3.4 — Climate

The climate at Bambusetum Baan Sammi

Baan Sammi is located in the north­-eastern region of the large Chiang Mai plain at an altitude of 305 m (1,001 ft). The plain is embedded by mountain ranges (1,700–2,400 m or 5,500–7,800 ft altitude) that extend from north to south and is bounded in the north by hills (500–800 m or 1,600–2,600 ft altitude).

The climate in the entire Chiang Mai plain can be described as a tropical savannah climate. Although there is only arable land (pre­dominantly rice fields) around urbanized areas on the plain and no savannah-like vege­tation, the plain was covered by mixed deciduous forest before human settle­ment millennia ago. When Baan Sammi was estab­lished in 2003, the intention was for some areas within Baan Sammi to enable natural regener­ation of the vege­tation (mainly for native tree seeds). Over about 20 years (observed at the original wasteland of Baan Sammi and neighboring unused wasteland from 2003 to 2024), several native trees developed from seeds, such as Butea monosperma, Tectona grandis (seeds from planted trees), Azadirachta indica, Senna siamea, Streblus asper, and Casearia sp. Introduced and naturalized species grew up abundantly from seeds, too, such as Samanea saman, Leucaena leucocephala, and numerous climbers, most of them introduced ones. After about 15 years, the tallest trees reached heights of 20–30 m (65–100 ft), and if most of them were not logged down, the area would soon have developed into the climax vegetation of a mixed deciduous forest.

The Chiang Mai plain has a pronounced long dry season from Novem­ber / Decem­ber to April / May. It hardly rains during this period, if at all, and the atmo­spheric humidity is rather low. The monsoon rain begins around April / May and lasts until around mid-October. The annual precipitation at Baan Sammi is a little over 1,100 mm (43 in), and the rainiest month is September.

At Baan Sammi, night temperatures in December and January can drop to around 11 °C (52 °F) on a few nights within a few weeks (usually only for 1–2 weeks). The lowest temper­ature ever measured between 2003 and 2020 was 9 °C (48 °F). Daytime temper­atures during April and May typically rise to 33–37 °C (91–99 °F), with peaks of around 38–39 °C (100–102 °F), and can reach 40 °C (104 °F) during a few days and occasion­ally slightly exceed this temper­ature for a few hours. In the neigh­boring urban area of Mueang Chiang Mai, about 15 km (≈10 mi) away, the temper­atures are usually 1–3 °C (to 4 °F) higher during the day and at night.

The climate at Baan Sammi limits the growth of certain bamboo species or generally prevents good growth. All estab­lished bamboo species, except for the few species that are native to this area (Thyrso­stachys and some Bambusa species), need to be irrigated more or less frequently during the dry season. In particular, irrigation is needed for all bamboo species native to southern Thai­land, and generally, for all those species from the humid tropics. There are only a few exceptions, such as Giganto­chloa atro­violacea from Java, which, once estab­lished, do not require irrigation. On the other hand, some species from the wet tropics that require high atmo­spheric humidity all year round may not thrive well at Baan Sammi, e.g., the under­storey bamboo Neo­loleba atra.

The temper­ature range at Baan Sammi over the year allows many tropical and sub­tropical bamboo species to be cultivated. However, species from higher elevations in the tropics (including some mountain­ous regions in Thai­land), and in the sub­tropics (such as mountain­ous regions in southern China) tend to suffer when planted at Baan Sammi, e.g., Dendro­calamus sikkim­ensis from the Himalayan region, and Borinda species from Yunnan.

Bamboo species native to temperate regions cannot be success­fully grown at Baan Sammi. We have had several casualties, and some species became hospital­ized and are expected to be unable to adapt to our climate, e.g., Fargesia, Plei­oblastus, Indo­calamus, Chusquea.