The Ecological Significance of Typhoon:

A Case Study of Fu-shan Forest Ecosystem

 

Hen-biau King1, Yue-joe Hsia2, Teng-chiu Lin3, Lih-jih Wang4, Shyue-cherng Liaw1

1Taiwan Forestry Research Institute, 2National Dong-hwa University, 3National Chang-hua University of Education, 4National Taiwan University

 

 

Natural disturbances are an integral part of ecosystems and more often than not are agents of renewal rather than destruction.                  David A. Perry 1994

 

 

Abstract

 

Typhoon is one of the major natural disturbances that restlessly shape our landscape and persistently disturb our society. Our society pays most attention to damage caused by typhoons on infrastructures, properties and human lives. We seldom view the occurrence of typhoon as a natural and necessary process on which all forms of life depend and to which all forms of life adapt and evolve. This paper focuses on the impacts of typhoon and its ecological significance, with a case study on Fu-shan subtropical forest ecosystem located about 40-km southeast of Taipei City. Typhoons impacts on hydrology, mechanics, geochemistry, vegetation and zoology of Fu-shan subtropical rain forest are reviewed and discussed in this paper.

Typhoons can occur in late spring through early winter but most frequently between July and September. Torrential rainfall associated with typhoon characterizes the hydrology of the forest watershed. About 60% more rainfall occurred during years with typhoons (1994, 1996, 1997 and 1998 for example) than that of years without typhoons (1993, 1995 and 1999 for example) at Fu-shan forest. In response to torrential rainfall of typhoon events, stream discharge peaked rapidly. Seventy to eighty percent greater stream discharges occurred in years with typhoon than that in non-typhoon years. Intense and frequent rainfall and storm runoff triggered soil erosion, mass movement, and sedimentation, which enhanced stream channel cutting. The abrupt change streamwater quantity and quality resulting from typhoon events dramatically altered the stream environment and the biology of aquatic life.

The mechanical impacts of typhoon such as defoliation, tree bole snagging and entire tree uprooting are obvious. It was found that 6 typhoons in1994 caused large losses of leaves and, to a lesser extent, breaking off branches and created snags and logs. This not only decreased the amount of photosynthetic product in the following year but also increased significantly the input of organic debris to the forest floor. Canopy defoliation affected directly the primary productivity, upon which all forest faunas depended directly and indirectly for their living and survival. These impacts also altered ambient light reaching forest floor. The patterns of regeneration and succession of the forest vegetation were also affected. Substantial changes in populations of leaf feeding mammals and insects immediately after the 6 typhoon events in 1994 in Fu-shan forest were noted and exemplified such influences.

A large pulse of litterfall resulted in two-fold increase over average annual litterfall. The increased organic debris on the forest floor was decomposed through the action of soil organisms and thus changed the flux of nutrient dynamics in the forest ecosystem. Increased numbers of snags and logs on the forestland changed the structure and functioning of the forest landscape.  

Other impacts of typhoon to the forest involved nutrient dynamics of forest ecosystem. It became particularly true when interactions occurred between acidic rain and nutrient cycling in the forest. Large amounts of acidic substances, such as sulfuric and nitric acids, from the atmosphere would leach equivalent amounts of base nutrients out of the forest ecosystem if these substances were not efficiently taken up by vegetation, immobilized by microorganisms or adsorbed by soils.  This leaching could deplete the available nutrient reserve of the system and accelerated soil acidification and hence altered soil ecology and long-term productivity of the site.

Typhoon events were regarded as natural forces affecting all aspects of living organisms in Taiwan. However, the interactions of typhoon and air pollutants that again acted synergistically with other adverse human activities (such as road and dam construction, forest cutting, pollution, and other land uses) tended to deteriorate natural environment and devalue ecosystem services.

A better understanding of the processes of ecosystems and their impacts by typhoon disturbance is ultimately important in managing our natural system ecologically and hence maintaining the ecosystem sustainably.

 

Keywords: biomass, typhoon, leaf area index, light environment, nutrient cycling

 

 

Introduction

 

The earth, both its interior and surface, has been undergone constant changes or disturbances since it was formed about 4.6 billions years ago (Press and Siever 1974). The natural disturbance is viewed as the rule, not the exception (Botkin 2000). Disturbances can also be anthropogenic. Processes responsible of disturbances are numerous and the major natural ones can be broadly grouped into internal and surface processes. The former includes plate tectonics, earthquakes and volcanoes, and the latter weathering, erosion, and climate (Thompson and Turk 1991). For the last few hundreds of years, anthropogenic disturbances have gradually shown their adverse impacts on the environments, notably warming climates, depleting ozone layer, generating acid rain, polluting biosphere, expanding deserts, and losing biodiversity. Either natural or anthropogenic disturbance not only affects the abiotic and biotic components of ecosystem independently but also interacts with each other, producing novel and unimaginable consequences beyond the control of human beings. The resulting impacts are sometimes compensable but in most cases are complicated and synergistic.

The major natural disturbances, which affect ecosystems of Taiwan, are plate tectonics, earthquakes, typhoons, soil erosion and landslides. They occur with different frequencies, intensities and patterns. They also vary widely in temporal and spatial scales. Plate tectonics in Taiwan is a vast force that is resulted from the east Philippines sea plate colliding northwesterly with west Eurasian continental plate (Ho 1975). Taiwan is a part of the eastern margin of the Eurasian plate located in the collision zone of the two plates (Isacks et al. 1968, Biq 1981). The resulting force is building the mountain central range and the east coastal range of Taiwan Island. Uplifting rate up to 50 mm per year in some locations was observed (Chen 1984). The denudation rate averaged over 1,365 mg/cm2 (Li 1976).

The theory of plate tectonics is partly supported by the occurrence of earthquakes. Disturbances originated from earthquake changed landscape features dramatically, forming ridges, lakes, faults and trenches. Substantial landmass of the island was deposited as sedimentary Miocene rocks, which cover the western and northern foothills where this studied site is located. Accumulation of these geological materials has been the source of mudflows and landslides, which are triggered mainly by earthquakes and torrential rainfall during the typhoon season. Landslide occurring in steeply sloping mountains is considered to be one of major disturbances, which deposits rock debris to lowland areas.

Natural forces (plate tectonics, earthquakes, and typhoon etc.) shaping landform and regulating life patterns are so vast that they are not fully comprehended or easily predictable. The effects of climatic factors, particularly typhoon, on the Fu-shan forest ecosystem have been studied. We presented our findings the effects of typhoon on ecological dynamics of the Fu-shan forest ecosystem, and how the ecosystem responds to the typhoon disturbance.

 

 

Regimes of typhoon disturbance

 

Typhoons originate in the western Pacific Ocean off the Philippines. About 80% of the events occur during July, August and September. These tropical storms normally headed for Taiwan, Okinawa and Japan after formation (Gregory 1990). It lands on Taiwan at least once a year except for in 1941 and 1964, for the last one hundred years. Typhoon averaged 3.5 events annually for the past 100 years (1897-1997) in Taiwan (Taiwan Provincial Government 1998). This frequency was lower than that of the last 40-years' average of 4.2 events (Central Weather Bureau, Taiwan 2000).

In Taiwan, tracks of typhoon approaching Taiwan varied spatially. About 350 typhoons and their tracks and landing places on Taiwan during recent one hundred years (1897-1997) are observed (Taiwan Provincial Government 1998). A majority of typhoons landed on the east coastal area of Taiwan. Typhoons usually associate with torrential rainfall and gusty winds, and both are very destructive. For example, typhoon Herb, which landed on Taiwan on 31 July 1996 dumped 1748.5 mm rainfall in a 24-hour period in Ah-li-shan, central Taiwan, and brought gusty wind (instantaneous wind speed) up to 59.5 m/s or 216 km/hr in Chi-lon, northern Taiwan. The typhoon flooded hundreds of thousands hectares of land, damaged highway and bridges, failed household's electricity, killed 73, and injured 463 persons. The loss of crops, livestock, fishery and forests amounted to about US$ 6 billions (Taiwan Provincial Government 1998). Forty years ago on 7 August 1959, a typhoon killed over 1000 persons and completely destroyed about 5000 homes (Wang 1967).

All these impacts of typhoon have been focused on loss of human property and lives. Little attention and research have been paid to the effects of typhoon on the ecological processes (primary productivity, nutrient cycling, regeneration of vegetation and adaptation of wildlife communities, etc) in natural ecosystems.

 

 

Description of Study Site

         

The study site (24o 46N, 121o34E) is located at the Fu-shan Forest, Taiwan Forestry Research Institute, about 40-km southeast of Taipei City (Figure 1). This forest ecosystem along with four other ecosystems form the Taiwan Ecological Research Network (TERN) sites that are specifically designated to study ecological phenomena and processes of major forest ecosystems in Taiwan (King and Hsia 1997, King 1998). Intensive, long term and interdisciplinary research has been carried out in Fu-shan Forest since 1992 (King 1997).

The site is warm and very wet during summer months, and cool, moist, and occasionally foggy during winter months. Annual rainfall, based on measurements from 1992 to 1999, varied widely ranging from 2850 to 6000 mm per year with an annual average of 4062 mm. Annual rainy days were around 220 days (Hsia 1999, Y.J. Hsia, unpublished data). Typhoons, associated

 

Figure 1.  Location and contour map of Fu-shan Forest (Hsia et al. 1996).

 

 

 

with torrential rainfall and strong wind, were frequent. Intensity of typhoon rainfall over 150 mm/hr and gusty wind of 39 m/s had been recorded. Annual mean monthly temperature averaged 18.3oC and ranged from 12.0oC to 23.9oC. Prevailing wind direction was SE in summer and NW in winter (Hsia and King 2000).

The Fu-shan Forest covers 1100 ha of land ranging in elevation from about 400 to 1400 m above mean sea level. The study site is a first order gauged watershed, 38 ha in size, constructed with a 90o V-notch weir. The woody vegetation on the site is composed predominantly of Fagaceae and Lauraceae in association with abundant epiphytes and understory vegetation.

The bedrock of Fu-shan site is weakly metamorphosed sedimentary rock from the Oligocene and Miocene and consists of argillites interbedded with fine sandstones (Ho 1975). Parent materials of the soils, developed from either residual or colluvial materials, are of the same geological origin. Two great groups of soils have been identified: Hapludults on more stable terrain and Dystrochrepts on more erosive slopes (Horng et al. 1997). More information on the studied site can be found in web site at http://wagner.zo.ntu.edu.tw/fushan/.

 

 

Typhoon and Forest Dynamics

 

The structure and function of forest ecosystem are controlled in part by the physical environment, of which natural disturbances are apparent forces that regulated ecosystem dynamics. Here, we emphasized the influences of typhoon and, to a lesser extend, earthquakes, erosions and air pollution on Fu-shan forest dynamics. The reason of it was that we have more research on typhoon than other disturbances affecting the forest ecosystem.

 

Typhoon Hydrology at the Research Site

The research has been carried out in Fu-Shan Forest (FSF) since 1992 (King 1997). The interpretation of this specific forest dynamics was based on the data and hypotheses generated since 1993. One watersheds, 38 ha in size, was gauged to monitor stream discharge. A weather station was established in 1992 to record rainfall and other meteorological data (Hsia 2000).

During the 7 years of monitoring, the site had experienced 13 typhoons in 4 years (i.e. 1994, 1996, 1997, 1998.) with 3 years (1993, 1995 and 1999) without typhoon. Hsia (2000) presented the rainfall and streamflow of each year from 1993 to 1999 at the research site.

The contribution of typhoon rainfall to total rainfall of a given year varied greatly ranging from 0 (the years without typhoon) to 46% (6 typhoons in 1994). The mean annual rainfall was 4,062 mm (from 1993 to 1999), of which 24% was contributed by typhoon.

Water level of stream responded almost spontaneously (Hsia and Hwong 1999,). Figure 3

 

  Figure 2.  Typhoon and total rainfall in the Fu-shan Forest from 1993 to 1999 (Hsia 2000)

 

 


 

 

 


  Figure 3.  The relationship of stream discharge over time of the studied watershed (Wang 2000).

 

shows the relationship of rainfall and daily discharge over time of the studied watershed (Wang 2000). The mean annual runoff ratio (proportion of stream discharge to rainfall in a given year) of typhoon year ranged from 50 to 68 %, with an average of 58%, indicating that about 60% of incoming typhoon rainfall was flushed out of the watershed within the typhoon period which is typically 1-2 days. The remaining 40% of typhoon rainfall that was not measured by the weir seeped to underground water reservoir and eventually appeared as streamflow during non-raining days.

 

Changes of Vegetation and Light Environment

High rainfall intensity (such as maximum hourly rainfall of 86 mm during the strike of typhoon Gladys in 1994) and gusty wind (such as 122 km/h during Typhoon Herb in 1996) had great impacts on vegetation (Hsia 1998). The immediate impacts of strong typhoon to the Fu-shan forest ecosystem was very obvious and the damage patterns were also very different from those of hurricane impacted forests, such as the Luquillo tropical forest located in Puerto Rico (Mabry et al. 1998, Lin et al.1999). Forest trees severely damaged, as large amount of leaves in canopy were striped, and tree boles were either snapped or whole trees uprooted.

Defoliation or loss of canopy leaves and formation of gaps through knockdown of trees were direct damages to the forests of the studied site. The magnitude of defoliation can be indicated partly by changes in leaf area index (LAI) which was the projected canopy area per unit of ground (Gholz 1982), and which correlated well with maximum foliage in forests (Webb et al. 1983).

Canopy LAI of a forest usually decreased sharply and immediately following typhoon hits. The LAI was 4.47 before the beginning of typhoon season in 1994 and decreased dramatically to 1.47 or by 67% after the forest was struck by 6 typhoons of the same year (Lin et al. 1999). The LAI increased to about 2.3 in the following spring, still about 40% less than the previous year. This level of LAI remained little change for the entire year of 1995, as there was no typhoon that year. The LAI increased farther to about 3.0 in July after the growth season of 1996 but decreased to 2.2 after the forest were again hit by 2 typhoons in 1996. In 1998, the LAI increased slightly to about 3.4 by the end of the major growth season and then decreased to 2.4 after 3 typhoons struck the forest late in the same year. The LAI of the studied forest clearly showed decreasing in response to the occurrence of typhoon. The current LAI has not recovered to the level before the commencement of the typhoon season in 1994. These variations of LAIs were observed in a forest located in the east ridge of the watershed where typhoon impact was most severe. However, LAI of the forest watershed in the valley during the same period showed little change (about 1% decrease) (Lin et al. 1999). It was concluded that LAI varied widely and spatially even in a small (ca. 38 ha) forested watershed.

 

 

  Figure 4. Annual litterfall of Fu-shan forest ecosystem (Lin 1999).

 

 

Leaf area index represents photosynthesis conducting forest canopy and provides a more general estimate of primary productivity of a given forest ecosystem (Waring and Schlesinger 1985). Primary productivity serves as a base upon which various consumer levels depend (Odum 1997).

The change of the LAI in response to typhoon was just one effect of the typhoon on ecosystem. Boles of trees were often snapped and trees uprooted in areas where strong windstorms were experienced. Hurricane Hugo struck Puerto Rico on 18 September 1989 and caused 9% of trees to be uprooted and 11% of tree boles to be snapped (Walker 1991). The response of stand density in the Fu-shan forest to typhoon was different from hurricane impacted tropical forest. The 1994 typhoons decreased the stand density of the Fu-shan forest only 4.2% (Mabry et al. 1998) as compared to 39% wreaked by the 1989 hurricane Hugo to the Luquillo forest (Fu et al. 1996). This suggested that response of stand density to storms varied with intensity, frequency and pattern of storms and local physical environments.

Change of LAI and the creation of snapping trees and logs altered ambient light environment for understory vegetation, which then affected structure, composition, regeneration and functions of the forest ecosystem. Ecological phenomena, such as germination of seeds long stored in the forest floor, and growth and survival of understory vegetation that may have been suppressed by canopy tree shading took place. In subtropical montane forests strongly disturbed by hurricane in Puerto Rico, Fernandez and Fetchner (1991) found that forest canopy took about 4 months to overshadow forest floor again due to rapid growth of herb and saplings of pioneer genera. Damaged trees sprouted higher in the canopy, which farther reduced the amount of light reaching the forest floor. Two strong typhoons that struck in 1996 increased light reaching the forest floor (Teng-chiu Lin, unpublished data). One-year foliar growth of the forest gradually reduced understory lighting to about 60% of that level prior to the 1996 typhoons. Light is generally considered as a limiting factor for the growth of seedling and sapling for the forest (Kimmins 1966). This might be true for many forests that without frequent visits by typhoons but not quite so for Fu-shan forest which experienced averagely more than one typhoons per year.

 

Litterfall and Nutrient Input

              Typhoon may induce pulses of litterfall, which includes mainly leaves, twigs, branches, broken boles, and even entire trees. Such massive input of fresh organic debris may alter the nutrient status of the forest as compared to the normal major annual falling of senescent plant parts to the ecosystem.

              The input of organic debris in non-typhoon years in Fu-shan forest ranged from about 3.8 tons/ha (Horng et al. 1995) to 5.5 tons/ha (Lin 1997), depending on the methods of estimation. The 6 typhoons in 1994 generated 12.0 tons/ha of litterfall as compared to 5.6 tons/ha in 1993, a non-typhoon year (Lin 1997). Other studies in hurricane-impacted subtropical forest in Puerto Rico revealed an even larger amount of input of litterfall due to strong storms (Lodge et al. 1991). These disturbances generated litterfall varying with intensity, frequency and pattern of the event (Plounin 1984).

Associated with litterfall is nutrient added into ecosystems. Typhoon-derived littefall is not only greater in amount but also usually richer in concentrations of certain nutrient, particularly mobile elements such as N, P, K, than litterfall derived from senescent plant parts. Relocation of mobile nutrients (N, P and K) from old leaves to new shoots usually occur just before the commencement of falling senescent leaves (Larch 1995). Greater amount and higher level of fresh organic debris caused by typhoons to forest floor affected budgeting and cycling efficient of nutrients, which in turns determined productivity of forests. It was found that annual input of nutrient to forest floor was 84 to 54% higher in typhoon year in1994 than the of previous non-typhoon year (1993) in the Fu-shan forest (Lin 1997). According to Lin's studies, the amounts of litterfall N input to forest floor was 177 kg/ha and 85 kg/ha in typhoon year (1994) and in non-typhoon year (1993), respectively. For P, it was 9.8 and 4.9 kg/ha, for K, it was 32 and 16 kg/ha, respectively.

To be useful to organisms, litterfall must be mineralized. Inorganic nutrients are absorbed in part by roots and synthesized to form organic compounds by vegetation and in part stored in

 

 Figure 5.  Changes of relative leaf area index over time in the Fu-shan forest (Lin et al. 2000)

 

 

foliage for photosynthesis. Leaves and other part of vegetation returning to forest floor as litterfall completes the nutrient cycle. The effect of typhoon on the rate of forest nutrient cycling is not well understood in the Fu-shan and in other storms impacted forest ecosystems.

 

 

Nutrient Budget and Cycling

Vegetation requires a supply of nutrient elements and much of it depends on a cycling of these elements in the ecosystem (Armson 1977). Nutrients in forest ecosystem are moved and transported in solution, hence their availability is highly dependent on hydrological processes. Rainfall that entering forest ecosystem may be broadly grouped into various components: canopy interception, throughfall, stemflow, soil solution and runoff (streamflow).

Canopy interception is the amount of water retained by canopy and evaporated back into atmosphere. Throughtfall is the amount of rainfall passing through vegetation canopy and reaching surface of forest floor. Stemflow is the portion of certain amount of water moving down to the soil. Runoff is the amount of water, reaching the soil, which will enter and exit the vegetation-soil system, and may eventually appear as streamflow (Armson 1997).

Amounts and concentrations of nutrient elements in various components of forest ecosystem change when rainfall pass through them. In 1993, a non-typhoon year, concentrations of some nutrients (such as K, Ca and Mg) were enriched in thoughtful and stemflow of the Fu-shan forest, up to 3- to 5-fold compared to rainfall indicating that great amounts of nutrients were washed down and entered into forest floor. Base cations (Ca and Mg) carried down by throughfall and stemflow and stored in the soils as not only available to organisms but also leached into stream (Wang et al. 1997). This caused potential soil acidification. Rainfall of the studied forest was strongly acidic with an annual average pH of 4.7. Annual deposition of sulfate and nitrate amounted 27 and 67 kg/ha in the Fu-shan forest, respectively (Lin et al. 1999). It was less acidic when it became thoughtful and stemflow. Their pH values averaged slightly higher than 5.6, indicating a neutralization capacity of the acid rain by this type of forest. Other widely distributed canopies of hardwoods, but not coniferous forest, in Taiwan also showed high neutralization capacity to acid rain (King et al. 1994).

The pH value of soil solution at 80-120 cm depth, however, was strongly acid with a pH of 4.3. Acidity of soil solution decreased substantially when the water appeared as streamwater with a pH of 7.5. This change of pH value was reflected by elevated Ca and Mg concentrations in the streamwater and served as an evidence of acidification of the forest ecosystem. Mechanisms that are responsible for neutralization or buffering capacity of soils to the acidic deposition are numerous, including sulfate retention capacity of the soils (Harrison et al. 1989). Organic matter in the surface layer and free susquioxides in the subsoil are controlling acid buffering capacity of the of the Fu-shan forest (Liang et al. 1998).

 Abrupt increase in level of stream discharge after torrential rainfall brought by typhoon dramatically altered streamwater chemistry. Wang, et al. (1997) found that some elements (Na, Ca, Mg, Cl and S) were depleted and others (K, N) enriched in streamwater during peak streamflow. . The magnitude of these changes was controlled by streamflow characteristics, which varied with typhoon storm events.

Two examples are presented here to illustrate the significance of typhoon events in contributing to annual nutrient budget of the studied forest ecosystem (Table 1). Typhoon contributed substantial amounts of nitrogen and potassium (about 29 and 22 % of annual input, respectively) to the ecosystem. The thoughtful further enriched in N concentration (2-fold increase) relative to rainfall as well as input 64% of annual total. Half of which was retained in the ecosystem. However, the 1994 typhoon events drained 5-fold more N out of the ecosystem with the stream than the input from the storms. For the K budget things were different. The ecosystem conserved small amount of K to maintain a balanced K budget. More than 2-fold loss of Ca, but not Mg, was found in stream output than input from storms. This may enhanced soil acidification process. Sulfate budget was balanced and the pH of typhoon rainfall was near

Table 1. Volume weighted concentration and annual average amount brought by 6 typhoons in 1994 in bulk rainfall, throughfall and stream runoff of Fu-shan Forest .

___________________________________________________________________________

                 Rainfall                            Throughfall             Stream Runoff

                              _____________________________           ____________________________        ___________________________   

 meq/l    kg/ha     %*      meq/l   kg/ha    %*     meq/d   kg/ha    %*

_ ______________________________________________________________________ ___

N      8.47          0.45            28.8            16.86    5.6    64.0               2.08   2.36    33.0

K      5.26          0.35            21.5             3.02   15.3    20.8               0.34   0.28    17.7

Na          41.61          3.42            57.2              4.33       19.5    36.0               2.51   2.09    13.9

Ca          13.78    1.12             32.1            37.79        17.2    35.2               3.15   2.62    12.1

Mg        14.12    0.63     47.7             25.65        7.1    37.0              0.80   0.67    12.2

Cl           51.65          7.10     41.9           64.13        51.5    45.0               2.62   2.18    18.9

SO4-S    9.56          0.58            3.3          20.42    7.5    23.0       2.55   0.70    13.0

____________________________________________________________________________

* Percentage of annual total amount.

 

 

neutral (not shown in the Table 1), ruling out its direct acid effect on the ecosystem. The effect of the 1996 typhoons confirmed this general observation but with different magnitude. They carried away more base cations and sulfate. Acidification was more pronounced in the 1996 typhoons.

Short term monitoring of acidic pollutants depositing to the Fu-shan forest revealed that <10% of total sulfate oxides and nitric acids accounted for the dry deposition (Lin et al. 2000). This indicated acidification of the forest ecosystem was mainly controlled by acid rain to the studied forest. Other study confirmed this observation that rainfall in the Fu-shan forest was contaminated with acidic pollutants (Lin et al. 1996)

Overall, typhoon event was one major rainfall contributor to the studied forest ecosystem and it changed the chemistry of nutrient cycling and budget of the system dramatically.

 

Other Speculated Impacts

Many other interesting phenomena, which might be related to typhoon events, were casually observed, but were not scientifically tested and studied. The 1994 typhoons dramatically defoliated the forest. Abnormally abundant population of caterpillars (such as Asota plana and A. helicona) was found to occur in the following early spring in 1995 (T.J. Chao, personal communication). It was assumed that new growth of leaves was more palatable and preferred by foliage-feeding caterpillars under fair weather conditions. It was also found that typhoon events killed abundant caterpillars but no statistics was recorded.

Bird population was affected by typhoons. For example, a study of a dominant bird species, forest-gray-checked fulvetta (Alcippe morrisonia) in the Fu-shan forest revealed that population of juveniles decreased significantly but adult population was not affected (Chou 2000).

Torrential rainfall associated with typhoon increase rapidly stream water level. Species diversity of fresh water fish decreased dramatically but restored about two weeks after storm when the stream remained wild and was not disturbed by humans (Y.S. Lin, personal communication).

Another interesting funding was a troop of Formosan macaques (Macaca cyclopis), which inhabiting the forest and living mainly on leaves of this lush hardwood forest, disappeared from the forest after 6 typhoons' struck in 1994, and then returned after one year.

Research on above mentioned ecological phenomena and others, such as effects of typhoon on root dynamics, soil solution chemistry, organic matter decomposition at short and long term, should be paid more attention. The adaptation and evolution of life under persistent typhoon threats should also be understood.

 

 

Conclusions

 

Typhoons are major and persistent catastrophic disturbances capable of changing ecosystem processes in both short and long-term scales. Major attention on their damages has long been paid to human lives and properties. Very little research has been directed toward understanding their short and long term impacts on processes of ecosystems. Our short term and single forest site ecological studies revealed that typhoon is the single most disturbing event capable of altering ecological processes at ecosystem level. Major typhoon directly defoliated about 2/3 of tree canopy, created forest gaps, snags and logs, increased light reaching forest floor, lost large amount of plant nutrients from watershed, removed bed loads and suspended sediments. Population of aquatic organisms, terrestrial insects, birds and mammals were also affected. This research led us to hypothesize that life has adapted under such long history and persistent typhoon in Taiwan. Human activities such as deforestation, road construction and pollution, inappropriate land uses at local and regional scale bear much stress on other life of the landscape.

 

 

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