Effects of land use history on hurricane damage and recovery in a neotropical forest

Prior land-use history might influence damage and recovery of plant communities from natural disturbance. We examined effects of previous agricultural land use on damage and recovery of plant communities affected by Hurricane Georges. The study was conducted in the karst region of Los Haitises National Park, Dominican Republic. We compared pre- and post-hurricane stem density, basal area and diversity of woody vegetation in sites within the park that had been subject to different land use histories. The type of land uses included a wide range of histories, ranging from abandoned pastures and conucos (mixed plantings) to cacao plantations, intact forests and mogotes (hilltop communities) with no recent history of land use. Previous land use and the amount of basal area present prior to the hurricane determined effects of, and recovery from hurricane disturbance. Systems with high pre-hurricane basal area lost many large trees, whereas the basal area hardly changed in systems without large trees. Thus, basal area decreased at forested sites, mogotes, and cacao plantations and remained comparable to pre-hurricane figures in all other land uses. Shifts in species diversity paralleled to some degree reductions in basal area. Species diversity increased in mogotes and cacao plantations, perhaps as a result of hurricane damage to the forest canopy, which facilitated regeneration of heliophilic species. Finally, regeneration of cacao seedlings in former cacao plantations, and growth of pioneer species in young conucos (mixed plantings) more than doubled post-hurricane stem densities for these two types of land use. Previous agricultural land use left a lasting impression on the structure and composition on plant communities, which persisted even after hurricane damage. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of a Hurricane Disturbance on Aboveground Forest Structure, Arbuscular Mycorrhizae and Belowground Carbon in a Restored Tropical Forest

To better understand how management and restoration practices influence the response of terrestrial ecosystems to large-scale disturbances, it is critical to study above- and belowground effects. In this study, we examined the immediate effect of a major hurricane on aboveground forest structure, arbuscular mycorrhizae (AM) and belowground carbon pools in experimentally thinned plots in a tropical forest. The hurricane occurred five years after a thinning treatment, when thinned plots had similar aboveground carbon stocks but different forest structure compared to control plots. Thinned plots had more large diameter (>10 cm) trees compared to the control plots, which were characterized by a higher density of small diameter (<10 cm) trees. Despite pre-hurricane differences in forest structure, there were no significant differences between treatments in changes of canopy openness or number of affected trees following the hurricane. Thinned plots had larger belowground carbon pools than the controls plots before the hurricane, and these differences remained after the hurricane despite rapid decomposition of organic matter rich in nitrogen. There were no pre-hurricane differences in AM fungal spores or total AM root colonization. The hurricane reduced AM sporulation by nearly 50% in both treatments, yet we observed a significant increase in AM root colonization after the hurricane with greater AM colonization in the thinned plots. Hurricanes have well-known visible aboveground effects, but here we showed that less visible belowground effects are influenced by forest management and may play an important role in forest recovery.     

Disturbance and recovery of microbial community structure and function following Hurricane Frances

Disturbance and recovery influence microbial community structure and ecosystem functions in most natural environments. This study from a hypersaline Bahamian lagoon details the response of a benthic cyanobacterial mat to disturbance by Hurricane Frances, a category-4 storm. Clone libraries of cyanobacterial small subunit r-RNA genes and nitrogenase genes revealed significant shifts in cyanobacterial and diazotroph community composition following the hurricane. Post-hurricane clone libraries were dominated by sequences that had been rare in pre-hurricane communities. In spite of this dominance shift, re-colonizing mat communities performed nitrogen fixation and photosynthesis at rates within the normal range of variation measured in the mat at similar salinities. There was a tendency for nitrogen fixation rates from mats re-colonizing sites with hurricane-related sand deposition to be higher than those from mats re-colonizing sites without significant sand deposition. This suggests that the altered communities responded to a carbon : nitrogen imbalance that was particularly pronounced in areas subjected to disturbance by sand burial. The post-hurricane dominance of organisms that had been previously rare suggests that pre-hurricane diversity and functional redundancy contributed to the rapid recovery of ecosystem function in the post-disturbance environment.     

Regeneration in fringe mangrove forests damaged by Hurricane Andrew

Mangrove forests along many tropical coastlines are frequently andseverely damaged by hurricanes. The ability of mangrove forests to regeneratefollowing hurricanes has been noted, but changes that occur in vegetationfollowing disturbance by hurricane winds and storm tides have not been studied.We measured changes in plant community structure and environmental variables intwo fringe mangrove forests in south Florida, USA that experienced high windvelocities and storm tides associated with Hurricane Andrew (August1992). Loss of the forest canopy stimulated regeneration via seedlinggrowth and recruitment, as well as resprouting of some trees that survived thehurricane. Initial regeneration differed among species in both forests:Rhizophora mangle L. regenerated primarily via growth ofseedlings present at the time of the hurricane (i.e., release of advancerecruits), but many trees of Avicennia germinans(L.) Stearn and Laguncularia racemosa Gaertn.f.resprouted profusely from dormant epicormic buds. In one forest, which wasformerly dominated by Laguncularia, high densities ofRhizophora seedlings survived the hurricane and grew toform dense stands of saplings and small trees ofRhizophora. In the other forest, there were lowerdensitiesof surviving Rhizophora seedlings (possibly due tohigher storm tide), and extensive bare areas that were colonized byAvicennia, Laguncularia, andherbaceous species. This forest, predominantly Rhizophoraat the time of the hurricane, now contains stands of saplings and small treesofall three species, interspersed with patches dominated by herbaceous plants.These findings indicate that moderately damaged fringe forests may regenerateprimarily via release of Rhizophora advance recruits,leading to single-species stands. In severely damaged forests, seedlingrecruitment may be more important and lead to mixed-species stands.Regeneration of mangrove forests following hurricanes can involve differentpathways produced by complex interactions between resprouting capability,seedling survival, post-hurricane seedling recruitment, and colonizationby herbaceous vegetation. These differences in relative importance ofregeneration pathways, which may result in post-hurricane forestsdifferent from their pre-hurricane structure, suggest that models forregeneration of mangrove forests will be more complex than directregeneration models proposed for other tropical forests whereregeneration after hurricanes is dominated by resprouting.     

Belowground nitrogen dynamics in relation to hurricane damage along a tropical dry forest chronosequence

Understanding and predicting the responses of plant communities to multiple overlapping disturbances remains a challenging task. Hurricane Wilma represents a large, yet infrequent type of disturbance that was superimposed on an existing disturbance gradient of time since fire. We examined disturbance and recovery patterns in response to these overlapping disturbances by measuring how canopy structure, fine roots, mycorrhizae, and soil nitrogen dynamics, varied along a fire chronosequence in the 2 years after Hurricane Wilma. Hurricane damage increased canopy openness in all seral stages. In the early-seral stage, canopy openness returned to pre-hurricane conditions within 2 years, whereas canopy openness in the late-seral stage remained significantly higher throughout the study. We observed no significant change in root length density in the early- and mid-seral stages. However, in the late-seral stage, root length density was significantly reduced immediately after the hurricane and remained so 2 years after the hurricane. In the late-seral stage, we also observed a significant reduction in percent soil nitrogen and a significant increase in soil nitrogen isotopic composition (δ¹⁵N) values, indicating a loss of soil nitrogen. In contrast, in the early- and mid-seral stages, there were no significant changes in percent nitrogen or soil δ¹⁵N values. Results from this study suggest that forest fire disturbance history influences responses to hurricane damage. Moreover, feedbacks between aboveground and belowground processes have the potential to influence forest recovery.     

Changes in forest structure, species diversity and spatial pattern following hurricane disturbance in a Piedmont North Carolina forest, USA

Aims: Large hurricanes have profound impacts on temperate forests,but owing to their infrequent nature these effects have rarelybeen examined in detail. In 1996, Hurricane Fran significantlydamaged many long-term tree census plots in the Duke Foreston the North Carolina Piedmont, thereby providing an exceptionalopportunity to examine pre- and post-hurricane forest compositionaltrajectories. Our goal was to examine immediate, short-term(0–4 years) and longer term (5 year) hurricane-inducedstructural, spatial and compositional changes in the tree population(stem d.b.h > 1 cm) in the context of our detailed, long-termknowledge of the dynamics of these forests. Methods: We surveyed stem damage and tree mortality in 34 long-term permanentplots (ca. 70-year record; 404–1 012 m²) and 7 large mappedtree stands (ca. 20-year record; 5 250–65 000 m²) representingboth transition-phase, even-aged pine stands and uneven-agedupland hardwood forests. We employed three types of damage measuresto quantify stand-level damage severity: percentage of stemsdamaged, percentage of basal area lost and a ‘stand-leveldamage index’. Second-order spatial analysis (Ripley'sK-function) was used to investigate patterns in tree mortality. Important findings: Our study found hurricane effects on the structural attributesof Piedmont forests to be variable and patchy. Changes in treespecies composition, however, were modest. Uprooting was themajor damage type for the overstory trees [diameter at breastheight (d.b.h.) >10 cm] apparently due to the exposure ofthe crowns to high wind combined with heavy rainfall prior toand during the storm. Saplings, juvenile trees and small trees(1–10 cm d.b.h.) of the understory and midstory were mainlydamaged by being pinned or bent by their damaged large neighbors.Hurricane-induced tree mortality varied weakly among species,was positively correlated with pre-hurricane tree size and remainedup to 2-fold higher than pre-hurricane background mortality5 years after the hurricane. Spatial point pattern analysisrevealed a patchy distribution of tree mortality during thehurricane sampling interval. Hurricane Fran resulted in a dramaticincrease in average gap size from ca. 400 m² pre-hurricane toca 1100 m² after the hurricane, whereas maximum gap sizes reached18–34 times larger than the pre-hurricane levels.     

Impact of a hurricane on the herpetofaunal assemblages of a successional chronosequence in a tropical dry forest

Land‐use change is the main cause of deforestation and degradation of tropical forest in Mexico. Frequently, these lands are abandoned leading to a mosaic of natural vegetation in secondary succession. Further degradation of the natural vegetation in these lands could be exacerbated by stochastic catastrophic events such as hurricanes. Information on the impact of human disturbance parallel to natural disturbance has not yet been evaluated for faunal assemblages in tropical dry forests. To evaluate the response of herpetofaunal assemblages to the interaction of human and natural disturbances, we used information of pre‐ and post‐hurricane herpetofaunal assemblages inhabiting different successional stages (pasture, early forest, young forest, intermediate forest, and old growth forest) of dry forest. Herpetofaunal assemblages were surveyed in all successional stages two years before and two years after the hurricane Jova that hit the Pacific Coast of Mexico on October 2011. We registered 4093 individuals of 61 species. Overall, there were only slight effects of successional stage, hurricane Jova or the interaction between them on abundance, observed species richness and diversity of the herpetofauna. However, we found marked changes in estimated richness and composition of frogs, lizards, and snakes among successional stages in response to hurricane Jova. Modifications in vegetation structure as result of hurricane pass promoted particular changes in each successional stage and taxonomic group (anurans, lizards, and snakes). Secondary forests at different stages of succession may attenuate the negative effects of an intense, short‐duration, and low‐frequency natural disturbance such as hurricane Jova on successional herpetofaunal trajectories and species turnover.     

A decade of belowground reorganization following multiple disturbances in a subtropical wet forest

Humid tropical forests are dynamic ecosystems that experience multiple and overlapping disturbance events that vary in frequency, intensity, and spatial extent. Here we report the results of a 10-year study investigating the effects of forest clearing and multiple hurricanes on ecosystem carbon reservoirs, nutrient pools and vegetation. The aboveground plant community was most heavily affected by multiple disturbances, with the 9-year-old stands showing high rates of hurricane-induced mortality relative to surrounding forest. Belowground pools were less affected. Live fine root biomass fluctuated in response to multiple disturbances, but returned to pre-disturbance levels after 10 years. Soil C was resilient to clearing and hurricanes, probably due to the large pool size and high clay content. Soil P fluctuated over time, declining during periods of rapid plant recovery and growth. With the exception of K, base cations recovered within 2 years following clearing and showed little response to hurricane disturbance.     

Use of fish behavior in assessing the effects of Hurricane Iniki on the Hawaiian island of Kaua'i

Synopsis Declared the most compact and powerful storm known to have reached the Hawaiian Archipelago, Hurricane Iniki destroyed terrestrial and freshwater habitats island-wide when it struck Kaua'i late on the afternoon of Friday, 11 September 1992. Five weeks after the storm, a research group began underwater studies on the north shore of Kaua'i to assess the physical and biological effects of the hurricane and to track at four-month intervals the recovery of three high quality streams that are home to Hawaii's native and mostly endemic freshwater fishes, mollusks, and crustaceans. Early in the investigation, information on the social behavior of resident fishes showed particular promise for assessing the impact of the hurricane and for tracing the recovery of stream ecosystems. In Hanakapi'ai Stream, the stream damaged most by the hurricane and a subsequent flash flood, two downstream species,Eleotris sandwicensis andStenogobius hawaiiensis, were missing, and members of a third one,Sicyopterus stimpsoni, were sufficiently crowded into the lower section of the stream that aggressive behavior, occasionally resulting in injury, sharply curtailed feeding and prevented all but the earliest phases of courtship. Although the study began in the middle of the spawning season forAwaous guamensis, the few males found were in poor condition and showed neither territorial behavior in response to other males nor courtship when gravid females were encountered. Farther upstream, males ofLentipes concolor directed an inordinate amount of effort toward maintaining territories. Similar, but less dramatic alterations in distribution and behavior were seen in fishes from the less damaged Wainiha River. In Nu'alolo Stream, protected from hurricane winds by nearly vertical valley walls, the behavior was typical for fishes throughout its length except forE. sandwicensis in the damaged section at the stream mouth. Most progress in the return to social behaviors characteristic of pre-hurricane conditions for fishes in Hanakapi'ai Stream and Wainiha River occurred during the first four months of the study, but it was not until October 1993, more than a year after Iniki, that the behavior of the fishes signaled a return to conditions that existed before the storm. The study demonstrated that Hawaii's stream fishes are remarkably capable of rebounding from the effects of hurricanes because of the hardiness of adults and the recruitment of young animals from the ocean as a natural part of each species' amphidromous life cycle.     

Deforestation of watersheds of Panama: nutrient retention and export to streams

A series of eight watersheds on the Pacific coast of Panama where conversion of mature lowland wet forest to pastures by artisanal burning provided watershed-scale experimental units with a wide range of forest cover (23, 29, 47, 56, 66, 73, 73, 91, and 92 %). We used these watersheds as a landscape-scale experiment to assess effects of degree of deforestation on within-watershed retention and hydrological export of atmospheric inputs of nutrients. Retention was estimated by comparing rainfall nutrient concentrations (volume-weighted to allow for evapotranspiration) to concentrations in freshwater reaches of receiving streams. Retention of rain-derived nutrients in these Panama watersheds averaged 77, 85, 80, and 62 % for nitrate, ammonium, dissolved organic N, and phosphate, respectively. Retention of rain-derived inorganic nitrogen, however, depended on watershed cover: retention of nitrate and ammonium in pasture-dominated watersheds was 95 and 98 %, while fully forested watersheds retained 65 and 80 % of atmospheric nitrate and ammonium inputs. Watershed forest cover did not affect retention of dissolved organic nitrogen and phosphate. Exports from more forested watersheds yielded DIN/P near 16, while pasture-dominated watersheds exported N/P near 2. The differences in magnitude of exports and ratios suggest that deforestation in these Panamanian forests results in exports that affect growth of plants and algae in the receiving stream and estuarine ecosystems. Watershed retention of dissolved inorganic nitrogen calculated from wet plus dry atmospheric deposition varied from 90 % in pasture- to 65 % in forest-dominated watersheds, respectively. Discharges of DIN to receiving waters from the watersheds therefore rose from 10 % of atmospheric inputs for pasture-dominated watersheds, to about 35 % of atmospheric inputs for fully forested watersheds. These results from watersheds with no agriculture or urbanization, but different conversion of forest to pasture by burning, show significant, deforestation-dependent retention within tropical watersheds, but also ecologically significant, and deforestation-dependent, exports that are biologically significant because of the paucity of nutrients in receiving tropical stream and coastal waters.     

Responses of the mangrove fern <Emphasis Type="Italic">Acrostichum danaeifolium</Emphasis> Langsd. &; Fisch. (Pteridaceae,Pteridophyta) to disturbances resulting from increased soil salinity and Hurricane Georges at the Jobos Bay National Estuarine Research Reserve,Puerto Rico

Mortality of plants in a mangrove forest dominated by the tree Avicennia germinans began to appear at the southern coastal edge of the forest in the central watershed of the Jobos Bay National Estuarine Research Reserve in Puerto Rico in 1977. The dieback was attributed to salinities in excess of 70 ppt and gradually continued north until some tree mortality was observed in 1995 at the forest’s landward interface with agricultural land. Mortality of the common understory mangrove fern Acrostichum danaeifolium occurred at a much slower rate than tree mortality. Remediation at the forest’s edge was recommended in 1997 and a study to monitor A. danaeifolium at 4-month intervals was begun in January 1998 to determine how the ferns would respond to hydrologic change. Hurricane Georges passed over the reserve in September 1998, so the effects of this disturbance were assessed as well. In May 1998, 4 months after tagging individual plants, the mean number of leaves plant⁻¹ at the impact site was only half that for plants in a control area in the nearby undisturbed eastern watershed. Fertile (spore-bearing) leaf production in both watersheds was very low accounting for plant fertility of 7% or less. Short leaf lengths in the impact site combined with smaller plant leaf counts and much lower leaf production rates in one area of the impact site had resulted in biomass production at the control site that was 18 times greater than in the impact site. After Hurricane Georges plant mortality in the impact area increased with individuals of A. danaeifolium found dead on every monitoring date except September 1999. However, when means for all variables measured in both sections of the forest were compared within 8 months after the hurricane there was an increase in all growth characteristics except sterile leaf length. Relative plant fertility increased from 10% before the hurricane to over 50% by May 2000. The fertile leaf production rate of these plants increased nine-fold by May 1999, and though it declined slowly thereafter it was still almost three time pre-hurricane levels at the end of the study almost 2 years later. Biomass production rates, though very low in the 4 months after the hurricane, had increased to five times pre-hurricane levels by the end of the study in January 2001. Efforts at remediation of the hypersaline conditions that were completed in May 1999 at the landward edge of the impact area appeared to have little effect on the ferns. For A. danaeifolium, plant mortality and decreases in plant size characteristics were the most notable responses to high salinity levels. In contrast, increases in fertile leaf and biomass production rates were the most significant response to hurricane disturbance.     

Predicting and quantifying the structure of tropical dry forests in South Florida and the Neotropics using spaceborne imagery

Aim This research examines environmental theories and remote sensing methods that have been hypothesized to be associated with tropical dry forest structure. Location Tropical dry forests of South Florida and the Neotropics. Methods Field measurements of stand density, basal area and tree height were collected from 22 stands in South Florida and 30 stands in the Neotropics. In South Florida, field measurements were compared to climatic (temperature, precipitation, hurricane disturbance) and edaphic (rockiness, soil depth) variables, spectral indices (NDVI, IRI, MIRI) from Landsat 7 ETM+, and estimates of tree height from the Shuttle Radar Topography Mission (SRTM) and the National Elevation Dataset (NED). Environmental variables associated with tropical dry forest structure in South Florida were compared to tropical dry forest in other Neotropical sites. Results There were significant correlations among temperature and precipitation, and stand density and tree height in South Florida. There were significant correlations between (i) stand density and mean NDVI and standard deviation of NDVI, (ii) MIRI and stand density, basal area and mean tree height, and (iii) estimates of tree height from SRTM with maximum tree height. In the Neotropics, there were no relationships between temperature or precipitation and tropical dry forest structure, however, Neotropical sites that experience hurricane disturbance had significantly shorter tree heights and higher stand densities. Main conclusions It is possible to predict and quantify the forest structure characteristics of tropical dry forests using climatic data, Landsat 7 ETM+ imagery and SRTM data in South Florida. However, results based on climatic data are region‐specific and not necessarily transferable between tropical dry forests at a continental spatial scale. Spectral indices from Landsat 7 ETM+ can be used to quantify forest structure characteristics, but SRTM data are currently not transferable to other regions. Hurricane disturbance has a significant impact on forest structure in the Neotropics.     

Invertebrate communities in a tropical rain forest canopy in Puerto Rico following Hurricane Hugo

1. Canopy invertebrate responses to Hurricane Hugo, tree species, and recovery time were examined at the Luquillo Experimental Forest in Puerto Rico during 1991–92 and 1994–95. Six tree species representing early and late successional stages were examined in paired plots representing severe hurricane disturbance (most trees toppled) and light hurricane disturbance (all trees standing and most branches intact). 2. Hurricane disturbance affected invertebrate abundances significantly. Sap-suckers and molluscs were more abundant, and defoliators, detritivores, and emergent aquatic insects were less abundant in recovering tree-fall gaps than in intact forest during this 5-year period. These changes in functional organisation are consistent with comparable studies of arthropod responses to canopy removal during harvest in temperate forests. 3. Tree species also affected invertebrate abundances significantly, but invertebrate communities did not differ significantly between the three early successional and three later successional tree species. 4. Most taxa showed significant annual variation in abundances, but only two Homoptera species showed a significant linear decline in abundance through time, perhaps reflecting long-term trends during recovery. 5. Leaf area missing, an indicator of herbivore effect on canopy processes, showed significant seasonal and annual trends, as well as differences among tree species and hurricane treatments. Generally, leaf area missing peaked during the wet season each year, but reached its highest levels during an extended drought in 1994. Leaf area missing also tended to be higher on the more abundant tree species in each disturbance treatment. 6. Herbivore abundances and leaf area missing were not related to concentrations of nitrogen, phosphorous, potassium, or calcium in the foliage. 7. This study demonstrated that invertebrate community structure and herbivory are dynamic processes that reflect the influences of host species and variable environmental conditions.     

The effect of permafrost on stream biogeochemistry: A case study of two streams in the Alaskan (U.S.A.) taiga

Understanding interactions between permanently frozen soils and stream chemistry is important in predicting the effects of management, natural disturbance and changing permafrost distribution on stream ecosystems and nutrient budgets in subarctic watersheds. Chemical measurements of groundwater, soil water and stream water were made in two watersheds in the taiga of interior Alaska. One watershed (HiP) had extensive permafrost and the other (LoP) had limited permafrost. Soil water collected within the rooting zone (0.3--0.5 m) in both watersheds was high in dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN) but low in dissolved minerals (dominantly Ca, Mg and Na) and conductivity. The reverse was true for groundwater from springs and wells. Permafrost in the HiP basin prevented deep percolation of water and generated stormflows rich in DOC. The presence of permafrost in HiP resulted in higher fluxes of DOC, DON and DIN into stream water from upland soils.     

Riparian nitrogen dynamics in two geomorphologically distinct tropical rain forest watersheds: subsurface solute patterns

Nitrate, ammonium, dissolved organic N, and dissolved oxygen were measured in stream water and shallow groundwater in the riparian zones of two tropical watersheds with different soils and geomorphology. At both sites, concentrations of dissolved inorganic N (DIN; NH₄ ⁺- and NO₃ ⁻-N) were low in stream water (< 110 ug/L). Markedly different patterns in DIN were observed in groundwater collected at the two sites. At the first site (Icacos watershed), DIN in upslope groundwater was dominated by NO₃ ⁻-N (550 ug/L) and oxygen concentrations were high (5.2 mg/L). As groundwater moved through the floodplain and to the stream, DIN shifted to dominance by NH₄ ⁺-N (200–700 ug/L) and groundwater was often anoxic. At the second site (Bisley watershed), average concentrations of total dissolved nitrogen were considerably lower (300 ug/L) than at Icacos (600 ug/L), and the dominant form of nitrogen was DON rather than inorganic N. Concentrations of NH₄ ⁺ and NO₃ ⁻ were similar throughout the riparian zone at Bisley, but concentrations of DON declined from upslope wells to stream water. Differences in speciation and concentration of nitrogen in groundwater collected at the two sites appear to be controlled by differences in redox conditions and accessibility of dissolved N to plant roots, which are themselves the result of geomorphological differences between the two watersheds. At the Icacos site, a deep layer of coarse sand conducts subsurface water to the stream below the rooting zone of riparian vegetation and through zones of strong horizontal redox zonation. At the Bisley site, infiltration is impeded by dense clays and saturated flow passes through the variably oxidized rooting zone. At both sites, hydrologic export of nitrogen is controlled by intense biotic activity in the riparian zone. However, geomorphology appears to strongly modify the importance of specific biotic components.     

Riparian Areas and Conservation of Herpetofauna in a Tropical Dry Forest in Western Mexico

Studies that assess the importance of riparian habitats in maintaining diversity of herpetofaunal assemblages in tropical dry forests are limited. We examined changes in abundance, diversity and composition of anuran, lizard and snake assemblages along stream edge–upslope gradients in conserved and disturbed areas of tropical dry forest on the Pacific coast of México. We sampled 659 plots in six watersheds over 2 yr. Two forest conditions (conserved and human disturbed, with three watersheds as replicates) were evaluated in the dry and rainy season. Within each watershed, plots were randomly located at three different distance categories from either stream edge: 0–10 m (near‐stream environment), 30–40 m (mid‐slope environment), and 50–60 m (upslope environment). Herpetofauna was surveyed by time‐constrained searches with a sampling effort of 1980 person‐hours. Eighteen anuran, 18 lizard and 23 snake species were recorded. Overall, abundance and diversity of lizards and snakes decreased from near‐stream to upslope areas in both forest conditions and seasons; while that of anurans followed this trend only for the conserved forest during the rainy season. Regardless of distance, abundance and diversity of anurans markedly decreased during the dry season, while that of snakes and lizards increased. Overall, our study shows that the importance of riparian areas for herpetofaunal conservation in dry tropical forests varies with forest condition and season.     

Restoration ecology in the Anthropocene: learning from responses of tropical forests to extreme disturbance events

Extreme disturbance events denote another aspect of global environmental changes archetypal of the Anthropocene. These events of climatic or anthropic origin are challenging our perceived understanding about how forests respond to disturbance. I present a general framework of tropical forest responses to extreme disturbance events with specific examples from tropical dry forests. The linkage between level of disturbance severity and dominant mechanism of vegetation recovery is reflected on a variety of initial trajectories of forest succession. Accordingly, more realistic and cost‐effective restoration goals in many tropical forests likely consist in maintaining a mosaic of different successional trajectories while promoting landscape connectivity, rather than encouraging full‐ecosystem recovery to pre‐disturbance conditions. Incorporating extreme disturbance events into the global restoration ecology agenda will be essential to design well‐informed ecosystem management strategies in the coming decades.     

Changes in Structure,Composition, and Nutrients During 15 Yr of Hurricane-Induced Succession in a Subtropical Wet Forest in Puerto Rico

The trajectory of hurricane-induced succession was evaluated in a network of forest plots measured immediately before and 3 mo, 5, 10, and 15 yr after the direct impact of a Category 4 hurricane. Comparisons of forest structure, composition, and aboveground nutrients pools were made through time, and between species, life-history groups and geomorphic settings. The hurricane reduced aboveground biomass by 50 percent, causing an immediate decrease in stem density and diversity indices among all geomorphic settings. After 15 yr, basal area and aboveground biomass returned to pre-hurricane levels, while species richness, diversity indices, and stem densities exceeded pre-hurricane levels. Differences in species composition among geomorphic settings had not returned after 15 yr but differences in stem densities and structure were beginning to emerge. Significant differences were observed in the nutrient concentration of the three species that comprised the most aboveground biomass, and between species categorized as secondary high-light species and primary, low-light species. Species whose abundance was negatively correlated with the mature forest dominant also had distinct nutrient concentrations. When total aboveground nutrient pools were compared over time, differences in leaf nutrients among species were hidden by similarities in wood nutrient concentrations and the biomass dominance of a few species. The observed successional trajectory indicates that changes in species composition contributed to fast recovery of aboveground biomass and nutrient pools, while the influence of geomorphic setting on species composition occurs at time scales >15 yr of succession.     

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.     

Spatial and temporal patterns of nitrogen concentrations in pristine and agriculturally-influenced prairie streams

Long-term data on nitrogen chemistry of streams draining Konza Prairie Biological Station (Konza), Kansas were analyzed to assess spatial and temporal patterns and examine the influence of agricultural activity on these patterns. Upland watersheds of Konza are predominantly tallgrass prairies, but agricultural fields and riparian forests border the lower reaches of the streams. We have up to 11 years of data in the relatively pristine upland reaches and 4 years of data on wells and downstream reaches influenced by fertilized croplands. Seasonal and spatial patterns in total nitrogen (TN) concentrations were driven largely by changes in the nitrate (NO₃ ^–) concentrations. A gradient of increasing NO₃ ^– concentrations occurred from pristine upland stream reaches to the more agriculturally-influenced lowland reaches. Nitrate concentrations varied seasonally and were negatively correlated with discharge in areas influenced by row-crop agriculture (p = 0.007). The NO₃ ^– concentrations of stream water in lowland reaches were lowest during times of high precipitation, when the relative influence of groundwater drainage is minimal and water in the channel is primarily derived from upland prairie reaches. The groundwater from cropland increased stream NO₃ ^– concentrations about four-fold during low-discharge periods, even though significant riparian forest corridors existed along most of the lower stream channel. The minimum NO₃ ^– concentrations in the agriculturally influenced reaches were greater than at any time in prairie reaches. Analysis of data before and after introduction of bison to four prairie watersheds revealed a 35% increase of TN concentrations (p < 0.05) in the stream water channels after the introduction of bison. These data suggest that natural processes such as bison grazing, variable discharge, and localized input of groundwater lead to variation in NO₃ ^– concentrations less than 100-fold in prairie streams. Row-crop agriculture can increase NO₃ ^– concentrations well over 100-fold relative to pristine systems, and the influence of this land use process over space and time overrides natural processes.