PS 27-112
Seeds versus seedlings to foster oak forest restoration: A new device to overcome old problems
Oak woodlands are one of the main vegetation types in the Northern Hemisphere. These forests have suffered disturbances for millennia, and they are currently one of the main targets in restoration policy. The most common oak reforestation technique is via plantations of nursery-grown seedlings, whereas acorn sowing is largely ruled out due to the high seed loss inflicted by vertebrate predators, mainly small rodents. However, the development of planted nursery-cultivated seedlings is poor, whereas the growth and survival of seedlings originated from sown acorns usually renders better results. Moreover, acorn sowing may be cheaper and is technically easier. We have developed a device that may potentially reduce (even eliminate) seed predation by rodents, while reducing seed predation by larger vertebrates such as ungulates. It is a structure with a truncated shape, either conical, pyramidal, or any other geometrical shape, that contains the seed in its interior and has an aperture for the shoot and the root. The whole device is a few centimetres in size and it is buried in the soil with the seed inside. We hypothesize that 1) this device will reduce acorn predation and 2) it will not affect the germination rate or seedling development. Consequently, we hypothesise that the device will enhance the success of reforestation via seed sowing. To test its viability we conducted seed-sowing experiments under field as well as nursery conditions. The access of different guilds of predators (rodents vs. ungulates) in the field experiments was controlled using either fenced vs. non-fenced areas, or habitats with different structural complexity.
Results/Conclusions
Seed predation in fenced areas was nil for acorns protected inside the device, whereas non-protected seeds suffered high rates of seed predation (overall above 60%, depending on the area). Ungulates such as the wild boar provoked seed losses even inside the devices, but its effect was reduced compared to non-protected acorns. Seedling development was not affected by the device. We conclude that the use of this seed protector may boost oak reforestation via acorn sowing provided that there is a way to reduce the access of ungulates. This may be achieved in situations of low population levels of ungulates, by fences or other artificial structures, or by taking advantage of habitat complexity provided by physical and biological structures such as snags, shrubs, etc… Overall, the results support the contention that oak reforestation via seed sowing is feasible.