Trees and turf

TREES growing in turf invariably introduce concepts of conflict and success of one at the expense of the other. However, in reality they should be considered together, complementing each other and adding to the design, structure and environment of the situation as a whole.

And nowhere more so than on golf courses, which by their very nature comprise turf of varying types, grades and qualities with trees added for playability, ecological or simply aesthetic and decorative purposes. Increasing numbers of arborists count the nation’s golf clubs among their clients.

Some of the best golf courses in southern England have been carved out of woodland and forest like this one in Sussex.

Trees and turf clearly have varying requirements each impacting on the other at various stages in growth cycles and at different times of the day and year. Provided individual needs can be catered for without prejudicing the other, there is no reason why trees and turf should not get along perfectly well.

Trees and turf are green plants competing for the same type of resource although differences in amount, timing and how secured sets turf and trees apart from each other. Dual positive growth and development of trees and turf essentially comes down to compatibility and compromise, ensuring tree planting enhances the environment with minimum effect on turf quality -- a basic requirement for prestige parkland and sporting situations like golf courses.

Trees and grasses are clearly not all things to all men. Grass is the biggest weed enemy of foresters who spend a great deal of time and money rescuing newly planted trees from grass competition. Trees springing up as seedlings or suckers in professional turf can present nightmare scenarios for groundsmen and greenkeepers.

Trees should not disrupt important ecosystems like fast-flowing streams.

Trees and turf exist side by side in a wide variety of amenity, landscape, sporting and leisure situations, but the one instance where the two are most inextricably linked is on the golf course. Greenkeepers will have planted their own trees or inherited them, and providing planting pattern and choice of species were well thought out, any negative impact on turf should be minimal and rectifiable, allowing managers to focus on broadleaved weeds which are the common enemy of both trees and turf on golf courses.

For playability reasons there is sometimes no other option but to fell trees or even lines of trees.

WHY PLANT TREES ON GOLF COURSES

Trees add to the golf course environment by enhancing the landscape, improving playability and broadening biodiversity. By the same token, tree planting should not be carried out in environmentally sensitive areas at the expense of biodiversity. Some key specific functions of trees on golf courses are:

Definition and delineation of the course including defining and dividing fairways, indicating the line of play and delineating out-of-bounds from playable areas.

Guarding greens, providing markers for locating lost balls and generally enhancing challenges presented to golfers.

Protecting the privacy of golf courses and providing shelterbelts and wind breaks especially in exposed locations and other situations like courses alongside railways.

Improving and complementing course character and aesthetics both visually and intrinsically through new and improved microclimates and ecosystems for extended biodiversity.

Overall success will ultimately depend on tree species selection and planting position. Trees are invariably planted around rather than inside main playing areas of fine and professional turf, but natural forest trees like English oak, common ash, common beech and lime can eventually impact both aerially and underground on greens, tees and fairway, even if planted well away from these key playing areas. Potential problems may not become reality until decades later so this should be borne in mind and factored in at planting.

Safety for players and the public is paramount. This old beech tree on a fairway and suffering serious wind damage had to be significantly reduced for safety reasons.

SUBTERRANEAN IMPACT OF TREES ON TURF

Calculations show 10 per cent of total tree biomass is underground as root tissue. Feeder roots of large forest tree species like English oak (Quercus sp), lime (Tilia sp) and common beech (Fagus sylvatica) stretch many metres beyond the edge of the tree canopy. Turf adversely affected by trees is persistently weak, off colour and will develop dry spots from which grass has disappeared but broadleaved weeds will continue to grow.

Trees and grass compete for the same resources (sunlight, water and nutrients) with trees usually at an advantage in the normal course of events. Tree feeder roots will be deeper underground exploiting water and nutrients that turf grass roots cannot reach. That said, trees may have exposed large roots at the soil surface, having arrived there by migration, or incidentally due to soil erosion. Hard roots protruding above the surface add a potentially dangerous dimension for mowing machinery.

Autumn leaves are attractive but can seriously damage the quality of professional turf.

Another problem is suckering where tree roots bear buds which develop into shoots and eventually self-supporting trees. Suckering is not common to all trees but prevalent nevertheless in a number of popular amenity trees. Common lime (Tilia x vulgaris) is a major culprit along with aspen (Populus tremula) and to a lesser extent common alder (Alnus glutinosa) and wild cherry (Prunus avium). Several exotic species, such as false acacia (Robinia pseudoacacia) and tree of heaven (Ailanthus altissima), are notorious for suckering and should only be planted after careful consideration though both are attractive trees.

Suckers can spring up a good distance from the tree, increasing as the old tree fades away and continuing to appear for many years after a tree is nominally dead. Not only are they unsightly and disruptive to turf but cause even more damage when attempts are made to physically remove them. The only effective way to eradicate sucker growth, without causing massive turf damage, is to use dedicated stump killers which contain systemically acting total herbicides used to kill woody species.

Very tall trees are normally avoided but one exception is Lombardy poplar (Populus nigra var.italica). Trees shoot straight up tall and narrow to give correspondingly slim shade with minimal impact on turf.

The biggest sucker in the tree world is the English elm (Ulmus procera), neutered by Dutch elm disease in the 1970s. Its suckers still appear 40 years later where large elms once stood. Continual production of suckers from fragments of root tissue left behind when trees were felled has allowed the English elm to remain as an integral part of hedgerows, and as poles growing up to around eight metres high until scythed down by Dutch elm disease, which is carried and spread by bark beetles. 

Greenkeepers faced with large trees causing damage to turf are essentially between a rock and a hard place. No option is ideal and all are essentially last-ditch responses.

The first is radical severe pruning of the canopy then waiting for the root system to react and retreat accordingly.

Dig a trench between the tree and the at-risk turf to sever the feeder roots.

Fell the tree and deal with the stump in a way that causes least disruption and damage to surrounding turf.

The best option is prevention rather than control. If a tree species has the growth and development potential to subvert turf with its root system or shade out turf under the canopy then don’t plant it in the first place.

AERIAL IMPACT OF TREES ON TURF

Aerial impact of trees is easier to assess and deal with because you can actually see what is going on. Trees may be planted to provide shelter, especially on exposed golf courses, but with shelter comes shade, lower light levels reaching the turf and reduced air circulation with higher humidity, more prolonged surface wetness and more turf disease.

Water stress in turf caused by tree roots is well known but large spreading and dense canopied trees also add to water stress by filtering out falling rain. Turfgrasses as a group do not respond well to shade and the overall effect is to compromise growth rate, turf strength and grass colour. Shade reduces grass root length and density thereby decreasing tolerance to traffic wear and tear. Experienced greenkeepers will tell you that morning sunshine is essential for turfgrass health and quality and difficult to achieve and maintain without it.

Shade and soil water imbalances brought about in turf by trees bring a range of biological baggage not normally seen on/in well drained sites and soils. This may include growth of moss, algae and a number of moisture-loving broad-leaved weeds, as well as a heightened threat of turf disease such as Fusarium patch (Microdochium nivale).

For accessibility reasons many of the country’s early golf courses ran alongside railway lines. Fast-growing conifers are commonly used to screen the course from a railway.

Greenkeepers need to think long and hard before planting trees around greens and tees. If shelter is the prime reason then evergreens and especially conifers including pines, firs and spruces are the obvious choice to provide shelter in winter (as well as summer), when clearly it is most needed. On upland courses with poor acid soil these conifers may be the only realistic tree planting option, but year-round foliage and shelter means year-round shade and higher humidity. This may prove critically damaging in spring and autumn seasons when Fusarium patch and other moisture-loving turf diseases are most active.

Deciduous trees which are in full leaf for the summer months only, when light and temperature are highest, may prove positive but when effects of leaf fall are factored in a different problem may arise. Fallen leaves encourage surface-feeding and casting earthworms and aggravate problems with thatch. Thatch is the layer of dead plant material at the base of the grass sward important to impart springiness in turf but negative when too thick.

Trees situated in playing areas should be pruned to a position above head height, especially thorny species like the hawthorn shown here.

Fallen leaves with a high tannin content are especially damaging because they will persist throughout winter and beyond without measurable decomposition.  Such leaves include pedunculate oak (Quercus robur) and sessile oak (Quercus petraea) and common beech (Fagus sylvatica) although pear (Pyrus sp) is the worst offender.

Better to go for trees like common lime with leaves that decompose and disappear quickly after fall. As a general rule best choices for turf sensitive situations are native species which are small in stature. Avoid species with spines and prickles such as hawthorn (Crataegus sp), blackthorn (Prunus spinosa) and holly (Ilex sp). Gorse is popular for shelter around greens on highland golf courses but tends to raise humidity levels as well as being particularly unpleasant to tangle with.

SELECTING AND PLANTING TREES

Trees planted in turf should tick the following boxes:

• Small in stature
• Non-suckering
• Deciduous or evergreen depending on situation
• Fallen leaves of deciduous species that decompose quickly
• No prickles, thorns or spines

Types of trees commonly seen on well-established golf courses show how greenkeepers know from experience those which can add to the course without impacting negatively on turf. Commonly seen trees include the smaller native species like field maple (Acer campestre), mountain ash (Sorbus aucuparia) and whitebeam (Sorbus aria), as well as exotics like red maple (Acer rubrum) and red Japanese maple (Acer palmatum atropurpureum). Lime is popular but usually as smaller stature types like Tilia cordata (small-leaved lime). Very tall trees are normally avoided but one exception is Lombardy poplar (Populus nigra var. italica). Trees shoot straight up tall and narrow to give correspondingly slim shade with minimal impact on turf.

Britain’s golf courses are custodians of some of the country’s oldest and most valuable trees, remaining from the estates and farmland on which they were constructed, like the ancient English oak seen here on a golf course in West Hertfordshire.

Using larger container-grown and root ball planting material, including standards, or smaller bare-rooted trees as whips or feathers is very much a horses for courses choice. Larger container-grown and root ball trees will establish more or less straightaway and reach the required size in a much shorter space of time. However, they are more expensive, require more disruptive planting methods and secure staking and tying and therefore adding to costs.

Even when afforded with protection and growth encouragement from tree shelters, small trees take much longer to establish and reach an adequate size. On the plus side, they are cheaper to buy (and replace if they fail), cause less disruption and damage to turf at planting and do not generally require staking and tying. All newly planted trees require good routine care and maintenance including weed control, fertiliser application and watering especially during summer. Tree guards of appropriate height are required if the course is home to bark-gnawing and foliage-browsing wild mammals like rabbits and deer.

THE DUAL NEEDS OF TURF AND TREES

Routine course maintenance, including fertiliser application, chemical weed control, irrigation and grass cutting, is when the need to satisfy the dual requirements of turf and trees becomes abundantly clear. Turf fertiliser regimes are clearly inappropriate for trees in composition and dosage, while fertiliser regimes recommended for trees may scorch the turf around the base of the tree. This can be avoided by using slow-release formulations.

The type and level of irrigation used on shallow-rooted turf grass in summer is inappropriate for trees. Water will evaporate from the topmost layer of soil before it can reach deeper seated tree roots, while standing water may build up around the base of the tree, causing physiological damage and encouraging disease. Newly planted and establishing young trees must be watered regularly. Well established and mature trees are unlikely to require irrigation except during really severe drought. Trees tend to benefit from a smaller number of higher volume and well-targeted applications of water.

Exposed surface roots of a conifer tree which have been shaved during mowing.

The situation regarding surface cover on the soil immediately around trunks of large mature trees is complex and vexed. Turfgrass cover close to large trees is difficult to maintain because broadleaved weeds will readily invade and take over. Mulching material or mulch structures such as mats that eliminate all growth, turf or weeds, may be used. The downside is disruption of fertiliser application and uptake by trees. The alternative is to leave the soil bare and control broadleaved weeds as they appear. But weeds are a year-round problem even in winter when fast-growing ephemerals like chickweed and speedwells quickly colonise bare ground. The best option is to persevere with shade-tolerant turfgrasses. Careless use of mowers or strimmers around trees inflicts bark damage, paving the way for entry of bark-infecting pathogenic fungi and bacteria. Likewise, any use of herbicides around trees must be conducted with care, using shrouded applicators. Herbicides used to control broadleaved weeds under trees will invariably be total in action, which means any turf grass will also be killed.