Hierarchical tree classifiers to find suitable sites for sandplain grasslands and heathlands on Martha’s Vineyard Island, Massachusetts

The grasslands and heathlands of Martha’s Vineyard Island, Massachusetts provide habitat for unusual, rare, and endangered species. Currently, these globally rare ecosystems exist as fragments on the southern coast of the island within a matrix of wooded, agricultural, and developed land. We used existing land cover patterns to train a hierarchical tree classifier model according to 10 biogeoclimatic and positional variables. This model was then used to predict suitable sites where grasslands and heathlands do not presently occur but could be efficiently established. The tree classifier model indicates that many sites compatible with sandplain grasslands currently contain agricultural lands, residential development, mowed grassland, and commercial development. Efficient establishment could be undertaken at locations buffering existing grasslands to increase their extent by 67% relative to current conditions and join isolated fragments. Sites compatible with heathlands also currently contain agriculture and residential development as well as later successional vegetation including maritime forests and pitch pine. Conversion of these sites to heathlands, as indicated by the model, would increase the current extent by 25% and increase average patch size. An adaptive management approach to grassland and heathland supplementation could be employed to validate the causal mechanisms between the predictor variables and the vegetative communities. Testing of the predictive accuracy of the Martha’s Vineyard Island tree classifier models at other coastal sites would also provide information on the true mechanisms responsible for distribution patterns.     

Microbial community changes in heathland soil communities along a geographical gradient: interaction with climate change manipulations

Climate change constitutes a serious threat for European heathlands as unlike other sources of damage, such as over-grazing, local remediation is not a possibility. Within the large pan-European projects, CLIMOOR and VULCAN, the effect of periodic drought and increased temperature were investigated in four heathland ecosystems along a geographical and climatic gradient across Europe. Fluorogenically labelled substrates for four enzymes (glucosidase, sulphatase, phosphatase, leucine amino peptidase) were used to measure extra-cellular enzyme activity in soil samples from each of the CLIMOOR sites. Microbial extra-cellular enzyme production is linked to microbial activity as well as soil physico-chemical properties, making soil enzymes one of the more reactive components of terrestrial ecosystems and potentially excellent indicators of soil microbial functional status and diversity.Across all sites and over all the substrates, organic matter content was exponentially, inversely related to enzyme activity. Although the increase in temperature produced by the CLIMOOR roofs was small (on average 0.9 °C), this was sufficient to increase enzyme activity in all sites (on average by 45%). The increase was within the range of seasonal variability at each of the sites. The effect of drought on enzyme activity was more pronounced in the Northern European sites than the southern European, and most moisture limited, site. This suggests that the effect of temperature increases may be observed across all regions; however, the soils of northern Europe may be more sensitive to changes in rainfall patterns than more moisture limited Southern European soils.     

Comparative Analysis of Runo and Sediment Yield with a Rainfall Simulator After Experimental Fire

Changes produced in runoff and sediment levels before and after fire and during the revegetation process were examined using a rainfall simulator. The area was burned in an experimental fire, reaching temperatures from 35° to 563° C. Then it was revegetated using different species combinations. Fifteen permanent plots were established in the burnt area (4 treatments and a control replicated three times). Simulated rainfall of 15 mm per 5 min was applied in each treatment. No significant differences were found in sediment yield and runoff between treatments, but greatest runoff was observed to occur immediately after the fire. A significant relationship was found between runoff and woody cover, and a decrease in runoff can be observed as cover increases. The relationship between sediment yields and runoff rates was also positive. The low rates observed during rainfall simulation are due to the effect of natural vegetation rather than revegetation treatments. The high organic matter content also had an influence on the low rates of runoff and sediment.     

The impact of nitrogen deposition on carbon sequestration by European forests and heathlands

In this study, we present estimated ranges in carbon (C) sequestration per kg nitrogen (N) addition in above-ground biomass and in soil organic matter for forests and heathlands, based on: (i) empirical relations between spatial patterns of carbon uptake and influencing environmental factors including nitrogen deposition (forests only), (ii) ¹⁵N field experiments, (iii) long-term low-dose N fertilizer experiments and (iv) results from ecosystem models. The results of the various studies are in close agreement and show that above-ground accumulation of carbon in forests is generally within the range 15–40 kg C/kg N. For heathlands, a range of 5–15 kg C/kg N has been observed based on low-dose N fertilizer experiments. The uncertainty in C sequestration per kg N addition in soils is larger than for above-ground biomass and varies on average between 5 and 35 kg C/kg N for both forests and heathlands. All together these data indicate a total carbon sequestration range of 5–75 kg C/kg N deposition for forest and heathlands, with a most common range of 20–40 kg C/kg N. Results cannot be extrapolated to systems with very high N inputs, nor to other ecosystems, such as peatlands, where the impact of N is much more variable, and may range from C sequestration to C losses.