Land use effects on tree species diversity and soil properties of the Awudua Forest, Ghana

Since the mid‐20th Century, Europe has experienced an unprecedented forest expansion associated with the abandonment of rural landscapes. Secondary forests may provide relevant ecosystem services such as landscape defragmentation, biodiversity conservation, control of hydrological cycling and carbon sequestration. Secondary forests may benefit from the legacies of the former agricultural land use, and exhibit enhanced growth. Moreover, they may differ from long‐established forests in terms of tree species composition and diversity, as community composition has been less modified by succession or management. However, we lack evidence whether the effects of land use legacies on tree species diversity may also result in differences in the response of secondary forests to biotic and abiotic disturbances. We aimed to evaluate the effects of land use legacies on taxonomic and functional diversity and their effects on the response of temperate broadleaf forests to drought and herbivory damage. For this aim, we compared secondary beech Fagus sylvatica forests established after 1950 in abandoned pastures with long‐established (pre‐1950) forests. We calculated indices of taxonomic and functional diversity and determined mean growth and growth response of beech to two drought events (1991, 2006), and insect herbivory damage. Secondary and long‐established beech forests marginally differed in species richness but the former exhibited a significantly higher Shannon diversity index and evenness. Yet, differences in taxonomic diversity did not result in differences in functional diversity between forest types. Mean tree growth was higher in secondary than in long‐established forests and it increased with functional diversity in both forest types. However, diversity was unrelated with the growth response to drought. Insect herbivory damage decreased with increasing functional diversity but only in secondary forests. Synthesis and applications. Promoting functional diversity in temperate broadleaf forests is a promising strategy for enhancing productivity (tree growth) while increasing the ability to cope with biotic disturbances (insect herbivory). This principle should be applied both in the management of long‐established as well as expanding secondary forests. Yet, functional diversity does not seem to ameliorate tree response to drought, highlighting the need for other silvicultural practices to address this environmental challenge.

Primary forest (reserved area), secondary forest and cocoa plantation land uses characterize uplands of Dwinyama watershed in Ghana within the dry semi-deciduous forest zone. The nutrients recycled in the land uses were studied through leaf litter fall, nutrient release, nutrient fluxes estimation and topsoil nutrient contents leading to the identification of appropriate land use in upland regions that may potentially influence lowland farming. Mean annual leaf litter produced by the primary and secondary forests was both 7.9 t ha-1 and that for cocoa plantation was 6.9 t ha-1. The primary forest leaf litter showed rapid decomposition than the secondary forest and the cocoa leaf litter. Nutrients released from the decomposing leaf litters were fast for N, P, K, Ca and Mg for the primary and secondary forests. Less leaf litter production and high rainfall regimes in South America and southeast Asia probably contributed to the lower annual nutrient fluxes recorded than that of the dry semi-deciduous tropical forest in Ghana. The soil under cocoa plantation was higher in Ca than in the secondary and primary forests soils. The primary forest recorded higher contents of top soil N, P. K, and Mg nutrients due to non-frequent removal of the vegetation, presence of organic matter that increases soil carbon content and cation exchange capacity. Generally, trends of nutrients released and the quantities of nutrient fluxes estimate in the land uses in Ghana suggested that nutrient cycling was better in the primary forest followed by the secondary forest and cocoa plantation. The trend in the land uses was primary > secondary > cocoa, suggesting that forests in uplands will protect watersheds, and, through leaching and erosion, nutrients may be transported to the lowlands for continuous and sustainable cropping with little or no inorganic fertilizer application.

Soil microplastic pollution under different land uses in tropics, southwestern China

Cacao (Theobroma cacao) cultivation maintaining a high proportion of shade trees in a diverse composition (agroforestry) is currently being viewed as a sustainable land use practice. Our research hypothesis was that cacao agroforests (AF) can support relatively high tree diversity, as compared to surrounding primary and/or secondary forests. The objective of this study was to assess the impact of forest conversion on tree communities by comparing tree composition, community characteristics (richness and diversity) and spatial structure (density, canopy height, basal area) among primary forest, secondary forest, and cacao AF. In total, we collected data from 30 25 × 25 m plots on three land use systems (20 in cacao AF, five in secondary, and five in primary forests) in San Alejandro, Peruvian Amazon. All trees with DBH ≥ 10 cm were counted, identified to species, and their height and DBH were recorded. Our results support the hypothesis that cacao AF present a relatively high tree species richness and diversity, although they are no substitute for natural habitats. We identified most common species used for shading cacao. Tree species composition similarity was highest between cacao AF and secondary forest. Vegetation structure (density, height, DBH) was significantly lower compared to primary and secondary forest. Species richness and diversity were found to be highest in the primary forest, but cacao AF and secondary forests were fairly comparable. The tree species cultivated in cacao AF are very different from those found in primary forest, so we question whether the relatively high tree diversity and richness is able to support much of the diversity of original flora and fauna.

The increasing global demand for vegetable oils has resulted in a significant increase in the area under oil palm in the tropics during the last couple of decades, and this is projected to increase further. The Roundtable on Sustainable Palm Oil discourages the conversion of peatlands to oil palm and rubber plantations. However, our understanding of the effects on soil organic carbon (SOC) stocks and associated greenhouse gas (GHG) emissions of land use conversion is incomplete, especially for mineral soils under primary forests, secondary forests, rubber and other perennial plantations in the tropics. In this review we synthesised information on SOC stocks and GHG emissions from tropical mineral soils under forest, oil palm and rubber plantations and other agroecosystems across the tropical regions. We found that the largest SOC losses occurred after land use conversion from primary forest to oil palm and rubber plantations. Secondary forest and pasture lands showed lower SOC losses as well as total GHG (CO2, N2O and CH4) emissions when converted to oil palm and rubber plantations. However, due to the limited data available on all three GHG emissions, there remains high uncertainty in GHG emissions estimates, and regional GHG accounting is more reliable. We recommend long-term monitoring of oil palm and other perennial plantations established on tropical mineral soils on different soil types and regions on SOC stock changes and total GHG emissions and evaluate appropriate management practices to optimise production and sustainable economic returns, and minimise environmental impact.

In Sumatra, Indonesia, the establishment of oil palm and rubber plantations is widespread. However, it occurs at the expense of forest area. Since global demand for palm oil and rubber is increasing, forest conversion is expected to continue. Furthermore, studies have shown that forest destruction and the establishment of agricultural land uses influence the soil–atmosphere exchange of the climate-relevant trace gases carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O) and nitric oxide (NO). Nevertheless, trace gas measurements from oil palm and rubber plantations are scarce. Additionally, researchers have so far not considered oil palm canopy soils as a possible source or sink of trace gases. The present thesis consists of three studies, which assess the impact of forest conversion into smallholder oil palm and rubber plantations on soil CO2 and CH4 fluxes, as well as on soil N2O and NO fluxes, and which investigate the importance of oil palm canopy soil for N2O and CH4 fluxes. We conducted the studies on highly weathered tropical soils in Jambi Province, Sumatra, Indonesia and selected two soil landscapes which mainly differ in texture (clay and loam Acrisol). To examine the impact of land-use change on soil trace gas fluxes we investigated four different land uses per landscape: lowland forest and jungle rubber (rubber trees interspersed in secondary forest), as reference land uses, as well as smallholder rubber (7–17 years old) and oil palm plantations (9–16 years old), as converted land uses. Each land use was replicated four times in both landscapes.
\n\tThe first study investigated changes in soil CO2 and CH4 fluxes with forest conversion to smallholder oil palm and rubber plantations. We determined soil CO2 and CH4 fluxes monthly from December 2012 to December 2013, using static vented chambers. Our findings show that soil CO2 fluxes in oil palm plantations were reduced and that fluxes from the other three land uses were comparable among each other in both landscapes. We attributed this decrease to strongly decomposed soil organic matter, reduced soil carbon (C) stocks as well as to phosphorus fertilization and liming, which led to a lower C allocation to roots. Due to reduced nitrogen (N) availability in the converted land uses CH4 uptake was lower in oil palm and rubber when compared to the reference land uses in both landscapes. Thus, soil fertility appeared to be an important controller of soil CO2 and CH4 fluxes in this tropical landscape.
\n\tThe second study focused on the impact of forest conversion into smallholder oil palm and rubber plantations on soil N2O and NO fluxes. Additionally, we compared soil N2O fluxes from smallholder oil palm plantations with fluxes from a large-scale oil palm plantation. We determined soil N2O fluxes monthly from December 2012 to December 2013 in the two landscapes and weekly to bi-weekly from July 2014 to July 2015 in the large-scale oil palm plantation, using static vented chambers. Using open dynamic chambers, we measured soil NO fluxes four times in all land uses of both landscapes between March and September 2013. Our results show that land use change did not affect soil N2O and NO fluxes because of low initial N availability in the reference land uses, so that N2O and NO fluxes were also low, and any changes due to conversion might have been too small to identify. However, the large-scale oil palm plantation, although not significantly different, showed, because of their higher fertilizer input, on average 3.5 times higher soil N2O fluxes than the smallholder oil palm plantations.
\n\tThe aim of the third study was to quantify N2O and CH4 fluxes from oil palm canopy soils. We measured soil N2O and CH4 from three different stem heights in eight smallholder oil palm plantations across the two landscapes from February 2013 to May 2014, on a bi-weekly to monthly basis, using in-situ incubation. Oil palm canopy soil emitted N2O and CH4 from all stem heights. However, fluxes were low compared to ground soil fluxes. This was due to a low amount of canopy soil on a hectare basis and due to high nitrate contents, which might have suppressed CH4 production.
\n\tIn the synthesis of this dissertation, data on soil trace gas fluxes were embedded into a broader context to gain information on changes of the net biome exchange (NBE) and on partial N budgets with land-use change. Soil CO2 and CH4 fluxes were combined with an ancillary study on net primary production and harvest as well as with estimations on the contribution of heterotrophic soil respiration to total soil respiration. Soil N2O and NO fluxes were combined with ancillary studies on N inputs and outputs via fertilization, bulk precipitation, leaching and harvest. The results revealed that the NBE of oil palm plantations was higher compared to forest. Nevertheless, implications for climate change are negative since forest conversion itself results in a huge C loss, which cannot be compensated over time by oil palm plantations. The lowest partial N budget was detected in oil palm, indicating that N inputs via precipitation and fertilization were smaller than the huge N loss via harvest. Overall, these results illustrate that land-use change has negative effects on the C and N budgets of tropical ecosystems.

Tree species diversity and population structure at different community types were described and analyzed for primary and secondary lowland moist deciduous forests in Tripura. Overall 10,957 individual trees belonging to 46 family, 103 genera and 144 species were counted at ≥30 cm DBH (diameter at breast height) using 28 permanent belt transects with a size of 1 ha (10 m × 1000 m). Four different tree communities were identified. The primary forests was dominated by Shorea robusta (mean density 464.77 trees·ha−1, 105 species) and Schima wallichii (336.25 trees·ha−1, 82 species), while the secondary forests was dominated by Tectona grandis (333.88 trees·ha−1, 105 species) and Hevea brasiliensis (299.67 trees·ha−1, 82 species). Overall mean basal area in this study was 18.01m2·ha−1; the maximum value was recorded in primary Shorea forest (26.21 m2·ha−1). Mean density and diversity indices were differed significantly within four different communities. No significant differences were observed in number of species, genera, family and tree basal cover area. Significant relationships were found between the species richness and different tree population groups across the communities. Results revealed that species diversity and density were increased in those forests due to past disturbances which resulted in slow accumulation of native oligarchic small tree species. Seventeen species were recorded with <2 individuals of which Saraca asoka (Roxb.) de Wilde and Entada phaseoloides (L.) Merr. etc. extensively used in local ethno-medicinal formulations. The present S. robusta Gaertn dominated forest was recorded richer (105 species) than other reported studies. Moraceae was found more speciose family instead of Papilionaceae and Euphorbiaceae than other Indian moist deciduous forests. Seasonal phenological gap in such moist deciduous forests influenced the population of Trachypithecus pileatus and capped langur. The analysis of FIV suggested a slow trend of shifting the population of Lamiaceae group by Moraceae species in secondary T. grandis L. dominated community.

Intensive deforestration for the purpose of agricultural field and transmigration area has happened lately in Dharmasraya Regency, West Sumatra. Land use change from forest into dry land farming, mixed trees and oil palm plantation, as well as rubber plantation has caused different level of soil fertility as a consequence of ecology changes of the areas. The objectives of this research were to identify the change of soil organic matter content, plant nutrition level, as well as bulk density of the soils at each land use. This research was conducted in Sungai Rumbai, Dharmasraya Regency in 2007. Soil samples were taken from 5 land use, those were dryland farming, mixed trees, oil palm plantation, rubber plantation, and natural forest. The soil samples, then, were analysed for the soil organic matter content (%), N-, P-, and K-content, as well as bulk density (BV) in soil laboratory, Agricultural Faculty, Andalas University Padang. The result showed that land use change from forest ecosystem into other ecosystems had decreased soil fertility level. This was reflected by the decreasing soil organic matter content, increasing soil bulk density. Nutrient status of the soil also decreased, especially potassium (K) level. Compared to the forest ecosystem, soil organic matter decreased by 13, 26, 33, and 36% respectively for dry land farming, mixed trees and oil palm plantation, as well as rubber plantation. Soil bulk density of the land use which was still close to soil under forest ecosystem (0.83 gcm-3) was found in rubber plantation (1.00 gcm-3), then followed by mixed trees (1.11 gcm-3). Potassium level of the land uses which were close to forest ecosystem (0.44 me/100g) was in rubber plantation (0,33 me/100 g), as well as in oil palm plantation(0,34 me/100 g). Based on the results above, it can be concluded that rubber and oil palm plantation was types of land use having better soil ecology compared to the other land use. Kata Kunci: Degradasi Lahan, Ekosistem Hutan, Penggunaan Lahan

Impact of progressive and retrogressive land use changes on ecosystem multifunctionality: Implications for land restoration in the Indian Eastern Himalayan region

The objective of the investigation was to determine the response of different taxa of mites across the land use types and demonstrate that soil mites could be used as an indicator of environmental change after the conversion of secondary forests into rubber plantations. The sampling was performed during the dry season on 12 sampling areas, consisting of four land use types: secondary forests, 7-year-old rubber plantations, 12-year-old rubber plantations, and 25-year-old rubber plantations, with three replications of each treatment. Soil cores were sampled along a 40 m transect with a steel corer. The soil mites were extracted using modified Berlese-Tullgren funnels during a 10 day period. Soil physico-chemical parameters were measured on each sampling area. The conversion of secondary forests into rubber plantations was characterized by a modification of the mean values of mite density (+103 and +262%), species richness (-11 and +32%), water content (-41 and -5%), bulk density (+6 and -3%) and soil organic carbon (-73 and -59%) respectively, after 7 and 25 years of conversion. The density of mites, species richness and soil water content increased with the aging of the rubber plantations, demonstrating an improvement in soil ecological quality and environmental conditions. These results are confirmed by the values of the Maturity Index of Gamasid mites, which increased with the increasing age of rubber plantations. In other words, the severity of environmental impact decreased with the aging of the rubber plantations and was ranked as follows: 25-year-old rubber plantations &lt; secondary forest &lt; 12-year-old rubber plantations &lt; 7-year-old rubber plantations. The Maturity Indexes estimated that 25-year-old rubber plantations (0.84) and in secondary forests (0.74) are relatively similar and characterize stable habitats, which are potentially dominated by Gamasid species with K selection.

The aim of investigation was to address the impacts of tropical forests conversion into agricultural land on changes in Oribatid mites’ communities as well as soil physico-chemical properties across 2–4 texturally distinct soils in La Mé and Grand Lahou, Côte d’Ivoire. The fieldwork was conducted in the humid period on two study sites: 1– rubber landscape (secondary forest, 7-, 12- and 25-year-old rubber plantations) and 2– oil palm landscape (secondary forest, 13-, 20- and 39-year-old oil palm plantations). Three sampling areas were established on each land-use type and age class, for a total of 24 sampling areas. In each sampling area, soil cores for Oribatid mite’s extraction were taken at a depth of 10 cm across a 40–50 m transect. The soil physical and chemical properties were also measured. The results showed a decrease in Oribatid density (–29% and –71%), species richness (–29% and –42%), diversity (–29% and –59%), soil organic carbon (–56% and –17%), total nitrogen (–55% and –12%) and soil organic matter (–56% and –17%), and an increase in bulk density (+28% and +21%), respectively after the conversion of the secondary forests into rubber and oil palm plantations. Whatever the study site, the soil physico-chemical and biological properties were more stabilized in the clay and clay sandy textures compared to sandy clay and sandy soil textures. Our findings suggest the incorporation of woody trees with an understory of nitrogen-fixing legume species as a cover crop, which can create a sustainable agroforestry system with improved land quality.

Effects of past land use on soil organic carbon changes after dam construction

Boreal forest ecosystems are predicted to experience more frequent summer droughts due to climate change, posing a threat to future forest health and carbon sequestration. Forestry is a regionally dominant land use where the managed secondary forests are typically even-aged forests with low structural and tree species diversity. It is not well known if managed secondary forests and unmanaged primary forests respond to drought differently in part because the location of primary, unmanaged, forests has remained largely unknown. Here we employed a unique map detailing over 300 primary forests in Sweden. We studied impacts of the 2018 nationwide drought by extracting and analyzing a high-resolution remote sensing vegetation index over the primary forests and over buffer zones around the primary forests representing secondary forests. We controlled for topographical variations linked to soil moisture, which was a strong determinant of drought responses, and analyzed Landsat-derived EVI2 anomalies during the drought year from a multiyear non-drought baseline. We found that primary forests were less affected by the drought compared to secondary forests. Our results indicate that forestry may exacerbate the impact of drought in a future climate with more frequent and extreme hydroclimatic events.

An in-depth exploration of plant–soil interactions can improve our knowledge of the succession and evolution of forest ecosystems. To understand the coupling relationship between species diversity and soil physicochemical properties in natural secondary forests during the process of vegetation restoration, the species diversity of trees, shrubs and herbs and the physicochemical properties of soil at different depths were investigated in six forest communities in the Qinling Huoditang area over two years (2013 and 2019). The analysis indicated that the soil nutrient content in the region decreased during this period, but the plant diversity index showed no obvious change. Through RDA and regression analysis, we determined that the correlations between plant diversity and soil physicochemical properties were discrete. The tree and herb species diversity were most closely related to the surface soil, while shrub diversity was more strongly regulated by the middle soil layer. Available phosphorus had the strongest effect on trees, and the main factors affecting shrubs were NO3-N and NH4-N. Herb growth was more limited by soil physical properties such as the soil bulk density and porosity. We concluded that evident correlations exist between soil physicochemical properties and plant communities. After six years of natural restoration, the plant diversity index did not change significantly. However, the soil nutrient content decreased obviously. This study provides a reference for the management of vegetation restoration processes in forest ecosystems.

Biodiversity is declining throughout southern African miombo woodlands due to poor land use practices that are detrimental to soil, vegetation and habitat. We aimed at examining tree and shrub species diversity and distribution in Uapaca kirkiana-dominated woodlands under three land tenure types; forest reserves, customary and leasehold land. The study was conducted at different forest sites within similar agroecological zone in southern Malawi. Study sites were located at a range of altitudes between 900 and 1,200 m a.s.l. Three circular plots each with 32.60 m radius were established at each study site to sample tree and shrub species composition, structure and distribution under three land tenure types. We found that forest reserves had higher species diversity with an average of 16 tree families, 27 genera and 34 species as compared to only 10 tree families, 6 genera and 6 species on customary forest lands. Comparisons of diameter at breast height size class distributions showed that customary land had significantly low numbers of small (5.0–10.0 cm) and very large (≥30 cm) diameter classes suggesting lower levels of regeneration and high rate of anthropogenic activities. The high species diversity and richness in forest reserves and leasehold land indicate high potential for protected lands to restore tree species diversity. It is concluded that levels of human activities as influenced by land tenure type reduce tree species diversity, composition and distribution at the different sites, and this confirms the hypothesis that open access lands are not compatible with conservation of tree and shrub species diversity because of high anthropogenic activities.