In recent decades, there have been significant advancements in understanding how ecological processes play out across spatial scales, but we have lagged in developing a similar framework for understanding communities as temporal phenomena. Humboldt's observations of vegetation zonation on Mount Chimborazo, Gleason's insight that communities are the outcome of species' individualistic response to their environments, Whitakker's gradient analyses, and the advancements of macroecology have contributed to an appreciation of the importance of nature's second and third dimensions. In contrast, a century of paleoecological research has shed light on how species and their assemblages change through time, but these are often considered to be irrelevant to understanding community assembly or other ecological mechanisms that play out on the lifespan of organisms (or the timeframe of investigations). Yet, the community patterns that emerge at long timescales are the amalgam of ecological processes that operate in the near-term. In the era of global change, ecologists are increasingly studying assemblages in transition. Conceptually, we accept that communities are dynamic, yet we continue to lack a theoretical framework with which to make predictions about the timescales at which community processes of interest play out.
From historical legacies to disequilibrium dynamics, to understand the "where" and "how" of communities, we must also understand the "when." The recent fossil record provides insights into communities as temporal phenomena: 1) The post-glacial fossil record for animals and plants reveals the transient nature of many communities, including non-analog assemblages as an emergent property of species' individualistic response to environmental change. 2) By linking demographic processes with observations of range dynamics in trees, we may better predict how communities may respond as the result of processes that play out across long and short timescales. 3) The timescale of community response to perturbation may be dependent on trophic interactions; large herbivores in particular may dampen the response of plant assemblages to climate change. 4) Disequilibrium dynamics, critical transitions, and threshold responses are difficult to predict, but long-term datasets and insights from climatology offer promising ways forward. 5) Community response to environmental change is a process that plays out across temporal scales; mid-Holocene and contemporary species losses may shed light on nested temporal responses to disturbance, from sub-annual to millenial timescales. These examples highlight the need for an improved conceptual framework to understand communites not only as dynamic entities, but as byproducts of processes across timescales.