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Creating new means of assigning old growth forest status


Indexes of high forest continuity associated species used to determine ecological value

The usage of tree age as the primary indicator of old-growth forest has been identified as flawed by many but in Northern America it has often been used to identify forests of high conservation priority though the presence of older trees in the stand. In Europe, the usage of forest continuity has been more popular and “ancient woodlands” in the UK are characterised by period of time continuously forested.

Areas which have been continuously wooded are thought to be more valuable from a conservation perspective even in the absence of old-growth indicator trees as they give longer for species to establish and microhabitats to form. Crucially, forests can contain old growth trees whilst still not having been continuously wooded making them an ineffective indicator of high conservation value forests. Critics of the forest continuity approach have pointed out that habitat quality is more valuable than duration of forest presence and that important microhabitats may also be formed spontaneously, independent of age.

Reliable long-term landcover maps are needed to establish continuity from records and these are not always available. As an alternative the authors proposed the usage of species indexes specific to high-continuity forests to allow identification of the most ecologically valuable forests. Using indicators in this way allows comparison of similarly-aged stands for ecological value where comparing tree ages would not. These niche-specific species are also directly impacted by microhabitat presence and so would also help select for high habitat quality.

In the UK some epiphytic lichens are associated with ancient woodland and have been compiled into a list of indicator species. Red-listed bryophytes have been applied in a similar manner, along with polypore fungi associated insects. These insects require a specialised microhabitat which is strongly associated with continuous availability of dead and decaying trees. Lichens are also popular indicator species, however, they often require taxonomic expertise to identify, particularly calicioid lichens. Whilst DNA barcoding and image recognition software may aid with cryptic species the authors propose that prioritising field-identifiable species which forest surveyors can be trained to recognise would be most efficient.

Abundance of an individual species was also suggested as an alternative to presence, however, establishing what level of species abundance qualifies the forest as ‘old growth’ would be challenging. In summary the authors suggest the development of indexes and corresponding proportions for different regions. The advantage of this approach is that not all species need to be present for the forest to be classified as old-growth and it would allow the identification of ecological value irrespective of tree age.

McMullin, R.T. and Wiersma, Y.F., Out with OLD growth, in with ecological contin NEW ity: new perspectives on forest conservation. Frontiers in Ecology and the Environment. https://doi.org/10.1002/fee.2016

To find over 600 similar papers use the following search in the forest science database: ("old-growth forest*" OR "ancient woodland") AND (identif*) AND (conserv*)