The 'spatial storage effect': the missing link in the conservation of temperate woodland annual plant species

A project undertaken at the Department of Ecology, Environment and Evolution, La Trobe University, supervised by John Morgan

Annual plants in temperate woodlands can make a substantial contribution to native plant biodiversity (~35%). They are probably disappearing before our eyes with barely anyone noticing. Local extinction has been reported, but the factors that affect their persistence are largely unknown.

In arid areas, annual communities are driven by rainfall - plants lie dormant (sometimes for many years) before emerging to take advantage of infrequent rains. In temperate ecosystems, rainfall is less limiting. Instead, it is much more likely that their 'safe sites' for germination are disappearing. Ground-dwelling animals that dig soils no longer exist across much of the range. Such diggings provide bare patches of soils for annuals to germinate on. Fire is now rare in many fragmented woodlands. Fire removes litter (hence also creating bare ground) and may also cue germination (via smoke effects).

The loss of safe sites because of fundamental changes in ecosystem disturbance regimes may deprive may species of the microhabitats they need to survive - scientists call this mechanism of species persistence the "spatial storage effect". In this study, we aim to explore the hypothesis that the germination and seedling microsite requirements of native species have disappeared from temperate woodlands.

In particular, we ask:

  1. Are native annuals declining because their cues for germination have declined (due to loss of native digging animals, fire exclusion)?
  2. Does modification of microsite patch-type (safe sites) effect germination and early seedling survival and growth of native annuals?
  3. Have annuals disappeared altogether after decades of disturbance exclusion because seeds lying dormant in the soil have now disappeared? At the conclusion of this study, we hope the profile of annual plants will have been raised and their conservation needs in temperate woodlands better understood.

Figure 1. One of the more common annuals of grassy woodlands in western Victoria is Hyalosperma demissum (Photo: Simon Heyes)

 

Figure 2. Annuals make an important contribution to woodland diversity but they have been declining over the last four decades. This projects seeks to understand why.  (Photo: John Morgan)

 

Figure 3. Seeds play a crucial role in enabling annuals to persist from one year to the next. This study will quantify how long they persist in soils, and the conditions that favour their germination. (Photo: John Morgan)