Woody plant encroachment of grasslands: a comparison of terrestrial and wetland settings

Abstract

SummaryA global trend of woody plant encroachment of terrestrial grasslands is co-incident with woody plant encroachment of wetland in freshwater and saline intertidal settings. There are several arguments for considering tree encroachment of wetlands in the context of woody shrub encroachment of grassland biomes. In both cases, delimitation of woody shrubs at regional scales is set by temperature thresholds for poleward extent, and by aridity within temperature limits. Latitudinal expansion has been observed for terrestrial woody shrubs and mangroves, following recent warming, but most expansion and thickening has been due to the occupation of previously water-limited grassland/saltmarsh environments. Increases in atmospheric CO 2 , may facilitate the recruitment of trees in terrestrial and wetland settings. Improved water relations, a mechanism that would predict higher soil moisture in grasslands and saltmarshes, and also an enhanced capacity to survive arid conditions, reinforces local mechanisms of change. The expansion of woody shrubs and mangroves provides a negative feedback on elevated atmospheric CO 2 by increasing carbon sequestration in grassland and saltmarsh, and is a significant carbon sink globally. These broad-scale vegetation shifts may represent a new stable state, reinforced by positive feedbacks between global change drivers and endogenic mechanisms of persistence in the landscape.

Life stage influences the resistance and resilience of black mangrove forests to winter climate extremes

“…To our knowledge, A. germinans is the only species of mangrove found in the study area and throughout the state of Louisiana. Although A. germinans has been present in parts of Louisiana for at least the last century (Penfound and Hathaway 1938, O'Neil 1949, West 1977 and probably much longer (Woodroffe andGrindrod 1991, Saintilan andRogers 2015), the abundance, structural complexity, and spatial coverage of mangrove forests in the Port Fourchon area over the past century have likely expanded and contracted in response to the duration, frequency, and intensity of extreme winter events (West 1977, Osland et al 2013. For the last several decades (i.e., since the last major freeze event in 1989), the spatial coverage of A. germinans has increased within Port Fourchon (Perry andMendelssohn 2009, Giri et al 2011) and other parts of the northern Gulf of Mexico (Stevens et al 2006, Montagna et al 2011 at the expense of salt marsh vegetation.…”

Fire prevents woody encroachment only at higher‐than‐historical frequencies in a South African savanna

“…), or occurring in the absence of a change in disturbance regime (Buitenwerf et al . ), suggest an overriding influence of global drivers (Saintilan & Rogers ). Consequently, some have suggested that widespread increases in woody plant growth are fundamentally changing tree–grass dynamics in savannas, such that managers may have to resign themselves to inevitable vegetation change (Buitenwerf et al .…”

The influence of habitat on the evolution of plants: a case study across Saxifragales

“…Variable environmental boundaries are also expected to be highly consequential to the distribution and range of discontinuous habitats such as wetlands (Hamilton, 2010; Oberlander et al , 2014; Saintilan and Rogers, 2015). Anticipating the biodiversity consequences of these changes in habitat distribution and availability requires the capacity to estimate the likelihood of the lineages occupying each habitat to adapt to new conditions and/or shift into surrounding environments.…”