Which is better for the environment; one large tree or ten small ones?

The Rivers of Carbon approach is one where we seek to protect first and restore second, as we know that intact remnant vegetation is more diverse and productive than new plantings which take time to grow and develop.   A recent journal article published in Biological Conservation in November 2015 entitled ‘Single large or several small? Applying biogeographic principles to tree-level conservation and biodiversity offsets’, examines the trade offs between keeping a few large trees or compensating them with many smaller trees – it makes for interesting reading…

Land development contributes to the clearance of large trees that are sometimes offset with many smaller trees as compensatory wildlife habitat. But are many smaller trees a valid biodiversity offset for the loss of a single large tree? To answer this question, members of The Fenner School of Environment and Society at the ANU tested predictions underpinned by island biogeography theory. Targeting birds, they investigated size and landscape context effects at 72 trees of three sizes (small, medium, and large) located in four landscape contexts (reserves, pasture, urban parklands, and urban built-up areas).

Key findings include:

  • There are significant positive relationships between tree basal area, bird abundance and species richness in landscape contexts
  • Many small or medium trees accumulated the same number or more species than larger trees in reserves and urban built-up areas
  • Many small or medium trees accumulated fewer species than large trees in pasture and urban parklands
  • Overall, 29% of bird species were recorded only at large trees

These findings concluded that many smaller trees will not be suitable habitat compensation for all species. Therefore, complementary approaches to biodiversity offsets are needed, balancing both revegetation and large tree preservation. Furthermore, it was discovered that response patterns for birds at trees conformed to some biogeographic predictions (species-area relationship), but not others (habitat-isolation relationship), underscoring the need for novel conceptual frameworks for habitat structures in modified landscapes.


Article reproduced from Single large or several small? Applying biogeographic principles to tree-level conservation and biodiversity offsets.

Original article written by: D. Le Roux, K. Ikin, D. Lindenmayer, A. Manning and P. Gibbons

More information: Full journal article available here.