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Tuatara: Volume 18, Issue 3, December 1970

Palaeoclimatic Change in the Last 1,000 Years

page 114

Palaeoclimatic Change in the Last 1,000 Years


Apart from collating recent advances in dynamic global meteorology, oxygen isotopic ratios, solar cycles, bog recurrence surfaces, glaciology and dendrochronology, this review centres on New Zealand literature on climatic change. The review is limited to the last 1,000 years in order to provide some basis for establishing a time control of processes of structural and compositional change in the current vegetation soil systems.

The essentially dynamic and youthful nature of New Zealand vegetation and soils has, for many years, been apparent in descriptive studies (Cockayne 1928, Raeside 1948, Holloway 1954, Nicholls 1957). In the absence of any direct evidence of climatic change, many indirect and often ecologically tenuous inferences have been drawn from the vegetation and soils to explain maladjustment of populations, soils out-of-place with their present environment and discontinuous distribution of vegetation types.

Recently there has been a shift in emphasis from wholly climatic causes to the recognition of other factors, notably catastrophes of various kinds (Cumberland 1962, Fleming 1963, Molloy 1968, 1969). Climate, from this point of view, is considered an ‘intellectual concept’. It is the day-to-day realities of weather that are said to matter, rather than the climate of the free atmosphere evaluated in yearly means (Cumberland 1962).

It is unfortunate that recent reviews of climatic change in New Zealand have not involved the advances made in the understanding of dynamic meteorology, solar cycles and isotopic composition of snow and speleothems,* nor had at their disposal local evidence of such direct effects of palaeoclimatic change (Hendy 1969) or global correlations (J. R. Bray, pers. comm.).

Global Evidence Of Palaeo-Climatic Change

Antevs (1955) and Deevey and Flint (1957) considered that long-distance climatic correlations could be made only on the basis of inferred long-range temperature shifts. Recorded moisture changes were considered to reflect local geographic factors and to be therefore not useful for long-range correlation purposes. Most of the recent research on oscillations in solar activity and oxygen isotopic concentrations have had a temperature basis. As a result, the concept of page 115 widespread if not global climatic synchroneity is supported by virtually in-phase climatic oscillations, as expressed by the various types of independently dated paleoclimatic chronologies in the Northern Hemisphere (Karlstrom 1966). For example, climatic cycles are in phase with solar radiation curves (Yamamoto 1966, Bray 1968 and Johnsen et al 1970) and oxygen isotope variation (Hendy 1969, Johnsen et al 1970). These same data favour extraterrestrial rather than local geographic factors as the probable primary cause of climatic change.

In sites of deposition, for example peats, varves, pollen profiles or in the ecological response to climatic change, for example forest composition, high water tables, lowered timber lines, there may be a considerable lag-period. This lag may vary from place to place and often be actually greater than the standard error of a date (Karlstrom 1966).

The climatic cycles postulated for the last 1,000 years were considered by Willett (1953) and Lamb (1959) to represent ‘alternate equatorward and poleward displacement of prevailing storm tracks’. In middle latitudes, such as New Zealand, this resulted in an alternation between warm-dry and cool-wet climates, whilst the alternation of warm-wet and cool-dry climates were characteristic of higher latitudes. Karlstrom (1966) and Yamamoto (1966) came to similar conclusions in a discussion of glacial-pluvial cycles and thermal advection.

Yamamoto (1966), Bray (1965, 1968), Johnsen et al (1970) confirmed a positive relationship between temperature and apparently regular solar-activity cycles, using botanical, geophysical, glaciological, geological and historical evidence. The ‘little climatic optimum’ of A.D. 1000-1300 and the ‘little ice age’ from A.D. 1600-1750 were both most apparent in the solar activity indices (Bray 1968) and ice-core data (Johnsen et al, 1970).

The detailed meteorological and historical data of Lamb (1965, 1966) were generally synchronous with the above research on extraterrestrial activity. Lamb et al (1966) described the period A.D. 1000-1300 as probably warmer and drier, in summer particularly, than any period since 1000 B.C. Lamb (1965) called this the ‘warm Mediaeval epoch’. He explained it meteorologically as a more frequent influence of the subtropical anticyclones extending over temperate Europe. ‘Then, as in the period 1900-1940 there was a greater frequency of westerly and anti-cyclonic westerly weather in Britain than in any other century.’ Lamb et al (1966) also considered that no cold period as measured by glacial advance, comparable with A.D. 1500-1700, had occurred since 8000 B.C. unless that of 500 B.C. They, Bray (1965) and Suess (1965) stated that most of the evidence had well established that the C14 variations in the atmosphere strengthened archaeological, botanical and glacial indications of a sharp climatic deterioration between A.D. 1300 and 1600.

page 116

Although annual rainfall was apparently lowest in the period between A.D. 1550 and 1700, the difference as regards soil moisture was probably offset by less evaporation and wetter summers (Lamb, 1965). This is evident from ‘recurrence surfaces’ — stratigraphic positions where peat accumulation recommenced in bogs throughout the Northern Hemisphere (Granlund 1932, Godwin 1954, Lundquist 1962, Nicholls 1969). All recurrence-surfaces restarted growth soon after A.D. 1200 after having ‘no-growth’ periods of 300-400 years duration.

From glaciological evidence, Porter and Denton (1967) termed the period from about A.D. 1300-1800, the ‘Neoglaciation’. They and Heusser (1966) extensively reviewed the evidence of glacial fluctuations throughout the world, particularly in the western United States of America, in the last 1,000 years. Data came from many historical records, C14 dates, dendrochronology and lichenometric dating of moraines. Porter and Denton (1970) reviewed the worldwide glacial recession beginning in the late Nineteenth Century and continuing to the 1940's. This closely coincided with a distinct global warming trend that led to an increase in world temperature by as much as 1.0°C. Yamamoto (1966) demonstrated a very close agreement of glacial fluctuations with the sunspot curve and the curve of rainfall in Korea from A.D. 1600 to the present.

The caution with which glaciological data must be treated has been noted by Aushmann (1966); ‘right at the margins of existing glaciers only quite drastic climatic variations are likely to have left a geological (moraine) imprint. The validity of global climatic correlation has been repeatedly questioned. But parallel glacial moraine sequences at far corners of the Pacific Basin afford growing confidence.’

Tree ring growth rates have been used by Antevs (1938) and Schulman (1953) in conjunction with lake-levels and run-off records in the intermontane basins of the western United States of America to demonstrate the time-distribution of wet and dry periods in the last 800 years. Schulman considered that the Thirteenth Century was very dry but became wet, with frequent storms in the Fourteenth Century.

Fluctuations of timberline have long been indicative of climatic change. In Canada, Brink (1959) demonstrated that current forest is invading alpine grassland at higher altitudes, where snow cover is diminishing. This could be related to the global retreat of glaciers and increasing temperatures since late last century.

New Zealand Evidence of Palaeo-Climatic Change

The hypotheses of van Post (1946) and Harris (1949) that during the last 700 years, beech (Nothofagus) forest was replacing podocarp forest, in response to changes in climate was disputed by Walker page 117 (1966) as premature on the grounds of differential rates of migration and soil development. Loss of soil fertility and changes in drainage can effect changes in the soil vegetation system that are quite unrelated to climate. Similar changes in forest composition were described by Holloway (1954) who considered that about 800 years ago there was a decrease in temperature and effective precipitation. As a result the present forests are in a state of population maladjustment. Holloway's hypothesis focussed on the instability of the various podocarp populations in particular. The nature of this instability was a predominance of mature and senile trees and a regeneration gap of smaller size classes. McKelvey (1953), Nicholls (1957), Grant (1963) and Wardle (1964) all indicated that the regeneration gap was real and widespread in a number of species in a range of environments throughout New Zealand. However, the synchroneity of its commencement is in doubt (Molloy 1969), varying from A.D. 1200 (Holloway) to A.D. 1650 (Nicholls). Only Wardle (1964) recorded an upsurge in regeneration, commencing after A.D. 1800. Wardle postulated a ‘worsening of the water regime’ as effecting decreased seed production and germination. He considered that regeneration was related more to rainfall than to temperature. Antevs (1955) and Deevey and Flint (1957) both stressed that palaeoclimatic correlation by moisture is useless. Wardle emphasised the variation in the ‘regeneration gap’ from site to site. Molloy (1969) suggested that normal regeneration of podocarp populations may not be continuous but periodic due to endogenous mechanisms. However, this would not explain the lack of rimu regeneration in forests where, in many cases, there are only one or two rimu trees per acre.

Holloway (1954), Wardle and Mark (1956) and others attributed the present forest/grassland boundary in parts of New Zealand, which is pedologically out-of-phase with what it was 800 years ago, to fire. These fires were made more effective as a result of climatic changes less than 2,000 years ago (Holloway). Their work, in part, supported the earlier conclusions of Raeside (1948) who interpreted anomalies in vegetation and soil in relation to the present climate. Raeside considered that between the Seventh and Thirteenth Centuries A.D., climates were warmer and wetter than at present. On pollen evidence, Moar (1970) confirmed widespread vegetation changes in Canterbury in the last 1,000 years, attributing them to fire-induced de-forestation, whilst noting that this did not invalidate the climatic change hypothesis.

Molloy (1969) considered that the climatic shift described by Raeside (1948) and Holloway (1954) from indirect evidence, was hard to trace. In agreement with Cumberland (1962), Molloy favoured catastrophic phenomena, particularly fire, as more likely to have caused the past vegetation changes in New Zealand. The effects of early fires has been extensively studied, for example Cox and Mead page 118 (1963), Molloy et al (1963), Grant (1963), Elder (1963), Esler (1963), Cameron (1964). McKelvey (1953), Vucetich and Pullar (1963) and Druce (1967) described the effects of recent vulcanicity on vegetation patterns. Molloy (1969) considered the European palaeo-climatic data of Lamb (1965) but concluded that ‘there is no evidence that any minor (climatic) variations were of sufficient amplitude and geographic extent to be ecologically significant’.

Cumberland's (1962) and Molloy's (1969) criciticism of palaeoclimatic factors evaluated as yearly, decade, or fifty-year means (e.g. Lamb 1965) being used to infer ecological change are invalid. The utility of grouped means lies in their indication of climatic extremes; the 2°C. amplitude between A.D. 1000-1300 and A.D. 1600-1750 periods are the climatic levels critical to major species in vegetation. Regeneration gaps, changes in timberline and peat accumulation require climatic factors to be continually either above or below critical levels. The most useful way of expressing palaeo-climatic data is to group data with similar quantitative attributes.

Recent work by Hendy and Wilson (1968), Hendy (1969) on the isotopic chemistry of C14 dated speleothems has made a great contribution to New Zealand-based interpretations of global palaeoclimatic data. Hendy obtained the ratios of the oxygen isotopes O16 and O18, the fractionation of which was temperature dependent. He concluded that for the last 1,000 years:—


throughout New Zealand, variation in O18 in speleothems was constant in time and quantity. This implied New Zealand-wide synchroneity of considerable climatic change in the last 1,000 years.


Palaeo-temperature changes deduced from the isotopic ratios of the speleothems were constant in time and quantity with the mean temperature deduced for central England (Lamb 1965).

On historical and dendrochronological evidence, J. R. Bray (pers. comm.) has recently demonstrated the synchroneity of glacial activity in southern New Zealand and British Columbia in the last 1,000 years. Other glaciological evidence agrees broadly with the trends noted by overseas research. C. J. Burrows (pers. comm) described glacial advances at Mount Cook, from moraine dates occurring about A.D. 1200 and in the Fifteenth, Seventeenth, Eighteenth and late Nineteenth Centuries. Burrows somewhat disputed the ‘little ice age’ on the basis that there was no overall glacial pattern in New Zealand. However, moraine evidence from the Cameron Glacier and lichenometric dating of the Mueller Glacier moraines (Burrows and Lawrence 1965), suggested a maximum terminal moraine at both glaciers forming about A.D. 1750. The same authors and McKellar (1955) also noted a well-developed morainal surface, consistently dated at about A.D. 1890. The observations of Gage (1966) on glacial activity in the South Island are particularly relevant to the problems of palaeo-climatic interpretation from indirect page 119 evidence in New Zealand. Referring to Suggate (1950) and Gage (1951), Gage noted that glacial response in Westland has been sensitive to both precipitation and temperature. A 2-3°F. temperature drop in Westland may have been sufficient to produce the same glacial response as a 5-7°F. drop east of the Alps.

Park (1970) evaluated a Maori oven found under silver beech forest at 2,600 ft. in the Tararua Range in terms of palaeo-climatic change. The oven, dated at A.D. 1227 ± 40, was evaluated in conjunction with soil stratigraphy, soil air/water balance, pollen analysis, and radial growth rate and age structure of Halls totara and silver beech populations. The oven suggested an appreciably warmer and effectively seasonally drier period than the present at the time of its construction.

The 1°C. change associated with the global temperature increase from 1890-1940 was quite pronounced throughout New Zealand (J. Finkelstein pers. comm.). Mean temperature rises of 1.21°C. and 1.10°C. occurred in Auckland and Dunedin respectively. From 1925-1950 the mean annual trend of temperature change for New Zealand (J. Finkelstein pers. comm.) were very similar to those of western United States of America (Heusser 1966). The long-term fluctuations of rainfall in the North Island from 1898 to the present day (de Lisle 1961) also show many similarities with the global tropical and subtropical synthesis of Kraus (1958).

Recent Vegetation Change in the North Island Uplands

In 1963 Elder published evidence of a general imbalance in mountain beech forests (Nothofagus solandri var. cliffortioides) in the Ruahine Range except at the lower altitudinal end of its range. The short life span of mountain beech restricted any environmental change to within the last 200 years. At the head of the Maropea River, Elder noted evidence of a former timberline some 200-300 ft. higher than at present. He considered that in the last 200 years there has been a retreat by mountain beech to lower altitudes and drier sites, suggesting that the climate has been getting progressively cooler and wetter. Throughout the northern and central Ruahines there is a downward and outward movement of beech forest into other types, including a retreat of red beech (Nothofagus fusca) and its replacement by mountain beech. Observations in red beech-silver beech forest east of Lake Taupo in the northern Kaimanawa Range by this author in 1969 suggested that the older senile red beech-silver beech canopy was being replaced through successive windfalls, by younger trees of solely silver beech. Throughout New Zealand silver beech appears to be a species of lower nutrient requirements and higher moisture tolerance than red beech. Such vegetation changes are supported by pollen evidence from Mokai Patea in the Western page 120 Ruahines (Moar 1967) which indicates that in the last 800 years there has been a decline of podocarps and a rise of beech, grasses and sedges in that region.

McQueen (1950) postulated a lowering of timberline by about 600 ft. to account for a lack of beech regeneration on silver beech sites on Mts. Quoin and Reeves, Southern Tararua Range. Pole stands of beech of Mt. Reeves, in sites normally dominated by red beech, had a higher proportion of silver than red beech. Reid (1948) and McQueen (1950) described recent changes in compositional structure of red beech-silver beech forest; the former relating changes to regeneration after excessive windthrow. In both cases silver beech was regenerating at the expense of red beech. Holloway (1954) described compositional changes of similar nature in the South Island. McQueen (1950) discussed the observation of A. C. S. Wright, who noted that the soils under tussock grassland at about 4,800 ft. on Mt. Dennan, Western Tararuas, were more in keeping with scrub, vegetation occurring between 300 ft. and 900 ft. lower altitude at present.

In contrast to the above vegetation changes, Wardle (1962) demonstrated an advance of silver beech into subalpine scrub and tussock grassland in the Southern Tararua Range, and a contraction in the territory of Dacrydium biforme in the northern part of the range. Ecologically it is likely that both the phenomena described by Wardle are in response to a recent change towards a warmer and sunnier climate, attributable to the well documented global warming since late last century. Wardle's results lacked any dates of forest advancement or contraction. Druce and Atkinson (1959) dated a timberline line advance of silver beech forest on Mt. Alpha to c.A.D. 1906.


The increasingly demonstrated synchrony of climatically induced events throughout New Zealand (Wardle 1964, Hendy 1969), within the Pacific Basin (Karlstrom 1966) and globally (Bray 1968, Hendy 1969) suggest that considerable changes in climate have, in fact, occurred in the last 1,000 years.

The argument against any climatic changes in the last 1,000 years being ecologically significant would appear to be a function of the lack of direct evidence of their occurrences. The indirect effects, forest instability and out-of-phase vegetation and soil boundaries, are more often than not explicable by catastrophic phenomena (Molly 1969).

Lamb et al (1966) noted the prominence of the warm, dry summers of the period A.D. 1100-1300 and the cold period A.D. 1550-1700 in the climatic record of the last 1,000 years. Between these two intervals there was a maximum temperature decline of 2°C. Lamb (1965) described the significance of this change to anthropogenic page 121 communities in the North Atlantic region, particularly in central England. Hendy (1969) demonstrated the close relationship of the nature and magnitude of temperature changes in this period between New Zealand and central England. A 2°C. decrease in mean annual temperature is equivalent to a decrease of about 1,200 ft. in the altitudinal belt of the Tararua Range (Zotov et al 1938). These authors considered temperature to be the most important single ecological factor in mountainous areas, where the response of the vegetation/soil system to space-environmental gradients is most marked. Before it can be said, e.g. Cumberland (1962), Molloy (1969) that there has been no ecological response to climatically-induced time-environmental gradients, the upland environments will require considerably greater investigation than they have yet received.

If forest vegetation is to be used to assess climatic change (Holloway 1954, Nicholls 1957) there is need for a far greater understanding of comparative vegetation and soil dynamics between forest, scrub and grassland systems. The concepts of vegetation/soil system development, steady-state, post steady-state, species age/tolerance (Becking 1969) and size class/age stratification (Goff 1968) have received little attention in New Zealand. Similarly, a quantitative knowledge of upland climates, apart from the work of Mark (e.g. 1965) and Coulter (1967) and suitable archaeological evidence of climatic change, particularly in upland areas, is lacking in New Zealand.


I would like to thank Dr. J. R. Bray for helpful discussion and Dr. D. R. McQueen for critically reading the manuscript.


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* e.g. stalactites, stalagmites.