Early-successional tree species may facilitate the establishment of the regenerating plant community in semi-arid environments by creating more favourable microenvironments and reducing environmental stress. However, it is not clear how these tree species can influence morphofunctional and physiological responses of the regenerating plant community. In field conditions, we used three early-successional tree species in the adult stage (Combretum leprosum, Cenostigma bracteosum and Mimosa tenuiflora) as potential facilitators, and two regenerating ones as target species (Cordia oncocalyx and Croton blanchetianus). We then evaluated the effect of the former on the leaf anatomy, physiology and growth of the latter. We found that C. leprosum and C. bracteosum acted as facilitators, resulting in a 55% and 22% reduction in solar radiation in the rainy season, and an 11% and 10% reduction in the dry season, respectively. In addition, we observed a higher soil moisture under the canopy of nurse species, especially under C. leprosum, which showed an increase of over 38% in gravimetric water content in the rainy and dry seasons. These results favoured gas exchange (CO 2 uptake, stomatal conductance and transpiration) and growth in Cordia oncocalyx and C. blanchetianus. Furthermore, we did not observe any stress reduction under the canopy of M. tenuiflora and in the open area, where target species showed reduced gas exchange and growth. The positive morphological and ecophysiological responses of the target species under C. leprosum and C. bracteosum reinforce the importance of studying microenvironments created by earlysuccessional tree species. This way, we can understand the mechanisms promoting facilitation and the influence of this positive interaction on the restructuring process of the plant community in a semi-arid environment.
In environments with water and nutrient constraints, some early successional shrub/tree species may promote facilitation by ameliorating the microclimate and increasing resource availability. We ask whether early successional semi‐arid shrub/tree species have facilitation effects for other woody species and if they do, which mechanisms are involved and how they affect the water status of juvenile plants. Three early successional woody species; Combretum leprosum, Cenostigma bracteosum and Mimosa tenuiflora, were chosen for investigation. The richness of regenerating woody species and their leaf water potential were used as response variables, while air and soil temperature, leaf area index, humidity and soil attributes were used as explanatory environmental variables. Species growing under the canopy of C. leprosum had better water status and growth at higher soil moisture and lower thermal and solar radiation stress, receiving a facilitative effect. The lower leaf area index, higher radiation and more negative soil water content under the canopy of C. bracteosum in comparison to C. leprosum may have a small negative effect on species richness. M. tenuiflora did not reduce environmental stress, and the species associated with it had low water potential, thus no increase in species richness was detected under its canopy. C. leprosum and C. bracteosum improve the environmental conditions under their canopies and provide favourable microsites for the establishment of other species. The positive effects may be generated by functional traits that modify microclimatic characteristics under the nurse species' canopy and lead to a higher water status of the juveniles growing under it.
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