Prediction of potential suitable areas and their trends for Picea worldwide under climate change

Potentially suitable areas for Picea under climate change and the relationship with climate change were investigated to provide an introduction and foundation for conservation. By collecting extant distribution point data for 34 Picea species and 19 environmental variables from WorldClim, potentially suitable areas were simulated via the improved MaxEnt model during the modern period (1960-1990), and Last Interglacial (LIG), Last Glacial Maximum (LGM), Mid-Holocene (MH), future periods (2050s and 2070s) across two climate emission scenarios (RCP6.0 and RCP8.5). The MaxEnt model results exhibited high simulation accuracy, and the predicted suitable areas conformed with real growth and distribution patterns. The annual mean temperature (BIO17) and precipitation of the driest quarter (BIO01) were the primary climate factors influencing Picea dispersion. The total suitable area during the LIG period was 7.43 x 107km2, which represents 93.34 % of the current total suitable area. The total suitable area during the LGM represents 76.31 % of the current total suitable area. The total suitable area during the MH represents 96.11 % of the current total suitable area. Under future climate scenarios, the total potentially suitable area exhibited a marginal increase of less than 3 %, while the highly suitable area experienced substantial reductions. Specifically, under RCP6.0, the highly suitable area decreased by 11.65 % and 13.60 % compared to current conditions. The most pronounced declines occurred under RCP8.5, with highly suitable area shrinking by 15.46 % and 20.41 % in the 2050 sand 2070 s, respectively, compared with that under the current scenario. Under future scenarios and among the 31 Picea species, the total suitable area for 22 species indicated a decreasing trend with the greatest decrease under the RCP8.5 scenario. Species with the largest total suitable areas were Picea obovata, Picea glauca, Picea mariana, and Picea abies, which all exceeded 1.00 x 106km2. Under future climate scenarios, Picea abies showed an increasing trend, whereas the other three species exhibited decreasing trends. The total suitable areas for Picea breweriana and Picea morrisonicola were the smallest (less than 1.00 x 106km2), and they showed decreasing trends. The main climate factors influencing Picea distribution were BIO17 and BIO01 with precipitation impacting the distribution more than the temperature. The total suitable area for Picea first decreased and then increased from past to present. The total suitable area was smallest during the LGM. The total suitable area under future scenarios exceeded the current total suitable area, but the observed trend shows minimal significance with an increase of less than 3 %. The projected highly suitable area was smaller than the current extent. The highly suitable area declined the most under the RCP8.5 scenario. Picea generally migrated northeastwards and to higher latitudes. Species with a wide range of suitable areas, such as Picea neoveitchii, Picea omorika, and Picea jezoensis, which could exhibit larger future suitable areas, could be considered candidates for introduction and cultivation. For species with smaller total suitable areas, such as Picea breweriana, Picea morrisonicola, Picea chihuahuana, Picea alcoquiana, Picea torano, and Picea glehnii, which could exhibit smaller future suitable areas, monitoring and protection measures should be enhanced to ensure their survival under climate change.