Aplicación del Método Hectárea de Hábitat en compensación ambiental: El caso del Embalse Río Piedras, Costa Rica

Introducción: La compensación ambiental es la alternativa final para enfrentar los impactos de proyectos de desarrollo que no pueden ser evitados, reducidos o mitigados. La compensación de hábitats pretende sustituir recursos ecológicamente equivalentes. El Método Hectárea de Hábitat se diseñó inicialmente para evaluar la equivalencia ecológica de vegetación nativa y emplea puntajes de indicadores relativos a un hábitat de referencia. La suma de estos puntajes mide la condición estructural del ambiente de manera relativa a la referencia, cuantificando el número de hectáreas necesarias para compensar la pérdida de un hábitat similar. Aunque el método no está exento de limitaciones, los valores se pueden estimar a partir de datos de campo recogidos sin ambigüedad, de forma reproducible, con menos sesgos que métodos más cualitativos. En este artículo, usamos una modificación del Método Hectárea de Hábitat para determinar el área equivalente necesaria para compensar la pérdida de hábitat en un área silvestre protegida en Costa Rica. Metodología: Trabajamos en la Reserva Biológica Lomas de Barbudal, Pacífico norte de Costa Rica, un área silvestre protegida donde se inundarán cerca de 113 hectáreas para el Embalse de Río Piedras. En una propiedad previamente identificada como un sitio potencial de compensación, evaluamos indicadores de paisaje, suelo, estructura de la vegetación y servicios ecosistémicos; asignamos los puntajes en relación con el sitio a inundar. Resultados: El puntaje de la condición ambiental en el sitio de compensación fue de 44,7% (±15,9%) del sitio inundado. En consecuencia, considerando la incertidumbre de nuestras mediciones, compensar la pérdida de cada hectárea requeriría entre 2.23 y 3.49 hectáreas de un ambiente similar. Conclusión: Se necesitan entre 2.23 y 3.49 hectáreas de reemplazo, para compensar la pérdida de hábitat en el Embalse de Río Piedras.

Introduction: Environmental compensation is the final alternative to face the impacts of development projects that cannot be avoided, reduced, or mitigated. The offset of affected habitats or environmental elements usually substitutes ecologically equivalent resources. The Habitat-Hectare Method was initially designed to assess the ecological equivalence of native vegetation, and employs indicator scores relative to a reference habitat. The sum of these scores measures the structural condition of the environment against the reference, quantifying the number of hectares needed to compensate for the loss of similar habitat. Although it is not exempt from limitations, the values can be estimated from field data collected without ambiguity, in a reproducible way, with less bias than more qualitative methods. In this paper, we use a modification of the Habitat-Hectare Method to determine the equivalent area needed to compensate for habitat loss in a protected wilderness in Costa Rica. Methods: We worked in the Lomas de Barbudal Biological Reserve, north Pacific of Costa Rica, a protected wilderness where nearly 113 hectares will be flooded for the Río Piedras Reservoir. In a property previously identified as a potential compensation site, we assessed indicators for landscape, soil, vegetation structure, and ecosystem services; the scores were assigned in relation to the environment found at the flood site. Results: The environmental condition score at the compensation site was 44.7% (±15.9%) of the impact site. Consequently, considering the uncertainty in our measurements, compensating for the loss of each hectare would require between 2.23 and 3.49 hectares of a similar environment. Conclusion: Between 2.23 and 3.49 hectares of are needed to compensate for the loss of habitat in the Río Piedras Reservoir.

Uso de la diversidad biológica de grupos indicadores para evaluar la compensación ecológica: el caso del Embalse Río Piedras, Costa Rica

Introducción: Cerca de 113 hectáreas dentro de la Reserva Biológica Lomas de Barbudal (RBLB) se inundarían si se llegara a establecer el embalse de riego Río Piedras en el noroeste de Costa Rica. Ante ese impacto inevitable, la legislación costarricense requiere evaluar la pérdida de diversidad en el sitio y compensarla siguiendo el principio de equivalencia ecológica. Objetivo: Nuestro objetivo fue evaluar la pérdida de diversidad en el sitio y, valorar esta condición en una propiedad privada adyacente considerada como sitio potencial para compensar por esas pérdidas. Metodología: La diversidad, composición y prioridad de conservación de plantas vasculares, fauna vertebrada y artrópodos del sotobosque fueron evaluadas en el sitio de inundación en RBLB y en una propiedad privada adyacente identificada como sitio potencial de compensación. La equivalencia en diversidad entre ambos sitios se valoró mediante un procedimiento que asigna puntajes a los diferentes indicadores del sitio de compensación respecto a los observados en RBLB. La suma de esos puntajes representa la condición de diversidad del sitio de compensación y puede utilizarse como criterio para fundamentar acciones resarcitorias. Resultados: Todos los grupos sustitutos registraron un alto número de especies, aunque la información aportada por las plantas herbáceas, los mamíferos no voladores y los reptiles fue limitada. En contraste, los otros grupos indican una mayor diversidad en el sitio potencial de inundación, atribuida a sutiles diferencias ambientales y a su mejor conservación. En consecuencia, se valoró sustituir el área afectada por un área mayor del sitio de compensación para resarcir las perdidas en diversidad estimadas. Conclusión: Nuestro análisis muestra que grupos sustitutos pueden ser empleados en estudios ambientales a corto plazo. Sin embargo, los grupos a utilizar deben seleccionarse cuidadosamente, considerando los objetivos y el alcance del proyecto. Cuantificar la condición de diversidad del sitio de compensación respecto a la que se encuentra en un sitio de referencia parece ser un procedimiento válido, repetible y evaluable que permite establecer criterios sobre los cuales basar medidas resarcitorias.

Introduction: About 113 hectares within the Lomas de Barbudal Biological Reserve (RBLB) would be flooded if the Río Piedras irrigation reservoir were established in northwestern Costa Rica. Given this inevitable impact, Costa Rican legislation requires evaluating the loss of diversity in the site and compensating for it following the principle of ecological equivalence. Objetive: Our goal was to assess the loss of diversity at that site and evaluate the condition of an adjacent private property as a potential site to compensate for those losses. Methodology: The diversity, composition, and conservation priority of vascular plants, vertebrate fauna, and understory arthropods were assessed at the RBLB flood site and on an adjacent private property identified as a potential offset site. The equivalence in diversity between both sites was evaluated by assigning scores to the different indicators at the compensation site concerning those observed in RBLB. The sum of these scores represents the diversity condition of the compensation site and can be used as a criterion to support compensatory actions. Results: All surrogate groups recorded a high number of species, although the information provided by herbaceous plants, non-flying mammals, and reptiles was limited. In contrast, the other groups indicate a greater diversity in the potential flood site, attributed to subtle environmental differences and the better conservation at this site. Consequently, it was assessed to replace the affected area with a larger offset site area to compensate for the estimated losses in diversity. Conclusion: Our analysis shows that surrogate groups can be used in short-term environmental studies. However, the groups to be used must be carefully selected, considering the objectives and scope of the project. Quantifying the diversity condition of the compensation site concerning that found in a reference site seems to be a valid, repeatable, and evaluable procedure that allows establishing criteria on which to base compensatory measures.

Compensación ambiental por la segregación y uso de un área dentro de un refugio de vida silvestre: un caso de estudio empleando coste de oportunidad

Introducción: El establecimiento del Puesto Fronterizo Las Tablillas implica la segregación de 12.12 ha del Refugio Nacional de Vida Silvestre Corredor Fronterizo (RNVSCF), en el norte de Costa Rica. El sitio tiene una larga historia de uso de la tierra y su entorno natural está muy degradado. Este es un caso que se puede abordar desde el coste de oportunidad que se refiere al valor de la alternativa a la que se renuncia al tomar una decisión económica. Objetivo: En este artículo, usamos este precepto para evaluar la compensación por pérdidas en la estructura del hábitat y la biodiversidad si se interrumpiera la dinámica de sucesión dentro de un área silvestre protegida. Métodos: Para encontrar la ganancia neta en compensación requerida por dicha segregación, analizamos la diversidad y composición de la cubertura forestal cercana para pronosticar el ambiente que se perdería si se interrumpieran sus objetivos de conservación (costo de oportunidad). Compensar estas pérdidas requiere un ambiente equivalente, por lo que seleccionamos dos propiedades, entre 27 investigadas adyacentes al RNVSCF, que comparten cobertura forestal, están registradas legalmente y poseen atributos ambientales favorables para el diseño de reservas. Las dos propiedades seleccionadas y el sitio Las Tablillas fueron caracterizados a nivel de atributos geológicos e hidrológicos y de composición biológica de grupos indicadores. Resultados: Ambas propiedades son física y biológicamente favorables para el intercambio. La escogencia de cualquiera aumentaría el área del RNVSCF en más de 100 ha de un ambiente con mejor cobertura, más diversidad y mejor conexión con otras masas forestales que el observado en el sitio de segregación. Esto es una ventaja para el objetivo de conservación del refugio. Conclusión: En este caso, el coste de oportunidad favoreció la ganancia ambiental para la propuesta de compensación y podría ser utilizado para evaluar otras compensaciones que involucren ambientes sensibles o protegidos.

Introduction: The establishment of the Las Tablillas Border Post implies the segregation of 12.12 ha within the National Wildlife Refuge Border Corridor (RNVSCF) in northern Costa Rica. The site has a long land use history, so its environment is highly degraded. This case can be studied from the opportunity cost, which refers to the amount of the alternative given up when making an economic decision. Objective: In this paper, we use this precept to assess the compensation for losses in habitat structure and biodiversity if succession dynamics within a protected wilderness area were interrupted. Methods: To find the net gain in compensation required by this segregation, we analyzed the diversity and composition of nearby forest cover to forecast the environment that would be lost if its conservation objectives were interrupted (opportunity cost). Compensating for these losses requires an equivalent environment, so we selected two properties, among the 27 investigated, that shared forest cover, are located adjacent to the RNVSCF, are registered, and possess other attributes favorable to the design of reserves. The two selected properties and the Las Tablillas site were characterized at the level of geological and hydrological attributes and the composition of indicator groups. Results: Both properties are physically and biologically favorable for the exchange. It would increase the area of the RNVSCF by more than 100 ha of an environment with better coverage, more diversity, and a better connection to other forest masses than the one observed in the segregation site, which is an advantage to the conservation objective of the refuge. Conclusion: In this case, the opportunity cost favored the environmental gain for the offset proposal and could be used to evaluate other compensation involving sensitive or protected environments.

Large tree mortality leads to major aboveground biomass decline in a tropical forest reserve.

Humans are transforming the ecology of the Earth through rapid changes in land use and climate. These changes can affect tropical forest structure, dynamics and diversity. While numerous studies have focused on diversity metrics, other aspects of forest function, such as long-term biomass dynamics, are often less considered. We evaluated plant community structure change (i.e., abundance, diversity, composition, and aboveground biomass) in a 2.25 ha forest dynamics plot located within a ~ 365 ha reserve in southern Costa Rica. We censused, mapped and identified to species all plants ≥ 5 cm diameter at breast height (DBH) in three surveys spanning 2010-2020. While there were no changes in late-successional species diversity, there were marked changes in overall species composition and biomass. Abundance of large (≥ 40 cm DBH) old-growth dense-wooded trees (e.g., Lauraceae, Rosaceae) decreased dramatically (27%), leading to major biomass decline over time, possibly driven by recent and recurrent drought events. Gaps created by large trees were colonized by early-successional species, but these recruits did not make up for the biomass lost. Finally, stem abundance increased by 20%, driven by increasing dominance of Hampea appendiculata. While results suggest this reserve may effectively conserve overall plant diversity, this may mask other key shifts such as large aboveground biomass loss. If this pattern is pervasive across tropical forest reserves, it could hamper efforts to preserve forest structure and ecosystem services (e.g., carbon storage). Monitoring programs could better assess carbon trends in reserves over time simply by tracking large tree dynamics.

Long-term declines in bird populations in tropical agricultural countryside.

Tropical agriculture is a major driver of biodiversity loss, yet it can provide conservation opportunities, especially where protected areas are inadequate. To investigate the long-term biodiversity capacity of agricultural countryside, we quantified bird population trends in Costa Rica by mist netting 57,255 birds of 265 species between 1999 and 2010 in sun coffee plantations, riparian corridors, secondary forests, forest fragments, and primary forest reserves. More bird populations (69) were declining than were stable (39) or increasing (4). Declines were common in resident, insectivorous, and more specialized species. There was no relationship between the species richness of a habitat and its conservation value. High-value forest bird communities were characterized by their distinct species composition and habitat and dietary functional signatures. While 49% of bird species preferred forest to coffee, 39% preferred coffee to forest and 12% used both habitats, indicating that coffee plantations have some conservation value. Coffee plantations, although lacking most of the forest specialists, hosted 185 bird species, had the highest capture rates, and supported increasing numbers of some forest species. Coffee plantations with higher tree cover (7% vs. 13%) had more species with increasing capture rates, twice as many forest specialists, and half as many nonforest species. Costa Rican countryside habitats, especially those with greater tree cover, host many bird species and are critical for connecting bird populations in forest remnants. Diversified agricultural landscapes can enhance the biodiversity capacity of tropical countryside, but, for the long-term persistence of all forest bird species, large (>1,000 ha) protected areas are essential.

A degradation debt? Large-scale shifts in community composition and loss of biomass in a tropical forest fragment after 40 years of isolation.

Habitat loss and fragmentation are among the biggest threats to tropical biodiversity and associated ecosystem services. We examined forest dynamics in a mid-elevation 365-ha fragment in southern Costa Rica. The fragment was isolated in the mid-1970s and belongs to the Las Cruces Biological Station. A 2.25-ha permanent plot was established in the center of the old-growth forest (>400 m to nearest edge boundary) and all plants >5 cm DBH were censused, mapped, and identified to species in two surveys taken ~5-6 years apart (>3,000 stems/survey). Although the reserve maintains high species richness (>200 spp.), with many rare species represented by only one individual, we document a strong shift in composition with a two-fold increase in the number of soft-wooded pioneer individuals. The dominant late-successional understory tree species, Chrysochlamys glauca (Clusiaceae), and most species in the Lauraceae, declined dramatically. Turnover was high: 22.9% of stems in the first survey were lost, and 27.8% of stems in the second survey represented new recruits. Mean tree diameter decreased significantly and there was a 10% decrease in overall biomass. Such alteration has been documented previously but only in smaller fragments or within ~100 m of an edge boundary. Further penetration into this fragment was perhaps driven by a progressive invasion of disturbance-adapted species into the fragment's core over time; the loss of once-dominant late successional species could be a contributing factor. The pattern found is of particular concern given that such fragments represent a substantial portion of today's remaining tropical habitat; further studies in similar-sized fragments that have been isolated for similar prolonged periods are called for.

Persistence of forest birds in the Costa Rican agricultural countryside.

Understanding the persistence mechanisms of tropical forest species in human-dominated landscapes is a fundamental challenge of tropical ecology and conservation. Many species, including more than half of Costa Rica's native land birds, use mostly deforested agricultural countryside, but how they do so is poorly known. Do they commute regularly to forest or can some species survive in this human-dominated landscape year-round? Using radiotelemetry, we detailed the habitat use, movement, foraging, and nesting patterns of three bird species, Catharus aurantiirostris, Tangara icterocephala, and Turdus assimilis, by obtaining 8101 locations from 156 individuals. We chose forest birds that varied in their vulnerability to deforestation and were representative of the species found both in forest and human-dominated landscapes. Our study species did not commute from extensive forest; rather, they fed and bred in the agricultural countryside. Nevertheless, T. icterocephala and T. assimilis, which are more habitat sensitive, were highly dependent on the remaining trees. Although trees constituted only 11% of land cover, these birds spent 69% to 85% of their time in them. Breeding success of C. aurntiirostris and T. icterocephala in deforested habitats was not different than in forest remnants, where T. assimilis experienced reduced breeding success. Although this suggests an ecological trap for T. assimilis, higher fledgling survival in forest remnants may make up for lower productivity. Tropical countryside has high potential conservation value, which can be enhanced with even modest increases in tree cover. Our findings have applicability to many human-dominated tropical areas that have the potential to conserve substantial biodiversity if appropriate restoration measures are taken.