In recent decades, anthropogenic activities have increased nitrogen (N) deposition in terrestrial ecosystems. This higher availability of N is expected to impact plant growth. However, the effects of N deposition on tree growth remain inconclusive due to the wide variability of experimental methods used. This study aimed to test the effect of short-term N addition on the intra-annual wood formation of Chinese red pine (Pinus massoniana Lamb.) in a warm-temperate forest of Central China. From 2013, solution containing 25 kg N ha⁻¹ year⁻¹ was applied monthly to the understory of experimental plots from April to December to double the current natural N deposition. Each week from March to December in 2014 and 2015, cambial activity and the timings and dynamics of xylem formation were monitored by collecting microcores from stems. Xylem formation lasted from March to November, producing an average of 19 and 33 cells for all studied trees in 2014 and 2015, respectively. No difference in xylem cell production was observed between control and N-treated trees. Moreover, N-treated trees had similar timings, rates and durations of xylem formation as control trees. These findings indicated that short-term N addition was unable to affect timings and dynamics of xylem formation in Chinese red pine of warm-temperate forest.

Key message: Forest assisted migration applied in combination with a climate-based seed transfer system to two North American tree species: lodgepole pine (Pinus contorta var. latifolia Dougl.) and interior spruce (Picea engelmanii x glauca (Moench) Voss and their hybrids), resulted in increased height growth and a substantially expanded seed deployment area, compared to a geographic-based seed transfer system in British Columbia, Canada. Context: Forest assisted migration and climate-based seed transfer (CBST) are two recent innovations that have received significant attention as climate change adaptation strategies, but claims regarding their merits have not been well evaluated. Aims: We aim to test the claim that CBST, combined with assisted migration, can provide closer matching of seed source and plantation climate, greater height growth, and wider seedlot deployment area than a conventional geographic-based seed transfer system (GBST). Methods: Using transfer functions developed from two comprehensive, wide-ranging provenance trials of lodgepole pine and interior spruce, with populations from across western Canada, we estimated relative tree height growth at rotation and seed deployment area for a large set of simulated seed transfers in a CBST system with and without assisted migration and in a GBST system. Results: When assisted migration and CBST were used in combination, volume growth was 13% (lodgepole pine) or 6% (interior spruce) greater at rotation age and deployment area was 2.2 times (lodgepole pine) or 7.3 times (interior spruce) greater than was expected in a GBST system. Height growth increases were primarily associated with assisted migration, whereas increases in seed deployment area were primarily associated with the use of CBST rather than GBST. Conclusion: Converting from GBST to CBST in conjunction with assisted migration should substantially improve adaptation of lodgepole pine and interior spruce in British Columbia. This approach will also significantly offset the impacts of climate change on growth rates, increase deployment area, reduce seed collection costs, and provide greater flexibility to seed users.