Spatio-temporal patterns of vegetation recovery in post-agricultural forests in Flanders

Spatio-temporal forest cover changes between 1775 and 2000 in Flanders were mapped in a GIS, to explain the recovery level of present-day forest vegetation in post-agricultural forests. By mapping forest cover changes in relation to a site qualification, the impact of spatio-temporal forest cover changes on habitat availability, quality, and connectivity, were quantified. The first chapters of this work covered the whole of Flanders, but in the following chapters additional information on soil, light, and forest management was used to explain patterns of vegetation recovery with a high spatial and temporal resolution

Reappearance of old growth elements in lowland woodlands in northern Belgium : do the associated species follow?

The forest cover of the western European lowland plain has been very low for centuries. Remaining forests were intensively managed, and old-growth elements like veteran trees and coarse woody debris became virtually absent. Only over the last decades have these old-growth elements progressively redeveloped in parks, lanes and forests, and have now reached their highest level over the last 500-1000 years. Biodiversity associated with these old-growth elements makes up an important part of overall forest biodiversity. The ability of species to recolonise the newly available habitat is strongly determined by limitations in their dispersal and establishment. We analyse the current status and development of old-growth elements in Flanders (northern Belgium) and the process of recolonisation by means of specific cases, focussing on saproxylic fungi and saproxylic beetles. Our results show that 'hotspots' of secondary old growth, even isolated small patches, may have more potential for specialised biodiversity than expected, and may provide important new strongholds for recovery and recolonisation of an important share of old-growth related species

Biomass and nutrient cycling of a highly productive Corsican pine stand on former heathland in northern Belgium

Biomass and nutrient cycling were examined in a 62-year-old highly productive Corsican pine stand (Pinus nigra Arn. ssp. laricio Poiret) growing on a coarse and dry sandy soil with low exchangeable nutrient pools. Total aboveground biomass was estimated at 240 tons dry weight per hectare of which 201 tons concerned boles. The belowground biomass amounted to 46 t ha -1 (16 % of total standing biomass). The current annual volume increment was estimated at 20.6 m 3 ha-1 year-1. Root study emphasized the role of the rooting depth as an important growth factor. Calculated uptake rates for N, P, K, Ca and Mg were respectively 50.5, 1.9, 38.2, 15.6 and 3.3 kg ha-1 year-1. Despite an abundant nitrogen deposition (46 kg inorg. N ha-1 year-1) between 23 and 35 % of the nitrogen demand was supplied by internal transfers. Retranslocation of phosphorus fulfilled 64 % of the annual requirement. The root uptake of potassium, calcium and magnesium were better coupled with the tree requirements. The uptake rates of Ca and Mg could be met by atmospheric deposition. The canopy leaching of potassium accounted for 70 % of the root uptake. The low uptake rates of P, Ca and Mg were inconsistent with the vigorous growth of the stand, which could only be maintained by a high nutrient use efficiency. The monitoring of the nutrient status between 1988 and 1995 revealed an obvious decline in the concentrations of Ca, Mg, K and P due to growth dilution. (© Inra/Elsevier, Paris.)La biomasse et le cycle des éléments minéraux d'un peuplement de pin laricio de Corse de forte production sur un sol sableux. La biomasse et le cycle des éléments minéraux ont été étudiés dans un peuplement de pin laricio de Corse (Pinus nigra Am. ssp. laricio Poiret) de 62 ans, de forte productivité, sur un sol sableux et sec, aux réserves d'éléments disponibles limitées. La biomasse épigée s'élévait à 240 tonnes de matière sèche par hectare dont 201 tonnes étaient incluses dans les troncs. La biomasse des racines était de 46 tonnes ha-1 (16 % de la biomasse totale). L'accroissement courant annuel atteignait 20,6 m3 ha-1 an-1. L'étude des racines a mis en évidence la profondeur de l'enracinement comme facteur de croissance important. Les prélèvements réels de N, P, K, Ca et Mg s'élévaient à respectivement 50,5, 1,9, 38,2, 15,6 et 3,3 kg ha-1 an-1. Malgré un apport abondant d'azote (46 kg N inorganique ha-1), entre 23 % et 35 % de la demande azotée était soutenue par le transfert interne. Les transferts internes de phosphore contribuaient pour 64 % à la masse minérale nécessaire pour la formation des tissus nouveaux. Les prélèvements réels de potassium, calcium et magnésium correspondaient mieux à leurs prélèvements apparents. Les prélèvements de Ca et Mg pouvaient être suppléés par des apports atmosphériques. Il ressort que le pluviolessivage de potassium constituait 70 % de l'absorption racinaire. Les prélèvements réels de Ca, Mg et P étaient en opposition avec la forte productivité qui ne pouvait qu'être soutenue par un usage efficace des nutrients. L'évolution de la nutrition foliaire décelait une baisse nette en teneurs de Ca, Mg, K et P engendrée par la discordance entre leurs réserves limitées et la forte croissance du peuplement. (© Inra/Elsevier, Paris.

Observer and relocation errors matter in resurveys of historical vegetation plots

Aim: Revisits of non-permanent, relocatable plots first surveyed several decades ago offer a direct way to observe vegetation change and form a unique and increasingly used source of information for global change research. Despite the important insights that can be obtained from resurveying these quasi-permanent vegetation plots, their use is prone to both observer and relocation errors. Studying the combined effects of both error types is important since they will play out together in practice and it is yet unknown to what extent observed vegetation changes are influenced by these errors. Methods: We designed a study that mimicked all steps in a resurvey study and that allowed determination of the magnitude of observer errors only vs the joint observer and relocation errors. Communities of vascular plants growing in the understorey of temperate forests were selected as study system. Ten regions in Europe were covered to explore generality across contexts and 50 observers were involved, which deliberately differed in their experience in making vegetation records. Results: The mean geographic distance between plots in the observer+relocation error data set was 24m. The mean relative difference in species richness in the observer error and the observer+relocation data set was 15% and 21%, respectively. The mean pseudo-turnover between the five records at a quasi-permanent plot location was on average 0.21 and 0.35 for the observer error and observer+relocation error data sets, respectively. More detailed analyses of the compositional variation showed that the nestedness and turnover components were of equal importance in the observer data set, whereas turnover was much more important than nestedness in the observer+relocation data set. Interestingly, the differences between the observer and the observer+relocation data sets largely disappeared when looking at temporal change: both the changes in species richness and species composition over time were very similar in these data sets. Conclusions: Our results demonstrate that observer and relocation errors are non-negligible when resurveying quasi-permanent plots. A careful interpretation of the results of resurvey studies is warranted, especially when changes are assessed based on a low number of plots. We conclude by listing measures that should be taken to maximally increase the precision and the strength of the inferences drawn from vegetation resurveys