Divergent fire management leads to multiple beneficial outcomes for butterfly conservation in a production mosaic

Abstract

1. Fire is an intrinsic component of many natural ecosystems. In human-modified landscapes that occur in fire-driven ecosystems, it can be difficult to make fire management decisions, as there must be a trade-off between ideal conservation management and the practicalities of management in an altered landscape.2. We assess how biodiversity is influenced by differences in fire regime in a landscape fragmented by timber production. Here, optimal fire management for maintaining grassland integrity is not always possible, due to logistical constraints and fire risk to plantations. We investigate thicket establishment arising from reduced fire frequency, and how this affects butterfly diversity, assemblage structure, indicator species and species associations to larval host plants with different growth forms. Butterflies were sampled along a gradient of woodiness in large-scale conservation corridors that separate timber compartments.3. The two extreme stages along the successional gradient, recently burned grassland and natural forests, supported relatively diverse and complementary butterfly assemblages. Grassland corridors without fire for 2 years were as high in butterfly diversity and similar in composition to recently burned grasslands.However, corridors without fire for >5 years were encroached by thicket and supported lower butterfly diversity. Thicket, with its intermediate vegetation character, was poor habitat for species adapted to either open grassland or to forests. Also, thicket-encroached areas carry high fire risk to plantations. 4. Synthesis and applications. In this fragmented, fire-driven ecosystem, there is more than one burning strategy for achieving positive biodiversity outcomes. We recommend a divergent management approach that covers both extremes of the fire frequency continuum, with the choice depending on the stage of succession and management logistics for each site: (a) frequent burning to prevent woody encroachment in less-encroached, logistically easier sites or (b) letting succession run its course through thicket to forest by excluding fire in heavily encroached, logistically challenging sites. Both options are practicable and maintain biotopes that have high value for butterfly conservation and low fire risk to plantations. This divergent management approach is a flexible strategy that benefits both conservation and commercial interests across fire-prone plantation mosaics.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Within‐corridor heterogeneity is more important than corridor design for maintaining butterfly functional and taxonomic diversity

“…Butterflies and local environmental variables were determined in a commercial timber estate in the KwaZulu-Natal Midlands, South Africa (29.6709S, 29.9639E, Figure 1). More details on the study area, sites and sampling methods are in Gaigher et al (2019), with a brief description below.…”

“…At least half of this estate is unplanted and forms interconnected corridors of mostly remnant grasslands interspersed with indigenous Afromontane Mistbelt Forest. Divergent fire management further adds to landscape heterogeneity, either maintaining open grasslands at one extreme or allowing the succession of grasslands to thickets, and ultimately indigenous forests, at the other (Gaigher et al, 2019). We refer to indigenous forest and thicket as 'seminatural woody elements', and exclude them from planted forestry stands ('compartments').…”

“…In this case, change in corridor width relates to change in the relative amount of compartment versus non-compartment and influences compositional heterogeneity, whereas change in the shape of a corridor influences configurational heterogeneity. At a finer resolution, planning and management that consider background environmental heterogeneity (Pryke & Samways, 2015) and provide a range of successional stages (Gaigher et al, 2019) are recommended. Here, again, the relative amount of patch types within a corridor influences compositional heterogeneity while their spatial arrangement influences configurational heterogeneity.…”

“…Most butterflies in these networks avoid forestry plantations (Pryke & Samways, 2001). Within corridors, butterflies track changes in local vegetation structure along a fire succession gradient, with distinct assemblages in relatively open, more frequently burned grasslands versus less burned, woody habitats (Gaigher et al, 2019). What remains unclear is the effect of vegetation structure at the landscape scale through its influence on landscape heterogeneity, as well as the influence of landscape heterogeneity measured at different resolutions of conservation planning.…”

“…We use previously published data (Gaigher et al, 2019), and assess how local variables relating to vegetation structure and landscape variables that reflect conservation planning at different resolutions influence taxonomic and functional diversity of butterfly assemblages in a South African EN. Butterflies were sampled in different biotopes (vegetation types) within a mosaic timber production landscape.…”