Ecosystemic structural-functional approach of the state and transition model

Abstract

Objective: To contribute to the integration of key ecological concepts such as dynamic equilibrium, critical threshold, resistance and resilience to the ‘State and Transition Model’ (STM), in order to apply them in a more feasible way for rangeland management. Methods: Review and discussion of conceptual models and applied literature, including examples of rangeland dynamics. Results and Conclusions: We propose to enhance the STM considering two principal axes: (a) the x axis determined by structural ecosystem changes (vegetation and soil) and (b) the y axis determined by ecosystem functions and/or processes (recruitment, rain use efficiency). These axes define what we will call Structural–Functional State and Transition Model (SFSTM). Both axes of SFSTM make it possible to determine and quantify states and transitions, critical thresholds and to evaluate the resistance and resilience of an ecosystem to a given disturbance. The critical threshold is identified by structural and functional thresholds (x and y axes), thus defining the point where the ecosystem loses its resilience. Furthermore, in the supplementary file we provide examples with field data from Patagonia to illustrate the SFSTM. The proposed SFSTM has large implications for rangeland research and management, facilitating the understanding and integration of key concepts to enhance the STM. The identification of variables to assess structure and processes makes the model more useful.

Species, functional groups and community structure in seed banks of the arid Nama Karoo: Grazing impacts and implications for rangeland restoration

“…Currently, these pools represent local variations, as the overall species composition remained largely unchanged. It still has to be established whether the detected differences represent community fluctuations within the same ecosystem state or two alternative resilient states (López et al, 2011).…”

“…Visual inspections are unable to provide adequate information on the nature of rangeland deterioration, i.e. whether it is permanent or short-term, and thus reversible, as they focus solely on structural properties (sensu López et al, 2011) of the ecosystem. Functional indicators related to recruitment processes, such as local seed reserves of key species, are necessary to estimate ecosystem resilience and to detect negative transitions in rangeland condition, which could cross a threshold beyond which active interventions becomes indispensable for rangeland improvement (Briske et al, 2008;López et al, 2011).…”

“…whether it is permanent or short-term, and thus reversible, as they focus solely on structural properties (sensu López et al, 2011) of the ecosystem. Functional indicators related to recruitment processes, such as local seed reserves of key species, are necessary to estimate ecosystem resilience and to detect negative transitions in rangeland condition, which could cross a threshold beyond which active interventions becomes indispensable for rangeland improvement (Briske et al, 2008;López et al, 2011). We addressed the issue of soil seed banks as an indicator of rangeland condition and regeneration potential using a stable fence-line contrast between a highly degraded communal rangeland and an adjacent reference site in the arid Namibian Nama Karoo.…”

Modelo de estados y transiciones de los ñirantales del NO de la Patagonia como herramienta para el uso silvopastoril sustentable

“…Las transiciones negativas consisten en un cambio abrupto de atributos clave de estructura y función del sistema, que resulta de las prácticas de manejo y de su interacción con disturbios naturales. Estos cambios en los atributos estructurales y funcionales marcan umbrales en la capacidad del ecosistema de reorganizarse y de retornar de manera natural al estado previo (Briske et al 2006;López et al 2011. Así mismo, dado que los umbrales difícilmente se revierten de forma natural (al menos en un lapso de más de 100 años, período del cual contamos con información), las transiciones positivas suelen requerir prácticas de intervención para restablecer las propiedades del ecosistema correspondientes a un estado previo (i.e., restauración propiamente dicha), o para mejorar la generación servicios ecosistémicos (i.e., re-habilitación) (Bestelmeyer et al 2010;Hobbs and Suding 2013).…”

“…Otros procesos o factores clave asociados a los umbrales son la tolerancia de la caña coligüe a distintas presiones de pastoreo y el proceso de competencia pastizal/arbustos ante diferentes intensidades de pastoreo. Los enfoques como el propuesto por López et al (2011, 2013) y Cavallero et al (2015 permitirían diferenciar estados y fases dentro de los mismos y cuantificar umbrales. Mientras tanto, aquellos como los propuesto por Rumpf et al 2011y Rusch et al (2017, que incorporan el grado de incertidumbre, ayudarían a establecer en forma más ajustada las probabilidades de las transiciones.…”