Not gone with the wind: Vegetation complexity increases seed retention during windy periods in the Argentine Semiarid Chaco

摘要

Questions We experimentally studied whether different degrees of vegetation structural complexity, developed under different land-use regimes, affected the retention of seeds in situ in the semiarid Chaco forest. We sought to answer the following questions: (a) Does vegetation complexity in interaction with climatic conditions affect seed retention on the soil surface? (b) Do seeds with contrasting traits show the same retention pattern? Location Chancani, Northwestern Cordoba, Argentina. Methods We run a field experiment to test seed retention across 16 field sites differing in physiognomy and land-use regime. We used artificial seeds with contrasting traits to simulate extreme morphologies found among dominant species of the Chaco forest (large-flattened and small-spherical seed types). We placed artificial seeds in 10 quadrats along a transect at each site and recorded the number of seeds retained after 25 days. We performed the experiment in the same season in two consecutive years. Through a Principal Component Analysis of a matrix of 320 survey plots by 6 structural variables, we extracted two major multivariate axes summarizing vegetation complexity. Results Vegetation complexity was strongly related to land-use regimes, and a more complex vegetation structure increased seed retention, particularly in the first year of the experiment, when wind velocity was twice the value of the historical mean. The same general retention pattern was observed for different seed types with contrasting size and shape, but the absolute amount of retention was lower for large-flattened than small-spherical seeds. Conclusion Vegetation complexity interacting with variable climatic conditions -especially wind velocity- and seed morphology increased seed retention on the soil surface. Because seed dynamics is known to play an essential role in vegetation recovery, manipulation of soil cover should be a key factor in vegetation resilience in these systems.