SUMMARY OF THESIS PROJECT:
ECOLOGICAL RESTORATION OF THE WAIRIO WETLANDS, LAKE WAIRARAPA: VEGETATION
DYNAMICS AND SUCCESSION.
AIM
Theoverall purpose is to conduct scientific research that will inform the management and ecological
restoration objectives of Wairio wetland. The thesis title is Ecological restoration of the Wairio
wetlands, Lake Wairarapa: vegetation dynamics and succession. This has been split into two
chapters: (1) An Investigation into the Interplay of Processes Influencing the Establishment and
Survival of Native Woody Vegetation at Wairio Wetlands Wairarapa and (2) Patterns of Native Turf
Species Vegetation during Summer Desiccation at Wairio Wetlands, Wairarapa.
This summary will deal with the first chapter. The objective of the research is to commence
investigating the interplay of processes that influence the establishment and survival of native
woody vegetation in the restoration area typical of historically present swamp forest e.g. Kahikatea,
Cabbage Tree, and Totara. The ecological mechanisms relevant to replanting include: plant
competition (e.g. with tall fescue (Festuca arundinacea) and other grasses), facilitation, disturbance,
successional trajectories and their interaction with abiotic conditions.
BACKGROUND
The Wairio Wetland, located on the eastern shores of Lake Wairarapa, once provided habitat for
substantial numbers of native waterfowl and waders. The wetland area was adversely affected by
the Lower Wairarapa Valley Development Scheme (LWVDS) during the 1960s and 1970s which
resulted in large areas being drained and cleared of forest and sedges. The region was further
affected by the construction of the Parera Road, which separated the area from the adjacent Boggy
Pond Wetland. In order to reverse the damaging effects of the drainage issues or the accidental
introduction of invasive species a detailed knowledge of the component species and ecological
processes is required.
Presently, within the Wairio wetland are three large fenced blocks (5-8ha each). Blocks 1 and 2 have
been managed to varying degrees by the creation of bunds, areas of seasonal open water and
planting clusters of native tree species. Survival of trees planted (in 2005, 2007 and 2009) has been
variable and competition with tall fescue grass is presumed to be the proximate reason for the
failure of many of the trees. Block 3 (5.6 ha) has undergone little earth work and no replanting has
taken place. This gives opportunity for a large scale design monitoring field experiment. The aim of
the experiment would be to determine the best (i.e. most cost-effective) combination of treatments
leading to establishment of tree saplings.
METHODS
Designing and implementing a large-scale manipulative field experiment involving the planting of
~2400 native trees subject to different methods of site preparation and after-care to determine the
best (i.e. most cost-effective) combination of treatments for successful establishment of tree
saplings. Bridget will monitor the survival and growth over the first six months, and develop
protocols for longer-term monitoring and follow-up studies.
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Trees will be planted in clusters at two different densities (either 1.5m or 0.75m apart) combined
with five possible management techniques: interspersed with a nurse crop (either concurrently
planted with focal species or planted in advance from the nurse species) , weed-mat, chemical
weed-control, top soil excavation and a no-planting control. These clusters will be replicated to a
total of 58 plots. Planting commenced on June 23rd 2011, with the survival being monitored in early
December 2011.
Trees have been categorised into two broad groups: “focal species” are species characteristic of
mature swamp forest, they typically regenerate under a partial canopy and are reasonably slowgrowing. “Nurse Species” are pioneers that “grow fast and die young”, they are expected to cope
better with competition from grasses and will provide shelter to help the establishment of slowergrowing focal species. The native focal species chosen for this project are: a) Totara (Podocarpus
totara), Kahikatea Dacrycarpus dacrydioides), Cabbage Tree (Cordyline australis), and Bush Daisy
(Olearia virgata).Four native nurse species will be paired to make two sets: Karamu (Coprosma
robusta) with Mingimingi (Coprosma propinqua) and Kohuhu (Pittosporum tenuifolium) with Manuka
(Leptospermum scoparium).
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