Chester Zoo: Fodder production from Short Rotation Coppice willows

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Prior to planting the willow setts are put in a shallow water bath for 24 hours to rehydrate.. The cuttings are planted with a Checchi and Magli planting machine that was purchased second hand for around £5,000. The stocking rate is 20,000 per hectare with 1m spaces between plants in the row and 0.5m spaces between the rows. The planting operation usually takes place in April and requires three persons (one driving a tractor and two planting). Planting one hectare takes 2.3 days in total (7 person days).

The small area planted, the weed free seed bed and slow methodical work rate means that there have been few failures. As a result, the team has never needed to gap up.

The main cost of planting are the labour costs and the willow plant material (£0.15 – £0.17 per 40 cm cutting, £3,000 to £3,400 per hectare).

Harvesting

Once established a plantation is left for at least 2 years before a first cut is taken. After that, the majority of the willow plots are kept at 1-2 years old regrowth. Some older plantations also provide thicker wood for other uses.

The willow is harvested between 1st March and the 31st October. An MCR crawler excavator and skid steer loader machine with an attached tree shear is used for the job. This cuts and places stems in a trailer. One of the operatives uses the tree shear for four hours per day. In this time period it is possible to harvest around 250 multi-stemmed stools (1 stool per minute) which provide around 1,500 stems and fills a single trailer.

The willow plantations are harvested sequentially, and it is possible to get two cuts per year. The only thing that halts progress is one of the team spotting a bird’s nest. In this situation the area around the nest is marked and the harvester goes around it giving it a wide berth. Since 2018, only around 5 or 6 nests have been spotted as immature, weed free willow plantations do not usually attract nesting birds.

Figure 10: Aerial photo showing the gradual harvesting and regrowth of the Buzzard field planted in 2019. The area on the left-hand side has been left, probably as a result of a nesting bird family.

The harvesting process is slow. If the willow was cut manually with chainsaws the team could cut more but it would take a longer time to gather the stems. In addition, the cut stools can act as a tripping hazard and cutting at ground level and excessive manual handling can cause operators to suffer from repetitive strains leading to work days being lost to staff sickness.

The main costs associated with harvesting are the rental of the excavator, the cost of labour each day and the diesel used (100 litres per week). The tree shear was a one-off capital cost of ca £7,000.

Animal browse preferences

The willow only remains fresh for 2-3 days, so it is moved immediately to the Zoo yard where the team processes it depending on the type of animals that eat it. To mimic natural habits of feeding from high tree branches, the willow stems are tied together and suspended from poles in the giraffe house. Some are stuck in the ground for elephants or pushed through cage sides to offer angled whips for rhinos and Congo buffalos. Some willows are stripped, and the bark and leaves placed in ball cages as a form of willow silage.

This is a laborious job and often is done by volunteers or people on corporate away days.

The typical yield of willow fodder (fresh stem, first year shoots after cut back, cut in May and September) is estimated to be 0.05 kg per stem, 2 kg per stool and 30 tonnes per hectare. Table 2 indicates the typical amounts of browse consumed by each type of animal and the area of willow required to meet 25% of their dietary needs.

Most animals get bored of eating the same food all the time so having lots of different willow varieties is important. Ideally, varieties should have big leaves that go all the way down to the base (such as Endurance, Paramore and Terra Nova). 

Other favoured trees are beech, hornbeam, silver birch, apple and ash. From November to the end of February the zoo has to rely on donations from tree surgeons. Currently they accept 4-5 donations of browse per week from golf clubs and fishing clubs.

Dealing with the waste matter 

Some animals eat the leaves and bark and other eat the wood too. But there is still a great deal of waste material to clear up. The leftover stem wood could be chipped and used as a biomass fuel to heat the premises. However, currently all the leftover willow is mixed with other arboricultural arisings and muck from the Zoo and shredded before being turned into compost. This can be spread out on the land or used as a soil improver around the zoo gardens.

Successes

The animals really enjoy willow fodder and eat it readily. It is also nutritionally valuable to the animals and is advantageous to the zoo as provides a very consistent and safe food source. This is one of the main worries for zoos as they have to find plentiful supplies of locally available browse. Some plants can be safe for some animals and poisonous to others. Furthermore, arboricultural arisings may contain material that is toxic, and this is difficult to pick out during sorting especially when a number of people with different plant identification skills are doing the job. As a result, it is hard to avoid some unwanted vegetation getting through the sorting process. Therefore, by using their home-grown willow, Chester Zoo can be sure that their prize assets, the zoo animals are less likely to be affected by poisonous plants.  

Challenges

There are several parts of the chain that could be improved on:  

• The harvesting and sorting process is slow and laborious. The efficiency could be improved but this would require investment to design, build and test bespoke machinery.  

• One area that would be beneficial is the potential to harvest earlier in the spring and later in the autumn. Certain willows produce leaves outside the seasonal norm. For instance, the variety Endeavour flushes early (February) whilst Endurance doesn’t lose its leaves until late in the year (early December).  

• The Zoo would like to increase the amount of willow and other browse material that they produce themselves. Currently, willow provides 25% of the fodder each year. The limiting factor is the amount of labour required to process this and remove the waste. The latter is particularly important as failure to deal with the waste material can cause a backlog earlier in the supply chain.  

• Using other favoured trees is interesting but problematic as they tend to take up a larger area (as they require more space between plants), grow slower and take longer to grow back once harvested.  

Economics

Chester Zoo’s total feed bill is £550,000 per year. The cost of willow production has not been fully determined as there are many variables, especially as many people are involved in different parts of the process and the amount of time for individual tasks is not recorded.  

However, based on discussions with staff members we have estimated the cost of production for each tonne and each kg of willow browse. This is detailed in Table 3. 

Table 3: Estimated annual costs of willow production and disposal at Chester Zoo.

Lessons learnt

The Chester Zoo willow browse production system enables an admirable closed loop allowing all the material produced to be utilised as feed and the waste recycled into compost. It is currently a very expensive and labour-intensive process, but this has to be weighed up against their number one priority for animal welfare. It is still early days, and the browse team are interested in developing ways for the process to be streamlined in order to improve efficiency and cut costs. 

Acknowledgements

With thanks to Philip Esseen, Mark Hargreaves, Christopher Gee, Will Condliffe and the giraffe keepers at Chester Zoo.