Alternative states of a semiarid grassland ecosystem: implications for ecosystem services

Abstract

Abstract. Ecosystems can shift between alternative states characterized by persistent differences in structure, function, and capacity to provide ecosystem services valued by society. We examined empirical evidence for alternative states in a semiarid grassland ecosystem where topographic complexity and contrasting management regimes have led to spatial variations in levels of livestock grazing. Using an inventory data set, we found that plots (n ¼ 72) cluster into three groups corresponding to generalized alternative states identified in an a priori conceptual model. One cluster (biocrust) is notable for high coverage of a biological soil crust functional group in addition to vascular plants. Another (grass-bare) lacks biological crust but retains perennial grasses at levels similar to the biocrust cluster. A third (annualized-bare) is dominated by invasive annual plants. Occurrence of grass-bare and annualized-bare conditions in areas where livestock have been excluded for over 30 years demonstrates the persistence of these states. Significant differences among all three clusters were found for percent bare ground, percent total live cover, and functional group richness. Using data for vegetation structure and soil erodibility, we also found large among-cluster differences in average levels of dust emissions predicted by a wind-erosion model. Predicted emissions were highest for the annualized-bare cluster and lowest for the biocrust cluster, which was characterized by zero or minimal emissions even under conditions of extreme wind. Results illustrate potential trade-offs among ecosystem services including livestock production, soil retention, carbon storage, and biodiversity conservation. Improved understanding of these trade-offs may assist ecosystem managers when evaluating alternative management strategies.Key words: biological soil crusts; Bromus tectorum; Colorado Plateau; drylands; dust; ecosystem services; functional groups; livestock grazing; resilience; state and transition model; wind erosion.

Evaluating rehabilitation efforts following the Milford Flat Fire: successes, failures, and controlling factors

“…However, we propose that evaluating the longer-term effects of rehabilitation treatments on plant community cover and composition is needed given the increasing interest from society in the multiple ecosystem services public lands provide (e.g., wildlife, nativeness, forage, etc. ; Havstad et al 2007, Dodds et al 2008, Miller et al 2011.…”

Biological Soil Crust effects and responses in arid ecosystems: recent advances at the species level

“…Los ecosistemas áridos y semiáridos ocupan casi un 40 % de la superficie terrestre , y son especialmente susceptibles a degradación de sus atributos estructurales y funcionales, y la CBS juega un papel crucial en el mantenimiento de su resiliencia (Miller et al 2011). Esto es debido a que por sus atributos fisiomorfológicos, las diferentes especies de CBS representan un conjunto de diferentes grupos funcionales de gran peso y carentes de redundancia funcional a nivel del ecosistema (Miller et al 2011).…”

“…Finalmente, la CBS interacciona con otros microorganismos y microfauna del suelo, ya que les proporciona recursos y un hábitat potencial (Neher et al 2003;Bamforth 2004;Castillo-Monroy et al 2011b). Es por ello, que la CBS ha sido considerada como un "ingeniero ecosistémico" y "elemento clave" en ambientes áridos y semiáridos (Eldridge et al 2010;Miller et al 2011). …”

State and Transition Models: Theory, Applications, and Challenges

“…Different authors have used different conventions to develop model diagrams and narratives. Models can be entirely qualitative/descriptive (Knapp and FernandezGimenez 2009;Kachergis et al 2013), quantify only properties of states Miller et al 2011), or quantify states and/or transitions (Jackson and Bartolome 2002;Czembor and Vesk 2009;Rumpff et al 2011). Across all model types, however, there are a set of common elements that define an STM.…”

“…In some instances, plant communities linked via transient dynamics are represented as "states" in the broad sense (Jackson and Bartolome 2002;Bagchi et al 2012) and in other cases, alternative stable states in the narrow sense are emphasized and transient dynamics within states are described separately or ignored (Miller et al 2011).…”