The impression given by the SPD was that the change observed in Kanto was more akin to a gradual return to “normal conditions” (after the peak of 5,000 cal BP) rather than an episode of a sudden “collapse”
All case studies show evidence of a decline after a period of relatively high density of 14 C dates associated with the Middle Jomon period (albeit in Aomori Prefecture there is a significant temporary drop in the SPD around 5,300–5,200 cal BP). In the Kanto region, this maximum is characterised as a single, statistically significant peak around 5,000 cal BP, thus few hundred years earlier than what has been suggested in previous works (e.g. [9,18,21]). In most cases, the pair-wise permutation test does not suggest significant divergences in these fluctuations, although the 5,000 cal BP peak in the SPD observed in Kanto showed a significantly higher density compared to the other two regions.
The comparison of the three SPD does, however, not indicate any statistically significant divergence after 5,000 cal BP. The timing of the decline of the general rise-and fall pattern seems to have occurred slightly earlier in the Kanto region (right after 5,000 cal BP) compared to the other two study areas (after 4,000 cal BP). The decline observed in the SPD of the Kanto region appears to be matching the lowering in the number of pit-houses and sites dated between the Middle and Late Jomon period (generally linked from the Kasori E4 to the Shomyoji phases; 4,520
4,000 cal BP) in any of the regions. It is worth stressing, however, that the fact that we failed to reject the null hypotheses for this stage does not imply that there was no decline. This is also in line with some recent studies based on the time-series of residential units and site counts where the absolute density of features remains higher than the conditions observed before the Middle Jomon peak (e.g. https://hookupdate.net/cs/woosa-recenze/ ).
The SPD of the Kanto Region does however suggest that this slow decline continued, and reached a statistically significant trough (when compared against the exponential model) at ca. 3,900
In Aomori Prefecture and Hokkaido, the patterns resemble more a high-density plateau between 5,500 and 4,000 cal BP, with some statistically significant fluctuations (when compared against the uniform null)
3,820 cal BP; ), when indeed some evidence of decline is observed from other proxies [9,21]. In Aomori, the observed decline seems to be concurrent to the decline in residential features observed in the Hachinohe city area around the middle of the Late Jomon period, although the lack of absolute dates does not allow us to further assess this claim. This interval is later than the estimated cooling of
2°C at around 4,100 cal BP in the sea surface temperature of the Mutsu bay area , located between Aomori and Hokkaido.
Determining whether these differences between the SPDs and the other existing proxies (i.e. counts of residential units and sites) are real, or dictated by chronometric uncertainty of the latter, is not trivial. Jomon pottery phases are assumed to be non-overlapping, and hence a decline in the number of features associated to a specific phase will undoubtedly generated a trough in the time-series. While this can be a genuine reflection of the underlying population dynamics, abutting and spatially synchronous archaeological phases is often an unrealistic assumption that might introduce a significant bias, especially when we consider larger study areas. In contrast, the probabilistic nature of SPDs implies that, in order to have a statistical significant trough in the time-series, the duration of the low-density interval must be sufficiently large. Hence a sudden drop and reprise in the population for a period of less than 100