Catchment News

Ecosystem hydrology: utilizing the functional ecology of forests and wetlands – Acknowledging the benefits of multiple land use

Recently published findings in the UN Food and Agriculture Organization’s (FAO) ‘State of the World’s Forests’ report, suggest that fostering co-operation between a country’s agriculture and forestry sectors improves food security and reduces deforestation. The report emphasised that such collaboration between these sectors reduces environmental damage and enhances social and economic outcomes – as similarly noted by Ramsar, the international organisation that promotes the values of wetlands.

Understanding the roles that forests and wetlands play in nutrient dynamics and hydrology of catchments yields insights into their capacities to intercept, recycle and retain nutrients, as well as delivering other social, economic and environmental benefits. Such roles may be purposefully reinstated where lost, and even redesigned to encompass a range of specific environmental tasks, including those related to water and land in catchment management.

This first of three articles for the ‘Catchment Newsletter’ outlines a range of enterprises undertaken during more than three decades for reinstating some of the country’s functional ecology which has been diminished over millennia. Working for VESI Environmental Ltd, the authors have helped pioneer many of the innovative concepts applied and have been involved in work at more than 150 sites throughout the country. The present article focuses on the background and the general principles applied. The remaining two describe their application in individual case studies, and will appear in future issues of the Newsletter.

The consequences of lost habitats

Although generally known, it is also unfortunately little appreciated that Ireland has almost entirely lost the two once most widespread habitats-types that had come to dominate the country after the last glacial period some 12,000 years ago. These were, on the one hand, forests dominated by pine, birch and aspen on the more free-draining upland soils, grading to oak, ash and elm on the mesic more nutrient rich soils at lower elevations. On the other hand, a wide variety of wetland categories of lakes, shallow ponds and marshes existed wherever water gathered. So great has this loss been, that there are hardly any traces left today of their once widespread existence. Consequently the key roles that forests and wetlands once played in the country’s nutrient dynamics and hydrology have been extensively reduced.

Comprehensive and insightful studies over many decades, such as by Bormann, Likens and their associates at Yale and Cornell Universities, USA, working at the US Forest Service catchments at Hubbard Brook, New Hampshire, have demonstrated that forest habitats would have reduced nutrient loss and beneficially influenced hydrological dynamics – a range of dynamic capacities that land and water management can only dream of aspiring to achieve under current practices. Tree canopy-interception, deep-rooting of trees and forest canopy transpiration, respond commensurably to precipitation. In the case of wetlands, impeding the flow of surface-waters and the absorption of its vectored constituents – wherever water slows on its journey to the sea. These key ecosystem functions are now sorely absent over most of the Irish countryside with profound and compounded negative impact on the country generally.

The original vegetation succession of these lost habitats, which would have continued over millennia, was of course influenced by the ecologically early arrival of humans and their use of fire – opening the forest canopy, releasing vegetation-stored nutrients and consequently increasing the flow of nutrients to downstream shallow lakes and marshes. The combined effects of repeated fire and the subsequent nutrient loss would have had profound direct and indirect ecological consequences in impoverishing upland soils and increasing the nutrient status of receiving shallow lakes and marshes. With the arrival of agriculture during the Neolithic era, these new anthropocentric dynamics were further augmented as even more forest was cleared, resulting finally in the development of moor-type peatland in areas of base-poor soils with relatively higher precipitation such as is evident at the Ceide Fields in north county Mayo. In shallow lakes, a common feature of the saucer-shaped topography of the country, released in-flowing nutrients probably initiated or at least, speeded up the development of raised bogs.

The need to understand

Understanding is central to human endeavour. Grasping how nutrients are utilised and recycled in an ecosystem improves comprehension of their community species’ evolution and biology, and their ecological dynamics, and also allows assessments to be made regarding their sustainable management. Knowing how forests, woods, marshes and associated wetlands function, provides a basis for their effective reanimation. Such ecological reanimation, can incrementally lead to better appreciation of how they function and of the associated ecosystem services that they provide.

Ecological reanimation versus restoration

• Ecological reanimation focuses on facilitating bio-geo-chemical processes delivering self-managing and self-facilitating systems sustainably minimizing leakiness and entropy.
• Ecological restoration focuses on facilitating the recovery of lost biological assemblages within recent evolutionary time lines.

In recent years these ecosystem based benefits have become more recognised at the fore of efforts for sustainable social and economic development. Their scope was quantified in the World Millennium Goals/Declaration 2002. These goals are a blueprint, agreed upon by nearly all countries and leading development institutions, towards helping the global community understand the close relationship existing between the Planet, nature and humans’ own long-term wellbeing.

Knowing how catchment management benefits from forests and flow-intercepting marsh-type wetlands, points to how they might also be reanimated and properly used for managing various known polluted water sources. This reanimated capacity of marsh-type wetlands has special relevance as it includes their capacity to effectively treat municipal waste waters, road drainage, agricultural and food processing waste waters, landfill leachate and mine drainage etc. Forest development on the other hand may be structured to enhance water retention, aid in recharging aquifers and neutralise acid through-fall. This ‘philosophy of understanding through doing’ reflects the rhetorical question posed by the Chinese Tang Dynasty poet-philosopher Han Yu:

“Does the bowl in the garden mock nature, when night after night green frogs gather to prove it’s a pool? Who says you can’t make a pond out of a bowl?”

The initial priming factors in almost any land and water endeavor

Recognising the complexities of each site and its innate characteristics, and innovatively using them resourcefully, are key to successfully implementing land and water management. This includes its soil base and water supply. With its repeated layers of disturbance, Ireland’s ecology and landscape are particularly challenging. This is especially so where understanding, conserving or restoring its natural capital and heritage are concerned. Attempting to introduce innovative change to current land and water management practices is difficult. It is also paradoxical, since probably no other country in Europe has seen its original ecological base more eroded, torched, drained, grazed, ploughed and manured. Consequently the country has retained little of its once wider functional ecosystems and associated biodiversity. Most of this loss has resulted from often assumed economic necessity. It has also been at times exploitative, an example being the loss of oak forests in the 1500’s. These sustained impacts have led to the field patterns and dispersed farms and dwellings generally seen as the ‘natural’ present day postcard-image of the countryside. Afforestation, peat harvesting and other initiatives, have suggested that the land might be used differently. Yet land use change remains a common challenge for many, including national institutions and governance, with politics interfering to a dominating degree.

This is particularly evident as rural Ireland strives to adapt to urban development, transport-infrastructure, wind turbines, electricity distribution, industry and rural dwellings. Only when economic and social arguments are coherently presented on a site-by-site basis does change seem to become acceptable. Different approaches to land usage have always been challenged, especially if seen as threatening existing economic and cultural interests. Thus any ‘new idea’ needs to be honed and tested within the ambit of social, economic and environmental management, with the frequently quoted axiom of “thinking globally and acting locally” having special relevance and application. Clearly experience and diversity of connected relevant competences are also required. New initiatives call for and benefit from a step-by-step approach, and ongoing reflection on the work in progress.

Innovation

Over the past 33 years, more than 100 functional wetlands, 18km of re-profiled riparian corridors and 25 novel forests have been developed or progressed by those at VESI, with State and private partnerships. A broad range of purpose has driven this work, in particular the need to address challenges relating to nutrient and water management, including flood attenuation and ecological reanimation. These endeavours have led to the development of the ‘Integrated Constructed Wetlands’ (ICWs) concept that is successfully applied and cost effective in the treatment of a wide range of polluted water sources. In addition, the development of alternative forest design and practice, including riparian and forest corridors, enhances nutrient management and water quality. Underlying all these initiatives has been the awareness that air, land and water are inextricably linked through bio-geo-chemical processes, and that water management is fundamentally a land use issue.

By grasping how a forest or a wetland functions, one can reanimate them and address the salient aspects of each site’s specific needs. One such example is the ICW treating combined municipal waste water at Castle Leslie, Glaslough, Co. Monaghan shown in the photograph.

Influences of each specific water-source

Each rivulet, stream and tributary influences the receiving water into which it flows, whether river, marsh, lake or inshore water. Each source differs in terms of its flow, velocity and vectored contents, including nutrients and suspended material, as well as its conductivity status. Furthermore these may differ from season to season.

Each water source is influenced by the initial interactive surface through and upon which it falls, including atmosphere, vegetation and soil/ geology. Effective forest and wetland reanimation design should address this elementary fact in ways that optimise water quality and flow. By explicitly integrating all source-water with each site’s location, soil, landscape setting and potential ecological-biodiversity, a sustained suite of benefits and synergies as exemplified by Integrated Constructed Wetlands can be achieved.

Establishment of forest

Trees, woods and forests have special merit for catchment management in providing capacities for capturing, recycling and retaining essential nutrients and carbon. Tree canopies intercept, absorb and transpire water. Their roots increase water infiltration to the ground and reduce overland flow. Together these have greater effect than the grasslands that dominate the land cover of the Country. Novel alternatives to conventional forest establishment have shown that a forest’s capacity for water retention can be additionally enhanced, thus achieving little or no surface discharge. This is of special relevance in the management of canopy-induced acidification and water quality during timber harvesting. Through the novel use of excavated borrow-pits, and the accompanying mound-planting of trees, effective alternatives to conventional ploughing and ripping in the establishment of forest may be achieved. The use of such integrated depressions is better at retaining surface water within the forested area, with tree stability enhanced by mounding. The establishment of forest corridors can provide shelter and access throughout farms, and is another approach that could better help protect receiving waters. These are especially effective when positioned across sloping ground with mounding, and sumps to further intercept surface water flow.

Key Message: Site-specific assessment and integrated design can benefit catchments

The work presented recounts the importance of site-specific assessment and the roles of integrated design that can benefit catchment management. Its importance and relevance are supported by the United Nations Environment Programme’s Convention on Biological Diversity ‘Ecosystem Approach’ and its 12 principles. In addition there is a need to avoid formulaic ‘tick-the-box’ approaches to design and implementation, just as there is an ever-present danger that where formulaic solutions are the norm, opportunities to deliver on multiple benefits – often only specific to a site – are missed.

Summary points

The implementation of forest and wetland functional ecosystem reanimation for catchment management requires:

• Accepting the inextricable linkage between social, economic and environmental needs in land and water management.
• Social-economic gains need not necessarily be tempered by ecological failure (loss of biodiversity, anthropogenic induced climate change, loss of ecosystem services/buffering etc.). There are opportunities for enhanced sustainable developments through integration and collaboration.
• Water management is largely a land use issue as it needs sufficient space to sustainably facilitate treatment and attenuate flow.
• An optimal approach to land and water resources is required rather than one that strives for the maximisation of a single outcome.

“Nature never did betray the heart that loved her”

William Wordsworth, 1770-1850

Aila Carty, Caolan Harrington, Rory Harrington and Janet Laffey – VESI Environmental Ltd. Little Island, Cork & Dunhill, Co. Waterford