Making woodlands future-proof

We must learn from the past if we are to create plantations that will survive the test of time. 

Growing good quality timber is a uniquely long-term proposition and the choices that we make now about a wide range of different aspects, including species selection and provenance, site suitability, ground preparation, drainage, planting density and thinning, directly affect the result decades down the line. 

This may seem self-evident but however carefully we think through our decisions, it’s difficult to predict what the outcome will be many years into the future and it will almost certainly be someone else dealing with the consequences. 

Accepted norms can turn out to be unreliable or just plain wrong and innovation always entails a level of risk. With the benefit of hindsight though, it’s possible to spot miscalculations made in the dim and distance past and learn valuable lessons from them. 

Understanding what didn’t work as well as what did work helps us to avoid making similar mistakes in the future.

Species selection

Everything we do when we establish a new woodland or replant an existing one affects the condition of the wood as it matures. Choosing species that are suited to the site is perhaps the most important decision of all. 

Due to oversupply in its nursery, one south Scotland estate chose to restock more than 100 hectares with Douglas fir in the 1980s. Unfortunately, the sites were poorly drained and too exposed and most blew over mid-rotation with the consequence that the income from clearing the timber fell well short of the restocking cost. 

The estate effectively lost half a rotation on the affected area, significantly denting future productivity. 

Although this is an extreme example, it highlights the importance of getting species selection right. 

Nowadays, climate change is also an important consideration. Eastern Scotland is projected to get significantly drier over the next 50 years so caution is required when selecting species on well drained sites. 

Sitka spruce, for example, is vulnerable to drought crack and on drier sites it is becoming increasingly susceptible to green spruce aphid Elatobium abietinum, which can substantially reduce growth rates. 

Ground preparation

Ground preparation is also an essential part of successful tree establishment and affects everything from the growth rate and stability of the crop to when it will eventually be harvested. 

For many years, deep double mouldboard ploughing was the industry standard for establishing trees in almost any soil conditions, eventually falling out of favour because it encouraged poor root development and increased the risk of windthrow. 

Ploughing was replaced by excavator mounding which became the ‘one size fits all’ solution for most ground prep needs. 

However, although mounding provides flexibility on a wide range of site types, it also has its disadvantages, particularly on restock sites. 

At Elderslie Estate in Renfrewshire, for example, some mid-rotation stands of Sitka spruce have established on top of large mounds and are poorly rooted, limiting management options by making thinned stands more vulnerable to wind damage. 

Hinge mounding produces a large hole with a mound next to it. When this is combined with old stumps from a previous crop, the uneven terrain can make the going difficult for smaller scale harvesting machinery. 

As the forwarder lurches from side to side, the bolsters at the back can scar remaining trees and the random spacing that mounding produces makes it difficult to cut racks through the crop in the usual way, sometimes resulting in the removal of too many trees. 

Spoil drain mounding is a widespread practice and on the face of it has a range of potential benefits on wetter restock sites with heavy brash, improving drainage and brash management and making it much easier to achieve the uniform tree spacing necessary for growing good quality timber. 

However, this method results in deep trenches scattered across the site which can seriously hinder future harvesting operations. On some Forest Enterprise sites in the Highlands, stands cannot be thinned and even clear felling may present a challenge in the future. 

Mounding may fit the bill on some sites but there are an increasing number of alternative treatments which can be tailored to particular site requirements. These include scarifying and shallow continuous mounding which are significantly cheaper on restock sites where brash conditions allow and also work well for many new planting sites. 

Thinning

Nowadays, thanks to the increased demand for wood fuel, thinning is a profitable activity again and, if conditions are suitable, the advantages are so overwhelmingly positive – increased volume, improved timber quality and improved crop stability, not to mention considerable biodiversity and amenity benefits – that it makes sense to plan ahead and ensure that thinning can be carried out efficiently when the time comes. 

By thinking through the process and considering how each stage is linked we can help to promote woods that are more productive, adaptable and vibrant in the future – and in the process hopefully avoid being cursed by the next generation of forestry managers