Tropical Cyclone Ecology: A Scale-Link Perspective
Authors: Teng-Chiu Lin, J.Aaron Hogan, Chung-Te Chang
Journal: Trends in Ecology & Evolution (2020)

Our understanding of cyclone ecology is biased toward the Atlantic Basin, but cyclone effects on forests differ among oceanic basins because of differences in storm frequency and strength.Projected increases in cyclone frequency, intensity, and geographic distribution will threaten the tall old trees of the world, especially those in old-growth forests, which historically have few cyclones, such as those in the southeastern USA and southern Japan.Cyclone effects on ecosystem processes, such as primary productivity and nutrient cycling, are mediated through the range of direct disturbance effects on individuals and species, such as defoliation and tree mortality.Forest dwarfing, because of the gradual removal of tall trees by individual cyclones, illustrates the accumulative short-term effects of individual cyclones on shaping long-term forest structure. Tropical cyclones are increasing in intensity and size and, thus, are poised to increase in importance as disturbance agents. Our understanding of cyclone ecology is biased towards the North Atlantic Basin, because cyclone effects do differ across oceanic basins. Cyclones have both short and long-term effects across the levels of biological organization, but we lack a scale‐perspective of cyclone ecology. Effects on individual trees, such as defoliation or branch stripping and uprooting, are mechanistically linked to effects at the community and ecosystem levels, including forest productivity and stand regeneration time. Forest dwarfing via the gradual removal of taller trees by cyclones over many generations illustrates that cyclones shape forest structure through the accumulation of short-term effects over longer timescales. Tropical cyclones are increasing in intensity and size and, thus, are poised to increase in importance as disturbance agents. Our understanding of cyclone ecology is biased towards the North Atlantic Basin, because cyclone effects do differ across oceanic basins. Cyclones have both short and long-term effects across the levels of biological organization, but we lack a scale‐perspective of cyclone ecology. Effects on individual trees, such as defoliation or branch stripping and uprooting, are mechanistically linked to effects at the community and ecosystem levels, including forest productivity and stand regeneration time. Forest dwarfing via the gradual removal of taller trees by cyclones over many generations illustrates that cyclones shape forest structure through the accumulation of short-term effects over longer timescales. Natural disturbances (see Glossary) have a key role in characterizing ecosystem structure and dynamics [1.White P.S. Pattern, process, and natural disturbance in vegetation.Bot. Rev. 1979; 45: 229-299Crossref Scopus (671) Google Scholar, 2.Foster D.R. Disturbance history, community organization and vegetation dynamics of the old-growth Pisgah Forest, south-western New Hampshire, USA.J. 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Moreover, a few cyclones dominate the literature on ecological disturbance, such as Hurricane Hugo (1989) in the Caribbean [13.Walker L.R. et al.An introduction to hurricanes in the Caribbean.Biotropica. 1991; 23: 313-316Crossref Google Scholar, 14.Walker L.R. et al.Ecosystem development and plant succession on landslides in the Caribbean.Biotropica. 1996; 28: 566-576Crossref Scopus (123) Google Scholar, 15.Zimmerman J.K. et al.Responses of tree species to hurricane winds in subtropical wet forest in Puerto Rico: implications for tropical life histories.J. Ecol. 1994; 82: 911-922Crossref Scopus (326) Google Scholar, 16.Heartsill-Scalley T. et al.Changes in structure, composition, and nutrients during 15 years of hurricane-induced succession in a subtropical wet forest in Puerto Rico.Biotropica. 2010; 42: 455-463Crossref Scopus (58) Google Scholar], Hurricane Katrina (2005) in the southeastern, USA [17.Ashley S.T. Ashley W.S. Flood fatalities in the United States.J. Appl. Meteorol. 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Between 1989 and 2018, 14% of cyclones (a total of 1490) occurred in the North Atlantic Basin; however, based on a search of published scientific papers using Web of Science, 67% of the studies (a total of 798) that investigated the impacts of cyclones on forests were conducted in the North Atlantic (Figure 1). In fact, the top eight most-studied cyclones, which comprise only 0.5% of cyclones occurring between 1989 and 2018, make up 36% of the studies on cyclone-induced forest disturbance, and are all North Atlantic Basin cyclones except for one, which was a Southwest Pacific Basin cyclone (Figure S2A in the supplemental information online). By contrast, during the same period, 32% of cyclones occurred in the Northwestern Pacific but only 18% of studies were conducted in this region, and only 5% of studies examined the effects of cyclones from the Indian Ocean, although 22% of the cyclones occurred in this region (Figure 1). The geographic bias toward the North Atlantic Basin is accompanied by a disproportional number of studies on intense cyclones. Cyclones in category 3 or greater on the Saffir-Simpson index comprise only 5.7% of cyclones globally but make up 66% of studies. Such a disproportional representation of intense cyclones is not present for other oceanic basins in the literature (Figure S2B in the supplemental information online). The bias is likely because intense cyclones tend to have greater effects on vegetation and, therefore, attract more studies (but see discussion on Ecosystem-Level Effects later). The effects of cyclones on ecosystems have been shown to differ among the different oceanic basins [21.Lin T.C. et al.Typhoon disturbance and forest dynamics: lessons from a northwest Pacific subtropical forest.Ecosystems. 2011; 14: 127-143Crossref Scopus (119) Google Scholar]. 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Damage to individual plants can affect species and community-level dynamics and, thus, influences both the speed and trajectory of forest regeneration [15.Zimmerman J.K. et al.Responses of tree species to hurricane winds in subtropical wet forest in Puerto Rico: implications for tropical life histories.J. Ecol. 1994; 82: 911-922Crossref Scopus (326) Google Scholar,27.Everham E.M. Brokaw N.V. Forest damage and recovery from catastrophic wind.Bot. Rev. 1996; 62: 113-185Crossref Scopus (522) Google Scholar,37.Saito S. Effects of a severe typhoon on forest dynamics in a warm-temperate evergreen broad-leaved forest in southwestern Japan.J. For. Res. 2002; 7: 137-143Crossref Scopus (23) Google Scholar]. Variation in rates of forest regeneration alters the spatial patterns of landscape-level ecosystem structure and function [38.Boose E.R. et al.Hurricane impacts to tropical and temperate forest landscape.Ecol. Monogr. 1994; 64: 369-400Crossref Scopus (345) Google Scholar, 39.Boutet J.C. 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A deeper mechanistic understanding of the links among scale-dependent processes will enable us to predict how future changes in cyclone frequency or intensity will affect forest structure and function. We focus in depth on two important, but understudied aspects of cyclone disturbance and forest recovery dynamics for understanding forest primary productivity and carbon sequestration: forest dwarfing and defoliation. The effect of tropical cyclones on individual trees ranges from defoliation, branch and canopy damage to bole snapping and uprooting. The level of damage depends on the intensity of the cyclone, the resistance properties of the trees [41.Niklas K.J. Computing factors of safety against wind induced tree damage.J. Exp. 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Among individuals of a species, trees that are taller, have larger crowns, less dense wood, grow in more exposed sites, or are in poor health (e.g., infected by pathogens, drought stressed, or with high liana load) are more likely to be severely damaged by cyclones [27.Everham E.M. Brokaw N.V. Forest damage and recovery from catastrophic wind.Bot. Rev. 1996; 62: 113-185Crossref Scopus (522) Google Scholar,45.Doyle T.W. et al.Wind damage effects of Hurricane Andrew on mangrove communities along the southwest coast of Florida, USA.J. Coastal Res. 1995; S21: 159-168Google Scholar,46.Garrido-Pérez E.I. et al.Effects of lianas and Hurricane Wilma on tree damage in the Yucatan Peninsula, Mexico.J. Trop. Ecol. 2008; 24: 559-562Crossref Scopus (24) Google Scholar]. Variation in cyclone damage among individual trees is directly linked to cyclone effects at the species and population levels. For example, variability in cyclone damage to trees of different sizes and species will cause immediate changes in population demography. If plant health has a genetic basis (e.g., pathogen susceptibility), then the removal of individuals in poor health will alter population genetics. Variation in cyclone damage to individuals growing in different locations will affect the spatial distribution of the species. In addition, the commonly observed increase in seedlings during the first couple of years following cyclone disturbance [47.Roth L.C. Hurricanes and mangrove regeneration: effects of Hurricane Joan, October 1988, on the vegetation of Isla del Venado, Bluefields, Nicaragua.Biotropica. 1992; 24: 375-384Crossref Scopus (121) Google Scholar] also alters population demography. Cyclone disturbance effects at the individual and species levels scale to the effects at the community level. Species in a community differ in wood traits, degree of exposure, and tree or crown size, leading to differential vulnerability to cyclones, through which cyclone disturbance alters community species composition [16.Heartsill-Scalley T. et al.Changes in structure, composition, and nutrients during 15 years of hurricane-induced succession in a subtropical wet forest in Puerto Rico.Biotropica. 2010; 42: 455-463Crossref Scopus (58) Google Scholar,48.Hogan J.A. et al.The frequency of cyclonic wind storms shapes tropical forest dynamism and functional trait dispersion.Forests. 2018; 9: 404Crossref Scopus (30) Google Scholar]. Cyclones increase wood density and decrease average tree height at the community level, due to the removal of trees with low wood density [49.Curran T.J. et al.Wood density predicts plant damage and vegetative recovery rates caused by cyclone disturbance in tropical rainforest tree species of North Queensland, Australia.Austral. 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Evol. 2001; 16: 45-51Abstract Full Text Full Text PDF PubMed Scopus (1065) Google Scholar], through which many tree species maintain their presence and develop multiple-stem morphologies in forests affected by cyclones [24.Van Bloem S.J. et al.Structural response of Caribbean dry forests to hurricane winds: a case study from Guanica Forest, Puerto Rico.J. Biogeogr. 2006; 33: 517-523Crossref Scopus (47) Google Scholar,58.Bellingham P.J. et al.Sprouting of trees in Jamaican montane forests, after a hurricane.J. Ecol. 1994; 82: 747-758Crossref Scopus (153) Google Scholar]. Differences in sprouting ability may lead to changes in the basal area and species composition of forests as they recover. Thus, overall, cyclones can affect plant community composition through the differential damage to adult tree species, the variable responses of seedlings of different species to the altered understory environment, and variation in postcyclone sprouting among different tree species. The effects of tropical cyclones on the community composition of tropical forests over time are largely dependent on cyclone frequency. In regions where cyclones occur at decadal or longer intervals, cyclones are known to cause shifts in the relative abundances of different tree species (e.g., pioneer versus late-successional species) [15.Zimmerman J.K. et al.Responses of tree species to hurricane winds in subtropical wet forest in Puerto Rico: implications for tropical life histories.J. Ecol. 1994; 82: 911-922Crossref Scopus (326) Google Scholar], while in regions with annual cyclone disturbance, such differential effects are diminished, if found at all [22.Mabry C.M. et al.Typhoon disturbance and stand-level damage patterns at a subtropical forest in Taiwan.Biotropica. 1998; 30: 238-250Crossref Scopus (84) Google Scholar,25.Lin S.Y. et al.Characteristics of old-growth and secondary forests in relation to age and typhoon disturbance.Ecosystems. 2018; 21: 1521-1532Crossref Scopus (10) Google Scholar]. However, over evolutionary timescales, all trees in cyclone-prone regions are subjected to the selection pressures of strong, damaging cyclonic windstorms. Some trees can tolerate cyclone disturbance better than others (i.e., are damaged less and survive and recover better). This differential response in terms of performance acts as driver of natural selection to increase tree resistance to cyclone storm wind damage. A study in northern Queensland proposed that an increased frequency of intense cyclones restricts the distribution of tree species susceptible to cyclone damage in sites prone to intense cyclone disturbance [59.Metcalfe D.J. et al.Cyclone damage to tropical rain forests: species-and community-level impacts.Austral. Ecol. 2008; 33: 432-441Crossref Scopus (60) Google Scholar]. Additionally, a summary of studies in the Luquillo Experimental Forest in Puerto Rico reported long-lasting effects of cyclone disturbance on fundamental forest structure [60.Brokaw N.V. Grear J.S. Forest structure before and after Hurricane Hugo at three elevations in the Luquillo Mountains, Puerto Rico.Biotropica. 1991; 23: 386-392Crossref Scopus (165) Google Scholar]. Thus, over evolutionary timescales on which cyclones have exerted selection pressure, it is likely that individual trees and species that are vulnerable to cyclone disturbance are selectively culled from the community, leaving the species that are resistant to cyclonic disturbance. Therefore, it is inappropriate to infer that cyclone disturbance has no effect on tree species composition in very frequently disturbed forests. The lack of any immediate disturbance effect on the forest community is the result of the cumulative effect of the greater historical cyclonic storm regime. The return time of damaging cyclone disturbances is the principle governing factor. Return time matters because the amount of damage a cyclone exerts on a forest is largely dependent on the time the ecosystem has to develop in the absence of a damaging cyclone (Box 1). Generally, if forests have over 40 years to develop between damaging cyclones, they can regenerate and add substantial biomass, making each storm a strong reset for the system [48.Hogan J.A. et al.The frequency of cyclonic wind storms shapes tropical forest dynamism and functional trait dispersion.Forests. 2018; 9: 404Crossref Scopus (30) Google Scholar]. As the return interval shortens, there is less time for the forest to regenerate and accumulate biomass. It is as though the overall disturbance regime at frequently disturbed sites dominates the disturbance dynamic, with a diminished effect of any single storm. By contrast, at sites with infrequent cyclones, a single disturbance event may greatly influence the overall disturbance regime.Box 1Tropical Cyclone Disturbance Effects on Forest HeightDuring a tropical cyclone, taller, more exposed trees are disproportionally affected (e.g., either removed from the community via mortality or damaged more severely). In forests with frequent cyclone disturbance, there may be insufficient time for full forest-canopy recovery before the next disturbance (the orange arrow in Figure I) so that the forest may gradually decrease in total canopy volume or tree stature over time (i.e., dwarfing, Figure IA). By contrast, for forests experiencing infrequent cyclone disturbance, there is likely to be enough time for full recovery of canopy and forest structure before the next disturbance and possibly time for further forest development. As a result, in areas with very frequent cyclone disturbance, the tropical cyclone regime potentially has less of an overall effect on forest stature over time, compared with areas with infrequent cyclone disturbance (Figure IB). However, if cyclone frequency increases, the time interval between successive cyclones will shorten, and may approach the time required for full recovery (Figure IC, third panel from the left); beyond this critical point, there is not enough time for the full recovery of forest structure, and trees will not reach their previous maximum height, resulting in forest dwarfing (Figure IC). Alternatively, if cyclone intensity increases, the effect of each cyclone will be more severe and the time required for full recovery will be longer and may approach the occurrence of the next cyclone disturbance (Figure ID, fourth panel from the left); beyond this critical point, there may not be enough time for the full recovery of the total canopy volume or forest structure, and trees may not reach their previous maximum height, leading to forest dwarfing (Figure ID). If both the frequency and intensity of tropical cyclones increase, the time required for full recovery becomes even longer, while the time between successive cyclone events shortens, potentially resulting in even more-severe dwarfing pressure (Figure IE). During a tropical cyclone, taller, more exposed trees are disproportionally affected (e.g., either removed from the community via mortality or damaged more severely). In forests with frequent cyclone disturbance, there may be insufficient time for full forest-canopy recovery before the next disturbance (the orange arrow in Figure I) so that the forest may gradually decrease in total canopy volume or tree stature over time (i.e., dwarfing, Figure IA). By contrast, for forests experiencing infrequent cyclone disturbance, there is likely to be enough time for full recovery of canopy and forest structure before the next disturbance and possibly time for further forest development. As a result, in areas with very frequent cyclone disturbance, the tropical cyclone regime potentially has less of an overall effect on forest stature over time, compared with areas with infrequent cyclone disturbance (Figure IB). However, if cyclone frequency increases, the time interval between successive cyclones will shorten, and may approach the time required for full recovery (Figure IC, third panel from the left); beyond this critical point, there is not enough time for the full recovery of forest structure, and trees will not reach their previous maximum height, resulting in forest dwarfing (Figure IC). Alternatively