Can management compensate for atmospheric nutrient deposition in heathland ecosystems?

Abstract

Summary 1.Atmospheric nutrient deposition has contributed to widespread changes in heathlands throughout Europe. As a consequence, management is now being considered as a potential tool with which to compensate for increased nutrient loads. Currently, only limited information is available on the extent to which management measures could compensate for atmospheric nutrient deposition. We hypothesized that low-intensity management measures are not sufficient to counterbalance current nutrient inputs, particularly of nitrogen (N). 2. In order to improve heathland management schemes, we evaluated the effectiveness of different management measures in reducing the impact of ongoing atmospheric nutrient loads. We compared the effects of mowing, prescribed burning (low-intensity management) and sod-cutting (high-intensity management) on heathland nutrient budgets [N, calcium (Ca), potassium (K), magnesium (Mg) and phosphorus (P)] in the Lueneburg Heath nature reserve (north-west Germany). Nutrient balances were calculated by analysing the present-day input, the output as a result of the removal of biomass/humus horizons, and changes in leaching rates. 3. Nutrient losses by increased leaching following management measures were negligible compared with nutrient losses caused by the removal of above-ground biomass or humus horizons. The total quantities of nutrients removed by sod-cutting were equivalent to between 37 and 176 years of atmospheric input (for N, 89 years). 4. In contrast, the quantities of N removed by mowing and prescribed burning were equivalent to only 5 years of atmospheric input. Thus, heathlands subjected to such treatments will accumulate N in the long term. In addition, output-input ratios for phosphorus (P) exceeded those for N in the mowing and sod-cutting experiments. It is therefore likely that heathlands currently (co-) limited by N will shift to being more Plimited in the long term. This will promote species that are well adapted to P-limited sites (e.g. Molinia caerulea ). 5. Synthesis and applications . This study shows that low-intensity management cannot compensate for atmospheric N loads in the long term. Consequently, high-intensity management measures are an indispensable tool in preserving a long-term balanced N budget in heathlands. In order to maintain a diverse structure, managers need to combine low-and high-intensity management measures. Prescribed burning proved to be the best means of avoiding an increasing P shortage, because this measure causes very low P outputs.

Environmental Impacts—Terrestrial Ecosystems

“…For heathlands, overall evidence for effects of recent climate change from experimental warming and drought treatments is also weak, variable and inconsistent, suggesting that now and in the near future, climate warming is of low significance compared to other predominant drivers of ecological change in heathland ecosystems such as eutrophication, acidification and altered management practices (e.g. Härdtle et al 2006). For more extreme climate scenarios, however, substantial effects could be expected in heathlands.…”

“…In these regions, they are at the edge of extinction in many sites and have become a major object of biodiversity and nature conservation efforts. Eutrophication and acidification through atmospheric inputs and changes in land management are currently the major drivers of change in these ecosystems (Härdtle et al 2006), which makes the identification of climate change impacts difficult.…”

Functional Relationships with N Deposition Differ According to Stand Maturity in Calluna-Dominated Heathland

“…Foliar N (mg g burning (e.g., on a 10-to 15-year cycle) can export up to 90 % of accumulated atmospheric N inputs (Niemeyer et al 2005), whereas turf cutting can export the equivalent of up to 90 years of deposition inputs in a single management cycle (Hardtle et al 2006). Soil pH in the building-phase and all phase datasets was strongly and significantly related to deposition rates for reduced N and this was in fact the only significant relationship with reduced N identified in this study.…”

“…Eutrophication of lowland heathlands by N deposition in the Netherlands has driven the conversion of Calluna vulgaris (L.) Hull (henceforth referred to as Calluna) dominated heathlands, to graminoid communities over the last 25 years (Aerts and Berendse 1988) and N eutrophication remains an important risk factor for heathland across Europe (Bobbink et al 2010). Management of heathland exports N by removing biomass and litter, typically via mowing, grazing, or burning, and is considered an important tool to help minimize impacts from accumulated N deposition (Power et al 2001;Terry et al 2004;Hardtle et al 2006). With increasing time since management, N accumulates in vegetation biomass, litter, and soil (Pilkington et al 2005;Power et al 2006), enhancing overall ecosystem nutrient status and increasing the risk of habitat degradation.…”

Increased inorganic nitrogen leaching from a mountain grassland ecosystem following grazing removal: a hangover of past intensive land-use?

“…Dorland et al, 2004) or above-ground biomass removal (e.g. Mitchell et al, 2000;Härdtle et al, 2006). While potentially viable for small areas of high (or potentially high) conservation value, such as lowland heaths or wetlands, this approach clearly would not be appropriate at the scale of large upland grassland landscapes.…”