Tropical production landscapes and conservation: a study investigating the biodiversity value of a native timber plantation landscape in Papua New Guinea

Pryde, Elizabeth Clare (2014) Tropical production landscapes and conservation: a study investigating the biodiversity value of a native timber plantation landscape in Papua New Guinea. PhD thesis, James Cook University.

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Abstract

The majority of old-growth tropical forests and the vast biodiversity they support exist outside of protected areas, either embedded within production landscapes or adjacent to them. As a consequence, conserving the world's tropical biodiversity depends largely on the effective management of production landscapes (landscapes containing one or multiple production land-uses). Effective conservation management necessitates a balance between production goals (e.g. crop or timber yields) and biodiversity conservation. 'Land-sharing' strategies attempt to achieve this balance in production landscapes by encouraging lower-intensity production land-uses and where possible, the retention of pre-conversion vegetation cover. This presents a promising way forward for conservation in production areas but is hampered by inadequate information on the capacity of production landscapes to support native biodiversity in most tropical ecosystems.

In this thesis I investigated the biodiversity conservation value of a multi-use production landscape comprised of native timber (Eucalyptus deglupta) plantations interspersed with (historically logged) secondary forests and unlogged forest remnants. The study was based in the lowlands of New Britain Island, Papua New Guinea and represents one of the only studies of the impact of production landscapes on Melanesian biota. To assess the state of biological diversity within this production landscape I had three principal objectives: (1) understand which forest species can and cannot persist in production land-uses and how these patterns are mediated by species' biological attributes; (2) evaluate the effect of land-use type on vegetation and stand-level structural attributes; and (3) examine which properties of the native plantation landscape most influence the occurrence patterns of lowland forest birds. Surveys were conducted at 156 survey sites over a two-year period (2007–2008). Sites were stratified among the five main management elements that comprised the plantation landscape and represented a gradient in land-use (from least-to-most disturbed): unlogged forest, secondary remnant forest, secondary riparian buffer strips, mature plantations and young plantations. At each survey site I recorded data on the occurrence of forest bird and tree species and measured the incidence of vegetation types and the stand structural attributes. Based on the knowledge gained from this research, I formulated conservation management strategies that can effectively balance the maintenance of forest biodiversity in the landscape with timber yield targets.

Investigation into the patterns of forest species occurrence among landscape elements (the main land-use types) revealed that at least 70% of tree species and 90% of bird species were capable of existing outside of unlogged remnant forest, within the matrix of mature plantations and forestry-affected secondary forest. These levels are high compared to the tropical literature on timber plantations and suggest both a resilient species pool along with management practices that may encourage biodiversity retention. However, species richness at sites within mature plantations was lower than within unlogged and secondary forest and their species assemblages were compositionally dissimilar to those of unlogged forest, demonstrating a successive loss of more vulnerable species (e.g. late-successional trees, and frugivorous and forest-specialist birds). In addition, young plantations (2–6 years old) supported very few forest species and these species were in low abundance. These trends highlight the importance of considering the temporal as well as spatial aspects of production types when assessing conservation value.

Evaluation of land-use effects on vegetation and habitat structure provided insight into both the post-disturbance recovery trajectory of the island's flora and the ramifications of this for their provision of potentially important habitat resources. In general, structural attributes recovered more rapidly than tree and plant species composition in the modified landscape elements. The secondary remnant forest, which was protected by a conservation reserve, demonstrated a very high regenerative capacity. By contrast, the unprotected secondary riparian element, which was subject to ongoing human disturbance and was of more linear shape and fragmented distribution, displayed simplified canopy structure and contained less late-successional vegetation. A similar but more extensive reduction in many old-growth habitat properties was observed for mature plantations, and young plantations suffered acute losses (and absences) for all habitat properties measured.

Building on these findings, I examined the influence of both habitat properties and landscape spatial context on the species richness of forest birds. I found that habitat attributes (e.g. canopy cover and tree species richness) had a greater influence than spatial context (the proportion of unlogged and high-quality secondary forest within a 2km radius) on the richness of bird species among survey sites. In addition, for a sub-set of more vulnerable species (forest-specialists) I found palm cover to also be an important predictor of richness. These results further demonstrate the value of unlogged and secondary forest in terms of their quality as habitat for sustaining avifaunal populations, underscoring the need to formally protect these forests to achieve long-term biodiversity conservation benefits. These results also revealed the properties of mature plantations that facilitated visitation by forest birds and conversely drew attention to management practices that could negatively affect this relationship.

The outcomes of this thesis indicate that land-sharing strategies incorporating production types such as native timber plantations, which permit high canopy cover and tree species richness, can be effective at balancing yield production with biodiversity conservation. Native species are used in <15% of tropical plantation forests globally and given their potential to deliver conservation outcomes, research should be directed at countering barriers to their use over exotic species. However, this study also concluded that such conservation outcomes are dependent on the sympathetic management of plantations, as well as land-use planning directed at facilitating the spatial and temporal continuity of old-growth forest features in the landscape. In addition, without the formal protection and careful management of unlogged and secondary forest reserves, the likelihood of long-term conservation of many forest-dependent species will diminish. Basing conservation management of production landscapes on scientific research is a vital but often unachievable undertaking in the tropics, particularly over the long-term. It is likely that the adoption of recommended management actions can be supported by more targeted research and importantly, through greater collaboration between research institutions, sustainable management organisations, land managers and local communities. Science can go a long way to assist with decision-making but ultimately decisions rest with the values of society.

Item ID: 43784
Item Type: Thesis (PhD)
Keywords: biodiversity value; conservation management; conservation protection; land management; Melanesia; Papua New Guinea; plantation crops; plantation forestry; plantation forests; plantation timber; PNG; preservation; production landscapes; timber plantations; tropical forests; tropics; vegetation
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 3: Pryde, Elizabeth C., Holland, Greg J., Watson, Simon J., Turton, Stephen M., and Nimmo, Dale G. (2015) Conservation of tropical forest tree species in a native timber plantation landscape. Forest Ecology and Management, 339. pp. 96-104.

Date Deposited: 18 May 2016 02:03
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050202 Conservation and Biodiversity @ 50%
05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050211 Wildlife and Habitat Management @ 50%
SEO Codes: 96 ENVIRONMENT > 9605 Ecosystem Assessment and Management > 960505 Ecosystem Assessment and Management of Forest and Woodlands Environments @ 50%
96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960806 Forest and Woodlands Flora, Fauna and Biodiversity @ 50%
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