This is an interesting and potentially important paper. However, I recommend the authors reconsider their model assumptions and conclusions based on the following points after a first read:
1) The model is basically based on one paper, Forrest (1971), but this paper collected data for a "tundra" peatland ecosystem at Sike Hill (extreme conditions are outlined in the paper); biomass and vegetation heights are, therefore, unsurprisingly small by comparison to other temperate systems. This data represent a very extreme environment and should not be generalised.
2) The harsh tundra conditions reflect the historically much colder (~5°C mean temp at the time - now much warmer) and frequently high winter snow packs together with high winds and thus frost killing of shoots. The vegetation was shaped by those conditions for hundreds of years (and notably a very cold 10-year period before sampling in the 1960s); especially the "Big Freeze" in 1962/63 needs to be considered when interpreting or using those data. Basically, the growth/age data represent regrowth responses and recovery under those (past) extreme conditions.
3) Since then, the climate changed considerably. The information from Forrest (1971) basically does not currently apply to any significant blanket bog habitat in the UK (certainly not in England) - I think it already did not apply to much at the time of the paper. Basically, the data do not relate to blanket bog overall and certainly not under current or future climate.
4) Layering of heather under such conditions (heavy snow pack) is normal and to be expected (a growth strategy to tundra conditions). The actual ages of the heather plants are therefore much older, but this was not determined by Forrest (only the recent vertical shoots were measured) - but the recorded mass of such horizontal shoots is considerable.
5) Therefore, the histogram of the (vertical) stem numbers versus age is only representative of such a highly disturbed system - not a system in a 'normal' steady state (it is recovering from extreme conditions - certainly of the "Big Freeze"); moreover, the heather ages are almost certainly way out as only vertical stems were measured, ignoring the much older horizontal stems (which can be more than a meter long at that site - evidence is in a freezer available for age determination) from which those shoots resprouted. Therefore, it should not be used to inform a model for generic blanket bog heather ages, where stems are growing without this killing off during winter and flattening from snow - it clearly will be very different (and there are data on this growth/age from other, more relevant studies).
Some other observations:
Defra has not banned burning (although in effect they have - but they do not like seeing such statements it seems).
Quite a few important studies seem to have been overlooked (e.g., MacDonald, 1995; Harris et al., 2011 - and many references therein; Glatzel et al., 2024).
Sub-optimal growth conditions of heather are not defined - this is clearly a complex issue as heather has a wide range of adapted 'ecotypes', even growing quite massive under very wet conditions (our Mossdale site is one example; Heinemeyer et al., 2019; 2023).
Past vegetation needs to consider past climate (Little Ice Age!) - more Sphagnum and less heather are unsurprising under wetter and colder conditions but things warmed up since the ~1750s (and continue to get much warmer and drier).
Mowing has many more issues (smoldering brash risks, perfect tick habitat, ..., but also clearly has some benefits on soil moisture but not necessarily net, long-term carbon storage) but key studies and related papers are, unfortunately, not cited/considered (including Peatland-ES-UK ones). Heinemeyer et al. 2019/23 study is not a chronosequence study as stated and, unfortunately, our cited 2023 report is not listed in the reference list and it provides much more relevant information in addition to our papers on various claims about burning, cutting, rewetting etc.).
It is important not to confound papers/studies from topogenous bogs (e.g., valley and raised bogs) with hill blanket bogs (e.g., I think many Wallen 1980s papers are as such) - ecohydrological conditions (wetness and thus vegetation potential) need to be considered and comparable.
Formatting etc. issues in the reference list.