Spatio-temporal invasion dynamics of maesopsis eminii in Amani nature forest reserve, Tanzania
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Date
2020
Journal Title
Journal ISSN
Volume Title
Publisher
Elservier
Abstract
Globally, invasive plant species cause negative impacts to human livelihoods and natural ecosystems, particu-
larly in biodiversity hotspots. Maesopsis eminii invasion in Amani Nature Forest Reserve, Tanzania, was con-
sidered an ecological disaster in the 1980s. After >50 years have elapsed since the species was first introduced
in the reserve, there is yet little information available on its invasion progress. We assessed spatio-temporal
invasion dynamics using forest inventory data collected in 1998 and resurveyed 60 (20 m × 50 m) sample plots
in 2018. Among resurveyed plots, 30 had been invaded by M. eminii in 1998 and other 30 sample plots as
control, which had no M. eminii in the year 1998. We also assessed vegetation cover change over a 20 year period
between 1998 and 2018 using Landsat satellite images. Over the last 20 years, 23% of control plots were newly
invaded by M. eminii. Tree species richness was 25% lower in invaded versus control plots (U = 1490, z = 2.9,
p = 0.04). Large trees (DBH ≥ 31–50 cm) of Maesopsis eminii were most abundant (62%) in invaded plots
whereas small trees (DBH ≤ 10 cm) were most abundant (>50%) in control plots, indicating that the tree
species might be prone to self-thinning. Woody species diversity was significantly lower in invaded
(1.63 ± 0.49) vs control plots (1.87 ± 0.35; t (58) = −2.19, p = 0.03). The number of M. eminii individuals ha −1
was positively associated with higher altitudes ranging above 800 masl (ρ = 0.33, P = 0.011) but there was no
correlation with distance away from the forest reserve boundary (ρ = 0.11, P = 0.394;) nor with distance away
from village centers (ρ = −0.08, P = 0.502). Change detection analysis indicated about 1,108 ha of non-forest
vegetation had regrown into forest over the last 20 years, particularly in the south - western region of the
reserve. The region included 4 sample plots newly invaded by M. eminii. We conclude that there is an increase in
spatial distribution of M. eminii individuals between the year 1998 and 2018. Furthermore, M. eminii has low
regeneration potential in already invaded sites of high invasive density and only slowly invading gaps in un-
invaded sites.
Description
Journal Article
Keywords
Invasive tree, Regeneration potential, Remote sensing, Distributional range, Population structure, Biodiversity hotspot