Abstract
AbstractAimThere is an intense debate about whether habitat fragmentation has a negative or positive effect on biodiversity. We examined whether species richness and incidence of forest plants were negatively or positively associated with fragmented forest configuration. We also analysed whether the results support the fragmentation threshold hypothesis with fragmentation effects only in landscapes with small habitat amount.LocationSödermanland province, south‐eastern Sweden (8,388 km2).MethodsData consisted of plant distribution maps and landscape data on forest amount and configuration in 2.5 km × 2.5 km quadrats. We carried out models including forest area together with clumpiness index (CL models) or edge density (ED models) as the measure of habitat configuration. We focused on plant taxa with positive association between incidence and forest area (163 taxa in CL models; 119 taxa in ED models).ResultsResponses to fragmented configuration were negative more often than by random (33 and 22 taxa in CL and ED models, respectively; includes only models without significant forest area × configuration interaction), whereas positive responses were rare (four taxa in both models). When forest area × configuration interaction was significant, the most common response had a negative effect of fragmented configuration when forest area was low and no effect of configuration when forest area was high, which agrees with the fragmentation threshold hypothesis. Species richness also had this type of response. In another common interactive response, the effect of fragmented configuration was negative at low forest area and positive at high forest area.Main conclusionsResponses to fragmented forest configuration, when significant, were usually negative. When responses to fragmented configuration were modulated by forest area, they were negative when forest area was low. The findings of complex interaction between forest area and configuration have implications for selection of appropriate patch sizes in sustainable forest management.
Highlights
While there is a consensus that habitat amount has a positive effect on species distribution and abundance, the role of habitat fragmentation has raised plenty of debate (Andrén & Andren, 1994; Fahrig, 2003, 2017; Haddad et al, 2017; Hadley & Betts, 2016)
The response to clumpiness was positive in forest areas lower than 54.1%, and response to edge density was negative when forest area was lower than 56.0% (Figure 4)
We found that fragmented forest configuration often had a negative effect on the incidence of the forest-associated plant taxa of Södermanland
Summary
While there is a consensus that habitat amount has a positive effect on species distribution and abundance, the role of habitat fragmentation has raised plenty of debate (Andrén & Andren, 1994; Fahrig, 2003, 2017; Haddad et al, 2017; Hadley & Betts, 2016). Haddad et al (2015), in their synthesis of fragmentation experiments, state that fragmentation negatively affected population abundance, species richness and ecosystem functions in forests. Contrary to these ideas, Fahrig (2003, 2017, 2018) recently challenged the paradigm of the negative effect of fragmentation. She argues that most studies have shown that effects of fragmentation per se on species richness and occurrence and abundance of species are positive rather than negative (Fahrig, 2017). Fahrig's claims are further supported by De Camargo, Boucher-Lalonde, and Currie (2018) who only found weak effects of fragmentation on the incidence of single species and on species richness of birds in Ontario, Canada, and when the effects were significant, they were usually positive
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