Effects of nurse shrubs and biochar on planted conifer seedling survival and growth in a high-severity burn patch in New Mexico, USA

The synergistic effects of widespread high-severity wildfire and anthropogenic climate change are driving large-scale vegetation conversion. In the southwestern United States, areas that were once dominated by conifer forests are now shrub- or grasslands after high-severity wildfire, an ecosystem conversion that could be permanent without human intervention. Yet, the reforestation of these landscapes is rarely successful, with a mean planted seedling survival of just 25 %. Given these low rates, we carried out a planting experiment to quantify the impacts of biochar as a soil amendment and shrubs as nurse plants on planted conifer seedling survival and growth following high-severity wildfire. We planted 1200 seedlings of three species (Pinus ponderosa, P. strobiformis, and Pseudotsuga menziesii) in a 2-ha area within the footprint of the Las Conchas fire in New Mexico, USA. We used four treatments: under shrubs, or in the open and with or without biochar in a full-factorial design. We f..., In 2011, the Las Conchas fire burned approximately 63,130 ha in the Jemez Mountains of New Mexico, USA, ∼30 % of which was high-severity as defined by Eidenshink and colleagues, (2007). The Las Conchas fire burned over footprints from five previous wildfires (​Coop et al, 2016​). This repeated high-severity burning has led to a large-scale vegetation shift, from ponderosa pine-dominated forest to a Gambel oak (Quercus gambelii) and New Mexico locust (Robinia neomexicna) shrub-dominated landscape (​Coop et al., 2016; Kaufmann et al., 2016​). We selected a 2 ha area within the footprint of the Las Conchas fire for our planting experiment (lat: 35.785, long: -106.415), due to its location within an area classified as having experienced high-severity wildfire, its elevation, 2520 m above sea level, (close to the mean elevation of the Las Conchas fire footprint, 2541 m) and proximity to a road to enable planting efforts. We planted all 1200 seedlings during July 15–17 of 2019, between 2516 m...,大范围高强度野火（high-severity wildfire）与人为气候变化的协同效应正推动大规模植被转换。在美国西南部，原本以针叶林为主的区域在经历高强度野火后已转变为灌丛或草地，若无人类干预，这种生态系统转换可能永久持续。然而，此类景观的再造林鲜有成功案例，种植幼苗的平均存活率仅为25%。鉴于如此低的存活率，我们开展了一项种植实验，以量化生物炭（biochar，土壤改良剂）与灌木（保育植物）对高强度野火后种植的针叶树幼苗存活与生长的影响。我们在美国新墨西哥州拉斯孔查斯火灾（Las Conchas fire）的过火迹地内选取了一块2公顷的区域，种植了3个物种共1200株幼苗：*Pinus ponderosa*、*P. strobiformis*以及*Pseudotsuga menziesii*。实验采用完全析因设计（full-factorial design），共设置4种处理：灌木下生境或开阔生境，搭配施加或不施加生物炭。2011年，拉斯孔查斯火灾在美国新墨西哥州赫梅斯山脉烧毁了约63130公顷土地，其中约30%属于Eidenshink及其同事（2007）所定义的高强度火烧区域。该火灾的过火范围覆盖了此前五次野火的迹地（Coop et al., 2016）。这种重复发生的高强度火烧已引发大规模植被转变：从以黄松为主的森林转变为以甘贝尔栎（*Quercus gambelii*）和新墨西哥刺槐（*Robinia neomexicana*）为主的灌丛景观（Coop et al., 2016; Kaufmann et al., 2016）。我们选取该过火迹地内的2公顷区域开展种植实验，其坐标为北纬35.785、西经106.415，选择依据如下：该区域被归类为经历过高强度野火的区域，海拔2520米（接近拉斯孔查斯火灾迹地的平均海拔2541米），且临近道路便于开展种植工作。我们于2019年7月15日至17日完成了全部1200株幼苗的种植，种植区域海拔约2516米。