Species-specific facilitation, ontogenetic shifts and consequences for plant community succession

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Abstract

Aims

Our main aims are to test how: (1) different nurse species modulate the early establishment of multiple beneficiary species in a degraded area; (2) the intensity and direction of species-specific interactions between nurse and beneficiary species change during beneficiary ontogeny.

Location

A shrubby Caatinga forest at Petrolina, northeast Brazil, degraded by grazing and logging activities in recent decades.

Methods

We conducted a factorial multi-species experiment in which seeds and seedlings of five beneficiary species were sown in the presence and absence of three pioneer tree species. Beneficiary species performance was monitored for different ontogenetic stages.

Results

We found evidence of species-specific facilitation in which the intensity and outcome of the interactions between nurse and beneficiary species varied depending on species identity. Additionally, for most combinations of nurse and beneficiary species, ontogenetic shifts from positive to neutral or negative interactions were observed with increasing beneficiary age.

Conclusions

We provide experimental evidence that nurse and beneficiary species identity simultaneously influence the balance between facilitation and competition. Our results suggest that ontogenetic shifts may be a widespread phenomenon in semi-arid ecosystems. We discuss that a key mechanism explaining these findings is the match between what nurse species offer and what beneficiary species require in terms of resources and conditions. As a consequence, different nurse species tend to favour or inhibit unique sets of beneficiary species beneath their canopies. We argue that species-specific facilitation is an overlooked mechanism promoting β-diversity during community succession.

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