Provenance variation of ecologically important traits of forest trees: implications for restoration.
Abstract
The source of seed or plant material can have profound implications for the success of restoration efforts because most species exhibit adaptive genetic variation within their range. Understanding the geographical distribution of ecologically relevant genetic variation and the environmental factors driving adaptive divergence within species will help to ensure appropriate sourcing of material for ecological restoration. We present a study of geographical variation of ecologically important traits of the forest tree jarrah Eucalyptus marginata from a 15-year-old provenance trial in south-western Australia. We assessed trait variation in association with rainfall, latitude and slope position at the site of origin. Survival and stem diameter varied at the largest scale, between northern and southern jarrah forest provenances. Stem diameter also varied among rainfall zones, while latitude was a more important determinant of variation of reproductive traits (flowers and buds). None of the environmental variables accounted for significant variation of height, growth form or the presence of capsules. Slope position at the site of origin did not account for significant variation of any trait. Trees from low rainfall sites had smaller stem diameters, possibly reflecting selection for slower growth. Such a strategy could prevent drought stress and may explain why trees from the high rainfall southern jarrah forest, which showed the fastest growth, had the poorest survival at the drier northern trial site. Variation in the presence of buds and flowers among latitudinal divisions may be because of variation in flowering time, which has been observed previously among E. marginata populations. However, variation among replicate blocks within the trial suggests that the environment also strongly influences expression of these traits. Synthesis and applications. We have demonstrated divergence of several ecologically important traits in association with different types of environmental variation. Our findings support an argument for 'habitat matching' when sourcing material for restoration; however, differences among trait types in the distribution of variation highlight the need to consider environmental variation at a range of geographical scales. Consideration of ecologically important genetic variation within species is important and this information should be integrated into seed collection strategies for ecological restoration.