Environmental watering for vegetation diversity outcomes must account for local canopy conditions

Abstract

Hydrology is widely considered to be the dominant driver of understorey vegetation dynamics in arid and semiarid riparian ecosystems. Consequently, environmental watering is often a key approach to restoring and promoting riparian vegetation diversity. Few studies however have considered the role of local factors, for example, shading or litter accumulation, on vegetation responses to flow and how these may influence the outcomes of watering actions. Knowledge concerning modifying effects of local canopy factors on vegetation responses to watering is needed to guide environmental water planning (e.g., setting objectives and targets) and delivery (e.g., timing and duration of managed flows). We conducted a greenhouse experiment to investigate the effects of shade and litter, and their interaction, on plant communities establishing from riparian soil seed banks, collected from the northern Murray–Darling Basin, under a range of hydrological conditions. We found that shade had a positive influence on the abundance, diversity, and reproduction of establishing plant communities under dry conditions but a negative, or null effect, under wet conditions. Litter exerted strong negative effects on plant community metrics under all hydrological conditions. Some understorey species emerged as hardy generalists capable of establishment under a range of conditions whereas others had more specific requirements. Our results highlight the importance of canopy structure for riparian understorey vegetation diversity and dynamics at both local and landscape scales. Land and water management practices seeking to protect or restore vegetation diversity in these systems must therefore take such local factors into account when planning and evaluating interventions.

Legacies, lags and long‐term trends: Effective flow restoration in a changed and changing world

“…Pre‐existing ecological condition of vegetation has been widely shown to affect responses to flows (e.g. Capon, Balcombe, & McBroom, ; Nagler et al., ; Smith, ), and there are similar findings for fish, in which the abundance and individual condition of the stock influence the magnitude of the responses (King et al., ; Koster et al., ). Lagged responses to eflows due to existing poor ecological condition have been identified as an important issue in many parts of the world (e.g.…”

Seedling root growth experiments for two Australian dryland riparian eucalypts provide new insights for environmental watering

“…Riparian vegetation is a critical component of inland riverine landscapes, supporting significant biodiversity and providing a wide range of highly valued ecosystem functions and services (Capon et al, 2013;Mahoney & Rood, 1998). In the northern Murray-Darling Basin, longlived riparian trees (largely E. camaldulensis and E. coolibah) play a disproportionate role in the health of both the flora and fauna that rely on the services provided by these trees, such as shade and litter (Capon, Balcombe, & McBroom, 2017) and a constant source of organic matter to the soil. Hence, the broader implications of both protecting standing trees and influencing the recruitment of seedlings cannot be understated.…”

Simulating the effect of environmental flow duration on seedling emergence from riparian seed banks of the Upper Hunter River, New South Wales

“…However, inundation duration is not the only component required for a fuller understanding of seed germination and vegetation establishment. For example, Capon et al () examined the effects of leaf litter and shade on germination, concluding that they may also be important local factors constraining germination during periods of inundation.…”

“…Capon () identified an increase in seedling emergence in a desert floodplain after 4–8 weeks of inundation and an increase in the proportion of annual monocot species. A simulated in‐channel flow event led to more abundant and species‐rich germination from the seed bank of bank top riparian sites from the northern Murray–Darling Basin, in comparison with inundation or non‐inundation (Capon, Balcombe, & McBroom, ). However, the authors also found that the leaf litter and shade present comparable controls on the seed bank material to the simulated hydrological events.…”

“…However Harris, Leishman, and Fryirs (), using a limited number of species, found that inundation depth (at 5, 75, and 180 cm) is not a key factor in germination from the seed bank of the desirable riparian species from our case study region, the Hunter Valley. Although other studies have examined the effects of inundation duration on species germination (e.g., Webb, Reid, Capon, Thoms, & Rayburg ; Higgisson, Briggs, & Dyer, ; Capon et al, ), the effects of flow duration on the suite of desirable Hunter Valley species have not been tested.…”