Question: Does canopy tree regeneration response to different large disturbances vary with soil drainage? Location: Old-growth conifer (Dacrydium and Dacrycarpus), angiosperm (Nothofagus and Weinmannia) rain forest, Mount Harata, South Island, New Zealand. Methods: Trees were aged (1056 cores) to reconstruct stand history in 20 (0.12 - 0.2 ha) plots with different underlying drainage. Spatial analyses of an additional 805 tree ages collected from two (0.3 - 0.7 ha) plots were conducted to detect patchiness for five canopy tree species. Microsite preferences for trees and saplings were determined. Results: There were clear differences in species regeneration patterns on soils with different drainage. Conifer recruitment occurred infrequently in even-aged patches (> 1000 m²) and only on poorly drained soils. Periodic Nothofagus fusca and N. menziesii recruitment occurred more frequently in different sized canopy openings on all soils. Weinmannia recruitment was more continuous on all soils reflecting their greater relative shade-tolerance. Distinct periods of recruitment that occurred in the last 400 years matched known large disturbances in the region. These events affected species differently as soil drainage varied. Following earthquakes, both conifers and N. menziesii regenerated on poorly drained soils, while Nothofagus species and Weinmannia regenerated on well-drained soils. However, Dacrydium failed to regenerate after patchy storm damage in the wetter forest interior; instead faster-growing N. fusca captured elevated microsites caused by uprooting. Conclusions: Underlying drainage influenced species composition, while variation in the impacts of large disturbance regulated relative species abundances on different soils.
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.
The New Zealand Kellogg Rural Leaders Programme develops emerging agribusiness leaders to help shape the future of New Zealand agribusiness and rural affairs. Lincoln University has been involved with this leaders programme since 1979 when it was launched with a grant from the Kellogg Foundation, USA.On 2 March 1987 the Bay of Plenty region suffered an earthquake
of magnitude 6.3 on the Richter scale, centred at Edgecumbe.
Severe damage to personal and industrial property and
drainage systems occurred.
In hindsight, although much of the damage was covered by insurance,
loans, public and government contributions, the continuing
reconstruction costs have had a tremendous impact financially
on individuals and the District as a whole.
By highlighting some of these ongoing costs and suggestions of
alternatives other Rural communities may be better prepared to
lessen the effect of a natural disaster such as the Edgecumbe
Earthquake of 1987.
Nature has endowed New Zealand with unique geologic, climatic, and biotic conditions. Her volcanic cones and majestic Southern Alps and her verdant plains and rolling hills provide a landscape as rugged and beautiful as will be found anywhere. Her indigenous fauna and flora are often quite different from that of the rest of the world and consequently have been of widespread interest to biologists everywhere. Her geologic youth and structure and her island climate, in combination with the biological resources, have made a land which is ecologically on edge. These natural endowments along with the manner in which she has utilized her land, have given New Zealand some of the most spectacular and rapid erosion to be found.
It is quite evident that geologic and climatic conditions combine to give unusually high rates of natural erosion. Present topographic features indicate the past occurrence of large-scale flooding as well. Prior to the arrival of the Maori, it is very likely that most of the land mass of New Zealand below present bush lines was covered with indigenous bush or forest. Forest fires of a catastrophic nature undoubtedly occurred as a result of lightning, and volcanic eruptions. The exposed soils left by these catastrophes contributed to natural deterioration. While vast areas of forest cover were destroyed, they probably were healed by nature with forest or with grass or herbaceous cover. Further, it is probable that large areas in the mountains were, as they are now, subject to landslides and slipping due to earthquakes and excessive local rainfall. Again, the healing process was probably rapid in most of such exposed areas.
Saltwater Forest is a Dacrydium cupressinum-dominated lowland forest covering 9000 ha in south Westland, South Island, New Zealand. Four thousand hectares is managed for sustainable production of indigenous timber. The aim of this study was to provide an integrated analysis of soils, soil-landform relationships, and soil-vegetation relationships at broad and detailed scales. The broad scale understandings provide a framework in which existing or future studies can be placed and the detailed studies elucidate sources of soil and forest variability.
Glacial landforms dominate. They include late Pleistocene lateral, terminal and ablation moraines, and outwash aggradation and degradation terraces. Deposits and landforms from six glacial advances have been recognised ranging from latest Last (Otira) Glaciation to Penultimate (Waimea) Glaciation. The absolute ages of landforms were established by analysis of the thickness and soil stratigraphy of loess coverbeds, augmented with radiocarbon dating and phytolith and pollen analysis.
In the prevailing high rainfall of Westland soil formation is rapid. The rate of loess accretion in Saltwater
Forest (ca. 30 mm ka⁻¹) has been low enough that soil formation and loess accretion took place contemporaneously. Soils formed in this manner are known as upbuilding soils. The significant difference between upbuilding pedogenesis and pedogenesis in a topdown sense into an existing sediment body is that each subsoil increment of an upbuilding soil has experienced processes of all horizons above. In Saltwater Forest subsoils of upbuilding soils are strongly altered because they have experienced the extremely acid environment of the soil surface at some earlier time. Some soil chronosequence studies in Westland have included upbuilding soils formed in loess as the older members of the sequence. Rates and types of processes inferred from these soils should be reviewed because upbuilding is a different pedogenic pathway to topdown pedogenesis.
Landform age and morphology were used as a primary stratification for a study of the soil pattern and nature of soil variability in the 4000 ha production area of Saltwater Forest. The age of landforms (> 14 ka) and rapid soil formation mean that soils are uniformly strongly weathered and leached. Soils include Humic Organic Soils, Perch-gley Podzols, Acid Gley Soils, Allophanic Brown Soils, and Orthic or Pan Podzols. The major influence on the nature of soils is site hydrology which is determined by macroscale features of landforms (slope, relief, drainage density), mesoscale effects related to position on landforms, and microscale influences determined by microtopography and individual tree effects. Much of the soil variability arises at microscales so that it is not possible to map areas of uniform soils at practical map scales. The distribution of soil variability across spatial scales, in relation to the intensity of forest management, dictates that it is most appropriate to map soil complexes with boundaries coinciding with landforms.
Disturbance of canopy trees is an important agent in forest dynamics. The frequency of forest disturbance in the production area of Saltwater Forest varies in a systematic way among landforms in accord with changes in abundance of different soils. The frequency of forest turnover is highest on landforms with the greatest abundance of extremely poorly-drained Organic Soils. As the abundance of better-drained soils increases the frequency of forest turnover declines. Changes in turnover frequency are reflected in the mean size and density of canopy trees (Dacrydium cupressinum) among landforms. Terrace and ablation moraine landforms with the greatest abundance of extremely poorly-drained soils have on average the smallest trees growing most densely. The steep lateral moraines, characterised by well drained soils, have fewer, larger trees. The changes manifested at the landform scale are an integration of processes operating over much shorter range as a result of short-range soil variability. The systematic changes in forest structure and turnover frequency among landforms and soils have important implications for sustainable forest management.
