Six stands located on different land forms in mixed old-growth Nothofagus forests in the Matiri Valley (northwest of South Island, New Zealand) were sampled to examine the effects of two recent large earthquakes on tree establishment and tree-ring growth, and how these varied across land forms. 50 trees were cored in each stand to determine age structure and the cores were cross-dated to precisely date unusual periods of radial growth. The 1968 earthquake (M = 7.1, epicentre 35 km from the study area) had no discernible impact on the sampled stands. The impact of the 1929 earthquake (M = 7.7, epicentre 20 km from the study area) varied between stands, depending on whether or not they had been damaged by soil or rock movement. In all stands, the age structures showed a pulse of N. fusca establishment following the 1929 earthquake, with this species dominating establishment in large gaps created by landslides. Smaller gaps, created by branch or tree death, were closed by both N. fusca and N. menziesii. The long period of releases (1929-1945) indicates that direct earthquake damage was not the only cause of tree death, and that many trees died subsequently most likely of pathogen attack or a drought in the early 1930s. The impacts of the 1929 earthquake are compared to a storm in 1905 and a drought in 1974-1978 which also affected forests in the region. Our results confirm that earthquakes are an important factor driving forest dynamics in this tectonically active region, and that the diversity of earthquake impacts is a major source of heterogeneity in forest structure and regeneration.
This report reviews the literature on regeneration requirements of main canopy
tree species in Westland. Forests managed for production purposes have to be
harvested in an ecologically sustainable way; to maintain their natural character, harvesting should facilitate regeneration of target species and ensure that their recruitment is in proportion to the extent of extraction. The reasons for species establishing at any point in time are unclear; however, they are probably related to the availability of suitable microsites for establishment, the size of the canopy openings formed by disturbance, and whether or not seeds are available at or around the time of the disturbance. Age structures from
throughout Westland show that extensive, similar-aged, post-earthquake cohorts of trees are a feature of the region. This suggests that infrequent, massive earthquakes are the dominant coarse-scale disturbance agent, triggering episodes of major erosion and sedimentation and leaving a strong imprint in the forest structure. In other forests, flooding and catastrophic
windthrow are major forms of disturbance. The findings suggest that, in general, large disturbances are required for conifer regeneration. This has implications for any sustained yield management of these forests if conifers are to remain an important component. Any harvesting should recognise the importance for tree establishment of: forest floor microsites, such as fallen logs
and tree tip-up mounds; and the variable way in which canopy gaps are formed. Harvesting should maintain the 'patchy' nature of the natural forest—large patches of dense conifers interspersed with more heterogeneous patches of mixed species.This is a client report commissioned by West Coast Conservancy and funded from the Unprogrammed Science Advice fund.
The Kaikoura earthquake in November 2016 highlighted the vulnerability of New Zealand’s rural communities to locally-specific hazard events, which generate regional and national scale impacts. Kaikoura was isolated with significant damage to both the east coast road (SH1) and rail corridor, and the Inland Road (Route 70). Sea bed uplift along the coast was significant – affecting marine resources and ocean access for marine operators engaged in tourism and harvesting, and recreational users. While communities closest to the earthquake epicentre (e.g., Kaikoura, Waiau, Rotherham and Cheviot) suffered the most immediate earthquake damage, the damage to the transport network, and the establishment of an alternative transport route between Christchurch and Picton, has significantly impacted on more distant communities (e.g., Murchison, St Arnaud and Blenheim). There was also considerable damage to vineyard infrastructure across the Marlborough region and damage to buildings and infrastructure in rural settlements in Southern Marlborough (e.g., Ward and Seddon).
Mixed conifer, beech and hardwood forests are relatively common in Aotearoa/New
Zealand, but are not well studied. This thesis investigates the coexistence, regeneration
dynamics and disturbance history of a mixed species forest across an environmental
gradient of drainage and soil development in north Westland.
The aim was to investigate whether conifers, beech and non-beech hardwood species were
able to coexist on surfaces that differed in their underlying edaphic conditions, and if so to understand the mechanisms that influenced their regeneration on both poorly drained and
well drained soils. The site selected was an area of high tree species diversity on a lowland
0.8 km² post-glacial terrace at the base of Mount Harata in the Grey River Valley.
My approach was to use forest stand history reconstruction at two spatial scales: an
intensive within-plot study of stand dynamics (chapter 1) and a whole-landform approach
(chapter 2) that examined whether the dynamics identified at the smaller within-plot scale
reflected larger patterns across the terrace.
In chapter 1, three large permanent plots (0.3-0.7 ha) were placed at different points along
the drainage gradient, one plot situated in each of the mainly well-drained, poorly drained
and very poorly drained areas along the terrace. Information was gathered on species age
and size structures, spatial distributions of tree ages, species interactions, microsite
establishment preferences, patterns of stand mortality, and disturbance history in each plot.
There were differences in stand structure, composition and relative abundance of species
found between the well drained plot and the two poorer drained plots. On the well drained
site conifers were scarce, the beeches Nothofagus fusca and N. menziesii dominated the
canopy, and in the subcanopy the hardwood species Weinmannia racemosa and Quintinia
acutifolia were abundant. As drainage became progressively poorer, the conifers
Dacrydium cupressinum and Dacrycarpus dacrydioides became more abundant and
occupied the emergent tier over a beech canopy. The hardwoods W. racemosa and Q.
acutifolia became gradually less abundant in the subcanopy, whereas the hardwood
Elaeocarpus hookerianus became more so.
In the well drained plot, gap partitioning for light between beeches and hardwoods enabled
coexistence in response to a range of different sized openings resulting from disturbances
of different extent. In the two more poorly drained plots, species also coexisted by
partitioning microsite establishment sites according to drainage.
There were several distinct periods where synchronous establishment of different species
occurred in different plots, suggesting there were large disturbances: c. 100yrs, 190-200
yrs, 275-300 yrs and 375-425 yrs ago. Generally after the same disturbance, different
species regenerated in different plots reflecting the underlying drainage gradient. However,
at the same site after different disturbances, different sets of species regenerated,
suggesting the type and extent of disturbances and the conditions left behind influenced
species regeneration at some times but not others. The regeneration of some species (e.g.,
N. fusca in the well-drained plot, and Dacrydium in the poorer drained plots) was periodic
and appeared to be closely linked to these events. In the intervals between these
disturbances, less extensive disturbances resulted in the more frequent N. menziesii and
especially hardwood regeneration. The type of tree death caused by different disturbances
favoured different species, with dead standing tree death favouring the more shade-tolerant
N. menziesii and hardwoods, whereas uprooting created a mosaic of microsite conditions
and larger gap sizes that enabled Dacrycarpus, N. fusca and E. hookerianus to maintain
themselves in the poorly drained areas.
In chapter 2, 10 circular plots (c. 0.12 ha) were placed in well drained areas and 10
circular plots (c. 0.2 ha) in poorly drained plots to collect information on species
population structures and microsite preferences. The aims were to reconstruct species'
regeneration responses to a range of disturbances of different type and extent across the
whole terrace, and to examine whether there were important differences in the effects of
these disturbances.
At this landform scale, the composition and relative abundances of species across the
drainage gradient reflected those found in chapter 1. There were few scattered conifers in well drained areas, despite many potential regeneration opportunities created from a range
of different stand destroying and smaller scale disturbances.
Three of the four periods identified in chapter 1 reflected distinct terrace-wide periods of
regeneration 75-100 yrs, 200-275 yrs and 350-450 yrs ago, providing strong evidence of
periodic large, infrequent disturbances that occurred at intervals of 100-200 yrs. These
large, infrequent disturbances have had a substantial influence in determining forest
history, and have had long term effects on forest structure and successional processes.
Different large, infrequent disturbances had different effects across the terrace, with the
variability in conditions that resulted enabling different species to regenerate at different
times. For example, the regeneration of distinct even-aged Dacrydium cohorts in poorly
drained areas was linked to historical Alpine Fault earthquakes, but not to more recent
storms. The variation in the intensity of different large, infrequent disturbances at different
points along the environmental drainage gradient, was a key factor influencing the scale of
impacts. In effect, the underlying edaphic conditions influenced species composition along
the drainage gradient and disturbance history regulated the relative abundances of species.
The results presented here further emphasise the importance of large scale disturbances as a
mechanism that allows coexistence of different tree species in mixed forest, in particular
for the conifers Dacrydium, Dacrycarpus and the beech N. fusca, by creating much of the
environmental variation to which these species responded. This study adds to our
understanding of the effects of historical earthquakes in the relatively complex forests of
north Westland, and further illustrates their importance in the Westland forest landscape as
the major influential disturbance on forest pattern and history.
These results also further develop the 'two-component' model used to describe
conifer/angiosperm dynamics, by identifying qualitative differences in the impacts of
different large, infrequent disturbances across an environmental gradient that allowed for
coexistence of different species. In poorer drained areas, these forests may even be thought
of as 'three-component' systems with conifers, beeches and hardwoods exhibiting key
differences in their regeneration patterns after disturbances of different type and extent, and
in their microsite preferences.
Initial recovery focus is on road access (especially the inland SH70) although attention also needs to be focussed on the timelines for reopening SH1 to the south. Information on progress and projected timelines is updated daily via NZTA (www.nzta.govt.nz/eq-travel ). Network analyses indicate potential day trip access and re-establishment of the Alpine Pacific triangle route. When verified against ‘capacity to host’ (Part 2 (15th December) there appears to potential for the reestablishment of overnight visits. Establishing secure road access is the key constraint to recovery.
In terms of the economic recovery the Kaikoura District has traditionallyattracted a large number of visitors which can be grouped as: second home (and caravan) owners, domestic New Zealand and international travellers. These have been seen through a behaviour lens as “short stop”, ‘day” (where Kaikoura is the specific focal destination) and overnight visitors. At the present restricted access appears to make the latter group less amenable to visiting Kaikoura, not the least because the two large marine mammal operators have a strong focus on international visitors. For the present the domestic market provides a greater initial pathway to recovery.
Our experiences in and reflections on Christchurch suggest Kaikoura will not go back to what it once was. A unique opportunity exists to reframe the Kaikoura experience around earthquake geology and its effects on human and natural elements. To capitalise on this opportunity there appears to be a need to move quickly on programming and presenting such experiences as part of a pathway to re-enabling domestic tourists while international visitor bookings and flows can be re-established. The framework developed for this study appears to be robust for rapid post disaster assessment. It needs to be regularly updated and linked with emerging governance and recovery processes.
This thesis investigates landscape disturbance history in Westland since 1350 AD. Specifically, I test the hypothesis that large-magnitude regional episodes of natural disturbance have periodically devastated portions of the landscape and forest, and that these were caused by infrequent earthquakes along the Alpine Fault.
Forest stand history reconstruction was used to determine the timing and extent of erosion and sedimentation events that initiated new forest cohorts in a 1412 ha study area in the Karangarua River catchment, south Westland. Over 85 % of the study area was disturbed sufficiently by erosion/sedimentation since 1350 AD to initiate new forest cohorts. During this time four episodes of catchment-wide disturbance impacted the study area, and these took place about 1825 AD ± 5 years (Ruera episode), 1715 AD ± 5 years (Sparkling episode), 1615 AD ± 5 years (McTaggart episode), and 1445 AD ± 15 years (Junction episode). The three most recent episodes disturbed 10 %, 35-40 % and 32-50 % respectively of the study area. The Junction episode disturbed at least 6 % of the study area, but elimination of evidence by more recent disturbances prevented an upper limit being defined.
The three earliest episodes correspond to the date-ranges for three Alpine Fault earthquakes from geological data, and are the only episodes of disturbance within each date-range. An earthquake cause is also consistent with features of the disturbance record: large portions of the study area were disturbed, disturbance occurred on all types 'of landforms, and terrace surfaces were abandoned upstream of the Alpine Fault. On this basis erosion/sedimentation induced by Alpine Fault earthquakes has disturbed 14-20 % of the land surface in the study area per century. Storms and other non-seismic erosional processes have disturbed 3-4 % per century.
To examine the importance of the Alpine Fault earthquakes to forest disturbance throughout Westland, I collated all available data on conifer stand age structures in the region and identified dates of disturbance events from 55 even-aged cohorts of trees. Three region-wide episodes of forest disturbance since 1350 AD were found in this sample, and these matched the three Alpine Fault earthquake-caused episodes found in the Karangarua. Forest disturbance at these times was widespread across Westland over at least 200 km from Paringa to Hokitika, and originated from both tree fall and erosion processes. This disturbance history can explain the long-observed regional conifer forest pattern in Westland, of a predominance of similar-sized stands of trees and a relative lack of small-sized (young) stands. The many similar-sized stands are a consequence of synchronous forest disturbance and re-establishment accompanying the infrequent Alpine Fault earthquakes, while the dominance of mature stands of trees and relative lack of young small-sized trees in stands is explained by the long lapsed time since the last Alpine Fault earthquake (c. 280 years).
I applied the landscape disturbance history information to the existing geological data to reconstruct the paleoseismicity of the Alpine Fault since 1350 AD. Best estimates for the timing of the most recent three rupture events from these data are 1715 AD ± 5 years, 1615 AD ± 5 years and 1445 AD ± 15 years. Earthquake recurrence intervals were variable, ranging from about 100 years to at least 280 years (the lapsed time since the last event). All three events caused forest and geomorphic disturbance over at least a 200 km section of Fault between the Karangarua and Hokitika Rivers, and were probably single rupture events. Suppressions in cross dated tree-ring chronologies in the western South Island suggest that the last rupture occurred in 1717 AD, and extended as a single rupture from Haupiri to Fiordland, a distance along the Fault of 375 km.
Globally, the maximum elevations at which treelines are observed to occur coincide with a 6.4 °C soil isotherm. However, when observed at finer scales, treelines display a considerable degree of spatial complexity in their patterns across the landscape and are often found occurring at lower elevations than expected relative to the global-scale pattern. There is still a
lack of understanding of how the abiotic environment imposes constraints on treeline patterns, the scales at which different effects are acting, and how these effects vary over large spatial extents. In this thesis, I examined abrupt Nothofagus treelines across seven degrees of
latitude in New Zealand in order to investigate two broad questions: (1) What is the nature and extent of spatial variability in Nothofagus treelines across the country? (2) How is this variation associated with abiotic variation at different spatial scales? A range of GIS, statistical, and atmospheric modelling methods were applied to address these two questions.
First, I characterised Nothofagus treeline patterns at a 15x15km scale across New Zealand using a set of seven, GIS-derived, quantitative metrics that describe different aspects of treeline position, shape, spatial configuration, and relationships with adjacent vegetation.
Multivariate clustering of these metrics revealed distinct treeline types that showed strong spatial aggregation across the country. This suggests a strong spatial structuring of the abiotic environment which, in turn, drives treeline patterns. About half of the multivariate treeline
metric variation was explained by patterns of climate, substrate, topographic and disturbance variability; on the whole, climatic and disturbance factors were most influential.
Second, I developed a conceptual model that describes how treeline elevation may
vary at different scales according to three categories of effects: thermal modifying effects, physiological stressors, and disturbance effects. I tested the relevance of this model for Nothofagus treelines by investigating treeline elevation variation at five nested scales (regional to local) using a hierarchical design based on nested river catchments. Hierarchical linear modelling revealed that the majority of the variation in treeline elevation resided at the broadest, regional scale, which was best explained by the thermal modifying effects of solar radiation, mountain mass, and differences in the potential for cold air ponding. Nonetheless, at finer scales, physiological and disturbance effects were important and acted to modify the regional trend at these scales. These results suggest that variation in abrupt treeline elevations
are due to both broad-scale temperature-based growth limitation processes and finer-scale stress- and disturbance-related effects on seedling establishment.
Third, I explored the applicability of a meso-scale atmospheric model, The Air
Pollution Model (TAPM), for generating 200 m resolution, hourly topoclimatic data for
temperature, incoming and outgoing radiation, relative humidity, and wind speeds. Initial assessments of TAPM outputs against data from two climate station locations over seven years showed that the model could generate predictions with a consistent level of accuracy for both sites, and which agreed with other evaluations in the literature. TAPM was then used to generate data at 28, 7x7 km Nothofagus treeline zones across New Zealand for January
(summer) and July (winter) 2002. Using mixed-effects linear models, I determined that both
site-level factors (mean growing season temperature, mountain mass, precipitation,
earthquake intensity) and local-level landform (slope and convexity) and topoclimatic factors (solar radiation, photoinhibition index, frost index, desiccation index) were influential in
explaining variation in treeline elevation within and among these sites. Treelines were
generally closer to their site-level maxima in regions with higher mean growing season
temperatures, larger mountains, and lower levels of precipitation. Within sites, higher
treelines were associated with higher solar radiation, and lower photoinhibition and
desiccation index values, in January, and lower desiccation index values in July. Higher treelines were also significantly associated with steeper, more convex landforms.
Overall, this thesis shows that investigating treelines across extensive areas at multiple study scales enables the development of a more comprehensive understanding of treeline variability and underlying environmental constraints. These results can be used to formulate new hypotheses regarding the mechanisms driving treeline formation and to guide the optimal choice of field sites at which to test these hypotheses.
