Typhoon York scores direct hit
Typhoon York scores direct hit
Typhoon York, which hit Hong Kong on September 16th, was reportedly the biggest typhoon for 16 years. There is surprisingly little information in the local literature on the ecological impacts of typhoons so it is important to record the effects of this one. The damage to thousands of roadside and park trees was the most conspicuous impact (see below) but trees rarely grow in isolation in nature so this devastation is not surprising. Damage to semi-natural forests and shrubland was a lot less dramatic, except near exposed edges, but was still impressive.
In most places, the forest canopy was noticeably more open after the storm, while the forest floor was strewn with still-green (and thus nutrient-rich) leaves, parts of leaves, and leaf-bearing twigs. Broken trunks and branches were rare (except in the Australian exotic, Lophostemon confertus) and most of the larger woody debris brought down by the wind was already dead. Presumably, a big typhoon strips the canopy of dead wood while, at the same time, creating a new supply for the next storm to remove.
Overall, the forest is more open and has more potential fuel on the ground: both factors which are likely to enhance fire risk this winter. It will be interesting see whether trees bother to replace lost leaves this late in the year. The impact on animals is less easy to predict. The typhoon stripped all ripe and near-ripe fruit from both trees and shrubs, and presumably also removed many canopy-feeding insects. Perhaps in response to this, bulbuls and other birds which usually feed in the canopy were feeding on the ground in unusual numbers in the days immediately after the storm.
Since we were interested in knowing the susceptibility of different tree species planted on roadsides or in parks to typhoon damage, a KFBG team surveyed Island South, Chai Wan, Wan Chai, Victoria Peak and Ngau Tau Kok on 19 September, and Wong Tai Sin, Tai Po, Fanling, Sheung Shui, Yuen Long and Tin Shui Wai on 20 September. Thirty-three species (8 were native) were recorded as either 'destroyed' (uprooted or main stem broken - 33 species, 969 trees) or 'damaged' (main branch broken - 21 species, 115 trees). Another 11 native species that appeared to occur naturally were also recorded (9 species, 21 trees destroyed; 4 species, 6 trees damaged). Bauhinia spp., Acacia auriculiformis, Eucalyptus spp. and Cassia siamea accounted for 48% of total number destroyed. Other species that were widely destroyed include Melaleuca quinquenervia (8.7%), Acacia confusa (7.1%), Lophostemon confertus (7%), Casuarina equisetifolia (6.4%). Casuarina was the most widely damaged tree (29%).
Though we did not count the unaffected trees due to time constraints, it is fair to say that Bauhinia spp. are amongst those most susceptible to typhoon damage. We cannot tell from this survey whether exotic or native species suffered more serious damage. However, a recent visit to Hatton Road, Hong Kong Island found that the Lophostemon plantation appeared to suffer far more serious damage from York than the natural Machilus forest immediately above it.
Richard Corlett, Lawrence Chau, Billy Hau and Ken So
P.1
Birds and Typhoon York: "sound and fury signifying nothing"?
The group of birds which appears to have been most obviously affected by Typhoon York, which passed directly over Hong Kong on 16 September, was the ardeids. It seems likely that many of these were migrating at the time and that flocks and individuals were caught up in the storm and displaced. At Cape D'Aguilar, which was within the eye of the storm for about one hour during late morning, about 30 Cattle Egrets Bubulcus ibis, two Little Egrets Egretta garzetta, one Black-crowned Night Heron Nycticorax nycticorax, two Chinese Pond Herons Ardeola bacchus and, most surprisingly, 11 Black Bitterns Ixobrychus flavicollis were observed. Other species seen at this time included a Common Teal Anas crecca, a handful of waders including four Black-winged Stilts Himantopus himantopus, three Dollarbirds Eurystomus orientalis, single Oriental Reed Warblers Acrocephalus orientalis and Arctic Warblers Phylloscopus borealis and a Japanese Paradise Flycatcher Terpsiphone atrocaudata. Almost all of these birds appeared whilst the eye was passing over, suggesting that they had become caught up in the storm and were being forced to move with it.
Perhaps because of the storm's track, resulting in north-westerly winds during its approach, Typhoon York did not produce any of the spectacular movements of seabirds which have been observed at Cape D'Aguilar during some other storms in recent years, notably Typhoon Dot in September 1993 and Typhoon Leo in May 1999 (Lam and Williams 1994, Lewthwaite 1999). The only seabirds observed were terns and the numbers were rather small: 54 Bridled Terns Sterna anaethetus were seen along with a handful of Common Terns S. hirundo, two Aleutian Terns S. aleutica, one Little Tern S. albifrons and one Sooty Tern S. fuscata - this last being the only evidence of any effect on pelagic bird species. Sixty Whiskered Terns Chlidonias hybridus were seen, but this species is a freshwater tern and this observation perhaps more properly belongs with the landbird sightings discussed above.
Away from Cape D'Aguilar other observations on the day of the storm related to similar species, with small numbers of terns seen at Ap Lei Chau and terns, egrets and 36 Black-winged Stilts recorded from Cheung Chau. Away from the track of the storm a flock of 200 terns, probably mostly Whiskered Terns, appeared at Mai Po during the afternoon. On the following day there were still numbers of Whiskered Terns in the Deep Bay area, including a group of 90 birds at Long Valley which passed over in the early morning, suggesting a reorientation movement.
Over the next few days there were a series of reports of Cattle Egrets in unusual locations, such as Kennedy Town and Ho Man Tin, as well as an exceptional count of 450 seen at Tseung Kwan O. Four exhausted Cattle Egrets were handed in to KFBG, as well as a single injured Black-crowned Night Heron, an Intermediate Egret Egretta intermedia and a Common Tern. One of the Cattle Egrets was found in a kitchen in Kowloon Tong, which suggests extreme disorientation, whilst the Common Tern, a species which is rarely reported away from open waters in Hong Kong, was founds on a road at Sham Tseng. Whilst this total of seven birds may not seem excessive, an examination of KFBG records since 1994 revealed that other storms during this period resulted in at most one or two birds being taken into care whose condition could be directly attributed to effects of storms.
Observations of passerine migrants in unusual locations might have been anticipated, but apart from reports of Pallas's Grasshopper Warblers Locustella certhiola and Dusky Warblers Phylloscopus fuscatus at Chek Lap Kok, there seem to have been few unusual sightings.
It is noticeable that all of these observations relate to migrant species which were probably caught up in the storm. No direct adverse effects on resident birds were noted. This is unsurprising, as any resident species would have had adequate opportunity to seek shelter and smaller, potentially more vulnerable, species would have been able to find sheltered areas in which to feed. Arguably, since the storm passed over during the day, many small landbirds may have lost feeding opportunities. For example, Crested Mynahs Acridotheres cristatellus did not leave their roost on Kau Pei Chau until late morning (as the winds dropped during the eye passage) instead of at dawn as is normal. However, even during the period when winds were strongest Chinese Bulbuls Pycnonotus sinensis and Common Magpie-robins Copsychus saularis were noted feeding in sheltered corners at Wo Shang Wai. In any case, even the loss of most of one day's foraging is unlikely to have been as stressful as a period of several days of cold wet weather in late winter when fruit is scarce and insect activity is low, or the passage of a wet frontal trough in late spring when breeding activity is at its peak and nests and nestlings would be most vulnerable.
Longer term effects arising as a consequence of damage to vegetation might be predicted but are essentially unknown. Reduced leaf cover might make roost sites more vulnerable to predators or they could be lost completely. A Chinese Pond Heron roost at Wo Shang Wai in a clump of White Popinac Leucaena leucocephala which suffered extensive leaf stripping and loss of branches held up to 60 birds before the storm. This roost was abandoned and had still not been re-occupied in mid October. Presumably also, damage to foliage will have affected insect numbers and damage to flowers or developing fruit will result in reduced fruit availability over the next few months, however the indirect impacts of such effects on birds are almost impossible to quantify.
Finally, it is interesting to speculate whether destruction of trees will have any genuine long term effects. Damage within secondary forests such as Tai Po Kau seems to be minor and even more isolated groups of trees such as those used as egretries at Mai Po and Tai Po are substantially intact. Whilst loss of large trees due to hurricanes in the Caribbean has been considered to have an adverse effect on populations of parrots Amazona spp. (Collar et al. 1994) such impacts seem to have been the consequence of much more devastating storms than York. Here, where large trees such as Chinese Banyan Ficus microcarpa or Big-leaved Fig Ficus virens have been affected this appears mostly to have resulted in the loss of branches rather than entire trees. Indeed, since Hong Kong has no woodpeckers and only one species, the Great Barbet Megalaima virens, which is capable of forming holes in healthy trees, the accelerated rate of hole formation which might be expected to result from the decay of broken limbs may have a beneficial effect in producing nest and roost sites for a range of species from Collared Scops Owls Otus bakkamoena to Hainan Blue Flycatchers Cyornis hainana which are unable to excavate holes themselves.
Acknowledgements: Thank you to the following observers whose observations are included above: Elizabeth Leven, Richard Lewthwaite, Roger Muscroft, Samson So, Yu Yat Tung and Lew Young, also those who phoned in their sightings to "Birdline". Inclusion of records in this summary does not imply acceptance by the Hong Kong Bird Records Committee and totals (for example of seabirds at Cape D'Aguilar) are likely to be amended once records are formally assessed.
Collar, N.J., Crosby, M.J. and Stattersfield, A.J. 1994. Birds to watch 2: the world list of threatened birds. Birdlife International, Cambridge.
Lam, C.Y. And Williams. M. 1994. Weather and bird migration in Hong Kong. Hong Kong Bird Report 1993: 139-169.
Lewthwaite, R.W. 1999. Recent reports March - June 1999. Hong Kong Bird Watching Society Bulletin 172: 6-8.
Michael R. Leven and Amanda Haig
P.22,23
Moths, butterflies & typhoons in 1999
Observations of moths recorded at lights (light traps and building lights at KARC) after Typhoon Sam (mid August) and T. York produced markedly low numbers of moths (both abundance and species richness reduced by between 50 and 75% on figures observed in 1997 and 1998 at KARC) for four to five days following the passing of both typhoons. Catch sizes approached more usual numbers within one week, indicating the adult populations are soon replenished from individuals that were pupae during the storms. Many moth larvae form subterranean cocoons in which to pupate and would thus be less affected by high winds, although these could be subject to landslides or being washed away.
Regular monthly butterfly monitoring was conducted at KFBG within a few days of both Typhoon Sam and Typhoon York. On both occasions, adult butterfly numbers (species and individuals) were noticeably depressed in comparison with general observations of numbers made in the days before the typhoons struck. However, as with adult moths, butterfly numbers had again noticeably increased back to 'normal' levels a week after the passage of the storms, indicating that pupae (and, presumably, larvae) were relatively unaffected by the adverse weather conditions associated with the typhoons.
Roger Kendrick & Graham Reels
P.23
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