1/ Can trees grow in Oostvaardersplassen (OVP)? This experimental study reported that no planted saplings survived when unprotected. But protected trees in pre-grazed/rooted areas had higher survival. Trees need grazing refugia. #rewilding #rewildingscience
2/ Large herbivore effects on vegetation structure is well studied in Europe but on managed rather than rewilded land. ‘An unanswered question is to which degree rewilding with large herbivores can form wood-pasture landscapes on productive abandoned agricultural lands?’
3/ “S. factors are known to affect sapling survival. 1) browsing and trampling by large herbivores limit sapling survival, esp. at high herbivore densities. 2) light competition with herbaceous plants can limit sapling survival, particularly in the more productive ecosystems.
4/ 3) soil properties such as low nutrients, high moisture and limited oxygenation can limit sapling survival.”
5/ This study used an experimental set up to look at sapling survival with no, partial, full large herbivore access, in areas of tall roughs or short lawns and soil-disturbance (undisturbed or soil-tillage). Transplanted saplings were six shrub & tree species. 4 year study.
6/ “Since their introduction, the herbivore population increased to 360 heads of cattle (0.18 ha-1), 1220 horses (0.61 ha-1) & 3580 red deer (1.8 ha-1) in 2012, resulting in a total number of 5160 large herbivores (2.6 ha-1, considering the dry
2000 ha only).”
7/ This is much higher than in areas where large herbivore density is managed which typically have densities between 0.1 and 1 animals/ha-1. Currently in OVP mature trees are dying from old age and debarking.
8/ Within 50 days of planting only 6% of saplings outside exclosures were still alive, compares to ~67% in full and partial exclosures, and no seedlings survived outside exclosures after 4 years.
9/ Within exclosures survival was 67% after 50 days, 42%, 32%, and 25% after 1, 2, and 4 years respectively. Spiny species Rosa and Crataegus and (42% and 43%, respectively) had highest levels of survival. And more trees survived in the lawn areas compared to rough.
10/ All species benefitted from tillage (mimicking wild boar rooting) after 1 year, but then rooted patches were associated with pioneer species (Sambucus and Salix) after that. While soil tillage was consistently bad for Crataegus in lawn areas.
11/ These results highlight that high herbivory can promote shrub and tree sapling growth but only with spatial and temporal refugia from grazing, browsing, & rooting. ie herbivory is beneficial where it is intense and then dramatically falls.
12/ Refugia from herbivores can be created by coarse woody debris, spiny thickets, rock outcrops or islands. At OVP greater temporal & spatial variation in herbivory could be achieved by raising the water table, creating corridors to neighbouring sites, or the return of the wolf.
13/ Harsh winters can also cause a die off in herbivore numbers that could be followed by a pulse in tree recruitment. Since this study was carried a harsh winter did result in high mortality. theguardian.com/environment/20…
14/ The paper is by @ChrisSm70086265 et al and titled Rewilding with large herbivores: The importance of grazing refuges for sapling establishment and wood-pasture formation. A very useful read for anyone interested in #rewilding with large herbivores.
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