Half a century of Scots pine forest ecosystem monitoring reveals long‐term effects of atmospheric deposition and climate change

Abstract

At two forest sites in Germany (Pfaffenwinkel, Pustert) stocked with mature Scots pine (Pinus sylvestris L.), we investigated changes of topsoil chemistry during the recent 40 years by soil inventories conducted on replicated control plots of fertilization experiments, allowing a statistical analysis. Additionally, we monitored the nutritional status of both stands from 1964 until 2019 and quantified stand growth during the monitoring period by repeated stand inventories. Moreover, we monitored climate variables (air temperature and precipitation) and calculated annual climatic water balances from 1991 to 2019. Atmospheric nitrogen (N) and sulfur (S) deposition between 1964 and 2019 was estimated for the period 1969–2019 by combining annual deposition measurements conducted in 1985–1987 and 2004 with long‐term deposition records from long‐term forest monitoring stations. We investigated interrelations between topsoil chemistry, stand nutrition, stand growth, deposition, and climate trends. At both sites, the onset of the new millennium was a turning point of important biogeochemical processes. Topsoil acidification turned into re‐alkalinization, soil organic matter (SOM) accumulation stopped, and likely turned into SOM depletion. In the new millennium, topsoil stocks of S and plant‐available phosphorus (P) as well as S and P concentrations in Scots pine foliage decreased substantially; yet, age‐referenced stand growth remained at levels far above those expected from yield table data. Tree P and S nutrition as well as climate change (increased temperature and drought stress) have replaced soil acidification as major future challenges for both forests. Understanding of P and S cycling and water fluxes in forest ecosystems, and consideration of these issues in forest management is important for successfully tackling the new challenges. Our study illustrates the importance of long‐term forest monitoring to identify slow, but substantial changes of forest biogeochemistry driven by natural and anthropogenic global change.

Forest Soil Cation Dynamics and Increases in Carbon on the Allegheny Plateau, PA, USA Following a Period of Strongly Declining Acid Deposition

“…The European studies that paid closest attention to C stocks in conjunction with acidification recovery found the opposite trends in C storage to ours, with a declining carbon pool in the Oa horizon [37]. This may be difficult to interpret as the European sites have a more complicated and longer history of manipulation [38].…”

“…They attributed this change to an inhibition of microbial activity and decomposition processes during higher acid loading. Similarly, in pine forests in Germany, Prietzel et al [38] in an unusually long study found that C stocks and base saturation decreased until about 2004 and then reversed showing signs of recovery in upper soil layers since then.…”

The social drift of trees. Consequence for growth trend detection, stand dynamics, and silviculture

“…The detection of growth disturbances improves with continuity of measurement on long-term experimental plots, e.g., using repeated surveys or permanent dendrometer records (Nehrbass-Ahles et al 2014;Prietzel et al 2020;Spiecker et al 2000). Thus, time series data should ideally be obtained over the entire tree lifetime of 100-200 years.…”

New Topsoil Sampler for the Assessment and Monitoring of Forest Soil Contamination

“…The most common objective of forest soil sampling, mainly from topsoil layers, is to provide reliable information about soil fertility and productivity [3], effects of forest management [4][5][6], and soil contamination with various substances [7][8][9][10][11][12]. Forest soils are also common objects of studies on water cycling, quality and retention [13,14], and carbon cycling and sequestration in relation to climate change [15][16][17]. Beside the unique scientific projects and problem-oriented inventories, large scale monitoring programs (i.e., on a regional, national, and continental scale) were launched to determine both the spatial and temporal trends in relation to environmental factors and human impacts [18][19][20][21].…”

“…Forest litter and mineral topsoil differ in their physical forms and are, thus, most commonly, separately sampled and analyzed, sometimes using different laboratory protocols [5,16,30,37,38,[42][43][44][45]. Alternatively, even in the contaminated sites, the litter layer is omitted and only the mineral topsoil is sampled and analyzed [7,9,11,27,32,34,39,46].…”