Data from: Experimental warming does not change fluctuating asymmetry in three willow species

Fluctuating asymmetry (FA) is often proposed as an early warning indicator
of subtle changes in plant functioning. Here, we tested whether leaf FA
responds consistently to the alleviation of cold stress in three boreal
willow species—Salix caprea, S. myrsinifolia, and S. phylicifolia. We
enclosed 10 naturally growing individuals of each species in open-top
chambers at budburst and compared their leaf traits to those of unenclosed
control plants after leaf development had ceased. All measurements were
conducted blind to treatment. Willows in open-top chambers showed a 9 %
increase in specific leaf area, indicating that the 1–2 °C warming within
chambers affected leaf development. However, neither leaf length nor FA
responded significantly to the warming treatment. FA also did not differ
among species or individual plants, suggesting that it may reflect
statistical noise rather than a reliable biological signal in this
context. These findings add to growing concerns that many reported FA
responses to environmental change may result from confirmation bias—an
issue that can be mitigated by adopting blind measurement protocols.