Tutkimukset

Prescribed fire and retention forestry enhances pollination services for bilberry and lingonberry

Prescribed fire and retention forestry enhances pollination services for bilberry and lingonberry

Source: Rodríguez, A. & Kouki, J. (2015): Emulating natural disturbance in forest management enhances pollination services for dominant Vaccinium shrubs in boreal pine-dominated forests. Forest Ecology and Management 350: 1-12.

Bilberry (Vaccinium myrtillus) and lingonberry (Vaccinium vitis-idaea) are the most common vascular plant species in North European conifer forest understory. Both dwarf shrub species provide additional income to households and are the center of recreational outdoor activities. In addition, bilberry and lingonberry provide food and shelter for many pollinators (e.g. bumblebees) and herbivores (e.g. capercaillie). They are indeed one of the major drivers in boreal forest ecosystem dynamics, influencing e.g. on soil nutrient and carbon cycles.

Lingonberry flowers

However, bilberry and lingonberry have decreased their cover over 50% since 1950s in Finland. There are many reasons for the decrease of berry yields. Clear-cuttings increase direct light and soil drought, tillage destroys shrub rhizomes and fertilization decreases shrub cover. Furthermore, forest density and the proportion of young forests have increased.

Due to the decrease of berry yields, it is important to develop forest management methods aimed to promote biodiversity through mimicking of natural disturbances. Prescribed fire and retention forestry are this kind of methods. Prescribed fire offers dead wood and suitable areas for post disturbance recovery and recolonization of dwarf shrubs. Tree retention, consisting of retaining single trees or forest patches, enriches the structure of harvested forest and provides functional continuity for the ecosystem. The aim of this study was to investigate how prescribed fire and retention forestry affect performance of bilberry and lingonberry.

Methods

The study was conducted in Lieksa, eastern Finland, within 24 separate study sites. All study sites represented originally ca. 150 years old forests dominated by Scots pine (Pinus sylvestris). Study sites were randomly divided in eight treatment combinations (table 1).

Table 1. Study sites were divided in eight treatment combinations.

Forests were harvested during the winter 2000-2001 and twelve of the sites were burned during the summer 2001. Data on bilberry and lingonberry percent cover, flowering and berry yield was collected during the summer 2013. Solitary bees and bumblebees are the main pollinators of bilberry and lingonberry in the study sites, and therefore they were sampled during the summer 2013 by using colour pan traps. Furthermore, many environmental variables were measured from the study sites, such as elevation a.s.l., coarse woody debris (CWD) and nesting resources for pollinators. Generalized linear mixed model (GLMM) was used to model the impact of prescribed fire and retention forestry on the performance of bilberry and lingonberry.

Results

According to results, bilberry performance was higher at uncut sites, while lingonberry flowering was positively affected by fire and retention. This is understandable, as in pine-dominated forests bilberry favours open and mesic condition in mature or old-growth forests. Lingonberry is well-adapted to higher light and drier conditions. Based on the results, both bilberry and lingonberry show good recovery after fire.

Bilberry flowers

Bee community composition was mainly influenced by percentage of bare ground and number of logs within study site, both nesting resources largely determined by fire and retention. High retention sites had 64% more bumblebee species than uncut forests.

Prescribed fire after tree retention provide abundant lingonberry flowering and nesting resources for pollinators. In contrast, burned clear-cuts provide only with nesting resources, but with hardly any floral resources. Clear-cuts do not have any value for the conservation of ecosystem services related with both shrubs.

Prescribed fire sites and retention trees serve as pollinator source habitats and contain floral resources. The results of the study highlighted the importance of natural disturbances in the conservation of pollination services from boreal forests.

Keywords: bilberry, lingonberry, pollination, prescribed fire, retention forestry

Text:

Anni Koskela, Arctic Flavours Association

anni.koskela@arctic-flavour.fi

+358 40 164 6177