Christmas tree farms
Across the world, many families enjoy a fresh cut Christmas tree during the holiday season. As of 2012, the United States had over 15,000 Christmas tree farms that were growing an estimated 350 million trees on over 300,000 acres, or roughly 450 square miles1,2. European annual production of Christmas trees is estimated at 75 million trees on almost 300,000 acres, and Christmas tree farms have been increasing substantially in many European countries. The increase in Christmas tree farms has led to landscape changes that include converting grasslands (i.e. hay meadows and pastures) into land for the production of Christmas trees. In Belgium, there has been a particular increase in Christmas tree farms in the southern part of the country. In this area, Nordmann fir (Abies nordmanniana) and Norway spruce (Picea abies) production covers over 12,000 acres and makes up 3.3% of all farmland production. The Nordmann fir (Fig. 1) is the most popular Christmas tree in Europe and is known for its soft foliage and strong branches3.
Landscape changes and the bird community
As agriculture has increased, many forestlands that provide habitat and food for birds have been converted into croplands. However, the impact that landscape changes will have on bird populations depends on how the structure of the landscape is changing and how the farmland is being managed. Intensive agriculture, which requires high inputs of fertilizers, pesticides, and labor, negatively impacts farmland birds. Croplands that create homogenous landscapes that lack structural complexity, such as fields that only grow a single crop, also negatively impact bird species since they have fewer opportunities to build nests, hide from predators, and forage for food. While many studies have looked at the effect of landscape changes on bird populations, little research has been done on the how the conversion of grasslands into Christmas tree plantations affects bird communities.
Robin Gailly and colleagues recently published results of a study that aimed to measure the effects of grassland (Fig. 2) conversion into Christmas tree farms on birds in southern Belgium. They visited each of their 58 sampling locations twice, once from mid April to early May and once during June in order to capture birds both early and late breeding birds. During each visit, they recorded the number and species of birds seen within a 325-foot radius around the observer’s location during a 5 minute period. At each site, the authors also characterized the landscape . They determined whether there were hedges (i.e. bushes or shrubs) near the sampling location and measured the length of the hedges, because hedges are known to provide high quality habitat for birds. They also recorded the presence of tree rows at each sampling location.
Christmas tree farms enhance bird communities
Robin Gailly and colleagues found that the conversion of grasslands to Christmas tree farms increased the number of birds and number of bird species, but only in grasslands that had few hedges (less than 230 feet of hedges in 2.5 acres). In grasslands that had more than 230 feet of hedges per 2.5 acres, the positive effect of conversion to Christmas tree farms disappeared. This means that developing Christmas tree farms is only beneficial to bird communities if a grassland with sparse hedges is converted to a Christmas tree farm.
Overall, the bird communities in the grasslands were significantly different from those in Christmas tree farms. Birds that were found in Christmas tree plantations included 7 species that are listed as near-threatened or vulnerable in southern Belgium. These species include the Linnet, which was particularly common in Christmas tree farms. Linnets are commonly found on farmlands and create thorny nests in hedges and shrubs4. In addition to the Linnet, there were three other birds that significantly benefited from conversion of landscapes from grasslands to Christmas tree farms: the Yellowhammer, the Dunnock, and the Stonechat. No bird species were found to increase significantly in grasslands, although many bird species were found in both habitats. These species may benefit from the habitat complexity provided by Christmas tree farms, especially when compared to grasslands with few hedges.
Importantly, Gailly and colleagues also found that Christmas tree farms were not of lesser habitat value to specialist bird species, which only use specialized habitats to breed and, therefore, are especially sensitive to landscape changes. Despite this result, it is important to note that prior to this study, many intensive landscape changes had already occurred in southern Belgium. As a result of these changes, many specialist bird species including the Great Grey Shrike and the Whinchat have already disappeared.
It is important to note that while conversion of grasslands with a low abundance of hedges to Christmas tree farms may benefit some species, little is known about the quality of habitat that these Christmas tree farms provide. The research of Robin Gailly and colleagues provides additional evidence that hedges are important for birds because they enhance habitat complexity and provide areas for birds to nest, forage, and hide from predators. In areas that are lacking hedges, Christmas trees may provide a similar role. However, many Christmas tree farms are managed with chemicals to reduce weeds and insect pests, and this may also reduce habitat and food availability for bird species. Additional research is needed to learn about the quality of food resources and habitat provided by Christmas tree farms, especially as the industry continues to expand.
Gailly, R., Paquet, J-Y, Titeux, N., Claessens, H., and Dufrênem M. 2017. Effects of the conversion of intensive grasslands into Christmas tree plantation on bird assemblages. Agriculture, Ecosystems and Environment. Volume 247, pages 91-97.