No, Trees Don't Grow Best in Cool, Dry Conditions — The Evidence Is More Nuanced
“Wood growth in trees is constrained to periods of low heat and low aridity”
The argument in brief
The claim that wood growth in trees is constrained to periods of low heat and low aridity gets the temperature part backwards. Wood formation is a warm-season biological process that requires temperatures above roughly 5°C to even begin — cold limits growth, it doesn't enable it. Aridity does suppress growth in dry climates, but only because it causes water stress, not because dryness itself is a growth trigger.
Data: Körner 2012; Vaganov et al. 2006
Why it spread
The claim taps into a familiar intuition: plants seem to thrive in mild, comfortable conditions, not extremes. It also echoes genuine science about drought harming trees, which makes the whole package sound credible. People may have encountered dendroclimatology discussions where cold and dry sites are both described as 'growth-limited' and reasonably — but incorrectly — concluded that low heat and low aridity are therefore the conditions trees prefer.
The claim states that trees form wood primarily when it is cool and dry. This is partially false. It gets one thing partly right — severe drought does suppress tree growth in arid regions — but it fundamentally misrepresents how temperature works, and it overgeneralizes aridity as a universal growth condition rather than a stress factor.
Wood formation, called xylogenesis, is a warm-season process. Research by Vaganov, Hughes, and Shashkin (2006) shows that cambial cells — the tissue responsible for producing wood — cannot divide below about 5°C. Cuny et al. (2015), publishing in Nature Plants, confirmed that cell division and wall thickening in temperate and boreal conifers stop entirely in cold conditions. Warmth does not constrain growth; it is what makes growth possible in the first place.
At high elevations and latitudes, this is even clearer. Körner (2012) found that the global treeline — the altitude above which trees cannot survive — is defined by a minimum growing-season temperature of around 6.4°C. Trees fail to grow there not because it is too warm, but because it is too cold. In these environments, more heat means more growth, not less.
The aridity piece is more complicated. Williams et al. (2013) in Nature Climate Change showed that high temperatures can indirectly suppress growth by increasing water stress. But the key word is indirectly — the mechanism is drought, not heat itself. A tree in a well-watered environment can grow vigorously at high temperatures. Babst et al. (2019), analyzing tree ring records globally in Science Advances, confirmed that growth responses to climate are site-dependent: warming helps cold-limited forests and hurts hot, dry ones. There is no single rule that applies everywhere.
The original claim likely spread because it contains a grain of truth. Drought stress really does limit growth in arid regions, and that part of the science is well established. It is easy to mentally bundle heat and dryness together — hot days often are dry days — and conclude that both suppress growth equally. Dendroclimatology literature does discuss cold-limited and drought-limited forests side by side, which may have led to a misreading. Watch out for claims that take a real ecological pattern from one context and apply it as a universal rule.
Sources
- Fritts, H.C. (1976) Tree Rings and Climate, Academic Press
Tree ring growth is controlled by the most limiting environmental factor at any given time (Liebig's Law of the Minimum). In cold climates, growth is limited by low temperatures; in arid climates, by moisture deficit. The claim reverses the cold-climate constraint — low heat (cold) actually limits growth, not enables it.
- Vaganov, E.A., Hughes, M.K., & Shashkin, A.V. (2006) Growth Dynamics of Conifer Tree Rings, Springer
Cambial activity and wood formation in conifers require temperatures above a biological threshold (typically ~5°C). Growth occurs during warm seasons, not cold ones. Extreme heat and drought together suppress growth, but moderate warmth is necessary for xylogenesis.
- Cuny, H.E. et al. (2015) Woody biomass production lags stem-girth increase by over one month in coniferous forests, Nature Plants
Xylogenesis (wood cell formation) in temperate and boreal conifers occurs during the warm growing season. Cell division and wall thickening cease in cold conditions. This directly contradicts the idea that low heat promotes wood growth.
- Williams, A.P. et al. (2013) Temperature as a potent driver of regional forest drought stress and tree mortality, Nature Climate Change
High temperatures increase vapor pressure deficit and drought stress, which can suppress growth. However, the mechanism is through moisture limitation, not heat per se. Trees in mesic environments can grow well under high temperatures if water is available.
- Körner, C. (2012) Alpine Treelines: Functional Ecology of the Global High Elevation Tree Limits, Springer
At high elevations and latitudes, tree growth is constrained by low temperatures (insufficient heat), not by high heat. The treeline is defined by a minimum growing-season temperature threshold (~6.4°C mean), confirming that warmth enables rather than inhibits growth.
- Babst, F. et al. (2019) Twentieth century redistribution in climatic drivers of global tree growth, Science Advances
Global analysis of tree ring networks shows that in cold/high-latitude sites, warming increases growth, while in hot/dry sites, heat and aridity reduce growth. Growth constraints are site-dependent and not uniformly tied to 'low heat and low aridity.'