Lightning injuries to trees
C.X. Furtado, a botanist at the Singapore Botanic Gardens, published this observational study in 1935 documenting three lightning strikes that occurred near the Gardens between July 1928 and January 1929. The article presents detailed morphological observations of the damage inflicted on Ficus variegata, Fagraea fragrans, and Albizia moluccana, and uses these cases to propose a three-class typology for the physiological effects of electrical discharges on tree tissues.
Summary
Furtado’s account is grounded in sustained personal observation over approximately six years, with the first two trees visited within half an hour of being struck and the third observed in real time as the discharge travelled spirally along a branch. The central problem he addresses is the paucity of recorded evidence on how lightning actually damages trees in tropical settings, and he uses the three cases to illustrate how the physical properties of bark and wood—density, moisture content, presence of milky latex, thickness of corky layers—determine the pattern of injury. In the Ficus, the latex-rich bark absorbed the discharge and detached as a cylindrical jacket while the wood remained largely intact; in the Fagraea, the thick dry outer bark and hard close-grained wood offered high resistance, producing violent splitting and bark fragments thrown up to twenty feet; in the Albizia, the soft wood and thin bark conducted the current equally through both tissues, resulting in uniform splitting.
A second thread of the article concerns secondary and collateral damage to neighbouring trees. Furtado records that several trees within fifteen to twenty feet of the struck Fagraea began dying gradually from the top down, while trees at similar distances in other directions were unaffected, suggesting a directional component to the discharge’s residual effects. He also notes that no grass or soil was damaged in any of the three cases, and that no parasitic insects were observed on the affected trees, though he acknowledges the possibility of fungal invasion complicating diagnosis.
In his discussion, Furtado draws on the limited phytobiological literature of the period—citing Riede, Baines, Stalfelt, Mercier, Weir, and Sharples—to frame his observations within a stimulus-response model. He argues that electrical currents below an optimum threshold are beneficial, at the optimum neutral, and above it progressively harmful, with the degree of harm determining whether a tree dies immediately, succumbs slowly, or recovers. He further notes Sharples’s finding that lightning-struck rubber trees become susceptible to parasitic attack, and that coconut “budrot” in the Malay Peninsula is nearly always a consequence of lightning damage to the apical meristem.
Key Findings
- Three lightning strikes were documented: two on the same day in mid-July 1928 (on Ficus variegata and Fagraea fragrans, approximately half a mile apart) and one on 1 January 1929 (on Albizia moluccana).
- The Ficus variegata (40–50 ft tall) died completely by March 1929, nine months after the strike; its bark detached as a cylindrical jacket up to 25 ft from the base while the wood showed no splitting.
- The Fagraea fragrans (60 ft tall) had bark fragments up to one yard long and six inches wide thrown as far as twenty feet from the trunk; the wood split so readily along its rays that it could be divided by axe into small bits, and it dried to usable fuel within a week.
- Three neighbouring trees (Knema intermedia, K. furfuracea, and Eugenia grandis) at 12, 15, and 20 feet to the north of the struck Fagraea began dying simultaneously approximately three months after the strike, while a tree only five feet away in another direction was unaffected.
- A second Ficus variegata at 15 feet to the north of the first showed progressive dieback from the tip of a side branch over approximately fourteen months but was still alive with healthy lateral shoots as of November 1934.
- In all three primary cases, death progressed from the top downwards, with the roots being the last tissue to die; Furtado concludes that dicotyledonous trees could generally be saved by pollarding during the early stages of lightning damage.
Conclusion
Furtado’s definitive takeaway is that the physical constitution of a tree’s tissues—particularly the relative electrical resistance of bark, cambium, and wood—determines both the immediate pattern of mechanical damage and the long-term physiological prognosis. He proposes that trees struck by lightning fall into three classes: those killed outright by a discharge exceeding tissue tolerance, those subjected to a harmful but sublethal charge that causes slow progressive death, and those in which the charge only slightly exceeds the optimum and from which the tree eventually recovers. He cautions, however, that in practice the boundaries between these classes are blurred by secondary parasitic infection, making definitive classification of slowly dying trees difficult.
Context
- Furtado was a botanist (B.AG.) attached to the Botanic Gardens, Singapore, a colonial scientific institution; the article reflects the applied botanical and forestry interests of the Straits Settlements research establishment in the 1930s.
- The study draws on the author’s own field observations supplemented by a small body of European phytobiological literature (Riede 1928, Baines 1919, Stalfelt 1919, Mercier 1919) and two contemporary Malayan studies (Weir 1928, Sharples 1933) on lightning effects in rubber and coconut cultivation.