Effects of land use change on biodiversity and ecosystem services in tropical montane cloud forests of Mexico

Tropical montane cloud forests deliver important goods and services to society, such as timber, the supply and purification of fresh water, and carbon sequestration. In spite of their relevance, current deforestation rates are very high, at the expense of affecting the provision of ecosystem services. We explore the impact of land use change in terms of provision of ecosystem services by following two approaches, one very detailed (focused on hydrological services – water quality) and another one with a broader perspective (at a large scale and considering the ecosystem service value (ESV) of several ecosystems and their ecosystem services at the same time). In the highlands of the State of Veracruz, previously forested lands were converted into coffee plantations and cattle ranches. To evaluate the role of species composition and community structure on water quality, we studied nine small watersheds (<15 ha) covered by pristine cloud forest, coffee plantations and cultivated grassland (three each). Species richness of the three land use types was similar, although species composition was as different as 90%. Overall species diversity as well as that of woody species, and growth form diversities decreased in the transformed land uses. Water quality of streams flowing through these watersheds declined: nutrients (nitrate), conductivity, cations, chloride and suspended solids were lowest in the forest streams and highest in streams from coffee watersheds, whereas grasslands were intermediate. We also calculated ecosystem service values (using the transfer value method) and estimated economic market–non-market gains and losses owing to land transformation. Loss of natural ecosystems may imply a significant economic loss to society in terms of ecosystem services, although market gains may still lead land owners to land conversion because revenues are higher. Adequate Payment for Ecosystem Services may be a good option to prevent deforestation, but the compensation should be at least equal to the opportunity cost of the promoted land use. Our estimates are indicative of the urgent need to go beyond water quantity as the most relevant ecosystem service considered in PES schemes.     

Monitoring the effects of land use and cover changes on net primary production: A case study in China's Yongding River basin

Changing land uses and cover types influence vegetation composition and health, so understanding the effects of these changes on net primary production (NPP) provides an important tool for monitoring ecosystem responses to environmental change. Using remote-sensing images and precipitation, temperature, and total solar radiation data from 1978, 1987, 2000, and 2005, and a light utilization efficiency model, we studied the effects of changes in these parameters and land use and cover types on NPP in China's Yongding River basin. We determined the NDVI of vegetation in the basin, and used these results to estimate the NPP of vegetation in the basin and the influence of land use and cover type changes on NPP under two climate scenarios: one in which the precipitation and temperature of the previous period remain unchanged into the following period, that is, use the climate in 1978, 1987 and 2000 to analyze NPP data in 1987, 2000 and 2005 respectively, and another in which both parameters remain constant at their 1978 values throughout the study period. With the climate unchanged from the former period, NPP in 1987 decreased compared with the 1978 value by 20–50 gC/m², and then increased by more than 40 gC/m² in western and central parts of the basin from 1987 to 2000. From 2000 to 2005, NPP decreased in the northwestern, northern, and eastern parts of the basin. With climate unchanged from 1978 to 2005, NPP increased from 1987 to 2000 by from 10 to 30 gC/m² in most areas. From 2000 to 2005, some farmland in western and northwestern parts of the basin and some forest land were converted into grassland, decreasing NPP by 40–50 gC/m².     

2种不同土地利用方式对山麓耕地土壤养分的影响

研究不同土地利用方式对土壤养分的影响,以便了解土壤质量状况,为实现不同植被管理和可持续利用提供科学依据。以小陇山山麓区移栽至耕地(前期种植柴胡)后生长3年的油松Pinus tabulaeformis Carr.苗木土壤为对象,并以长期种植柴胡Bupleurum chinense的耕地作对照,采用对比和主成分分析方法,对2种人工植被类型下不同土层(0～10、10～20和20～30 cm)土壤养分特征进行了分析。结果表明:1)油松苗地3个土壤层的有机质、全磷和全钾含量均小于柴胡耕地,除0～10 cm土层有机质外,其余差异均达到显著水平(P <0.05);3个土壤层的全氮含量在油松地和柴胡地两者之间均无显著差异(P> 0.05)。油松苗地3个土壤层的速效钾均显著大于柴胡地(P <0.05);而有效磷含量却小于柴胡地(10～20 cm除外),且仅在20～30 cm土层两者差异达显著水平(P <0.05);同样,3个土壤层的碱解氮含量在油松地和柴胡地两者之间均无显著差异(P> 0.05)。2)2种植被类型下土壤的有机质、全氮、全磷、碱解氮、有效磷和速效钾含量表现出"表聚现象",即养分含量从表层向下层呈递减趋势;而全钾含量在2种植被类型下均表现出相反的变化趋势,即从表层向下层呈递增趋势,但差异均不显著(P> 0.05)。3)主成分分析表明:速效钾和全磷是影响油松苗地土壤质量的最主要土壤因子,而全氮和全磷是影响柴胡地土壤质量的最主要土壤因子,且土壤养分综合得分表现为油松地(1.467)<柴胡地(1.504)。可见,油松人工苗明显地降低了耕地土壤养分含量,长期栽植将会导致土壤养分处在较低水平,因此在大苗培育期间要因土施肥,提高土壤肥力,尤其需要及时补充土壤有机磷肥;而对柴胡耕地也应该补充有机氮肥和磷肥。这些结论可为小陇山山麓区域耕地进行土地合理利用和土壤科学管理提供科学参考。     

Recovery of saturated hydraulic conductivity under secondary succession on former pasture in the humid tropics

Landscapes in the humid tropics are undergoing a continuous change in land use. Deforestation is still taking its toll on forested areas, but at the same time more and more secondary forests emerge where formerly agricultural lands and pastures are being abandoned. Regarding soil hydrology, the extent to which secondary succession can recover soil hydrological properties disturbed by antecedent deforestation and pasture use is yet poorly understood. We investigated the effect of secondary succession on saturated hydraulic conductivity (Ks) at two soil depths (0-6 and 6-12 cm) using a space-for-time approach in a landscape mosaic in central Panama. The following four land-use classes were studied: pasture (P), secondary forest of 5-8 years of age (SF5), secondary forest of 12-15 years of age (SF12) and secondary forest of more than 100 years of age (SF100), each replicated altogether four times in different micro-catchments across the study region. The hydrological implications of differences in Ks in response to land-use change with land use, especially regarding overland flow generation, were assessed via comparisons with rainfall intensities.Recovery of Ks could be detected in the 0-6 cm depth after 12 years of secondary succession: P and SF5 held similar Ks values, but differed significantly (α = 0.05) from SF12 and SF100 which in turn were indistinguishable. Variability within the land cover classes was large but, due to sufficient replication in the study, Ks recovery could be detected nonetheless. Ks in the 6-12 cm depth did not show any differences between the land cover classes; only Ks of the uppermost soil layer was affected by land-use changes. Overland flow - as inferred from comparisons of Ks with rainfall intensities - is more likely on P and SF5 sites compared to SF12 and SF100 for the upper sample depth; however, generally low values at the 6-12 cm depth are likely to impede vertical percolation during high rainfall intensities regardless of land use.We conclude that Ks can recover from pasture use under secondary succession up to pre-pasture levels, but the process may take more than 8 years. In order to gain comprehensive understanding of Ks change with land use and its hydrological implications, more studies with detailed land-use histories and combined measurements of Ks, overland flow, precipitation and throughfall are essential.     

Effects of changes in land use and land cover on sediment discharge of runoff in a typical watershed in the hill and gully loess region of northwest China

Land use plays a much more important role than other factors, such as climate, soil properties, topographic features, vegetation coverage, human activities and others, in affecting soil erosion and sediment discharge. In order to understand the effects of changes in land use on sediment discharge and to provide a theoretical basis for land use planning, management and ecological restoration, we used the controlled Qiaozidong watershed and the uncontrolled Qiaozixi watershed in the third sub-region of the Loess Plateau as examples and analyzed the effects of land use and land cover on the discharge of sediments. The results show that the impact of land use and land cover on the annual amount of sediment discharge is significant. Compared with the uncontrolled watershed during similar periods, the amount of sediment discharged from the controlled watershed was reduced by 44%, 75% and 86%, respectively, in wet, normal and dry years. In the controlled watershed, compared with the period from 1986 to 1994, the amount of sediments discharged was less during the period from 1995 to 2004. The impact of land use and land cover on sediment discharge demonstrated characteristics of seasonal fluctuation. The effects of sediment reduction in the controlled watershed were greater than those in the uncontrolled watershed in May and September. In the controlled watershed, the reduction effect coincided with the distribution of rainfall. The amount of discharged flood sediments is closely correlated with rainfall, rainfall intensity in a 60 min period and the volume of flood. The rainstorm-runoff process and the rainstorm-sediment discharge process demonstrate that land cover has a strong regulatory and control function in the flood process and sediment discharge in rainstorms. For the controlled watershed, given the same precipitation frequency distribution, the average amount of sediment discharged during the land use period from 1995 to 2004 was less than that during the earlier land use period from 1986 to 1994 under every recurrent period. __________ Translated from Journal of Beijing Forestry University, 2007, 29(6): 115–122 [译自: 北京林业大学学报]     

Vegetation community and soil characteristics of abandoned agricultural land and pine plantation in the Qinling Mountains,China

In order to determine the changes in the characteristics of the vegetation and soil following agricultural abandonment and compare the effects of different restoration approaches on ecosystem recovery, we studied the vegetation community and soil characteristics (nutrients, bulk density, water content and pH) of Pinus tabulaeformis plantations and abandoned croplands in different successional stages in the Foping National Nature Reserve, located in the Qinling Mountains, northwest China. The results indicated that natural vegetation and habitat could be restored via natural regeneration. These spontaneous restoration forests were characterized by high diversity, high soil fertility and rich unique species. The soil organic matter, total carbon, total nitrogen, available potassium, community cover, depth of litter, depth of humus and soil water content increased significantly with years after abandonment, while the total potassium, total phosphorus, available phosphorus, soil pH did not seem to change significantly with abandonment time. The soil mineral nitrogen (NH₄-N + NO₃-N) tended to increase during the first 50 years after abandonment and then decreased. The pine plantations tended to show a low level of biodiversity in tree and herb layer, but the shrub layer (including sapling) composition and diversity were similar to secondary forests. Although the pine plantation showed lower soil fertility, they did not seem to result in the habitat-degradation.     

The effects of topography on forest soil characteristics in the Oregon Cascade Mountains (USA): Implications for the effects of climate change on soil properties

Forest soil measurements were made at over 180 sites distributed throughout the H.J. Andrews Experimental Forest (HJA) in the Oregon Cascade Mountains. The influences of both elevation and aspect on soil variables were measured in the early (1998) and late summer (1994). Increased elevation significantly increased soil moisture, mean annual precipitation, soil organic matter, labile C and mineralizable N, microbial activities, extractable ammonium, and denitrification potentials. In contrast, bulk density, pH and soil temperature (1998 only) were significantly lower at the higher elevations. Relative to labile C, mineralizable N was preferentially sequestered at higher elevations. Aspect significantly affected annual mean temperature and precipitation, soil moisture and temperature, soil organic matter, mineralizable N, extractable ammonium, denitrification, and microbial activities. There were no significant higher statistical interactions between elevation and aspect on climatic or soil factors. Soil organic matter (SOM) accumulation at higher elevations is likely driven by a reduction in decomposition rates rather that an increase in primary productivity, however, SOM accumulation on north facing slopes is probably due to both a decrease in decomposition and an increase in primary production. Models of climate change effects on temperate forest soils based on elevational studies may not apply to aspect gradients since plant productivity may not respond to temperature–moisture gradients in the same way across all topographical features.     

Exotic Pinus carbaea causes soil quality to deteriorate on former abandoned land compared to an indigenous Podocarpus plantation in the tropical forest area of southern China

Soil properties under an exotic plantation (Pinus caribaea) and an indigenous plantation (Podocarpus imbricatus) were compared with adjacent secondary forests and abandoned land in the tropical forest areas of Jianfengling National Nature Reserve in Hainan province, southern China. The surface soil (0–0.2 m) under Pi. caribaea has higher bulk density, lower soil organic carbon, total N, total K, available N, microbial biomass carbon, and smaller soil microbial communities (as indicated by soil Biolog profiles) than under Po. imbricatus. Both land use types showed negative cumulative soil deterioration index (DI) compared to secondary forests. However, compared to abandoned land (DI = –262), the soil quality of Po. imbricatus showed improvement (DI = –194) while that of Pi. caribaea showed deterioration (DI = –358). These results demonstrated that these exotic pine plantations can significantly and negatively influence soil properties. By contrast, our results showed that adoption of indigenous species in plantations, or natural regeneration, can improve soil quality.     

Effects of contour hedgerows on water and soil conservation,crop productivity and nutrient budget for slope farmland in the Three Gorges Region (TGR) of China

Soil erosion has long been recognized as a major environmental problem in the Three Gorges Region (TGR) where slope farming is commonly practiced but the local topography is hilly. In consideration of the poor socioeconomic position of local farmers, low cost hedgerows had been introduced as a soil conservation measure to the TGR in the late 1980s. A collaborative research programme was initiated by the Chinese University of Hong Kong, the Chinese Academy of Science, the Huazhong Agricultural University, and the Bureau of Soil and Water Conservation of Zigui County to study the potential of adopting hedgerows in the TGR. Six experimental plots (10 m × 2 m, gradient = 25°) were constructed at Zigui County, Hubei Province to study effects of hedgerows on erosion, nutrient loss and crop productivity. Results indicated that there were significant relationships between rainfall and runoff, and rainfall and soil loss, respectively. Conventional slope farming could not be considered a sustainable agricultural practice because it resulted in severe erosion and low crop yield. Hedgerows per se seemed not to be effective in reducing soil loss and boosting crop productivity, but performances could be greatly improved when they combined with the use of fertilizers. Current farming and fertilization practices, however, generally did not meet N demands of crops. Results and findings of this paper will contribute towards a technical reference for the promotion and adoption of hedgerows in the TGR.     

Linking physical, economic and institutional constraints of land use change and forest conservation in the hills of Nepal

This paper analyses the changes in spatial patterns of agricultural land use during the period 1976–2000 along the altitudinal gradients in a watershed in Nepal. Land change patterns during this period were examined using information on land use derived from satellite images from 1976, 1990 and 2000. During the 24-year period from 1976 to 2000 agricultural land use increased by 35% at a cost of loss of forestland. Agricultural expansion was most conspicuous at higher elevations (1150–2000-m). About 36%, 18% and 6% of forestland was converted into agricultural activities from higher, middle and lower elevations respectively in the period from 1990 to 2000. Spatial distribution of living standard parameters, including farm family income and, food availability obtained from family surveys, shows a decreasing trend as the elevation increases whereas percentage of food bought shows an increasing trend. In this way it was found that, lost forest areas were smaller when located around high-income areas with good quality agricultural land and near an administrative centre as compared to areas located around low-income areas with low quality agricultural land and far from an administrative centre. Additionally, a regression model is constructed, to link the socioeconomic variables with the conversion of forestland into agricultural activities, breaking the study area into smaller zones. The spatial trajectories of these zones are then contrasted, paying particular attention to the socioeconomic conditions and institutional arrangements governing access to land resources. The study finds that while overall land change patterns in the region are largely explained by elevation and the socioeconomic conditions of people living adjacent to the forestland, more specifically, in sub-regional areas, trajectories reflect the signatures of institutions governing access to land. As sustainability of the watershed is dependent on forests, continued depletion of forest resources will result in poor economic returns from agriculture for local people together with loss of ecosystem services.     

陈山红心杉连栽林地土壤肥力综合评价

【目的】研究红心杉连栽对地力和林分生产力的影响,为红心杉人工林的可持续经营提供数据参考。【方法】选取立地条件相同的第1(G1)、2(G2)、3(G3)代红心杉人工幼林林地为研究对象,采用空间替换时间的方法,测定第1、2、3代红心杉幼林地0~20 cm,20~40 cm,40~60 cm土层中的土壤酶活性及主要理化性质,利用主成分分析法综合评估不同代次红心杉幼林林地的土壤肥力,探究与分析连栽红心杉林地肥力下降的主要影响因子。【结果】土壤肥力的综合评价指数F值的变化范围为5.993^-4.436,23个评价指标通过“降维”成3个主成分,累计贡献率达88.913%,其中,第1主成分贡献率为71.862%,第2主成分的贡献率为9.123%,第3主成分的贡献率仅有7.927%;随着连栽代次增加和土层加深,土壤水分和孔隙指标均呈降低趋势;大量元素、有效微量元素、脲酶和磷酸酶活在第1、2、3代之间均具有显著差异(P<0.05)。【结论】在当前的种植方式下,随着红心杉连栽代次的增加,土壤肥力和容蓄能力下降,脲酶、磷酸酶、全P、碱解N、速效K、有效Cu、有效Mn和有效Fe是影响土壤肥力的关键要素。     

Effects of history of use on secondary forest regeneration in the Upper Parana Atlantic Forest (Misiones, Argentina)

The Upper Parana Atlantic Forest, as with other areas, has been modified due to anthropogenic activities, generating a mosaic of agricultural fields and forests of varying ages and levels of conservation. The objective of this study was to identify structural and floristic patterns in secondary forests generated in abandoned fields with varying historic uses. Changes in vegetation were surveyed using chronosequences from 2 to 70 years. Stands with different land use histories in three areas of northern Misiones, Argentina, were considered. Adults (DBH ≥ 10 cm), saplings (3 ≥ DBH < 10 cm), seedlings (DBH < 3 cm and height ≥ 50 cm) and non-arboreous vegetation (herbaceous plants and shrubs) were surveyed. Data was analyzed using multivariate techniques (TWINSPAN, Detrended Correspondence Analysis, Cluster Analysis, and Kruskal–Wallis test). In the floristic analysis, two main forest groups were identified: one made up of primary forest and oldest secondary forest (>20 years), and another of the youngest secondary forests (<20 years). Basal area and density of individuals (seedlings, saplings, and adults) rapidly increased during the first two decades, and subsequently the adult category reached values comparable to those of mature forests (32 m²/ha and 850 individuals/ha). During the early years of succession, the forests showed floristic and structural differences related to history of use previous to abandonment; abandoned annual crops showed the greatest densities of saplings and seedlings, while abandoned pastures presented only individuals in the seedling category, and at very low densities. In stands analyzed since the beginning of succession, species of several ecological groups were present (pioneer, initial secondary, late secondary), while climax species appeared only in the seedling category, and in abandoned pastures no species of the later groups were recorded. Our results suggest that differences recorded during the early years of regeneration in sites with varying historic uses may be generated mainly by remnant vegetation at the time of abandonment of the fields (grasses and remnant monoculture plants). After 20 years of succession, it was no longer possible to differentiate the forests structurally or floristically, regardless of age or historic use of each stand. Due to their rapid regeneration capacity, the forests studied play an important role from the start of the successional process in heterogeneous anthropogenic landscapes such as that of Misiones, and contribute to maintaining biodiversity while providing numerous environmental services.     

Persistence of soil and foliar azadirachtin treatments to control sweetpotato whitefly Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) on tomatoes under controlled (laboratory) and field (netted greenhouse) conditions in the humid tropics

Persistence of neem-based products against sweetpotato whitefly Bemisia tabaci Gennadius (Homoptera: Aleyrodidae) was tested in air conditioned rearing rooms and tropical netted greenhouses (GHs). Two commercial neem products, NeemAzal^®-T/S (1% azadirachtin) and NeemAzal^®-U (17% azadirachtin), were used. Foliar application, under room conditions at dose-rates of 7 and 10 ml NeemAzal^®-T/S, induced an immature mortality of 32 and 44%, respectively, whereas 7 days post-application, under GH conditions, mortality rates declined to 5 and 7%, respectively. This result indicated rapid dissipation of the active ingredients. However, systemic application by soil drenching resulted in more stable effects under both laboratory and GH conditions. After soil drenching with solutions of 3.0 g NeemAzal^®-U until 7-day, immature mortality declined from 88% for the first day to almost half (45%) by day-7 in the GH, and from 90% on first day to 64% by day-7 under laboratory condition. Similar response trends for B. tabaci were obtained for other parameters such as adult colonisation, egg deposition, and egg hatch. The loss of efficiency of the neem products was clearly related to dose-rate, methods of application, and environment (temperature and UV). Soil application is therefore, a convenient approach to achieve high efficiency and persistence with neem products under the conditions in tropical GH environments for whitefly management.