Seeds need to ensure they can disperse far and wide to enable the survival of their species. Seed dispersal acts to minimise competition between plants of its own species, expand the species’ range through exploitation of new habitats, and maintain genetic diversity in the population by reducing potential of inbreeding. Effective seed dispersal is not only important for the plants themselves but also for the animals that rely on them for survival.
One of our Konik ponies grazing at New Fen, a wetland site.
The animals on our reserves are carefully selected with many factors in mind, including their seed dispersal potential for the specific habitat type we want to place them in. Different species are used in different terrains and habitats as some are more effective at seed dispersal in particular environments than others; for example, Konik ponies are effective at dispersing aquatic plant seeds in wetlands.
Our conservation grazing cattle play a huge part in seed dispersal and germination. Compared to roe deer which can act to disperse 28 types of seed, cattle can disperse up to 230 types of seed. We use a variety of cattle breeds because they all have different personalities and qualities.
Highland cattle grazing on Hothfield Heathlands reserve.
Therefore, we can tailor our grazing effect to each different site depending on what we want to achieve there. For example, longhorn cattle are able to pull down trees with their horns; shaking them in the process and dispersing their seeds. The long coats of Highland cattle are perfect for acquiring sticky seeds that drop and disperse when the cow rubs itself. Sussex cattle have a large appetite, so they are most effective at dispersal by ingesting and excreting seeds. Using cattle and ponies in a mixed grazing setting allows for a greater range of plants to be consumed and dispersed.
Zoochory is the act of an animal dispersing seeds. It can occur through a variety of methods. Mainly livestock will transport seeds either through transportation outside the animal (epizoochory) or within their digestive system (endozoochory).
The transport of seeds by an animal externally is termed epizoochory. For example, the transport of seeds on the coat, fur, or wool of an animal. Seeds transported in this way are enclosed within capsules adapted with hooks, barbs, spines, or adhesive mucus which attach to the animal and will eventually break apart and release the seeds.
Generally sheep are sheared around the time burrs become abundant, so there is limited dispersal by adults as their fleece is too short for burrs to attach. However, lambs that are not sheared (such as the brown coloured Herdwick X South Down lambs pictured) will experience some attachment of burrs to their fleece. Like ponies the lambs can rub themselves against trees and break up the burrs to release the seeds. Grazing animals can also transport seeds that may get lodged in their hooves as they move around the reserve.
Goats disperse seeds in a similar fashion to sheep (through ingestion and on fur/fleece), however the species they can transport differ. For example, goats can ingest and disperse heather (Calluna vulgaris) whereas sheep often avoid it.
The act of an animal ingesting a seed and transporting it within their internal digestive system is termed endozoochory. 41% of plant species use ingestion by large grazing animals (such as cows and ponies) as their primary method of dispersal.
While grazing, animals often unintentionally ingest seeds. These ingested seeds then move through their digestive system and are excreted. The animal’s dung (such as the pony dung pictured) acts as fertiliser for excreted seeds, resulting in seeds germinating from their dung! If the animals trample the dung, seeds have the potential to be dispersed to an even greater degree. If seeds have been ingested by a ruminant (such as cattle or sheep) they may be spit from the cud (rather than excreted) and dispersed in this way. Cud is regurgitated food from the rumen that must be re-chewed before digestion.
Small shoots germinating from Fell pony dung at Queendown Warren.
Some seeds can only germinate once passing through the digestive system of an animal. For example, the hard seed coat protecting blackberry seeds need to be eroded in digestive acid before they can germinate. Without grazing animals (who eat the plants and break down the seed coat in their digestive system), plants such as these could be lost; simply using a strimmer to control vegetation would not give the same results!
The animals on our sites not only distribute seeds but help with their germination too. The dung of monogastric animals such as ponies contains more nitrogen, low moisture, and has good drainage, providing an ideal habitat for certain plant species to grow (e.g. nettles, thistle). Ruminants such as cattle excrete less nitrogen and more moisture, providing habitat for different plants species.
Different breeds of livestock with differing weights can be useful on different sites depending on the soil type, creating space for plants. For example, our Dexter cattle are very small and light, so we put them on sites where we don’t want the ground to become too heavily poached as we are aiming for light disturbance.
One of our Dexter cattle at Hunstead.
Sometimes larger animals that create hoof holes in mud are useful; some plants can only germinate and survive in wet, muddy holes created by hooves such as the endangered three-lobed water-crowfoot (Ranunculus tripartitius) that grows on heathland and acid grassland habitats in the South East. It therefore thrives in areas with heavy livestock, such as cows, that disturb the ground.
Grazer dung also provides habitat for dung beetles. As dung beetles bury in dung, they may pull seeds down into the ground, allowing the seeds to escape being eaten by other animals, enhancing their chances of germination.
Pigs are another species we use on our sites to enhance seed germination and seed dispersal. The rootling behaviour of pigs (when pigs dig up the soil in search of food and minerals) acts to turn over the soil and break up dense vegetation to assist seeds of lesser competitive plants to germinate. Some plants (e.g. corncockle) are only able to grow on disturbed ground, thus pigs are essential for their survival. For example, our large black pigs on Nashenden Down rootle the ground, opening the soil for the seeds of rare chalk downland plants to enter and germinate. Unlike mechanical ploughs, rootling pigs don’t break up the mycorrhizal network, therefore preserving these complex fungal interactions between established and germinating plants. The action of pigs is more comparable to a trowel, gently turning the soil over.
Please see Alison’s blog on Pigs and Wildflower meadows for more information.
