Influence of conspecific and heterospecific adults on riparian tree species establishment during encroachment of a humid palm savanna
Woody plant encroachment of savanna ecosystems has been related to altered disturbance regimes, mainly fire suppression and herbivore exclusion. In contrast, neighbourhood interactions among resident and colonising woody species have received little attention, despite their likely influence on the pattern and rate of tree establishment. We examined how resident palm trees [Butia yatay] and established adults of two riparian forest tree species [Allophylus edulis and Sebastiania commersoniana] influenced seed arrival and seedling performance of the latter two species in a humid savanna of east-central Argentina. Seed traps and seedlings of both riparian species were placed in herbaceous openings, and beneath palm, conspecific and heterospecific adult trees in two unburned savanna patches, and were monitored for 2 years. Only seeds of the bird-dispersed Allophylus arrived in palm microsites, yet survival of Allophylus seedlings near adult palms was limited by animal damage through trampling and burrowing, a non-trophic mechanism of apparent competition. Seeds of both riparian species dispersed into conspecific microsites, although adult trees selectively reduced growth of conspecific seedlings, a pattern consistent with the "escape hypothesis". Further, survival of Sebastiania increased in the moister Allophylus microsites, suggesting a one-way facilitative interaction between woody colonisers. Our results indicate that dispersal facilitation by resident savanna trees may be critical to riparian species invasion after fire suppression. Distance-dependent effects of conspecific and heterospecific adult trees could contribute to shape the subsequent dynamics of woody seedling establishment. Overall, we show that indirect interactions can play a prominent role in savanna encroachment by non-resident woody species.
APPARENT COMPETITION ESCAPE HYPOTHESIS FACILITATION FOREST EXPANSION INVASION ADULT BURROWING CONSPECIFIC ENVIRONMENTAL DISTURBANCE ESCAPE BEHAVIOR FOREST FIRE HUMID ENVIRONMENT INVASIVE SPECIES MONOCOTYLEDON RIPARIAN FOREST SAVANNA SEEDLING ESTABLISHMENT SURVIVAL TRAMPLING ARECACEAE ARGENTINA ECOSYSTEM EUPHORBIACEAE GEOGRAPHY PHYSIOLOGY RIVER SAPINDACEAE SEED DISPERSAL SEEDLING SPECIES DIFFERENCE TREE RIVERS SPECIES SPECIFICITY TREES ALLOPHYLUS ALLOPHYLUS EDULIS ANIMALIA AVES BUTIA YATAY SEBASTIANIA SEBASTIANIA COMMERSONIANA