Drought-induced shift of a forest–woodland ecotone: Rapid landscape response to climate variation

TLDR

Global climate change is projected to drive unprecedented, rapid shifts in vegetation, especially at ecotones in semiarid regions, yet current models lack field data on mortality-driven dynamics. This study highlights the need to incorporate accurate mortality processes into climate‑change impact assessments. In northern New Mexico, a severe 1950s drought triggered a >2 km, <5‑year shift of the ponderosa pine–piñon–juniper ecotone, a change that has persisted for 40 years, increasing forest fragmentation and accelerating soil erosion.

Abstract

In coming decades, global climate changes are expected to produce large shifts in vegetation distributions at unprecedented rates. These shifts are expected to be most rapid and extreme at ecotones, the boundaries between ecosystems, particularly those in semiarid landscapes. However, current models do not adequately provide for such rapid effects—particularly those caused by mortality—largely because of the lack of data from field studies. Here we report the most rapid landscape-scale shift of a woody ecotone ever documented: in northern New Mexico in the 1950s, the ecotone between semiarid ponderosa pine forest and piñon–juniper woodland shifted extensively (2 km or more) and rapidly (&lt;5 years) through mortality of ponderosa pines in response to a severe drought. This shift has persisted for 40 years. Forest patches within the shift zone became much more fragmented, and soil erosion greatly accelerated. The rapidity and the complex dynamics of the persistent shift point to the need to represent more accurately these dynamics, especially the mortality factor, in assessments of the effects of climate change.