飓风和台风对沿海地区森林生态系统的影响

飓风和台风是影响热带和温带沿海区域的主要灾害性气候之一,飓风和台风对于森林生态系统的影响是生态学关注的课题。综述了飓风和台风登陆对于森林生态系统树木和林分的危害影响形式及主要影响因素,着重举例阐述了树种和森林类型是影响台风危害程度的一个重要因素。分析了目前国际上开展的关于飓风和台风登陆对于森林生态系统碳、氮循环的影响,结果表明飓风、台风干扰导致的森林凋落物输入量、凋落物分解速率以及森林碳储存量动态变化较为复杂,与森林类型、林分空间位置以及台风过后的时间段密切相关。飓风引起的森林受损的恢复途径和机理与树冠受损严重程度直接相关,并受到光和水分条件的影响,及时的开花、结果以及充足的土壤种子库对森林植被恢复具有促进作用。在景观和区域尺度量化飓风和台风对沿海地区森林生态系统的影响也日益引起关注,在这方面,整合气象数据、遥感数据和地面调查的模型模拟方法起到重要的作用。今后应加强对于我国东南沿海地区森林生态系统遭受台风影响损失的生态监测和长期定位研究,加强关于台风对于不同森林生态系统类型和不同树种的危害形式和危害程度的研究,以及台风对于森林生态系统碳、氮循环影响的研究,弥补我国在以上领域的空白。     

Factors Affecting Mortality and Resistance to Damage Following Hurricanes in a Rehabilitated Subtropical Moist Forest1

The ability to resist hurricane damage is a property of both individuals and communities, and can have strong effects on the structure and function of many tropical forests. We examined the relative importance of tree size, species, biogeographic origin, local topography, and damage from previous storms in long‐term permanent plots in a rehabilitated subtropical moist forest in Puerto Rico following Hurricane Georges in order to better predict patterns of resistance. Severe damage included uprooted trees, snapped stems, or crowns with greater than 50 percent branch loss. Hurricane induced mortality after 21 mo was 5.2 percent/yr, more than seven times higher than background mortality levels during the nonhurricane periods. Species differed greatly in their mortality and damage patterns, but there was no relationship between damage and wood density or biogeographic origin. Rather, damage for a given species was correlated with mean annual increment, with faster growing species experiencing greater damage, suggesting that growth rate may reflect a variety of life history tradeoffs. Size was also predictive of damage, with larger trees suffering more damage. Trees on ridges and in valleys received greater damage than trees on slopes. A strong relationship was noted between previous hurricane damage and present structural damage, which could not solely be explained by the patterns with size and species. We suggest that resistance of trees to hurricane damage is therefore not only correlated with individual and species characteristics but also with past disturbance history, which suggests that in interpreting the effects of hurricanes on forest structure, individual storms cannot be treated as discrete, independent events.     

Forest response to chronic hurricane disturbance in coastal New England

Question: Hurricanes and cyclones cause a wide range of damage to coastal forests worldwide. Most of these storms are not catastrophic in ecological terms, but forest responses to storms of moderate intensities are poorly understood. In regions with a high frequency of moderate hurricanes, how does variation in disturbance intensity affect the magnitude of ecological responses? Location: Naushon Island, Massachusetts, USA. Methods: We use historical records and dendroecological methods to characterize establishment and growth of Fagus grandifolia, Quercus alba, and Quercus velutina in response to seven non‐catastrophic hurricanes of varying intensity, and a major logging event, relative to baseline conditions, over the past 150 years. Our aim was to document variation in the magnitude of responses to known disturbance events of varying intensity, and to determine whether tree growth after moderate hurricanes differs from growth during periods of no disturbance. Results: Forest harvesting in 1824‐1827 had a strong impact on forest composition and growth. Since then, the study region has been characterized by little harvesting but frequent hurricanes. However, only one of the seven storms examined caused substantial increases in growth and new establishment for the dominant species; most moderate disturbances had minimal impact on growth and regeneration dynamics. We also document highly variable responses among species to individual storms, including substantial growth decreases that may not be detected by standard analytical approaches. Conclusions: Our results caution against the use of simple metrics such as wind speed to predict forest response to specific hurricanes, and highlight the importance of individual disturbance events in controlling long‐term forest dynamics, even in regions characterized by high disturbance frequency. In addition, we show that standard approaches to reconstructing disturbance history based on increases in radial growth and pulses of tree establishment are likely to underestimate the frequency of moderate disturbances.     

Ice‐storm disturbance and long‐term forest dynamics in the Adirondack Mountains

Ice storms cause periodic disturbance to temperate forests of eastern North America. They are the primary agents of disturbance in some eastern forests. In this paper, a forest gap model is employed to explore consequences of ice storms for the long‐term dynamics of Tsuga canadensis‐northem hardwoods forests. The gap model LINKAGES was modified to simulate periodic ice storm disturbance in the Adirondack Mountains of New York. To adapt the gap model for this purpose, field data on ice storm disturbance are used to develop a polytomous logistic regression model of tree damage. The logistic regression model was then incorporated into the modified forest gap model, LINK ADIR, to determine the type of damage sustained by each simulated tree. The logistic regression model predicts high probabilities of bent boles or severe bole damage (leaning, snapping, or uprooting) in small‐diameter trees, and increasing probability of canopy damage as tree size increases. Canopy damage is most likely on gentle slopes; the probability of severe bole damage increases with increasing slope angle. In the LINKADIR simulations, tree damage type determines the probability of mortality; trees with severe bole damage are assigned the highest mortality rate. LINKADIR predicts Tsuga canadensis dominance in mesophytic old‐growth forests not disturbed by ice storms. When ice storms are simulated, the model predicts Acer saccharum‐dominated forests with higher species richness. These results suggest that ice storms may function as intermediate disturbances that enhance species richness in forested Adirondack landscapes.     

A CSR classification of tree life history strategies and implications for ice storm damage

Differences in life history strategy influence the ecological roles of plant species, including their susceptibility to disturbance events. According to Grime's CSR model, plants exhibit three primary strategies, which reflect tradeoffs between stress and disturbance. Here we classify eastern North American tree species into life history strategies on the basis of the CSR model. Then, using data on ice storm damage to trees, we investigate how the level of damage varied among the different CSR categories. We used tree damage data for almost 2000 individual trees representing 30 species collected during two ice storms in the Appalachian Mountains. We augmented the study with ice damage data gleaned from nine published ice‐storm studies containing over 30 000 individuals representing 22 species. The trees we identified as stress‐tolerators (S) consistently sustained less damage than the other species. This finding matches the stress‐tolerant strategy: damage‐resistance is imperative for the persistence of trees that exhibit slow growth, low reproductive capacity and long lifespan. Our analyses also suggest that competitors (C) suffer widespread damage, particularly branch breakage, but experience low mortality. This pattern likely reflects features of the competitive strategy, such as wood strength and canopy form, which preclude resistance to damage but facilitate rapid recovery. The ice damage datasets did not contain trees that we classified as ruderals (R). Competitive ruderals (C‐R) and stress‐tolerant ruderals (S‐R), however, sustained heavy damage and high mortality, consistent with low investment in tree defense and a prioritization of reproduction. Our analyses suggest the usefulness of the CSR model for interpreting forest dynamics and understanding the implications of tree life‐history strategies for forest disturbance responses.     

Tree Species Traits but Not Diversity Mitigate Stem Breakage in a Subtropical Forest following a Rare and Extreme Ice Storm

Future climates are likely to include extreme events, which in turn have great impacts on ecological systems. In this study, we investigated possible effects that could mitigate stem breakage caused by a rare and extreme ice storm in a Chinese subtropical forest across a gradient of forest diversity. We used Bayesian modeling to correct stem breakage for tree size and variance components analysis to quantify the influence of taxon, leaf and wood functional traits, and stand level properties on the probability of stem breakage. We show that the taxon explained four times more variance in individual stem breakage than did stand level properties; trees with higher specific leaf area (SLA) were less susceptible to breakage. However, a large part of the variation at the taxon scale remained unexplained, implying that unmeasured or undefined traits could be used to predict damage caused by ice storms. When aggregated at the plot level, functional diversity and wood density increased after the ice storm. We suggest that for the adaption of forest management to climate change, much can still be learned from looking at functional traits at the taxon level.     

Stand dynamics of a yellow-poplar (Liriodendron tulipifera L.) forest in the Appalachian Mountains, Virginia, USA

Yellow-poplar (Liriodendron tulipifera L.) is a large, rapidly growing, shade-intolerant tree species common after disturbances on moist sites in the Appalachian Mountains. The species is typically scattered throughout old-growth mesophytic forests, where periodic gap formation creates conditions favorable for yellow-poplar establishment and growth. On abandoned agricultural fields, however, it is common for nearly monospecific forests of yellow-poplar to develop.This study examines stand dynamics of a yellow-poplar forest in western Virginia, USA that was established on agricultural fields abandoned in the late 1940s. Increment cores were collected from yellow-poplar trees growing on exposed ridgetops and in a more sheltered hollow. Tree-ring data show that the forest is even-aged. Tree establishment began about 5 years earlier on the ridgetops than in the hollow. Major ice storms disturbed the forest in 1978 and 1994, with two separate events in 1994. Ice storms disturb forests by depositing heavy loads of freezing rain on trees, breaking or uprooting them. The dendroecological data collected for this study provide little support for the hypothesis that ice storm disturbance promotes the establishment of new yellow-poplar cohorts. However, the data show that radial growth of some trees increased after ice storm disturbance, a pattern that reflects the increased availability of light following disturbance. Radial growth declined in some other trees as a consequence of severe injury during the storms.Radial growth responses following the 1978 ice storm were stronger on the ridgetops than in the hollow, suggesting that tree damage was more severe on the higher, more exposed sites. Growth responses were relatively mild following the storms of 1994, and did not exhibit pronounced topographic variations.     

A Flood Plain Palm Forest in the Luquillo Mountains of Puerto Rico Five Years After Hurricane Hugo1

Long-term studies are needed to understand the dynamics of tropical forests, particularly those subject to periodic disturbances such as hurricanes. We studied a flood plain Prestoea montana palm forest in the Luquillo Mountains of Puerto Rico over a 15-yr period (1980–1995), which included the passage of Hurricane Hugo in September 1989. The passage of the hurricane caused the dominant species to become more dominant and created low instantaneous tree mortality (1% of stems) and reductions in tree biomass (-16 Mg/ha/yr) and density, although not in basal area. Five years after the hurricane, the palm flood plain forest had exceeded its prehurricane aboveground tree biomass, tree density, and basal area. Aboveground tree biomass accumulated at a rate of 9.2 Mg/ha/yr, 76 percent of which was due to palms. Before the hurricane this rate was on the order of 3 Mg/ha/yr. Forest floor litter decreased to prehurricane levels (6.7 Mg/ha), within 5 yr, mostly due to the disappearance of woody litter. Thirteen tree species not represented in the canopy entered the forest by regeneration, and 2 species suffered almost 20 percent/yr mortality over a 5-yr period after the storm (floodplain average of 2%/yr). Delayed tree mortality was twice as high as instantaneous tree mortality after the storm and affected dicotyledonous trees more than it did palms. Regencration of dicotyledonous trees, palms, and tree ferns was influenced by a combination of factors including hydroperiod, light, and space. Redundancy Data Analysis showed that the area near the river channel was the most favorable for plant regeneration. Palm regeneration was higher in locations with longer hydroperiods, while regeneration of dicotyledonous trees was higher in areas with low risk of flooding. This study shows how a periodic disturbance provides long-term opportunities for species invasions and long-term ecosystem response at the patch scale of < 1 ha.     

The perfect storm: Weed invasion and intense storms in tropical forests

Climate change scientists predict an increased intensity of storms (cyclones, hurricanes and typhoons) in the future. Intense storms facilitate plant invasion by increasing resource availability, reducing competition and increasing opportunities for propagule dispersal. We document here the state of current understanding about the response of invasive plant species to intense storms and suggest that the structure and function of forests in storm‐prone regions may be much altered in the future as a result of weed invasion. Intense storms provide a large spatial and temporal window of opportunity for invasion and empirical research demonstrates growth and recruitment rates of invasive species increase following such events, and they spread readily. In particular, lianas and woody invasive species that are shade tolerant and recruit from the seedling layer may constitute the greatest threat to tropical forests following storm events. Forests persisting in fragmented landscapes will be exposed to some of the most severe consequences of intense storms and subsequent weed invasion. In storm‐prone regions, forests of the future are likely to experience a decrease in diversity of native species and homogenization of communities at landscape and regional scales, slower rates of forest succession, increasing degradation of forest fragments and ultimately a decrease in ecosystem function.     

Coupled effects of wind‐storms and drought on tree mortality across 115 forest stands from the Western Alps and the Jura mountains

Damage due to wind‐storms and droughts is increasing in many temperate forests, yet little is known about the long‐term roles of these key climatic factors in forest dynamics and in the carbon budget. The objective of this study was to estimate individual and coupled effects of droughts and wind‐storms on adult tree mortality across a 31‐year period in 115 managed, mixed coniferous forest stands from the Western Alps and the Jura mountains. For each stand, yearly mortality was inferred from management records, yearly drought from interpolated fields of monthly temperature, precipitation and soil water holding capacity, and wind‐storms from interpolated fields of daily maximum wind speed. We performed a thorough model selection based on a leave‐one‐out cross‐validation of the time series. We compared different critical wind speeds (CWSs) for damage, wind‐storm, and stand variables and statistical models. We found that a model including stand characteristics, drought, and storm strength using a CWS of 25 ms^?1 performed the best across most stands. Using this best model, we found that drought increased damage risk only in the most southerly forests, and its effect is generally maintained for up to 2 years. Storm strength increased damage risk in all forests in a relatively uniform way. In some stands, we found positive interaction between drought and storm strength most likely because drought weakens trees, and they became more prone to stem breakage under wind‐loading. In other stands, we found negative interaction between drought and storm strength, where excessive rain likely leads to soil water saturation making trees more susceptible to overturning in a wind‐storm. Our results stress that temporal data are essential to make valid inferences about ecological impacts of disturbance events, and that making inferences about disturbance agents separately can be of limited validity. Under projected future climatic conditions, the direction and strength of these ecological interactions could also change.     

Damage and Recovery of Riparian Sierra Palms after Hurricane Georges: Influence of Topography and Biotic Characteristics

Tropical forests are often shaped by disturbance events, especially in regions where hurricanes and other severe storms occur. We studied the effects of Hurricane Georges (September 1998) on the sierra palm ( Prestoea acuminata var. montana ) in the Luquillo Mountains of Puerto Rico. We established riparian transects along two headwater streams that were similar in size and location, but differed in riparian tree species composition and land-use history. Following Hurricane Georges, sierra palms were surveyed periodically for damage and recovery (measured by initial loss and subsequent regrowth of palm leaves), tree height, sun exposure, and production of inflorescences and infructescences. Palm height had the highest association with damage, with most damage occurring to canopy palms. Palm recovery (4 mo and 10 mo post-hurricane) was associated with high tree density, indicating that sun exposure was not limiting. Hurricane Georges likely reduced production of flowers and fruits in sierra palms for at least 10 mo following the storm, although production of new leaves was rapid. Although palms recovered quickly from defoliation after the hurricane, decreased reproduction resulted in reduced availability of fruit for terrestrial and aquatic consumers.     

Tree Species Composition and Harvest Intensity Affect Herbivore Density and Leaf Damage on Beech,Fagus sylvatica,in Different Landscape Contexts

Most forests are exposed to anthropogenic management activities that affect tree species composition and natural ecosystem processes. Changes in ecosystem processes such as herbivory depend on management intensity, and on regional environmental conditions and species pools. Whereas influences of specific forest management measures have already been addressed for different herbivore taxa on a local scale, studies considering effects of different aspects of forest management across different regions are rare. We assessed the influence of tree species composition and intensity of harvesting activities on arthropod herbivores and herbivore-related damage to beech trees, Fagus sylvatica, in 48 forest plots in three regions of Germany. We found that herbivore abundance and damage to beech trees differed between regions and that – despite the regional differences - density of tree-associated arthropod taxa and herbivore damage were consistently affected by tree species composition and harvest intensity. Specifically, overall herbivore damage to beech trees increased with increasing dominance of beech trees – suggesting the action of associational resistance processes – and decreased with harvest intensity. The density of leaf chewers and mines was positively related to leaf damage, and several arthropod groups responded to beech dominance and harvest intensity. The distribution of damage patterns was consistent with a vertical shift of herbivores to higher crown layers during the season and with higher beech dominance. By linking quantitative data on arthropod herbivore abundance and herbivory with tree species composition and harvesting activity in a wide variety of beech forests, our study helps to better understand the influence of forest management on interactions between a naturally dominant deciduous forest tree and arthropod herbivores.     

Patterns of Forest Damage in a Southern Mississippi Landscape Caused by Hurricane Katrina

Understanding and predicting the ways in which large and intense hurricanes affect ecosystem structure, composition and function is important for the successful management of coastal forest ecosystems. In this research, we categorized forest damage resulting from Hurricane Katrina into four classes (none, low, moderate, heavy) for nearly 450 plots in a 153,000 ha landscape in southern Mississippi, USA, using a combination of air photo interpretation and field sampling. We then developed predictive damage models using single tree classification tree analysis (CTA) and stochastic gradient boosting (SGB) and examined the importance of variables addressing storm meteorology, stand conditions, and site characteristics in predicting forest damage. Overall damage classification accuracies for a training dataset (n = 337 plots) were 72 and 81% for the single tree and SGB models, respectively, with Cohen’s weighted linear κ values of 0.71 and 0.86. For an independent validation dataset (n = 112 plots), classification accuracy dropped to 57% (κ = 0.65) and 56% (κ = 0.63) for the single tree and SGB models. Proportions of agreement between observed and predicted damage were significantly greater (P < 0.05) than would be expected by chance alone for all damage classes with the training data and all but the moderate class for the validation data. Stand age was clearly the best predictor of damage for both models, with forest type, stand condition, site aspect, and distance to the nearest perennial stream also explaining much of the variation in forest damage. Measures of storm meteorology (duration and steadiness of hurricane-force winds; maximum sustained winds) were of secondary importance. The forest-wide application of our CTA model provided a realistic, spatially detailed map of predicted damage while also maintaining a relatively high degree of accuracy. The study also provides a first step toward the development of models identifying the susceptibility of forest stands to future events that could be used as an aid to incorporating the effects of large infrequent disturbances into forest management activities.     

Recovery of a tropical rain forest after hurricane damage

More than a year after Hurricane Hugo damaged a Puerto Rican tropical rain forest, recovery of the forest was assessed by observing resprouting of damaged trees in eleven transects which were established before the hurricane in 1989. In each transect, I relocated and identified standing trees and observed if they were resprouting after injury. I found that resprouting was rapid and depended on species. There was no significant relationship between sprouting and diameter classes of trees. This study suggests that resprouting of damaged trees plays major roles in the recovery of the tropical forests which are prone to hurricanes and are in non-equilibrium state.     

冰雪灾害对中亚热带人工针叶林净初级生产力的影响

结合中亚热带江西千烟洲人工针叶林2005、2008和2011年3次树木清查数据以及树木相对生长方程,比较了2008年1月南方冰雪灾害前后的NPP,评价了森林生态系统灾后的恢复能力。结果表明:乡土树种马尾松(Pinus massoniana)与杉木(Cunninghamia lanceolata)比外来树种湿地松(Pinus elliottii)抗灾害能力强;在个体水平上,胸径(D)较大的树木抗灾害能力较差。灾后马尾松与杉木的D增长率降低,而湿地松增大。冰雪灾害导致大量碳(10.44 t C/hm2)从乔木层碳库转移到死生物量碳库,占乔木层碳储量的18.28%。灾前NPP和碳利用效率(CUE)分别为736.23 g C m-2a-1和0.41;灾后经过近4年的恢复,NPP和CUE分别为683.08 g C m-2a-1和0.38。     

Hurricanes overcome migration lag and shape intraspecific genetic variation beyond a poleward mangrove range limit

Expansion of many tree species lags behind climate change projections. Extreme storms can rapidly overcome this lag, especially for coastal species, but how will storm‐driven expansion shape intraspecific genetic variation? Do storms provide recruits only from the nearest sources, or from more distant sources? Answers to these questions have ecological and evolutionary implications, but empirical evidence is absent from the literature. In 2017, Hurricane Irma provided an opportunity to address this knowledge gap at the northern range limit of the neotropical black mangrove (Avicennia germinans) on the Atlantic coast of Florida, USA. We observed massive post‐hurricane increases in beach‐stranded A. germinans propagules at, and past, this species’ present day range margin when compared to a previously surveyed nonhurricane year. Yet, propagule dispersal does not guarantee subsequent establishment and reproductive success (i.e., effective dispersal). We also evaluated prior effective dispersal along this coastline with isolated A. germinans trees identified beyond the most northern established population. We used 12 nuclear microsatellite loci to genotype 896 hurricane‐driven drift propagules from nine sites and 10 isolated trees from four sites, determined their sources of origin, and estimated dispersal distances. Almost all drift propagules and all isolated trees came from the nearest sources. This research suggests that hurricanes are a prerequisite for poleward range expansion of a coastal tree species and that storms can shape the expanding gene pool by providing almost exclusively range‐margin genotypes. These insights and empirical estimates of hurricane‐driven dispersal distances should improve our ability to forecast distributional shifts of coastal species.     

The Influence of Hurricane Winds on Caribbean Dry Forest Structure and Nutrient Pools1

In 1998, we measured the effects of Hurricane Georges after it passed over long‐term research sites in Puerto Rican dry forest. Our primary objectives were to quantify hurricane effects on forest structure, to compare effects in a large tract of forest versus a series of nearby forest fragments, to evaluate short‐term response to hurricane disturbance in terms of mortality and sprouting, and to assess the ability of hurricanes to maintain forest structure. We sampled damage from 33 plots (1.3 ha) across a 3000‐ha tract of forest as well as in 19 fragments. For stems with 2.5‐cm minimum diameter, 1004 stems/ha (12.4%) suffered structural damage, while 69 percent of the undamaged stems were at least 50 percent defoliated. Basal area lost to structural damage equaled 4.0 m²/ha (22%) in south‐facing native forests. Structural damage and defoliation increased with stem diameter and were more common in certain dry forest species. South‐facing forests and those on ridgetops incurred more damage than north‐facing forests or those comprised primarily of introduced species. Stem mortality was only 2 percent of all stems after 9 mo. Structural damage did not necessarily result in stem mortality. Hurricane‐induced mortality was not associated with stem height or diameter, but was ten times greater than background mortality. Basal sprouting was proportional to the amount of structural damage incurred in a stand. Forest fragments experienced the same patterns of hurricane effects as the reference forest. The low, dense structure of Caribbean dry forest can be maintained by hurricane damage to larger stems and induction of basal sprouting to generate multistemmed trees.     

Winter in the Ouchitas—A severe winter storm signature in Pinus echinata in the Ouachita Mountains of Oklahoma and Arkansas,USA

Each year severe winter storms (≈ice storms) damage trees throughout the southern USA. Arkansas and Oklahoma have a history of severe winter storms. To extend that history back beyond the reach of written records, a distinctive tree ring pattern or signature is needed. Storm-caused breakage, branch loss and bending stress provide that signature. We found a severe storm signature in shortleaf pine (Pinus echinata). We used three published site chronologies, a set of five new site chronologies from a growth-and-yield study conducted by Oklahoma State University and the unpublished Shortleaf Canyon chronology from a master’s thesis at the University of Arkansas. Our method is based on two ring width values for the first and second growing seasons after the storm standardized to the ring widths of the seven growing seasons after the storm. Concordance between storm years predicted by tree ring patterns and actual storm years was tested using Cohen’s Kappa. Concern about confounding of ice storm signals by droughts led us to test concordance between severe storms and drought in July, August and September; results were inconclusive but stand as a warning that these two phenomena cannot be distinguished with certainty in the tree ring record. Damaging severe storms occurred in about 2.8% of all years. Two out of three storms identified as “severe” produced glaze icing.     

Structural response of Caribbean dry forests to hurricane winds: a case study from Guánica Forest, Puerto Rico

Aim Tropical dry forests in the Caribbean have an uniquely short, shrubby structure with a high proportion of multiple‐stemmed trees compared to dry forests elsewhere in the Neotropics. Previous studies have shown that this structure can arise without the loss of main stems from cutting, grazing, or other human intervention. The Caribbean has a high frequency of hurricanes, so wind may also influence forest stature. Furthermore, these forests also tend to grow on soils with low amounts of available phosphorus, which may also influence structure. The objective of this study was to assess the role of high winds in structuring dry forest, and to determine whether soil nutrient pools influence forest response following hurricane disturbance. Location Guánica Forest, Puerto Rico. Methods Over 2000 stems in five plots were sampled for hurricane effects within 1 week after Hurricane Georges impacted field sites in 1998. Sprout initiation, growth, and mortality were analysed for 1407 stems for 2 years after the hurricane. Soil nutrient pools were measured at the base of 456 stems to assess association between nutrients and sprout dynamics. Results Direct effects of the hurricane were minimal, with stem mortality at < 2% and structural damage to stems at 13%, although damage was biased toward stems of larger diameter. Sprouting response was high – over 10 times as many trees had sprouts after the hurricane as before. The number of sprouts on a stem also increased significantly. Sprouting was common on stems that only suffered defoliation or had no visible effects from the hurricane. Sprout survival after 2 years was also high (> 86%). Soil nutrient pools had little effect on forest response as a whole, but phosphorus supply did influence sprout dynamics on four of the more common tree species. Main conclusions Hurricanes are able to influence Caribbean tropical dry forest structure by reducing average stem diameter and basal area and generating significant sprouting responses. New sprouts, with ongoing survival, will maintain the high frequency of multi‐stemmed trees found in this region. Sprouting is not limited to damaged stems, indicating that trees are responding to other aspects of high winds, such as short‐term gravitational displacement or sway. Soil nutrients play a secondary role in sprouting dynamics of a subset of species. The short, shrubby forest structure common to the Caribbean can arise naturally as a response to hurricane winds.     

Assessing the effects of elephant foraging on the structure and diversity of an Afrotropical forest

African forest elephants (Loxodonta cyclotis) are ecosystem engineers that browse and damage large quantities of vegetation during their foraging and movement. Though elephant trail networks and clearings are conspicuous features of many African forests, the consequences of elephant foraging for forest structure and diversity are poorly documented. In this study in northeastern Gabon, we compare stem size, stem density, proportional damage, species diversity, and species relative abundance of seedlings and saplings in the vicinity of seven tree species that produce elephant-preferred fruits (“elephant trees”) relative to control trees that do not. Across 34 survey trees, with a combined census area of 2.04 ha, we recorded data on 26,128 woody stems in three sizes classes. Compared with control trees, the area around elephant trees had the following: (a) a significantly greater proportion of damaged seedlings and a marginally greater proportion of damaged saplings (with 82% and 24% greater odds of damage, respectively); (b) no significant difference in stem density or species diversity; and (c) a significantly greater relative abundance of seedlings of elephant tree species. Increasing distance away from focal elephant trees was associated with significantly reduced sapling stem damage, significantly increased sapling stem density, and significantly increased sapling species diversity. Considered in sum, our results suggest that elephants can affect the structure and diversity of Afrotropical forests through their foraging activities, with some variation based on location and plant size class. Developing a more complete understanding of elephants’ ecological effects will require continued research, ideally with manipulative experiments.