In the high-altitude grasslands of Colorado, known for their dense summer blooms of corn lilies, aspen sunflowers and sub-alpine larkspur, a decades-long ecological experiment is providing new evidence of how climate change is altering fragile mountain ecosystems.

Established in January 1991, the study is among the earliest and longest-running efforts to examine how rising temperatures influence plant and soil systems in alpine environments.Scientists initially expected that warmer conditions would extend the growing season and increase vegetation density.

Instead, the experimental plots showed a steady decline in grasses and wildflowers. Over time, these species were replaced by sagebrush, transforming sections of the meadow into landscapes resembling arid scrubland. Researchers also observed significant changes below ground, where fungal communities in the soil shifted in response to sustained warming.

The findings, published in the Proceedings of the National Academy of Sciences, indicate that such ecosystems may not respond to warming in ways previously anticipated. The study concludes that these meadows could largely disappear in the coming decades if global temperatures rise by 2°C above preindustrial levels.

The transformation observed in Colorado is part of a broader ecological process increasingly documented in cold regions worldwide, commonly referred to as “shrubification.” This process involves the gradual replacement of grasses and low-lying vegetation with woody shrubs and, in some cases, trees.

According to Sarah Dalrymple, a conservation ecologist at Liverpool John Moores University who studies similar changes in Iceland, warming temperatures are reducing environmental constraints that historically limited plant growth in cold climates.

She said that as conditions become less severe, plant communities shift from grasslands or heath ecosystems toward shrub-dominated landscapes, with potential progression to forested environments.

Dalrymple noted that grasses and alpine plants are adapted to short growing seasons and harsh climatic conditions. As these constraints ease, shrubs and trees, which require longer periods to establish leaf and stem structures, gain a competitive advantage.

This transition represents a fundamental reorganization of ecosystems that have remained relatively stable for thousands of years.

While the expansion of shrubs and trees can provide benefits such as increased shelter for wildlife, livestock and human activity, researchers say the broader implications are more complex. Dalrymple said that the spread of woody vegetation in cold regions is associated with processes that can accelerate climate change, particularly through the thawing of permafrost.

Permafrost contains large quantities of stored carbon, and its melting can release greenhouse gases into the atmosphere. Dalrymple said that afforestation in these environments can intensify this process, contributing to increased carbon emissions. She emphasized that the rapid pace of ecological change is a key concern, particularly given its potential effects on the global carbon cycle.

Researchers stress that shrubification itself is not inherently negative but is indicative of broader systemic changes driven by rising global temperatures. Dalrymple said the primary issue lies in the inability to control carbon emissions, with vegetation shifts representing a downstream consequence rather than a direct cause.

Scientists involved in the Colorado study and related research warn that the rate of change appears to be faster than earlier projections suggested. The assumption that ecosystems would respond gradually to warming is being challenged by evidence from long-term observations, which show rapid and sometimes irreversible transitions.

Dalrymple said these changes are not confined to a single region but are occurring across multiple high-altitude and high-latitude environments. This suggests that similar transformations could take place in mountain systems globally, affecting biodiversity, water cycles and land use patterns.

Despite these trends, parts of the Colorado meadows continue to display the dense, insect-rich floral landscapes that have drawn visitors for decades. Souza, who has been visiting the research area since 2012, described the environment as unusually vibrant, noting the intensity and abundance of flowers during peak bloom periods.

She said the visual richness of the landscape remains striking but acknowledged concerns about its long-term stability under continued warming.

The contrast between present-day conditions and projected future changes underscores the uncertainty facing ecosystems that have historically depended on stable climatic conditions.

Global demand for sand, a key component in concrete, glass, and infrastructure development, has increased sharply in recent decades, driven by rapid urbanisation and large-scale construction projects.

According to the United Nations Environment Programme, sand and gravel are the most extracted solid materials worldwide, exceeding fossil fuels and biomass in volume.

The material is essential for producing concrete, which underpins infrastructure such as roads, bridges, housing, and commercial developments. Rapid urban expansion in emerging economies has intensified demand, particularly in regions undergoing large-scale infrastructure investment.

However, not all sand is suitable for construction. Desert sand, shaped by wind erosion, is generally too smooth for use in concrete, leading to increased extraction from riverbeds, coastlines, and marine environments.

The extraction of sand from rivers and coastal areas has raised concerns about environmental degradation. UNEP reports indicate that excessive sand mining can lead to erosion, reduced water quality, loss of biodiversity, and increased vulnerability to flooding.

River ecosystems are particularly affected, as sediment removal alters natural flow patterns and habitats.In several countries, unregulated or illegal sand mining has emerged as a governance challenge. The high demand and relatively low cost of extraction have contributed to informal markets, complicating enforcement of environmental regulations.

Governments and international organisations have begun to address the issue through policy measures aimed at sustainable resource management. UNEP has called for improved monitoring, better data collection, and the development of alternatives to natural sand, including recycled construction materials.

The growing demand for sand has implications for global supply chains and construction costs. As easily accessible sources become depleted, transportation costs increase, affecting project economics.

In some regions, sand has become a strategic resource, influencing local markets and development planning.Efforts to promote sustainable construction practices, including material efficiency and recycling, are gaining attention among policymakers and industry stakeholders.

However, large-scale adoption remains limited, and natural sand continues to dominate supply.The issue highlights the broader challenge of balancing economic growth with resource sustainability.

As urbanisation continues, the pressure on sand resources is expected to persist, requiring coordinated policy responses at national and international levels.

The analysis, led by Dr. Zeb Hogan of the University of Nevada, evaluated data on more than 15,000 freshwater species and identified a significant collapse in migratory populations across major river systems.

The report highlights that these migrations, which rank among the largest animal movements globally, are increasingly disrupted. Species such as the dorado catfish, which travels an estimated 11,000 kilometres between the Andes foothills and the Amazon estuary, exemplify the scale of these journeys.

More widely known migratory species, including salmon and eels, are also affected.

According to the CMS assessment, freshwater ecosystems are particularly vulnerable to human activity. Pollution entering rivers and lakes, the construction of dams that obstruct migration routes, and overfishing have collectively reduced fish populations.

Rising water temperatures linked to climate change are compounding these pressures.Amy Fraenkel, executive secretary of CMS, stated that migratory species face increasing challenges throughout their life cycles, often crossing multiple national boundaries.

The report underscores that coordinated international action is necessary to address these pressures, particularly as river systems frequently span more than one country.

Migratory freshwater fish support some of the world’s largest inland fisheries and are a critical source of food and livelihoods for hundreds of millions of people. In Cambodia’s Tonlé Sap lake, part of the Mekong river system, more than 100 migratory species contribute to high-yield fisheries, with catches reaching several tonnes within short periods, according to Hogan.

The report identifies 325 freshwater fish species that cross international borders and could qualify for enhanced protection under CMS frameworks. However, only 24 species are currently listed, many of them sturgeon historically targeted for caviar production.

Delegates from 132 CMS member states are meeting in Brazil, where improving river connectivity and protecting migratory pathways form a central part of discussions.

Proposed measures include removing or preventing barriers such as dams, maintaining adequate water flows, reducing pollution, and coordinating fisheries management across borders.

The Amazon basin remains one of the last relatively intact strongholds for migratory freshwater fish. Regional initiatives, including a proposed decade-long conservation plan for migratory catfish, are being considered as potential models for other river systems.

The Mekong basin is identified as a region of acute concern, with large migratory species facing heightened extinction risks due to overfishing and habitat disruption. Key countries in the basin, including Thailand, Cambodia, Laos and Vietnam, are not currently part of the CMS treaty framework.

Other priority basins highlighted in the assessment include the Danube, Nile and Ganges-Brahmaputra systems.

The report also notes past losses, including the extinction of the Chinese paddlefish in the Yangtze River, attributed to habitat disruption following the construction of the Gezhouba dam in 1981.