Ecology of economically important teak Tectona grandis and sal Shorea robusta informed by palaeo-data

In managing ecosystems, it is important to understand the ‘natural’ regime in an ecosystem (Willis and Birks 2006), wherein what is ‘natural’ means the variation in ecosystem traits and properties as a function of climate variables and disturbance regimes across time. Components of ecosystems may be very dynamic (Brown et al. 2001) and be formed by historical legacies of disturbance regimes (Maezumi et al. 2022). However, modern scientists are unable to understand the underlying dynamism in ecosystems because they only have access to present-day distribution of species and ecosystem traits. Long-term ecological research stations are at best <200 years old and may not be able to provide the necessary length of time in which ecosystem dynamics play out. The problem of understanding what is natural is further compounded in the case of economically important timber species as their present-day distribution may far exceed their natural range due to past efforts in creating and managing plantations of these species. The current distribution of many timber species may not be due to natural dispersal, or natural affinity for the environmental conditions in that area, but due to silvicultural imperative. Using only present-day distribution for understanding species also may under-estimate their tolerance for different environmental conditions. This is particularly true for teak (Tectona grandis) and sal (Shorea robusta), two of the most economically valuable timber species in India. At present, they cover large tracts of India (~40%), but their future persistence and resilience under future climate change scenarios is uncertain. We create a paleo-dataset for Central India that includes climate, species composition and human disturbance across space (15 sites across the region) and time (across the Holocene)(Agarwala and Kulkarni, 2024) and use it to understand long-term factors associated with dispersal and extinction of teak and sal. We create spatially-explicit models for teak and sal dispersal and extinction across space and time, and parameterize these models using greenhouse experiments. We find that Sal occurrence is significantly explained by times of higher temperature and sites with higher precipitation and temperature, while teak occurrence is explained by significantly higher temperature. Role of fire appears weak despite being considered important in modern literature. Using this approach, we are able to successfully model teak and sal expansion and extinction, understand the interaction between climate, disturbance and demography. This approach may be used to create more accurate species distribution models than those using only contemporary distribution data.

Agarwala M, Kulkarni C (2024) Quat Environ Hum 100032. https://doi.org/10.1016/j.qeh.2024.100032
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https://doi/10.1126/science.293.5530.643
Maezumi SY et al. (2022). Philos Trans R Soc B Biol Sci 377:20200499. https://doi.org/10.1098/rstb.2020.0499