OOS 64-4 - Anticipating the demographic response of woodland tree species to climate change using forest inventory data

The geographic distributions of tree species are expected to shift in response to climate change. The ecological consequences of these shifts are likely to be particularly pronounced in dry woodlands, where declines in tree species are likely to give way to transitions to grasslands and shrublands. Yet anticipating where tree populations may be most vulnerable remains a challenge. Using Forest Inventory and Analysis and remote sensing datasets, we developed demographic and population models to anticipate where and under what conditions pinyon-juniper woodlands are most vulnerable and expected to contract. At range-wide scales, using forest inventory data, we find 4 of 5 of the pinyon-juniper species we examined are declining in in some part of their range driven by both increasing mortality and declining recruitment, with declines concentrated in the warmest and driest regions were as much as 50% of populations are declining. However, at more local, landscape scales using remote sensing data, we find that interactions between density-dependence and climate conditions produce counter intuitive patterns. Lower-density populations located on the climatically harsh range-margin are often stable or expanding, while interactions between warming climate conditions and density dependence are leading to declines in more climatically favorable, but high-density areas. Our results indicate that range contractions along warm-dry margins are already occurring and likely to continue, however interactions between abiotic (climate) and biotic (tree density) conditions may lead to unexpected patterns of expansion and decline at local scales in the near-term.