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An example collection, so you can see what this page does. Nothing added here is kept: leaving deletes it.
Betula occidentalis; photograph (c) machaut2, some rights reserved (CC BY) CC BY(c) machaut2, some rights reserved (CC BY) · observed growing wild · 2026-08-21

Betula occidentalis Hook.

Water birch; River birch; Black birch; Mountain birch

Betulaceae · Alaska, Northwest Territories +20

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Betula occidentalis, photograph author not stated, no rights reservedBetula occidentalis, photograph author not stated, no rights reservedBetula occidentalis, photograph author not stated, no rights reservedBetula occidentalis, photograph author not stated, no rights reservedBetula occidentalis, photograph author not stated, no rights reservedBetula occidentalis, photograph author not stated, no rights reserved 79 photographs ›
Habitat figures
Cold floor (1 night in 100)
-16.4°C
Record low -25.8 °C in 44 years, at a typical spot in the range NASA POWER
Warmest month, mean daily high
26°C
Jul at the habitat CHELSA
Rain a year (median across the range)
476mm
12 months of 25 mm or more in the median year CHELSA
Open-sky light
11–47DLI
Lowest to highest month (DLI) CHELSA
The year in your months, northern hemisphere
  1. Jan
  2. Feb
  3. Mar
  4. Apr
  5. May
  6. Jun
  7. Jul
  8. Aug
  9. Sep
  10. Oct
  11. Nov
  12. Dec
Rain spread: 70% of the median year's rain takes 8 months, so no short rainy season. rain rule, CHELSA
Northern hemisphere unless you set your site. The chart is in the habitat's months.

Summary

Betula occidentalis, the water birch or red birch, is a species of birch native to western North America, in Canada from Yukon east to Northwestern Ontario and southwards, and in the United States from eastern Washington east to western North Dakota, and south to eastern California, northern Arizona and northern New Mexico, and southwestern Alaska. It typically occurs along streams in mountainous regions, sometimes at elevations of 2,100 metres (6,900 feet) and in drier areas than paper birch.

Quoted from Wikipedia, "Betula occidentalis", CC BY-SA 4.0.

Cultivation

Seasons

The rain rule reads no short rainy season: 70% of the median year's rain (309 mm of 439 mm) takes 8 months, April to October and December. Mean temperature moves 24.6 °C between the warmest and coldest month. Months are the habitat's, northern hemisphere; shifted six months for a southern-hemisphere collection: October to April and June.

Rain

439 mm in the median year at the habitat, 309 mm of it April to October and December. Wettest month May at 48 mm, driest month February at 28 mm. Across the grid cells of the range the year's total runs 293 mm to 772 mm, the 10th to 90th percentile of each cell's own year. The median of the cells' own yearly totals, 476 mm, is the year's rain at the top of the page; the 439 mm here is the median year's, the twelve monthly medians added, which the rain rule reads. Habitat calendar, northern hemisphere; median year across the grid cells of the range, CHELSA.

Light

Open sky over the habitat: 11 to 47 mol/m²/day across the year (daily light integral, median year across the grid cells of the range, CHELSA; the lowest 10th-percentile month across the cells is 5, the highest 90th-percentile month 53).

Warmth and air
Temperature

Coldest: the 1st-percentile night over 44 years at a typical spot in the range is -16.4 °C, the absolute minimum -25.8 °C, 9,103 frost nights in 44 years, 206.9 a year (NASA POWER daily minima). Warmest: the 99th-percentile day is 32.1 °C. Monthly means: the coldest month's mean nightly low -10.1 °C in December (across the grid cells of the range -16.0 °C to -4.8 °C), the warmest month's mean daily high 25.8 °C in July (median year across the grid cells of the range, CHELSA). Cold floor: -16.4 °C, which is the 1st-percentile night over 44 years at a typical spot in the range (NASA POWER).

Humidity

Relative humidity at the habitat: 49 to 60% across the year (monthly means, median year across the grid cells of the range, CHELSA). A figure about the air, saying nothing about how the plant takes water.

How this section is made

Each card states this species' habitat figures with their sources, and what two fixed rules read from them; nothing here says what the plant does, wants or tolerates. The rules · the terms.

Seasons. Read from the median year of CHELSA monthly rainfall and mean temperature across the grid cells of the range: 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 moves 4 °C or more and the habitat lies 10° or more from the equator. A reading of the curves, not an observation of the plant.

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

Light. 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.

Temperature. NASA POWER daily minima and maxima over 44 years at a typical spot in the range, lapse-corrected +388 m to its elevation; CHELSA monthly means, median year across the grid cells of the range. The cold floor is the 1st-percentile night named in its sentence. Not a measured survival limit for any plant in a pot.

Humidity. CHELSA relative humidity, median year across the grid cells of the range.

Climate across the habitat

Habitat months, northern hemisphere

Habitat climate of Betula occidentalis through the yearWarmest month July, mean daily high 26 °C; coldest month December, mean nightly low -10.1 °C; 439 mm of rain in the median year (the twelve monthly medians added). Medians across the range, from CHELSA; the extremes at the edge from NASA POWER. Habitat months, northern hemisphere.-30°-20°-10°0°10°20°30°40°frost32.1° 99th-percentile day, NASA POWER-25.8° lowest night in 44 years, NASA POWER°C · day and nightcold quarter0255075100mm rainDLI 11–47RH 49–60%JanFebMarAprMayJunJulAugSepOctNovDec
day night rain medians and 10th–90th percentile across 782 habitat cells, CHELSA cold quarter: the three months around the coldest month's mean nightly low extremes over 44 years at a typical spot in the range, from NASA POWER, marked at the edge, in no month DLI, mol/m²/dayRH %each on its own scale
Figures by month
JanFebMarAprMayJunJulAugSepOctNovDec
Day °C0 / -6–42 / -4–66 / 1–1011 / 5–1517 / 11–2122 / 17–2626 / 21–3025 / 20–3020 / 15–2513 / 8–185 / -1–10-1 / -7–4
Night °C-10 / -16–-5-9 / -15–-3-5 / -11–-1-1 / -6–34 / -1–78 / 5–1212 / 8–1612 / 8–167 / 3–111 / -3–6-5 / -10–0-10 / -16–-5
Rain mm33 / 14–8828 / 13–7134 / 20–7235 / 19–6648 / 21–8246 / 14–9035 / 14–8035 / 13–7637 / 15–6036 / 19–6035 / 16–8437 / 15–92
DLI13 / 7–2120 / 14–2829 / 23–3738 / 33–4544 / 38–5047 / 40–5347 / 40–5142 / 34–4733 / 24–3923 / 15–3014 / 8–2211 / 5–18
RH %60 / 51–6759 / 52–6356 / 51–6053 / 49–5753 / 46–5651 / 41–5649 / 40–5649 / 42–5651 / 43–5753 / 47–6057 / 50–6660 / 51–68
How this section is made
Each figure is the median across the 782 grid cells holding the 1185 in-range records, with the 10th–90th percentile span across those cells after the slash where it differs. A dash is a month one or more of those cells has no figure for in the grid (a variable CHELSA does not carry there), so no median is taken rather than one over fewer cells. Extremes and elevation were read at a typical spot in the range, cell 975:1197 (41.225, -120.125). Over 44 years there: absolute minimum -25.8 °C, 1st-percentile night -16.4 °C, 99th-percentile day 32.1 °C. Normals: CHELSA V2.1 1981–2010 climatology, 0.05° cells (each the mean of ~36 1 km pixels). Across the range: median and 10th–90th percentile of each month across the 782 distinct grid cells holding 1185 of the 1185 in-range records; extremes and elevation at the typical cell 975:1197 (its coldest month's mean nightly low nearest the median across cells); its position is the cell centre. Extremes: NASA POWER (MERRA-2) daily 1981–2024, cell 41.00_-120.000, lapse-corrected +388 m at 6.5 °C/km. Elevation: ETOPO 2022, 2125 m (cell mean).

Natural habitat

Native range as published by WCVP; the marker is where the records are densest and decides nothing: the climate was read across the cells of the in-range records placed well enough to read one, not at the marker.
Openly licensed records inside the range, framed on where they fall.
NativeAlaska, Northwest Territories, Yukon, Alberta, British Columbia, Manitoba, Saskatchewan, Ontario, Colorado, Idaho, Montana, Oregon, Washington, Wyoming, North Dakota, Nebraska, South Dakota, Arizona, California, Nevada, Utah, New Mexico · regions are the level-3 units of the World Geographical Scheme for Recording Plant Distributions, as Kew's World Checklist records ranges, some under historical names such as Yugoslavia or Czechoslovakia (how).
Map marker37.406, -118.315 · in the densest population, 770 records (47% of those in range)
Kew's description“shrub or tree” · “temperate” · quoted from WCVP, RBG Kew (CC BY 4.0); not derived here
Evidence usedThe map marker rests on all 1624 georeferenced records inside the native range; the climate across the range on the 1185 of them placed to within 10 km; the map shows only the 772 openly licensed ones, which alone would put the marker 711 km away. 12 records outside the WCVP native range not used. 439 in-range records are placed to worse than 10 km, or with no stated accuracy (admitted only as a person's observation to three decimals), and stay on the map but off the climate.
How this section is made
The map marker: the openly licensed record nearest the middle of the densest 1° population inside the densest 4° block of the 1624 in-range records; it decides nothing. Records outside the native range, living specimens and records marked introduced are not used; which records count.

Photographs

Betula occidentalis, photograph 1did not loadBetula occidentalis, photograph 2did not loadBetula occidentalis, photograph 3did not loadBetula occidentalis, photograph 4did not loadBetula occidentalis, photograph 5did not loadBetula occidentalis, photograph 6did not load

Photographs: author not stated, no rights reserved · CC0 (6).

Similar habitat climate The 6 nearest by mean daily high, mean nightly low and rain, month by month. How.

Linum lewisii Linum lewisii Lewis' flax Photo: CC BY, Tom HiltonLithospermum ruderale Lithospermum ruderale Columbia puccoon Photo: CC0, author not statedSymphyotrichum ascendens Symphyotrichum ascendens Western aster Photo: CC BY, Daughter DadSymphoricarpos oreophilus Symphoricarpos oreophilus Mountain snowberry Photo: Public domain, JW StockertThermopsis montana Thermopsis montana Mountain golden-banner Photo: CC BY-SA, Matt LavinCastilleja linariifolia Castilleja linariifolia Wyoming Indian paintbrush Photo: CC BY, Kate Kruesi

Other Betula 47 in the reference

Betula alleghaniensis Betula alleghaniensis Yellow birch Photo: CC BY, naturalist charlieBetula alnoides Betula alnoides Indian birch Photo: CC BY, Ramnarayan KBetula × aurata Betula × aurata Betulaceae Photo: CC0, Stephen James McWilliam Betula bomiensis Betulaceae Betula × caerulea Betula × caerulea Blue birch Photo: CC0, author not stated Betula calcicola Betulaceae Betula celtiberica Betula celtiberica Betulaceae Photo: CC BY, Jose CastroBetula chichibuensis Betula chichibuensis Chichibu Birch Photo: CC BY-SA, Krzysztof Ziarnek, KenraizBetula chinensis Betula chinensis China birch Photo: CC0, author not statedBetula cordifolia Betula cordifolia Mountain paper birch Photo: CC BY, Tyler Ekholm Betula corylifolia Hazel-leaf Birch Betula costata Betula costata Korean birch Photo: CC BY, Jane Charlen all 48 ›

Names & registers

Also known as Betula alba f. occidentalis; Betula alba subsp. occidentalis; Betula beeniana; Betula elrodiana; Betula fontinalis and 13 more. (GBIF Backbone)

GBIFPOWOIPNIWFOWikidataWikipediaiNaturalist

The record

Family
Betulaceae
Described by
Hook.
Native to
Alaska, Northwest Territories, Yukon +19
Wild records
1624 in range · 772 open

Every figure here is derived from public data by a stated rule and names its source; nothing about this species is written for its page by a person or by AI, apart from the marked, credited quotations. How →

Where this page came from built 2026-10-21
GBIF species record gbif.species answeredasked 2026-10-21
GBIF synonyms gbif.synonyms answeredasked 2026-10-21
GBIF common names gbif.vernacular answeredasked 2026-10-21names fetched 2026-10-21
WCVP native range wcvp.distribution answeredas of 2026-06-04
GBIF occurrence records gbif.occurrences answeredas of 2026-10-21GBIF occurrence download https://doi.org/10.15468/dl.hbdw64, of 2026-10-21; 24 records within 1 km of a botanic garden, herbarium or zoo left out (23 at a botanic garden or arboretum, 1 at a zoo; Wikidata's list)
Habitat climate climate answeredasked 2026-10-21
Daily extremes (NASA POWER) climate.extremes answeredasked 2026-10-21NASA POWER (MERRA-2) daily 1981–2024, cell 41.00_-120.000, lapse-corrected +388 m at 6.5 °C/km
Wikidata wikidata answeredasked 2026-10-21
Wikipedia wikipedia answeredasked 2026-10-21
iNaturalist photographs, wild inat.photos.wild answeredasked 2026-10-22from iNaturalist's open data of 2026-09-27: research-grade observations with an open-licence photograph, the 24 whose photographs iNaturalist received last (the open data holds no votes); filled 2026-10-22
iNaturalist photographs, cultivated inat.photos.cultivated not asked
GBIF media gbif.media answeredasked 2026-10-21
OpenAlex papers openalex not askednot yet asked for this reference; a later fill takes the papers from OpenAlex's snapshot

Every source is recorded as having answered, reported nothing, refused, failed, not been asked, or answered twice where one answer is taken (“not taken: two items answered”), and, for a source asked when this page was built, when: the figures are as the source held them that day; a source read from a file (Kew's World Checklist, a GBIF download) says "as of" the file's day instead; a row carried from an earlier build of the page names that build instead. Only “nothing to report” is ever shown as an absence. Records came from 106 datasets via GBIF.org; each carries its own licence.

Cultifolio

Opening your plants…