Chasing change from fynbos to forest: Exploring drought impacts in an old growth stand of the Knysna Forest

Reaching the leaves of our study species was no mean feat. Despite having extendable tree-pruning shears, Jasper and Tom spent a fair amount of time on each other’s shoulders desperately trying to reach even the lowest branches of some of our species (Photo: Genevieve Thompson) Genevieve (left) and Emma collect leaf and wood samples while recording taxonomic and geographic information of tree species in Lelievlei (Photo: Thomas Morris) Large trees create gaps in the forest, providing space for new individuals to establish (Photo: Thomas Morris)

By Emma Gray, SAEON Intern and Genevieve Thompson, SAEON Postdoc

Within the inner sanctum of the Knysna Forest lies the Lelievlei Nature Reserve, an IUCN registered protected area that has never been harvested for timber.

A grid of 108 survey plots established almost three decades ago provide an excellent source of data to explore forest dynamics and test the impacts of global change.

The plots have been resurveyed on three occasions since 1985 (in 1991, 2001 and 2011), sample 5% of the total area of the forest, and provide records of tree diameter, species identity and condition (i.e. healthy versus stems infected with pathogens).

Exploring the Knysna Forest

While Fynbos is usually the name of our game, exploring a different biome that occurs within the same climatic regime but is subject to dissimilar ecosystem dynamics, may provide valuable insights. This impressive dataset provides an excellent opportunity for SAEON to assess changes in forest dynamics with changes in climate.

Life-history data were collected to supplement the earlier SANParks surveys. We aimed to determine if variation in plant traits could explain species specific responses to change in climate.

A team from the SAEON Fynbos Node led by Jasper Slingsby (Scientist), joined by Genevieve Thompson (Postdoc), Emma Gray (Intern) and Thomas Morris (UCT Botany Honours Student) spent a week in the forest, sampling and processing 10 individuals of each of the 27 tree species in the long-term dataset.

The trip began with some intensive field identification training by forest ecology guru and SANParks scientist, Graham Durrheim. Long days spent searching for, tagging and bagging specimens, complemented with pop quizzes at night meant that, by day three, all members of the team could identify even the leaf fragments that fell from their socks at night!

Aims and relevance of research

This extensive dataset will be used to ask the following questions:

1. Has the total basal area, biomass, or growth rate in the forest changed over time?
2. Can these changes be related to species specific responses and/or plant traits?
3. Has there been a change in recruitment and mortality rates?
   
4. Can the observed patterns be correlated by climate changes?

The results will allow us to measure potential responses (at the species or community level) to changing environmental conditions. Ultimately, we hope this information will aid our understanding of the effects of climate change on the Fynbos, as well as inform forest conservation and management of the protected area.