Calluna vulgaris (L.) Hull

This species’ habitat figures, and what two fixed rules read from them.

The rain rule reads no season: 70% of the year's rain (648 mm of 896 mm) takes 8 months, June to January. Mean temperature moves 15.0 °C between the warmest and coldest month. Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: December to July.

Read from the median year of CHELSA monthly rainfall and mean temperature across the envelope cells: the rain rule takes the smallest set of months carrying 70% of the rain and calls it winter when its mean is more than half a degree below the year's, summer when more than that above, and neither in between; the temperature rule, used only under 120 mm, names the cooler six months when they are at least a degree cooler than the other six. Months are shifted for the other hemisphere only where the temperature curve gives a season to reverse. A reading of the curves, not an observation of the plant.

This species’ habitat figures, with their source.

896 mm a year at the habitat, 648 mm of it June to January. Wettest month October at 85 mm, driest April at 49 mm. Across the envelope cells the year's total runs 701 mm to 1476 mm (10th to 90th percentile of each cell's own year) (median year across the envelope cells, CHELSA; habitat calendar, northern hemisphere).

CHELSA monthly precipitation, median year across the envelope cells. The rain that falls where the species is recorded; nothing about how the plant takes water.

This species’ habitat figures, with their source.

Open sky over the habitat: 4 to 33 mol/m²/day across the year (daily light integral, median year across the envelope cells, CHELSA; the lowest 10th-percentile month across the cells is 2, the highest 90th-percentile month 38).

CHELSA shortwave radiation at each envelope cell, a daily-mean flux taken to a daily total and converted at 2.07 mol of PAR per MJ. The sky over the habitat, measured; what reaches a plant under a rock, a shrub or a shade cloth is not.

This species’ habitat figures, with their source.

Coldest: the 1st-percentile night over 44 years at the typical cell is -5.6 °C, the absolute minimum -14.4 °C, about 39 frost nights a year (NASA POWER daily minima). Warmest: the 99th-percentile day is 23.3 °C. Monthly means: coldest night 0.1 °C in February (across the envelope cells -5.0 °C to 2.8 °C), warmest day 21.5 °C in July (median year across the envelope cells, CHELSA). Cold floor: -5.6 °C, which is the 1st-percentile night over 44 years at the typical cell (NASA POWER).

NASA POWER daily minima and maxima 1981–2024 at the typical cell, without lapse correction; CHELSA monthly means, median year across the envelope cells, CHELSA. The cold floor is the figure named in its sentence. Not a measured survival limit for any plant in a pot.

Relative humidity at the habitat: 60 to 69% across the year (monthly means, median year across the envelope cells, CHELSA). A figure about the air, saying nothing about how the plant takes water.

CHELSA relative humidity, median year across the envelope cells.