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Climate change and disturbance make it difficult to project long‐term patterns of carbon sequestration in tropical forests, but large ecosystem experiments in these forests can inform predictions. The Canopy Trimming Experiment (CTE) manipulates two key components of hurricane disturbance, canopy openness and detritus deposition, in a tropical forest in Puerto Rico. We documented how the CTE and a real hurricane affected tree recruitment, biomass, and aboveground carbon storage over 15 years. In the CTE treatments, we trimmed branches, but we did not fell trees. We expected that during the 14‐year period after initial canopy trimming, regrowth of branches and stems and stem recruitment stimulated by increased light and trimmed debris would help restore biomass and carbon loss due to trimming. Compared to control plots, in the trimmed plots recruitment of palms and dicot trees increased markedly after trimming, and stem diameters of standing trees increased. Data showed that recruitment of small trees adds little to aboveground carbon, compared to the amount in large trees. Nevertheless, this response restored pretreatment biomass and carbon in the experimental period. In particular, the experimental additions of trimmed debris on the forest floor seemed to stimulate increase in aboveground carbon. Toward the end of the experimental period, Hurricane Maria (Category 4 hurricane) trimmed and felled some trees but reduced aboveground carbon less in the plots (including untrimmed plots) than experimental trimming had. Thus, it appears that the amount of regrowth recorded after experimental trimming could also restore aboveground carbon in the forest after a severe hurricane in the same time span. However, Hurricane Maria, unlike the trimming treatments, felled large trees, and it may be that with predicted, more frequent severe hurricanes, that the continued loss of large trees would over the long term decrease aboveground carbon stored in this Puerto Rican forest and likewise in other tropical forests affected by cyclonic storms.

Recognition of the importance of land-use history and its legacies in most ecological systems has been a major factor driving the recent focus on human activity as a legitimate and essential subject of environmental science. Ecologists, conservationists, and natural resource policymakers now recognize that the legacies of land-use activities continue to influence ecosystem structure and function for decades or centuries—or even longer—after those activities have ceased. Consequently, recognition of these historical legacies adds explanatory power to our understanding of modern conditions at scales from organisms to the globe and reduces missteps in anticipating or managing for future conditions. As a result, environmental history emerges as an integral part of ecological science and conservation planning. By considering diverse ecological phenomena, ranging from biodiversity and biogeochemical cycles to ecosystem resilience to anthropogenic stress, and by examining terrestrial and aquatic ecosystems in temperate to tropical biomes, this article demonstrates the ubiquity and importance of land-use legacies to environmental science and management.

Humid tropical forests play a dominant role in many global biogeochemical cycles, yet long-term records of tropical stream chemistry and its response to disturbance events such as severe storms and droughts are rare. Here we document the long-term variability in chemistry of two streams in the Luquillo Mountains, Puerto Rico over a period of 27 years. Our two focal study watersheds, the Río Icacos and Quebrada Sonadora, both drain several hundred hectares of tropical wet forests, and each received direct hits from Hurricanes Hugo (1989) and Georges (1998). They differ primarily in lithology (granitic vs. volcaniclastic) and elevation. Changes in major cations, anions, silica, and dissolved organic carbon were minimal over the study period, but the concentrations of nitrate show a strong response to hurricane disturbance and the longest time to recovery. Potassium also showed a large, although less consistent, response to disturbance. In the granitic terrain, nitrate concentrations exceeded long-term pre-hurricane background levels for over a decade, but were elevated in the volcaniclastic terrain for only 1–2 years. Lithology appears to be the primary driver explaining the different response trajectories of the two watersheds. In the granitic terrain, which showed slow recovery to pre-hurricane conditions, the quartz diorite bedrock weathers to produce coarser soils, deeper groundwater flow paths, and riparian zones with sharp spatial variation in redox conditions and very high nitrogen levels immediately adjacent to the stream. Groundwater flow paths are shallow and the levels of N in streamside groundwater are much lower in the volcaniclastic terrain. The recovery of vegetation following hurricane disturbance appears similar in the two watersheds, suggesting that the extent of structural damage to canopy trees determines the magnitude of NO₃ increases, but that the duration of elevated concentrations in stream water is a function of lithology.

Global change threatens ecosystems worldwide, and tropical systems with their high diversity and rapid development are of special concern. We can mitigate the impacts of change if we understand how tropical ecosystems respond to disturbance. For tropical forests and streams in Puerto Rico this book describes the impacts of, and recovery from, hurricanes, landslides, floods, droughts, and human disturbances in the Luquillo Mountains of Puerto Rico. These ecosystems recover quickly after natural disturbances, having been shaped over thousands of years by such events. Human disturbance, however, has longer-lasting impacts. Chapters reflect many years of experience in Puerto Rico and other tropical areas and cover the history of research in these mountains, a framework for understanding disturbance and response, the environmental setting, the disturbance regime, response to disturbance, biotic mechanisms of response, management implications, and future directions. The text provides a strong perspective on tropical ecosystem dynamics over multiple scales of time and space.

The US Long Term Ecological Research (LTER) Network enters its fourth decade with a distinguished record of achievement in ecological science. The value of long-term observations and experiments has never been more important for testing ecological theory and for addressing today's most difficult environmental challenges. The network's potential for tackling emergent continent-scale questions such as cryosphere loss and landscape change is becoming increasingly apparent on the basis of a capacity to combine long-term observations and experimental results with new observatory-based measurements, to study socioecological systems, to advance the use of environmental cyberinfrastructure, to promote environmental science literacy, and to engage with decisionmakers in framing major directions for research. The long-term context of network science, from understanding the past to forecasting the future, provides a valuable perspective for helping to solve many of the crucial environmental problems facing society today.

The literature on the effects of catastrophic wind disturbance (windstorms, gales, cyclones, hurricanes, tornadoes) on forest vegetation is reviewed to examine factors controlling the severity of damage and the dynamics of recovery. Wind damage has been quantified in a variety of ways that lead to differing conclusions regarding severity of disturbance. Measuring damage as structural loss (percent stems damaged) and as compositional loss (percent stems dead) is suggested as a standard for quantifying severity. Catastrophic wind produces a range of gaps from the size caused by individual treefalls to much larger areas. The spatial pattern of damage is influenced by both biotic and abiotic factors. Biotic factors that influence severity of damage include stem size, species, stand conditions (canopy structure, density), and the presence of pathogens. Abiotic factors that influence severity of damage include the intensity of the wind, previous disturbance, topography, and soil characteristics. Recovery from catastrophic wind disturbance follows one of four paths: regrowth, recruitment, release, or repression. The path of recovery for a given site is controlled both by the severity of disturbance and by environmental gradients of resources. Recovery is influenced also by frequency of wind disturbance, which varies across geographical regions. To develop robust theories regarding catastrophic wind disturbance, the relative roles of different abiotic and biotic factors in controlling the patterns of severity of damage must be determined. These patterns of severity and environmental gradients must then be tied to long-term dynamics of recovery. /// La literatura sobre los efectos de disturbios catastróficos del viento (tormentas, ventarrones, ciclones, huracánes, tornados) sobre la vegetación de bosque es revisada para examinar los factores que controlan la severidad del daño y la dinámica de recuperación. El daño del viento puede ser cuantificado en varias formas, lo cual conlleva a diferir en las conclusiones en cuanto a la severidad del disturbio. Medir daños como la pérdida estructural (por ciento de tallos dañados) y la pérdida composicional (porcentaje de tallos muertos) son normas sugeridas para cuantificar la severidad. Los vientos catastróficos producen una extensión de aperturas de gran tamaño causados por árboles caídos sobre muchas otras áreas mayores. El patrón espacial de daño es influenciado por factores abióticos y bióticos. Factores bióticos que influyen severamente al daño pueden ser tamaño del tallo, especie, condición de tolerancia (estructura del dosel, densidad), y la presencia de patogénos. Factores abióticos que influyen severamente sobre el daño incluyen la intensidad del viento, disturbios anteriores, topografía, y las características del suelo. La recuperación de las catástrofes causados por el viento siguen uno de cuatro patrones: crecimiento, reclutaje, liberar o reprimir. La trayectoria de recuperación para un lugar es controlado por ambos: por lo severo del disturbio y por los gradientes ambientales del recurso. La recuperación es influenciada también por la frecuencia del disturbio por viento, el cual varia sobre el globo. Para desarrollar una fuerte teoría en cuanto a disturbios catastróficos por viento, los roles relativos de los factores abióticos y bióticos en el control de modelos de severidad de daño tienen que ser determinados. Estos modelos de severidad y gradientes ambientales tienen que ser enlazados para una dinámica de recobro a largo plazo. /// Обзор литературы о воздействии катастрофических ветров (штормов, циклонов, ураганов, смерчей) на лесную растительность с целью выявления факторов, влияющих на величину ущерба и на динамику рекомпенсации. Ущерб от ветра оценивается различными методами, приводящими к разным выбодам. Измерение ущерба как структурного воздействия (процент поврежденных стволов) и как композиционного воздействия (процент погибших стволов) предложено в качестве стандарта. Катастрофический ветер образует серию проплешин, размер которых колеблется в широком диапазоне. Пространственная конфигурация ущерба находится под воздействием как биотических, так и абиотических факторов. Биотические факторы величины ущерба включают: размер ствола, особенности особи, условия древостоя (структура и плотность листвы) и присутствие патогенов. Абиотические факторы величины ущерба включают интенсивность ветра, предшествующие атмосферные возмущения, топографию и характеристики почвы. Рекомпенсация после катастрофического ветрового воздействия следует по одному из четырех путей: спонтанное возобновление, спонтанное замещение дпугими древесными особями, подавление нижних ярусов древостоя (нуждающееся в их \"высвобождении\" от листвы верхнего яруса), нашествие сорняковой растительности. Какой из путей рекомпенсации возобладает, зависит от масштаба атмосферного возмущения и от целого ряда средовых градиентов. Рекомпенсация также зависит от глобально изменчивой частоты ветровых возмущений. Для создания продуктивных теорий измерения ветрового ущерба необходима оценка различных биотических и абиотических факторов, влияющих на величину и конфигурацию ущерба. Последняя, а также средовые градиенты должны быть увязаны с долгосрочной динамикой рекомпенсации.

1 We used inverse modelling to parameterize spatially-explicit seedling recruitment functions for nine canopy tree species in the Luquillo Forest Dynamics Plot (LFDP), Puerto Rico. We modelled the observed spatial variation in seedling recruitment following Hurricane Georges as a function of the potential number of seedlings at a given location (based on local source trees and the potential contribution of parents from outside of the mapped area) and of light levels and density-dependent mortality during establishment. We adopted the model comparison paradigm and compared the performance of increasingly complex models against a null model that assumes uniform seedling distribution across the plot. 2 Our data supported a model in which parents must reach a threshold size before any seedling production will occur. Once parents attain that size, the relationship between tree diameter and the number of seedlings produced is fairly flat for the majority of species. These results contradict previous analyses that simply assumed a linear relationship between biomass and seedling production and a uniform size threshold for seedling production across species. 3 The majority of species tested supported models that included at least one of a bath term (contribution from non-local trees), conspecific density dependence and light availability after the hurricane. Density dependence shifted the mode of the effective dispersal kernel away from potential parent trees and significantly reduced the number of seedlings established near parent trees. Recruitment from non-local sources accounted for 6-81% of observed seedling recruitment depending upon the tree species. Light availability appeared to divide species into three groups that showed more successful seedling establishment at low (< 5% of full sun), intermediate or high light levels (> 30% full sun). 4 Differences between individual species in the importance of local vs. bath recruitment and the intensity of density dependence suggest the existence of distinct recruitment syndromes that go beyond the traditional focus of tropical tree life histories. Understanding these syndromes will provide valuable insights into the spatial distribution of tropical tree species and the maintenance of tropical forest diversity.

The effects of historical land use on tropical forest must be examined to understand present forest characteristics and to plan conservation strategies. We compared the effects of past land use, topography, soil type, and other environmental variables on tree species composition in a subtropical wet forest in the Luquillo Mountains, Puerto Rico. The study involved stems ≥10 cm diameter measured at 130 cm above the ground, within the 16-ha Luquillo Forest Dynamics Plot (LFDP), and represents the forest at the time Hurricane Hugo struck in 1989. Topography in the plot is rugged, and soils are variable. Historical documents and local residents described past land uses such as clear-felling and selective logging followed by farming, fruit and coffee production, and timber stand improvement in the forest area that now includes the LFDP. These uses ceased 40-60 yr before the study, but their impacts could be differentiated by percent canopy cover seen in aerial photographs from 1936. Using these photographs, we defined four historic cover classes within the LFDP. These ranged from cover class 1, the least tree-covered area in 1936, to cover class 4, with the least intensive historic land use (selective logging and timber stand improvement). In 1989, cover class 1 had the lowest stem density and proportion of large stems, whereas cover class 4 had the highest basal area, species richness, and number of rare and endemic species. Ordination of tree species composition (89 species, 13 167 stems) produced arrays that primarily corresponded to the four cover classes (i.e., historic land uses). The ordination arrays corresponded secondarily to soil characteristics and topography. Natural disturbances (hurricanes, landslides, and local treefalls) affected tree composition, but these effects did not correlate with the major patterns of species distributions on the plot. Thus, it appears that forest development and natural disturbance have not masked the effects of historical land use in this tropical forest, and that past land use was the major influence on the patterns of tree composition in the plot in 1989. The least disturbed stand harbors more rare and endemic species, and such stands should be protected.

Where large disturbances do not cause landscape-wide mortality and successional change, forested ecosystems should exhibit landscape metastability (landscape equilibrium) at a scale equal to the dominant patch size of disturbance and recovery within the landscape. We investigated this in a 16-ha contiguous plot of subtropical wet forest in Puerto Rico, the Luquillo Forest Dynamics Plot (LFDP), which experienced two major hurricanes during the 15-year study and has a land use history (logging and agriculture 40 or more years hence) that differs in intensity between two areas of the plot. Using he LFDP as our “landscape,” we studied the spatial pattern of community change through time (3-5 year intervals) by calculating community dissimilarity between tree censuses for two size classes of trees (1 to <10 cm DBH and ≥10 cm DBH) in quadrats ranging in size from 0.010-1 ha and for the entire landscape, i.e., plot or land use type. The point at which the decline in community dissimilarity with quadrat size showed maximum curvature identified the dominant patch size (i.e., point of metastability). For canopy trees ≥10 cm dbh, there was no evidence that the community experienced landscape-wide successional changes in either land use type, and we found a consistent patch size of community change around 0.1 ha (range 0.091-0.107). For the understory tree and shrub community (1 to <10 cm dbh) there was some evidence of landscape-wide community changes over time in response to hurricane damage, apparently driven by interactions with the dominant canopy species, whose composition varied with land use intensity, and their species-specific susceptibility to hurricane damage.

Cecropia schreberiana Miq. (Cecropiaceae) is a common tree in the Luquillo Mountains of Puerto Rico because it is a pioneer that establishes abundantly after recurrent hurricanes that damage Luquillo forests. In these forests C. schreberiana typically reaches about 20 m in height and 60 cm dbh and has few branches, these bearing large, deeply lobed leaves. The wood is light and weak. Unlike most of its congeners, C. schreberiana in Puerto Rico does not have symbiotic ants. It is dioecious and produces wind-pollinated flowers in spikes and abundant minute seeds broadly dispersed by birds and bats. Forest soils contain a high density of its seeds, which lie dormant until canopy opening stimulates germination. With adequate nutrients C. schreberiana grows fast in high light, while nondominant individuals suffer heavy mortality. An individual of the species is thought to live 30 to 50 years. Cecropia schreberiana is uncommon in abandoned pastures in the Luquillo Mountains. It colonizes road cuts, landslides, and infrequent, large treefall gaps. Yet these disturbances provide only a limited \"background regeneration,\" which is not sufficient to maintain the species' observed high abundance in Luquillo forests. However, there is widespread and abundant C. schreberiana regeneration after hurricane damage opens the forest canopy. Despite high mortality among these post-hurricane colonizers, enough survive and grow so that C. schreberiana is generally among the ten most common canopy trees in the widespread \"tabonuco\" forest type. Post-hurricane colonizers mature, senesce, and decline in number, but C. schreberiana remains abundant as seeds in the soil ready to form tree cohorts after disturbance. The status of the C. schreberiana population indicates the developmental status of the forest as a whole. Moreover, C. schreberiana performs a key function in the reorganization of Luquillo forest ecosystems after disturbance, when its abundant regeneration and rapid growth capture and store nutrients. Also, its colonizing saplings may facilitate succession to mature forest by excluding grasses, herbs, and vines that hinder forest development. The biology of this species both reflects and helps drive the dynamics of forests in the Luquillo Mountains. /// Cecropia schreberiana Miq. (Cecropiaceae) es un árbol común en las Montañas Luquillo de Puerto Rico, porque es una especie pionera que se establece abundantamente despues de huracanes que dañan frecuentamente los bosques Luquillos. En estos bosques C. schreberiana normalamente alcanza 20 m de altura y 60 cm dap. Tiene pocas ramas, las que sostienen hojas grandes y lobadas. La madera es leve y débil. A diferencia de la mayoría de sus congeneros, C. schreberiana no tiene hormigas simbióticas. Es dioico y produce flores en espigas, polenados por el viento, y las semillas abundantes son dispersadas por aves y murciélagos. Los suelos en bosques contienen muchos de sus semillas, las que tienen germinación retardada hasta de que un claro del dosel la estimule. Con alimentos adecuados, C. schreberiana crece rapidamente en la luz alta; a la otra mano, los árboles que no se encuentran en luz alta sufren un nivel alto de mortalidad. Parece que vive hasta 30 a 50 años. Cecropia schreberiana es poco común en pastizales abandanados en las Montañas Luquillo. Coloniza los margenes de caminos, deslizamientos de tierra, y claros grandes aunque raros hechos por árboles caidos. Sin embargo, estos perturbaciones permiten solamente una \"regeneración de transfondo\" que está limitada y no suficiente sostenir la abundancia alta de la especie que se ve en los bosques Luquillos. Pero hay regeneración abundante y dispersa de C. schreberiana despues de los huracanes dañan el dosel del bosque. Luego, a pesar de la mortalidad alta, hay regeneración y sobrevivicencia suficiente para que C. schreberiana sea normalamente uno de los árboles más común en el bosque del tipo \"taboncuo.\" Estes colonizadores maduran y disminuyen en abundancia, sin embargo hay semillas abundante de C. schreberiana en el suelo, listas para formar un población de árboles despues de una perturbación. El estado de la población de C. schreberiana indica el estado de desarrollo del bosque en general. Además, C. schreberiana realiza una función clave en la reorganización de la ecosistema en los bosques Luquillos despues de una perturbación, cuando su regeneración abundante, y su crecimiento rapido, capturan y guardan alimentos. Además, sus arbolitos colonizadores pueden facilitar la sucesión vegetal, por excluir lianas y hierbas que impeden el desarrollo de bosque. La biología de esta especie refleja y influye la dinámica de los bosques en las Montañas Luquillo.