Combined Grazing and Drought Stress Alter the Outcome of Nurse: Beneficiary Interactions in a Semi-arid Ecosystem

Abstract

Positive interspecific plant-plant interactions in (semi-)arid ecosystems are crucial for supporting ecosystem diversity and stability, but how interactions respond to grazing combined with temporal variation in drought is poorly understood. In a semi-arid area in southeastern Spain (Murcia region), we planted 1280 saplings of the palatable shrub Anthyllis cytisoides (beneficiary) under the canopy of the unpalatable shrub Artemisia herba-alba (nurse) or in open microsites between shrub patches. We applied four grazing treatments (no grazing, low goat grazing pressure, high goat grazing pressure and rabbit grazing) and two watering treatments. Sapling height and survival were followed for two consecutive years, during which one extreme drought event occurred. We analysed how grazing, watering and their combination affected nurse effects throughout the course of the study. Grazing and the drought event, but not watering, significantly altered the nurse effects. Under ungrazed conditions prior to the extreme drought event, nurse effects on sapling survival were neutral, whereas they were positive at rabbitgrazed plots. At low goat grazing, sapling growth was higher under nurse shrubs than in open microsites. However, after the extreme drought event, sapling survival was higher in open microsites at ungrazed plots, whereas at rabbit-grazed plots, nurse effects shifted from positive to neutral. Our findings highlight the importance of rabbit grazing in determining the direction of plant-plant interactions in arid ecosystems. Moreover, our findings support the idea that positive plant-plant interactions may wane under the combination of high grazing and drought stress.

Intra‐seasonal rainfall variability and herbivory affect the interaction outcome of two dryland plant species

“…Also, in line with field observations and parallel experiments (Verwijmeren et al 2019), we used Anthyllis cytisoides as protégé species in our model. A. cytisoides is a drought-deciduous shrub from the Fabacaea family, and it is highly palatable for both goats and rabbits.…”

“…In our model study, we distinguished two distinct plant functional types, a nurse ( N ) and a protégé ( P ) species. Both are woody perennial species that were selected in a parallel experiment in which plant growth of protected and unprotected planted saplings of Anthyllis cytisoides was monitored (Verwijmeren et al 2019). In line with this experiment, we used Artemisia herba‐alba as nurse plant in this study and modeled its growth .…”

“…In this study, we used a mechanistic two-species ecohydrological model to investigate how plant coexistence and plant-plant interactions are dependent on different rainfall amounts, rainfall intermittency, and herbivory pressure scenarios. Model assumptions and parameter settings are based on the experimental outcomes of a plant-plant interactions setup at a field site in southeastern Spain (Murcia region 37°57 0 28.37″ N, 1°0 0 16.14″ W), where a relatively drought-resistant nurse plant protected a protégé plant-that had a higher optimal growth rate-from being grazed (Verwijmeren et al 2019). We modeled realistic (stochastic) rainfall scenarios to explore the effect of rainfall intermittency on the coexistence of the two species, which differed in their optimal growth rate and wilting points, and on the net effect of their interactions.…”

Unpalatable plants induce a species-specific associational effect on neighboring communities

“…Generally, in the literature on associational effects of unpalatable species, effects of grazing intensity have been neglected. Nevertheless, it is well-established that interaction between plants is likely to be changed with different grazing intensities 6 , 16 .…”

Stronger intra-specific competition aggravates negative effects of drought on the growth of Cunninghamia lanceolata

“…Many of them have suggested that competition among plants becomes weaker or even shifts to facilitation when soil water reduces (e.g. He et al, 2013;Baudis et al, 2014;Verwijmeren et al, 2019); on the contrary, many studies have reported an opposite pattern (e.g. Tielbörger and Kadmon, 2000;Hommel et al, 2016;Zhang et al, 2017).…”