Results
All calibrated models performed well with an average TSS value above 0.8
(Supporting Information Fig.S2). The results reported below were
consistent across all GCMs
explored (Supporting Information Fig. S5). The number of grid cells
projected suitable for the 1,527 cultivated alien species in Southern
Africa under current conditions varied from 0 to 9,244, or approximately
51% of Southern Africa’s area. The number of species projected to
encounter climatically suitable conditions in at least one grid cell
under the current conditions also varied greatly, ranging from 0 to 313
species per grid cell, or approximately 20% of the modeled cultivated
alien flora of Southern Africa (Fig. 1a). Under climate warming
scenarios (SPP1 and SSP5), these numbers were projected to decrease
(Fig. 1b-e). Projected changes in Maximum Temperature of the Warmest
Month resulted in the highest future contraction of potential ranges of
alien cultivated plants in Southern Africa (Supporting Information Fig.
S3).
Of Southern Africa, 10.0% were defined as invasion hotspots that were
considered climatically suitable under current climatic conditions for
at least 128 from the pool of 1,527 modeled cultivated alien species
(Fig. 2a). Until the end of the century, the size of the invasion
hotspot is predicted to decrease slightly under SSP1 climatic scenario
(to 7.1%; Fig. 2b), but substantially under the worst-case climatic
scenario SSP5 (to 2.0%; Fig. 2c).
We compared the number of alien species predicted to find suitable
conditions in the various biomes in Southern Africa under current and
future climatic conditions and found slight differences among them (Fig.
3a, b). Based on both future scenarios, tropical biomes are likely to
experience less of a reduction in species richness, while other biomes
may either not differ significantly from random expectations or even
lose more species richness than anticipated by chance. Furthermore,
under the worst-case scenario SSP5, the average potential species
richness was significantly less than zero in all biomes (indicating a
significant decrease in cultivated alien species richness) (Fig. 3a, b).
Under current climatic conditions, naturalized plants were predicted to
have a larger potential range than non-naturalized cultivated plants in
Southern Africa (GLM: Z = 9.64, P ≤ 0.001; Fig. 3a, Supporting
information Table S1). However, as climate becomes warmer, the size of
potential ranges is projected to decline for all species (Fig. 3b&c).
While contraction is projected to be more significant for
non-naturalized species than for naturalized ones under the moderate
future climatic scenario SSP1 (GLM: Z = 2.15, P = 0.031; Fig. 3b,
Supporting information Table S1), under the worst-case scenario SSP5,
there will be no significant difference between the two groups (GLM:
Z = 1.87, P = 0.060; Fig. 3c, Supporting information Table S1).
While the average cultivated plant in Southern Africa will experience a
reduction of its potential range, an increase is projected for
~13% and 9% of species under the scenarios SSP1 and
SSP5, respectively.
Our results indicated that under the SSP1 climate-change scenario,
species native to TDWG continents mainly located in the Southern
Hemisphere (i.e., Pacific Islands, Australasia, Tropical Asia, and
Southern America) would likely lose less climatically suitable areas
than the average cultivated species. Species native to Pacific Islands
and Australasia have an average change in range size significantly
greater than zero, indicating a significant increase in areas with
suitable climates. In contrast, species native to continents mainly
located in the Northern Hemisphere (i.e., Europe, other parts of Africa,
and Asia Temperate) will likely lose climatically suitable range in
Southern Africa at an above-average rate (Fig. 4a). However, for SSP5
climate-change scenario all species are predicted to have an average
change in range size significantly less than zero, indicating a
significant contraction in areas with suitable climates (Fig. 4b).