐sustaining wild populations (i.e.…”

European ornamental garden flora as an invasion debt under climate change

“…Globally, already over 13,000 alien vascular plant species have established persistent wild populations outside of cultivation (Pyšek et al., ; van Kleunen et al., ) A subset of these so‐called naturalised species (sensu Richardson et al., ) are known to have negative ecological impacts and are considered invasive (sensu Secretariat of the Convention on Biological Diversity, ). Most naturalised alien plants have originally been introduced intentionally from their native regions into other regions for cultivation in domestic or botanic gardens (van Kleunen et al., ). Given that globally, at least 170,000 plant species are in cultivation (van Kleunen et al., ), the garden flora constitutes an enormous pool of potential alien invaders (Pergl et al., ).…”

“…Most naturalised alien plants have originally been introduced intentionally from their native regions into other regions for cultivation in domestic or botanic gardens (van Kleunen et al., ). Given that globally, at least 170,000 plant species are in cultivation (van Kleunen et al., ), the garden flora constitutes an enormous pool of potential alien invaders (Pergl et al., ).…”