Effects Of Previous Land Use Research Articles

Soil Use Legacy as Driving Factor for Soil Erosion under Conservation Agriculture

Water erosion can cause irreversible depletions in soil quality and crop productivity. The susceptibility of the soil to erosion is affected by current and historical management practices. Historical soil management practices like ploughing or subsoil loosening may lead to irreversible degradations of soils, which in turn increases soil erosion risk. Six “Wischmeier” plots under conservation agriculture, but with different historic treatments regarding soil use and management, were evaluated. These plots were installed in 1984 in Colonia del Sacramento, Uruguay on a Vertic Argiudoll. The objective of this study was to quantify how changes in soil quality, generated by different historical soil use and management over the last 35 years, contribute to current runoff and soil erosion in a cropping system under soil conservation practices using no-till, residue retention and cover crops. Considering differences in soil legacy effects of previous land use, plots were grouped in three treatments with contrasting historic index of agricultural intensification (IAI). The IAI was developed combining the duration of land use under agricultural production and the number and intensity of tillage activity resulting in the treatments: tillage with crop-pasture rotation (TIL_CP), no-tillage under several rotations (NT_Mix) and tillage with continuous cropping (TIL_CROP) with an increasing IAI of 3.5, 7.1 and 11.8, respectively. Rainfall events, runoff water and total, fixed and volatile solids were studied from 2017 to 2019. Soil physical (bulk density, penetration resistance, infiltration rate, aggregate stability), chemical (soil organic carbon (SOC), pH, phosphorous (P-Bray)) and biological properties (particulate organic matter (POM), potentially mineralizable nitrogen (PMN)) were assessed in 2019. Yearly average runoff amounted 209, 579 and 320 mm in 2017, 2018 and 2019, respectively. Yearly average soil losses were 233, 805 and 139 kg/ha with significant differences among years. The lowest soil losses were observed in TIL_CP (231, 615 and 146 kg/ha in 2017, 2018 and 2019, respectively) with lowest IAI of 3.5. Infiltration rate was the lowest in plots with highest IAI. Soil bulk density was highest (1.3 g/cm3) in plots with high IAI. SOC and PMN were lowest in TIL_CROP (3.0% SOC and 34 mg/kg PMN), holding the highest IAI of 11.8. Conservation agriculture minimized soil erosion losses in all plots and years, and erosion was much lower than the maximum tolerable threshold of 7,000 kg/ha for this particular soil. However, in historically intensively tilled and cropped soils, soil quality showed long-term adverse effects pointing towards a reduced resilience of the agricultural system.

Changes in sediment characteristics in the first year of a realigned saltmarsh

Saltmarsh restoration is described as a cost-effective response to coastal biodiversity loss and flood management, although, to date such conservation practices yield different characteristics than natural marshes, such as in plant communities and sediment properties. The outcome of these differences is thought to be influenced by the initial conditions set within the first year of marsh re-establishment, which are often overlooked or neglected as part of the restoration process. Therefore, our study aimed to address this gap by examining the spatial and temporal variations in sediment characteristics of a newly (<15 months) realigned saltmarsh in Essex, UK and the effects of previous land use (arable and pasture). Sediment properties (bulk density, nutrients and pH) were sampled monthly from the realigned site as well as from an adjacent reference natural marsh. After 14 months from initial inundation the two realigned marsh regions (arable and pasture) behaved similarly despite different starting points in terms of pH, water content, bulk density and nutrient load. Physical aspects of the realigned sediments (bulk density and water content) matched those of the reference natural marsh within 14 months post-breach in the 0–5 cm depth range. By contrast, the lower depth sediments within realigned sites remained more dense and drier compared to natural marsh sediments. Chemical properties of the realigned sediments matched those of the natural marsh throughout the sediment profile 14 months post-breach. Success of restoration is measured in the ability of the site to provide the desired ecosystem services and short-term recoveries and set goals may not imply long term sustainability as these observed differences may have ramifications for future biological community development and the success of a restoration.

Effects of previous land use on genotype-by-environment interactions in two loblolly pine progeny tests

Loblolly pine (Pinus taeda L.) is widely used for forestry in southern Brazil, with most seeds coming from clonal seed orchards. This study investigated the effects of previous land use on the adaptability, stability, and productivity of loblolly pine progenies in southern Brazil, aiming to produce a second-generation clonal seed orchard (CSO). Two progeny tests were installed in southern Brazil. In FARA, 52 open-pollinated loblolly pine progenies were tested, and in TUNAS, 65 open-pollinated loblolly pine progenies were tested, 35 of which were common to both tests. FARA is a rotation area previously used for annual agronomic crops (oats, corn, soy, beans), whereas, TUNAS is a recycled loblolly pine plantation forest. The diameter at breast height (dbh) and stem height were measured at six years of age, and the wood volume was calculated. Genetic parameters were estimated using REML/BLUP method in SELEGEN software. The adaptability, stability, and productivity of the progenies were estimated by the relative performance harmonic mean of the breeding values method (MHPRVG). The breeding values for volume were used to estimate genetic gains through selection. The heritability values were slightly higher in FARA compared to those in TUNAS. Most of the individual narrow-sense heritability values were between 0.10 and 0.20 for growth traits. And most of the family-mean heritability values were above 0.50. In FARA, the selection strategy resulted in up to 26.37% genetic gain, while for TUNAS, it reached about 20%. GE effects are significant for volume. Because of the significant GE effects it is necessary to consider previous land use in the selection of genotypes for the formation of loblolly pine CSOs in the tested region. Considering the MHPRVG ranking, the maximum genetic gain estimated is 13.20%. The choice of more stable genotypes can circumvent the challenges imposed by crop rotation in the tested areas.

A Bayesian modeling framework for estimating equilibrium soil organic C sequestration in agroforestry systems

Agroforestry is a form of productive land management that combines trees or bushes with annual crops or pasture, and it can bring benefits in terms of food security and increased carbon (C) sequestration compared with conventional agriculture. But agroforestry as a structured form of agronomic management is relatively new compared with well-established and widespread agronomic systems. Consequently, there is a lack of data and few models of soil organic carbon (SOC) have been developed specifically for agroforestry systems. Also, agroforestry SOC sequestration data measured in field experiments are often reported only as average linear sequestration rates over the study period. This approach, equivalent to zero-order kinetics, makes it difficult to compare results since, in reality, SOC sequestration rates are variable over time and change depending on the duration of measurements. Sequestration rates are also strongly dependent on former C stocks in the soil, further hampering comparisons between agroforestry systems established on different former land uses.To describe the SOC stocks variation over time, researchers often employ models considering at least first-order kinetics. This approach can take care of the two above mentioned issues, considering both the variation of the sequestration over time and the effect of previous land use. However, the variability of agroforestry systems makes applying these models more challenging compared to simpler agricultural systems. To deal with this problem we propose to use detailed uncertainty estimation methods, based on stochastic calibrations that can deal with broad probability distributions.To do so, we adapted a first-order compartmental SOC model to agroforestry systems. It was calibrated within a Bayesian framework on global agroforestry data. Compared to linear coefficients, the model (ICBMAgroforestry) estimates equilibrium SOC stocks of different agroforestry systems probabilistically and is providing uncertainty bounds. These values are independent of initial land use and time duration of the experiments. ICBMAgroforestry can be used for rapid assessment and comparison of the maximum potential SOC stocks for different agroforestry systems and climatic zones. In this study, we could use our approach to estimate the global maximum C that can be sequestered by agroforestry systems at equilibrium, which ranged between 156 and 263 Mg C ha−1 on average, above but comparable with similar estimates for simpler agricultural systems.

Comparison of growth and wood quality of Norway spruce and European larch: effect of previous land use

Afforested farmland is a phenomenon of Central Europe. In this study, we evaluate the radial growth of Norway spruce [Picea abies (L.) Karst.] and European larch (Larix decidua Mill.) in forest stands established on abandoned agricultural land compared to forest stands on standard forest soils. As the quality of wood from such sites is often challenged, we also focused on wood quality of those species. The following characteristics of wood were evaluated: wood density, bending strength, impact bending strength, modulus of elasticity and radial growth in relation to climatic factors. The radial growth of both tree species showed higher radial increment to tree age of 19–23 years on former agricultural land compared to forest land. Norway spruce growing on forest land was significantly (p < 0.05) more sensitive to climatic factors than on agricultural land (7 significant moths vs. 3 months), while there were low differences in larch. Spruce produced wood with significantly higher density on agricultural land (399 kg m−3), while larch had higher density on forest land (583 kg m−3). In other characteristics, significant differences were found only in the case of larch. Higher values were detected for impact bending strength (4.5 J cm−2) and bending strength (87 MPa) on forest land. The detected differences between wood characteristic were not important for industrial purposes and final usage of the wood. Therefore, afforested agricultural lands provide wood of similar quality and also showed higher resistance in relation to climatic change compared to permanent forest lands.

The effect of thinning on annual net nitrogen mineralization and nitrogen leaching fluxes in silver birch and Scots pine stands

ABSTRACTThinning changes the functioning of the whole forest ecosystem, including carbon and nitrogen (N) cycling. The input of organic matter and N into soil, as well as soil temperature and moisture regimes change, which may have an impact on the intensity of the net nitrogen mineralization (NNM) process. The main aims of this study were to estimate the effect of thinning on annual NNM as well as N leaching intensity in young silver birch and Scots pine stands. Thinning increased annual NNM flux in the silver birch stand, as well as annual net nitrification, while there was no change in the annual net ammonification flux. The effect of thinning on nitrification was more pronounced in the first post-thinning year. The 13-year dynamics of annual NNM in the birch stand revealed a significant decrease, which may be attributed to the effect of previous land use. The annual NNM flux in the Scots pine stand was practically equal in both plots; thinning did not affect N net mineralization intensity. The effect of thinning on the annual NNM flux was site and tree species specific. Thinning did not induce more intensive N leaching. Moreover, in the birch stand thinning even reduced N leaching.

Ecosystem description and diversity of the Jurisdam–Seekoegat sections of the Mountain Zebra National Park, South Africa

The purpose of this paper is to give an ecological description of the vegetation of the Jurisdam-Seekoegat section of the Mountain Zebra National Park in the Eastern Cape Province, South Africa. The effect of different land use practices on the vegetation composition was also investigated. Vegetation classifications and descriptions are of immense value to scientists and land managers and provide information on the composition, structure, diversity and effect of management on the different ecosystems present. The Braun-Blanquet approach was used to classify the different plant communities, while the veld condition was determined using the Ecological Index Method. Plant community data was analysed using the JUICE software package while diversity of the different plant communities was determined using the Shannon–Wiener and Gini–Simpson Indices. From a TWINSPAN analysis eight plant communities that can be grouped into six major communities were identified. Two plant communities not previously described for the Park were identified. The different plant communities can all be related to topography and effect of previous land use. Grasses and dwarf shrubs are the most prominent species. The plant communities of the rocky midslope areas achieved the highest species richness and diversity for the study area. The areas least affected by heavy grazing had a higher veld condition score than those heavily grazed by domestic animals in the past. The results of this study also emphasises the importance of resting overgrazed veld, while it seems that heavily grazed areas will not recover without further human intervention. A vegetation map of the different plant communities was produced using ArcGIS.

Warming deferentially altered multidimensional soil legacy induced by past land use history

The legacy effects of previous land use and climate history may affect current soil function. However, the manner in which these legacy effects of land use are modulated by the subsequent climate remains unclear. For this reason, we investigated how the legacies of soil multiple functions left by conversion of grassland to agricultural management were mediated by climate warming with a reciprocal transplant approach. The overall legacy was further separated into the contributions by changes in the abiotic properties of the soil (abiotic process) and microbial community (biotic process). We here hypothesized that warming may mediate the legacy effects of previous land use, mainly by changing biotic processes. Results indicated that warming significantly influenced the total legacies of soil respiration and three exoenzyme activities representing recalcitrant carbon, nitrogen, and phosphorus cycling, but did not affect the total legacy of β-1,4-glucosidase activity, which is involved in labile carbon cycling. The relative contributions of abiotic and biotic processes to the warming effects on the total legacy depended on the type of soil function. The effects of warming on land use change legacies were derived from altered bacterial community structure. The results of the present study suggest that climate conditions could interact with land use legacy to determine the ecosystem functions in a process-specific way.

Response of oribatid mites to reforestation of degraded tropical montane pastureland

Tropical montane forests are being turned into pastures for cattle at an unprecedented rate. However, efforts are being made to reforest pastures in particular if invaded by weeds of low nutritional value, but until today little is known on the response of the decomposer system to reforestation. We focused on the response of soil fauna, specifically oribatid mites, which play an important role in the breakdown of organic matter. In the south Ecuadorian Andes we chose two sites with distinct vegetation: one pasture site invaded by Setaria sphacelata (grass pasture) and another invaded by Pteridium arachnoideum (bracken pasture). At both sites plots reforested with native (Alnus accuminata) and exotic tree species (Pinus patula and Eucalyptus saligna) were established. We hypothesized that oribatid mite abundance, species richness and community structure differ between reforestation treatments. To identify driving factors for oribatid mite community structure, we measured environmental variables, e.g. C-to-N ratio, water content, and microbial biomass. Overall, 65 species of oribatid mites were found with small species such as Suctobelbidae and Rostrozetes ovulum dominating. In contrast to our hypotheses, the abundance and species richness of oribatid mites differed more between pasture types than between reforestation treatments. This resembled the response of soil microbial biomass. Presumably, the duration of the experiment of seven years was too short to allow establishment of forest specific oribatid mite and microbial communities, suggesting that oribatid mites and microorganisms respond slowly to reforestation and changes in plant cover, reflecting long lasting legacy effects of previous land use.

Effects of Previous Land-Use on Plant Species Composition and Diversity in Mediterranean Forests

At some point in their history, most forests in the Mediterranean Basin have been subjected to intensive management or converted to agriculture land. Knowing how forest plant communities recovered after the abandonment of forest-management or agricultural practices (including livestock grazing) provides a basis for investigating how previous land management have affected plant species diversity and composition in forest ecosystems. Our study investigated the consequences of historical “land management” practices on present-day Mediterranean forests by comparing species assemblages and the diversity of (i) all plant species and (ii) each ecological group defined by species’ habitat preferences and successional status (i.e., early-, mid-, and late-successional species). We compared forest stands that differed both in land-use history and in successional stage. In addition, we evaluated the value of those stands for biodiversity conservation. The study revealed significant compositional differentiation among stands that was due to among-stand variations in the diversity (namely, species richness and evenness) of early-, intermediate-, and late-successional species. Historical land management has led to an increase in compositional divergences among forest stands and the loss of late-successional forest species.

An enhanced method for using the IPCC approach to estimate soil organic carbon storage potential on U.S. agricultural soils

The Intergovernmental Panel on Climate Change (IPCC) provides a method to estimate soil organic carbon (SOC) stock changes relative to the SOC stock under native vegetation. This manuscript modifies the IPCC approach to use the ending SOC stock from the previous inventory as the SOC stock that is changed by land use and management activities during the next inventory and to track the crop rotation and tillage intensity through three inventories. The approach allows annual rates of change of carbon sequestration from different historic land uses and management to be estimated explicitly for each assessment point based on the effect of previous land use and management. The model generates 3524 unique annual SOC sequestration rates that vary by land use and management history on U.S. agricultural land based on the 30 SOC stock reference values provided by IPCC documentation. An average of 0.33MgCha−1yr−1 is stored when cropland that was conventionally tilled in two previous inventories is set-aside in the third inventory, but only 0.14MgCha−1yr−1 when it is conventionally tilled in the first inventory and no-till in the second inventory before it is set aside. Incorporating a winter cover on cropland that was conventionally tilled in the first inventory and no-till in the second and third inventories is estimated to store 0.49MgCha−1yr−1, but could store 0.81MgCha−1yr−1 if it was conventionally tilled in the first two inventories and under no-till in the final inventory. Cropland under conventional tillage in the first two inventories and no-till the final inventory could store an average of 0.34MgCha−1yr−1, but cropland under conventional tillage in the first, reduced tillage in the second, and no-till in the third inventory is estimated to store 0.19MgCha−1yr−1. The detailed annual rates of SOC stock change estimated using the approach is useful for economic or other analyses and for policymakers.

Towards practices favourable to plant diversity in hybrid poplar plantations

Much research effort is being devoted to developing forest management practices with limited impacts on biodiversity. While the impact of poplar Populus sp. plantations on biodiversity is relatively well-known at the landscape scale, the impact of alternative management practices at the plantation scale has received much less attention. Yet biodiversity is likely to be impacted by the choice of the poplar clone, stem density at plantation, type and duration of the understory control, and age at which the poplars are harvested. In this study, we investigated the impact of these factors on herbaceous plant communities with data from plant surveys conducted in 85 young (2–5 years) and 96 mature (11–17 years) hybrid poplar high-forest plantations in northern France. On average, ruderal or generalist plants contributed to 40.5% of the plot species richness; tall herbs (60.2%), forest (26%) and meadow plants (13.8%) contributed to the remaining 59.5% more specialised species. Soil moisture and soil nitrogen were major determinants of plant communities: wet soils were favourable to tall herbs, while meadow and forest species preferred moist soils; a significantly lower diversity of the three species groups was reported in the nutrient richer soils (in mature plantations only for forest plants). Mean species richness decreased with plantation age except for forest species. Plant communities in young plantations showed little differences in composition according to the type of understory control (chemical, mechanical or both). The development of a shrubby layer in mature plantations was restricted to the drier soils and was detrimental to both meadow plants and tall herb species. Effects of previous land use on forest and tall herb species were found only in young plantations, suggesting a rapid reset of plant communities for these two groups. This may not be the case for meadow species as the influence of previous land use was significant in mature plantations only. Finally, clone type and stem density at plantation had no significant impact on plant communities. Adjusting age at which the poplars are harvested seems the only effective way to drive plant communities in high-forest poplar plantations: delaying poplar harvest (probably beyond 15–20 years) would benefit forest plants, while advancing poplar harvest (about 10 years) would benefit tall herbs, especially in wet soil conditions.

Long-Term Human Impact and Vegetation Changes in a Boreal Forest Reserve: Implications for the Use of Protected Areas as Ecological References

Northern boreal forest reserves that display no signs of modern forest exploitation are often regarded as pristine and are frequently used as ecological reference areas for conservation and restoration. However, the long-term effects of human utilization of such forests are rarely investigated. Therefore, using both paleoecological and archaeological methods, we analyzed temporal and spatial gradients of long-term human impact in a large old-growth forest reserve in the far north of Sweden, comparing vegetational changes during the last millennium at three sites with different land use histories. Large parts of the forest displayed no visible signs of past human land use, and in an area with no recognized history of human land use the vegetation composition appears to have been relatively stable throughout the studied period. However, at two locations effects of previous land use could be distinguished extending at least four centuries back in time. Long-term, but low-intensity, human land use, including cultivation, reindeer herding and tree cutting, has clearly generated an open forest structure with altered species composition in the field layer at settlement sites and in the surrounding forest. Our analysis shows that past human land use created a persistent legacy that is still visible in the present forest ecosystem. This study highlights the necessity for ecologists to incorporate a historical approach to discern underlying factors that have caused vegetational changes, including past human activity. It also indicates that the intensity and spatial distribution of human land use within the landscape matrices of any forests should be assessed before using them as ecological references. The nomenclature of vascular plants follows Krok and Almquist (Svensk flora. Fanerogamer och ormbunksvaxter, 2001).

Land use legacies in post‐agricultural forests in the Doupovské Mountains, Czech Republic

AbstractQuestions: Do differences in previous land use cause long‐lasting changes in soil chemistry? Is vegetation composition affected by the previous land use after 50 years of secondary succession? Is the effect of previous land use caused by pre‐existing differences in environmental conditions or mediated through changes in soil chemistry? How important is the effect of previous land use in relation to other factors?Location: Doupovské Mountains, Czech Republic.Methods: A stratified random sampling design was used to collect 91 vegetation relevés with accompanying soil samples. The effects of previous land use (arable field, meadow, pasture) on soil pH, organic carbon (C), total nitrogen (N), C:N ratio and available phosphorus were tested by an analysis of covariance. A canonical correspondence analysis and variation partitioning procedure were used to reveal relationships among previous land use, environmental factors and species composition.Results: Organic C, total N and C:N ratio were significantly influenced by previous land use, while available phosphorus and soil pH were not. Previous land use explained a significant part of the variation in species composition and its effects only partly overlapped with the effects of soil chemistry and terrain attributes. However, the species composition of post‐agricultural forests was mostly determined by environmental factors not modified by previous land use.Conclusions: Forest communities that originate on abandoned agricultural land are primarily determined by natural environmental conditions. Nevertheless, the type of previous land use also modifies the species assemblages of these forests and needs to be considered as an important determinant of their composition.

Recovery of a Subtropical Dry Forest After Abandonment of Different Land Uses1

ABSTRACTWe studied the ecological characteristics of 45–50‐yr‐old subtropical dry forest stands in Puerto Rico that were growing on sites that had been deforested and used intensively for up to 128 yr. The study took place in the Guánica Commonwealth Forest. Our objective was to assess the long‐term effects of previous land use on this forest—i.e., its species composition, structure, and functioning. Previous land‐use types included houses, farmlands, and charcoal pits. Stands with these land uses were compared with a nearby mature forest stand. The speed and path of forest recovery after deforestation and land‐use abandonment depended on the conditions of the land. Study areas where land uses had removed the forest canopy and altered soil conditions (houses and farmlands) required a longer time to recover and had a different species composition than study areas where land uses retained a forest canopy (charcoal pits). Different forest attributes recovered at different rates. Crown area index, stem density, and litterfall rate recovered faster than stemwood and root, biomass, tree height, and basal area. Where previous land uses removed the canopy, Leucaena leucocephala, a naturalized alien pioneer species, dominated the regrowth. Native species dominated abandoned charcoal pits and mature forest. The change in species composition, including the invasion of alien species, appears to be the most significant long‐term effect of human use and modification of the landscape.

Effects of previous land-use on plant species diversity in semi-natural and plantation forests in a warm-temperate region in southeastern Kyushu, Japan

We compared the species composition, occurrence and diversity of understorey of forestry plantations and semi-natural secondary forests in a warm-temperate region in southeastern Kyushu, Japan, in which the previous land-use history had been documented. Cluster analysis and a stand ordination, using detrended correspondence analysis, indicated that plant species composition in forest stands was primarily influenced by the previous land-use history (as meadows or coppices) compared with either the current status of the stand (semi-natural forest or plantation) or site micro-topography. Species occurrence was also dependent on the previous land-use, with a significantly greater proportion of native woodland species being present in former coppice stands. Species richness, however, was higher in plantations and stands developing on former meadow sites. This was true of perennial forbs and climbing plants, but not the evergreen species which were originally common in native woodland of the region. Species diversity indices (Shannon’s H′) showed a similar tendency to species richness. The light environment within forest stands, evaluated by gap light intensity (GLI) using hemispherical photography, had less effect on species richness. We conclude that previous land-use has a significant effect on the species composition and diversity of forest, persisting even after the establishment of conifer plantations, and that the restoration of the original ‘woodland’ species composition and diversity will require the retention of efficient seed sources near stands which have developed on land previously cleared of native forest cover.

UNDERSTORY VEGETATION AND ENVIRONMENT RESPONSES TO TILLAGE, FOREST HARVESTING, AND CONIFER PLANTATION DEVELOPMENT

Increasing demand to conserve biodiversity in managed forests necessitates better understanding of the impacts of forestry practices on the species‐rich herbaceous layer. We compared composition and diversity of understory vegetation, environmental features, and stand structure of forests in New Brunswick, Canada, under four different management scenarios, including: young (24–66 yr) naturally regenerated forests and conifer plantations (19–64 yr) established after clear‐cutting, mature (77–100 yr) naturally regenerated forests originating from natural disturbance (insect defoliation), and old‐field plantations (31–77 yr) established on abandoned agricultural fields. The objectives were to determine how plant composition, forest structure, and microenvironment differed among stand types and which environmental or structural features were related to understory species. Detrended correspondence analysis (DCA) and multiresponse permutation procedure (MRPP) indicated that stand types differed in species composition and environments. Plantations were significantly lower in density of snags, deciduous canopy cover, and leaf substrate, and higher in coniferous canopy cover and needle, twig, and moss substrates than the natural stands. Old‐field plantations had less cover of pits and mounds than all other stand types. Mature natural stands contained the greatest amount of coarse woody debris (CWD) in all decay classes and snags &gt;14 cm diameter, and the lowest density of trees &gt;5 cm diameter and moss cover. Canonical correspondence analysis (CCA) showed that species in both natural stand types are associated with decayed CWD, deciduous cover, and leaf substrate. Species in cutover plantations were associated with coniferous cover and needle substrate. Species composition in old‐field plantations was distinct, with the lowest species richness and diversity of all stand types. We present a conceptual model illustrating the initial direct effects of previous land use and harvesting or postharvest treatments and the subsequent indirect effects associated with plantation or natural stand development on environmental features and understory vegetation. We recommend extending plantation harvest cycles to facilitate reestablishment and expansion of plant populations and maintaining diverse tree canopy composition, coarse woody debris, and pit and mound topography to sustain critical habitat for vascular understory plant species in managed forests.

Experiments on tree and shrub establishment in temperate grassy woodlands: Seedling survival

Abstract Experimental studies of the emergence of shrubs and trees in grassy woodlands on the New England Tablelands, New South Wales, Australia, showed that emergence of seedlings was determined by seed supply, seed predators and seed burial. The survival of these seedlings was then observed in an experiment to test the effects of previous land use, grazing by stock and grazing by other vertebrates. The fate of four eucalypts and six shrub species was followed over 5 years. Across all species more than 50% mortality occurred in the first 6 months prior to the imposition of grazing treatments. These deaths were attributed to the combined effects of insect defoliation, cold, and low soil moisture. Average mortality over all treatments showed two distinct trends: eucalypts and one unpalatable shrub (Leptospermum) had greater than 1% survival over 5 years, whereas Acacia, Cassinia, Indigophera, Lomatia and Xanthorrhoea either had very low or no survival after 5 years. The effect of livestock grazing on seedling numbers was rarely detected because of patchy emergence and mortality due to other causes. However, proportional hazard regression models showed that there was often an increased hazard associated with grazing or grazed landscapes. Overall, those species with high hazard coefficients associated with stock are rare in the landscape, whereas those with lesser risk are more common. Recruitment is likely to be an extremely rare event because the highest proportion of germinable seed sown that survived to a juvenile stage was 0.42% and the mean across all species was 0.12%. No natural recruitment of shrub species was observed over 5 years of observation, suggesting that recruitment is episodic and disturbance driven. Enhancing natural ‘regeneration’ of woody plants under these circumstances may be more challenging than simply fencing off remnants.

Merchantability of Pinus radiata in relation to previous land use

Summary An integrated thinning operation was carried out in 21-year-old radiata pine stands in the central tablelands of New South Wales to examine the effect of previous land use and associated problems of poor tree form on recovery of merchantable timber. The areas thinned were contiguous sections of plantation which had different types of land use prior to plantation establishment; native forest, cleared grazing land (pasture) and cleared land initially grazed and subsequently cultivated and cropped (cultivated pasture). Total volumes of harvested trees (to 8 cm small end diameter) were estimated (assuming no poor tree form) from regressions relating volume to stem diameter. This estimate was compared with the actual volume of saw logs and pulp wood recovered on site and with merchantable yields predicted using a locally derived Forestry Commission equation. On-site yields of saw logs plus pulp wood were 143 m3 ha−1 from the ex-native forest site, 191 m3 ha−1 from the ex-cultivated pasture site and 210 m3 ha−1 from the ex-pasture site. This represented a total recovery of more than 90% of the total stem volume to 8 cm small end diameter from ex-native forest and ex-pasture trees compared with 73% from the ex-cultivated pasture trees. Of the trees harvested, 45% from the ex-native forest site had stem defects compared with 65% from the ex-pasture site and 88% from the ex-cultivated pasture site. These defects reduced the average saw log volume per tree by at least 50% in trees greater than 35 cm DBHOB. In contrast, the yield of pulpwood was similar for deformed and non-deformed trees because some logs which did not meet saw log specifications were down-graded to pulp logs.

Nitrogen availability in radiata pine plantations on former pasture sites in southern New South Wales

Studies of nitrogen availability were carried out in radiata pine (Pinus radiata D. Don) plantations on former pasture sites in N.S.W. in conjunction with studies of the effects of previous land use on tree form. Sites were selected on previously improved pastures (cleared with introduced legumes) and unimproved pastures (partially cleared without legumes) to form age sequences of stands which had been established for periods of up to fifteen years. Mineral-N pools in soils and forest floor samples were determined monthly for thirteen months and nitrification potentials were determined from periodic laboratory incubations.