Do early‐successional weeds facilitate or compete with seedlings in forest restoration? Disentangling abiotic versus biotic factors

Semi-arid forests need cost-effective restoration strategies to address their severe degradation. Tree shelters are often used minimize abiotic and biotic stress during seedling establishment. We asked if early-successional weeds act as a natural shelter by facilitating native seedlings, contingent on stressors ecological strategy. conducted manipulative weed exclusion experiment at semi-arid site in South Texas targeted for large-scale forest discern the net effect of growth survival target thornscrub tree shrub seedlings. assessed roles contrasting (fast vs. slow habit), temporal variation stress, microclimate mammalian herbivory modulating weed–seedling interactions. Ungulate seedlings was common, similar frequency across most species, but not diminished presence neighbours. On average, growing adjacent neighbours experienced modest non-significant increases both height mortality after 6 months, relative weed-excluded areas. However, without significant grew more vigorously (increased branching) hot dry periods, particularly those species with fast habit. Although light-saturated photosynthetic capacity (Asat) air temperature were unaffected afternoon light levels reduced approximately 50%, possibly indicative lower leaf temperatures improved water status. Our results show that realizing facilitative potential requires minimizing temporally separating competition resources. Managing intermediate excessive forb canopy cover is likely required reduce high radiation loads transpiration adverse competitive effects. Longer-term experiments manipulating crop identity, will inform whether forbs can be effectively exploited enhance success large scales.