Forest-fragment quality rather than matrix habitat shapes herbivory on tree recruits in South Africa

Abstract

Abstract:Forest fragmentation can alter herbivory on tree recruits with possible consequences for regeneration. We assessed effects of forest-fragment quality (tree diversity, vegetation complexity, relative abundance of pioneer trees) and matrix habitat on arthropods and herbivory in KwaZulu-Natal, South Africa. We compared arthropod abundances and herbivory on woody seedlings and saplings among four forest-fragment types differing in size and matrix (large fragments and small fragments surrounded by natural grassland, eucalypt and sugarcane plantations; nplots = 24) using analyses of covariance. We recorded 3385 arthropods and inspected 897 seedlings (71 species) and 876 saplings (91 species). Relative abundance of predators increased with fragment quality; that of herbivores decreased. Herbivory responses to fragment quality varied: seedling herbivory decreased with relative abundance of pioneers and sapling herbivory increased with vegetation complexity. Matrix effects were low with little variation in relative abundance of predators (0.39–0.53) and herbivores (0.22–0.32), proportion of seedling (8.3–11.0%) and sapling herbivory (12.4–14.3%) among the forest-fragment types. These findings indicate that herbivory on tree recruits is mediated by forest-fragment quality rather than matrix habitat. Future studies should evaluate whether contrasting effects of fragment quality on arthropods and herbivory are caused by weak trophic interactions and variable herbivore compositions.

Forest Fragmentation Drives the Loss of Insectivorous Birds and an Associated Increase in Herbivory

“…The low insect herbivore abundances may be explained by some non-mutually exclusive factors, e.g., the comparably high rainfall from August to December 2012 (731 mm; 146 AE 38 mm/mo) which may have reduced overall activity of the herbivorous insects (Ezemvelo KZN Wildlife 2009). However, previous studies from the same region also found insect herbivore abundances to be rather low (Moran et al 1994, Botzat et al 2013, Peter et al 2014 and possibly a result of seasonal variability within the insect herbivore community (Da Silva et al 2011). The picture of the insect herbivore community at the time of our sampling may, thus, not necessarily display the insect herbivore community throughout the whole season.…”

“…, Botzat et al . , Peter et al . ) and possibly a result of seasonal variability within the insect herbivore community (Da Silva et al .…”

Invasive alien plant species, fragmentation and scale effects on urban forest community composition in Durban, South Africa

“…The size and types of matrices surrounding forest patches have an influence on the establishment of invasive species (Hansen and Clevenger 2005;Bartuszevige et al 2006;Botzat 2012;Nitoslawski and Duinker 2016). The niches that have high numbers of IAPs correspond with the areas that have high values for the correlated similarity indices of residence and industry (Fig.…”

“…Management of IAPs outside the boundaries of forest reserves might be poor; therefore, adjacent forest patches that are invaded may be propagule sources of wind-dispersed IAPs as suggested by Macdonald and Jarman (1985). So, such forest patches occurring outside of nature reserves, even when they have low transformation and resembling natural habitats, are potential propagule sources of IAPs regeneration in nearby forest reserves (Botzat 2012). The E community is more pronounced in patches of lowland coastal forest, and the K community is more pronounced in patches of high-elevation scarp forest.…”

“…The high proximity to non-managed forest patches found outside boundaries of nature reserves act as corridors that could be occupied by plants with wind-dispersed invasive seeds. The configuration of a landscape and the proximity to propagule sources increases dispersal towards nature reserves which increases invasion risk (Borgmann and Rodewald 2005;Botzat 2012). Management of IAPs outside the boundaries of forest reserves might be poor; therefore, adjacent forest patches that are invaded may be propagule sources of wind-dispersed IAPs as suggested by Macdonald and Jarman (1985).…”