Quantifying long‐term plant community dynamics with movement models: implications for ecological resilience

Abstract

Quantification of rates and patterns of community dynamics is central for understanding the organization and function of ecosystems. These insights may support a greater empirical understanding of ecological resilience, and the application of resilience concepts toward ecosystem management. Distinct types of dynamics in natural communities can be used to interpret and apply resilience concepts, but quantitative methods that can systematically distinguish among them are needed. We develop a quantitative method to analyze long-term records of plant community dynamics using principles of movement ecology. We analyzed dissimilarity of species composition through time with linear and nonlinear statistical models to assign community change to four classes of movement trajectories. Compositional change in each sampled plot through time was classified into four classes, stability, abrupt nonlinear change, transient reversible change, and gradual linear drift, each representing a different aspect of ecological resilience. These competing models were evaluated based on estimated coefficients, goodness of fit, and parsimony. We tested our method's accuracy and robustness through simulations, or the ability to distinguish among trajectories and classify them correctly. We simulated 16,000 trajectories of four types, of which 94-100% were correctly classified. Next, we analyzed 13 long-term vegetation records from North American grasslands (annual grasslands with warm-season and cool-season communities, shortgrass, mixedgrass, and tallgrass prairies, and sagebrush steppe), and a record of primary succession at Mt. St. Helens volcano. Collectively, we analyzed 14,647 observations from 775 plots, between 1915 and 2012. Dynamics could be reliably assigned for 705 plots (91%), and overall statistical fit was high (goodness of fit, 0.77 ± 0.15 SD). Among the perennial grasslands, stability was most common (44% of all plots), followed by gradual linear (22%), abrupt nonlinear (17%), and reversible (6%) change. Among annual grasslands, abrupt nonlinear shifts (33%) were more common in the warm-season community than in the cool-season (20%). As expected, abrupt nonlinear change was common during primary succession (51%) while reversible change was rare (3%). Generally, reversible dynamics often required 2-3 decades. Analysis of long-term community change, or trajectories, with principles of movement ecology provides a quantitative basis to compare and interpret ecological resilience within and among ecosystems.

Linking the ball‐and‐cup analogy and ordination trajectories to describe ecosystem stability, resistance, and resilience

“…), resilience (Holling , Bagchi et al. ), stability (Forman and Godron , DeAngelis and Waterhouse ), and regime shifts (Scheffer and Carpenter , Osland et al. ).…”

“…One-or-more neighboring cups represent alternative stable states in the stability landscape , Scheffer 2009) for that ecosystem. Willems (1970) used this analogy to describe ecosystem stability, and this diagram has since been used to describe ecosystem responses to disturbance (Hurd and Wolf 1974, Godron and Forman 1983, Hamilton and Haeussler 2008 including resistance (Hirst et al 2003, resilience (Holling 1973, Bagchi et al 2017, stability Godron 1986, DeAngelis andWaterhouse 1987), and regime shifts (Scheffer andCarpenter 2003, Osland et al 2016).…”

Long‐term community change through multiple rapid transitions in a desert rodent community

“…), with little or no focus on the pattern of that change (but see Bagchi et al. ). A growing number of studies document the occurrence of rapid ecological transitions (Beaugrand , Thibault and Brown ), but whether these events are rare or a common mechanism by which long‐term change occurs is unclear.…”

Resistance and resilience: ten years of monitoring shrub and prairie communities in Orange County, CA, USA

“…The consistency observed in the proportion of native species in chaparral and coastal sage scrub transects over ten years supports the resistance of these communities, yet the significant fluctuations in species composition, especially the high variation in degree of fluctuation for coastal sage scrub transects, demonstrates reversible changes (resiliency) in species composition (Bagchi et al. ). The significant decline in the proportion of native plants for the grassland transects points to a concern regarding native grass persistence, yet investigating the variance of transects through time in species space demonstrated that grassland transects have not experienced significant variance and appear to be stable as a highly invaded community type that may be difficult to restore to a native‐dominated community (Suding et al.…”

“…, Bagchi et al. ), even though non‐native annual grass cover was equal to or greater than native shrub cover in three out of the ten years. Despite demonstrating no changes in vegetation state, the multivariate trajectories, mean distances, and patterns of variation among transects associated with the ordination suggest an interesting hypothesis—chaparral communities likely demonstrate substantial resilience in composition, while coastal sage scrub appears to demonstrate greater variation in the amount of resistance and resilience.…”