A spatial triage of at-risk conifer forests to support seed collection efforts and sustainable forestry.

Abstract

At-risk conifer stands growing in hot, arid conditions at low elevations may contain the most climate change-adapted seeds needed for sustainable forestry. This study used a triage framework to identify high-priority survey areas for Pinus ponderosa (Pipo) within a large region, by intersecting an updated range map with a map of seed zones and elevation bands (SZEBs). The framework assesses place-based climate change and potential wildfire risks by rank-order across 740 potential collection units. The study separately combined three operational measures of cone priority SEZBs from a government reforestation nursery in California - current inventory, target seed supply levels, and areas with high seed demand - to create operational SZEB priority rankings. Combining the risk and operational SZEB rankings permitted an overall priority ranking of survey areas, and road extents within each SZEB's Pipo area indicate accessibility. Pipo's California range covers 62,456.9 km², which intersects 740 of 1212 total SZEBs. Of these, 43 have high climate exposure under baseline (1980-2010) conditions, and 139 more become highly exposed by the end of the century. Of these 182 highly climate-exposed SZEBs, our index of high-intensity fire risk indicates 42 were also at high risk of stand replacing fire at the beginning of the 2023 fire season. Of these 42, only 4 are currently represented in the seed lot inventory. In contrast, the top 73 operational priority SZEBs all have relatively low risk rankings. Integrating models of landscape risk with operational seed collection priorities can direct collection efforts to high-risk stands before those are lost, and improve spatial coverage in seed bank inventories. The triage framework can provide spatial guidance for cone crop surveying efforts, and has the potential to improve forest nursery and field management. Triage elements can be updated or added to provide more comprehensive tracking over time. For example, wildfire perimeters and seed inventories could be updated annually and fuels reduction treatments, cone crop survey routes, annual assessments of cone crop condition, and additional seedbanks (e.g. for the USDA Forest Service) could be included.