Long-term restoration success of re-sprouter understorey species is facilitated by protection from herbivory and a reduction in competition

Abstract

Factors affecting the long-term survival and growth of planted understorey species in reintroductions and restoration are poorly known. Seven understorey species were planted in jarrah forest restored after bauxite mining in the Southwest of Western Australia to test the effects of the competitive environment (both over-and understorey) and herbivory by large mammals on survival and growth over a 16-year period. Differences in the overstorey environment were achieved by planting the study species into restored sites differing in age (0, 1, 4 and 10 years of age). The understorey competitive environment was manipulated by removing other understorey species at the time of planting. Reducing both herbivory (using plant guards) and competition with other understorey plants significantly increased survival, spread and height growth of the study species. Planting into different ages of restored site significantly affected plant responses: survival and growth were maximal in either newly restored (year 0) or the oldest (10 years of age) sites. Across species, survival decreased to *50 % after 2 years, but thereafter mortality was low. These data demonstrate survival and spread of planted species over a 16-year period indicating that planting nursery-raised plants can be a viable strategy for establishing long-term persistent plant populations in both newly restored and older restored sites.

Re‐establishing the mid‐storey tree Persoonia longifolia (Proteaceae) in restored forest following bauxite mining in southern Western Australia

“…Rainfall during September and October of 2010 was well below average (Dwellingup weather station no. 009538) (Bureau of Meteorology 2015), however, despite this very low rainfall, seedling survival in the first trial was still 60 % after 3 months which is similar to survival experienced with other jarrah forest species planted into restored areas in normal rainfall years (Daws and Koch 2015). However, seedling survival when planted in the surrounding jarrah forest was variable.…”

“…In fact, the increased availability of water in newly restored areas compared with the surrounding natural forest appears to be somewhat advantageous for P. longifolia and it is likely that this is related to a lower level of competition from surrounding vegetation on the newly restored sites. Reducing competition has been found to also improve survival and growth of many other jarrah forest species during early growth and development and has lead Alcoa to adopt a one-pass approach to restoration whereby all restoration works involving the reintroduction of native plants is completed within a short window following the completion of all earthworks and landscaping (Abbott 1984;Daws and Koch 2015). Seedling deaths were greatest in the first few months following planting in both seedling trials, indicating that most deaths are likely to occur as a result of the profound change in conditions as they transition from the nursery environment to in situ conditions.…”

“…Nevertheless, while microclimatic variation was not measured as part of this study, Close et al (2009) found that shade cloth tree guards provide several tangible benefits to young plants by preventing browsing, minimising temperature effects on seedlings and creating a microenvironment that significantly elevates the levels of photosynthesis in spring which, in turn results in greater growth of seedlings. Other species have also been observed to increase in height and spread with the installation of tree guards including several jarrah forest species that are sympatric with P. longifolia (Daws and Koch 2015).…”

“…However, competition is greatly reduced and therefore water, light and nutrient availability is higher allowing some species to rapidly establish. Predation by herbivores may be more of a problem in these largely denuded landscapes as animals actively target the limited vegetation that may be present (Koch et al 2004;Stanton-Clements et al 2013;Daws and Koch 2015;Nield et al 2015). Thus the survival and growth of young P. longifolia plants could potentially be affected by the age of the restoration sites (microclimate effects), grazing from highly mobile herbivores and the age (size) of the seedling at the time of planting.…”

Saving threatened plant species: Reintroduction of Hill’s thistle (Cirsium hillii. (Canby) Fernald) to its natural habitat

“…With C. pitcheri, leaf damage was caused by insects that consumed segments of the leaves. Daws and Koch (2015) determined that herbivory can be reduced by barricading the reintroduction sites [40]. Physical barriers may improve survival rates of smaller Hill's thistle plants, however complete herbivory could be reduced in future transplants by taking advantage of the species natural defence system, spiny leaves, which seems to be a more effective deterrent as seen with larger thistle plants.…”