Summary of presentation on beech forest ecology

Rob Allen

Landcare Research

I have worked as a forest ecologist for 20 years specialising in the areas of species composition patterns in forests, tree population dynamics, and forest nutrient cycling. Currently I am a research leader at Landcare Research, and am responsible for a large Foundation for Research Science and Technology programme on "Indigenous Forest Ecosystem Processes and Management". A brief CV is attached to this summary of my presentation.

There are many facets to beech forest ecology, which are all complexly interrelated, but in this presentation my focus is largely on their variability in time and space. The New Zealand beech forests are dynamic - with disturbances causing sudden and dramatic changes that are followed by gradual changes occurring as different kinds of forest develop after disturbance1.

A disturbance can be thought of as a single event, either natural or human induced, that cause a disruption to an ecosystem (e.g., windfall) causing a change in resources available to plants (e.g., light and nutrients). Therefore, forest structure, composition and functioning vary continuously across individual stands partly reflecting past disturbance2.

In Timberlands West Coast beech forests we know, to varying levels of detail, about the nature (distribution, intensity, and frequency) of some of these disturbances3,4,5. In briefly outlining the impacts of some of these disturbances I will also draw on beech forest information from elsewhere to provide a broader understanding of disturbance impacts.

In some parts of the landscape, the scale of variation caused by disturbance is small and corresponds to the deaths of individuals or small groups of trees. According to the work of Glenn Stewart and colleagues such natural treefall canopy gaps (up to 0.1 ha) in Maruia Valley terrace forests dominated by red /silver beech were most often caused by standing trees resulting from drought and/or insect attack, or by trees snapped by wind6.

Most canopy gaps involved more than one tree - and there were differences in the number of trees usually involved at different sites within the Maruia Valley. Such canopy gap formation was episodic and growth ring analyses of trees indicate has occurred in most decades over the last several hundred years. Growth ring analyses also indicate there is only a partial synchrony in canopy disturbance among localities within the Maruia Valley.

Ongoing observations indicate often such canopy gaps close over by growth of branches of nearby tree crowns - rather than expand as a consequence of further tree death caused by pinhole beetles or instability of edge trees. The abundance and growth of tree seedlings depends upon species, location in a canopy gap, and the size of canopy gap7. Exotic weeds (e.g., Himalayan honeysuckle, and blackberry) also invade natural canopy gaps.

Because canopy gap closure is common, regeneration, and hence forest age structure, often reflects intensive canopy damage rather than small treefall gaps. This leads to the question as to what are these more catastrophic disturbances?

In the late 70s many red beech trees died on toe slopes in the Maruia Valley following a scale insect outbreak. Gordon Hosking suggested the primary cause was a set of droughts and the major consequence was the death of red beech trees. Residual silver beech trees grew rapidly following death of red beech trees - and silver beech was not heavily attacked by the insect8. It is an important point that such natural disturbances affect different tree species in different ways. Interestingly, a recent outbreak of this scale insect in the Maruia Valley forests has not so far resulted in tree mortality.

Over decades and centuries, which is not long relative to tree longevity, the forests are likely impacted by major earthquakes resulting from movements along the Southern Alp's Alpine Fault9.

The view that earthquakes are a key determinant of forest structure in Westland is gaining acceptance in New Zealand9.

Although the distribution, intensity, and frequency of earthquakes can be determined for forested areas using seismological data, not much is known about their impacts on forests10. Several studies elsewhere have determined the proportion of an area where forest has been completely removed, or inundated by, earthquake-induced catastrophic landslides. In Canterbury mountain beech forests we know such landslide analyses seriously underestimate earthquake impacts as partial canopy damage is much more pervasive11 - to say nothing of the impacts of subsequent pest outbreaks. Where we have studied disturbance impacts over time in even a large area of beech forest we know that:

  • If some disturbances operate at large spatial scale (say 10 000 ha., or the area of a Timberlands Working Circle) we would expect fluctuations in forest biomass and imbalances between tree mortality and recruitment at this scale. Evidence from re-censused individual trees that are tagged on permanent plots representatively sampling forests throughout New Zealand support the view that forests at a several thousand hectare scale are often not in steady state12,13,14. This large-scale instability may also involve adjustments to human-induced global increases in atmospheric C0215.
  • I have selected a few of the disturbances we know are relevant in north Westland yet:
  • In my presentation of disturbance impacts I have said little about subsequent consequences. For example, the issue of ongoing tree death caused by pinhole borer, and associated diseases, that build up in recently dead woody material is intriguing. The widely held view is that a build of dead woody material, and injured trees, always leads to a build up of the borer. This is not necessarily the case even at the same location. In Canterbury mountain beech forests pinhole did build up after wind damage in the 1960s, also after snow damage to forests in the 1970s, but not in the same forests following an earthquake in the 1990s. Observations suggest pinhole is more likely to build up in woody material in drought years. In general, we know little about interactions among various types of disturbance that lead to canopy death.
  • At least in the Maruia forests, the forest age structure reflects periodic recruitment following major canopy disturbances. There is often a lag between recruitment and mortality in forests, the length of which can depend on site conditions2,12, although beech species in Westland usually regenerate following many forms of disturbance.
  • I have previously considered how silver beech trees displayed a growth response following the death of red beech trees8. Glenn Stewart and colleagues are now finding a similar sequence in these forests may have occurred following the Murchison earthquake - with survivorship and growth favouring silver beech. It has been a commonly held view that disturbance favours red beech, over silver beech, because red beech seedlings and saplings respond more rapidly to an increase in resources. In general we have little information on how different species may differ in their resistance to various forms of disturbance.
  • Another level of complexity is that the growth response by trees surviving disturbance will vary along environmental gradients. For example, mountain beech trees at low altitude show a greater diameter growth response to canopy disturbance than trees at higher altitudes12. This altitude effect on a growth response16, which may be similar in relation to decreasing soil fertility12, could also operate in Timberlands forests.
  • So far, I have largely considered the impacts of disturbance on stands of trees - with some implications for the important regeneration phase. There are many other consequences, one is that in removing logs, irrespective of silvicultural system, the functions of woody debris are modified. One function of woody debris is as a store of nutrients and, in beech forests, on infertile soils, log removal could influence the cyclable pool of nutrients. A large cation pool is found in tree trunks, with particularly high concentrations found in bark3. As woody debris is a poor substrate for decomposer activity it also has many other functions in forest ecosystems - for example, a diverse assemblage of fungi occur on logs and which taxa are represented is strongly related to a logs stage of decay and chemistry17.
  • Where management is altering the consequences of disturbance regimes, there is an ongoing need to understand the implications for structure, composition and functioning of forests.
  • Some important conclusions to be drawn from what we know about beech forest dynamics:
  • Of all our indigenous forest types, it is the beech forests we know most about. In addition, the beech forests of the Maruia Valley are particularly well studied. But it must be remembered that the time period of our beech forest observations is short - and we are often exposed to new observations and perspectives. As a consequence, there remain many questions relevant to their management.

  • Summary of presentation on floristic composition of forests

  • A vegetation survey was undertaken of each of the Timberlands Working Circles18,19,20. The purpose of these vegetation surveys was to describe the plant communities present and to interpret their patterns in relation to environmental factors.
  • The vegetation survey used methods that have been widely applied in New Zealand and elsewhere21,22. Vegetation plots (ca. 400 m2 each) were randomly located throughout each Working Circle and vascular plant species were recorded in various height tiers. Various site (e.g., altitude and mineral soil pH) and stand structure (e.g., tree diameters) characteristics were also recorded on each plot.
  • The plots from each Working Circle were then classified into a number of types of forest based on similarity in species composition of plots. This allowed a description of each of the forest types to be made, in terms of the species assemblages found, and contrasts to be made with the composition of forests elsewhere. These forest types were also related to measured site and stand characteristics.
  • The vegetation sampling design and analysis allowed an objective and repeatable description of the dominant plant communities found on each Working Circle.
  • In conclusion: References 1. Ogden, J., Stewart, G.H. & Allen, R.B. 1996. Ecology of New Zealand Nothofagus forests. Pp. 25-82, In: Veblen, T.T., Hill, R.S., & Reid, J. (eds), The Ecology and Biogeography of Nothofagus forests. Yale University Press, New Haven, Connecticut.
    1. Glenn-Lewin, D.C., Peet, R.K. & Veblen, T.T. 1992. Plant succession: theory and prediction. Chapman and Hall, Cambridge.
    2. Wardle, J.A. 1984. The New Zealand beeches: ecology, utilisation and management. New Zealand Forest Service, Christchurch, New Zealand.
    3. Allen, R.B. & Wardle, J.A. 1985. Role of disturbance in New Zealand montane and subalpine forests. In: Turner, H. & Tranquillini, W. (eds.), IUFRO Project Group pl.07-00, Establishment and tending of subalpine forests : Research and management. Swiss Federal Institute of Forestry Research Berichte 270: 151-157.
    4. Stewart, G.H. & Rose, A.B. 1990. The significance of life history strategies in the developmental history of mixed beech (Nothofagus) forests, New Zealand. Vegetatio 87: 101-114.
    5. Stewart, G.H., Rose, A.B. & Veblen, T.T. 1991. Forest development in canopy gaps in old-growth beech (Nothofagus) forests, New Zealand. Journal of vegetation science 2: 679-690.
    6. Runkle, J.R., Stewart, G.H. & Veblen, T.T. 1995. Sapling diameter growth in gaps for two Nothofagus species in New Zealand. Ecology 76: 2107- 2117.
    7. Hosking, G.P. & Kershaw, D.J. 1985. Red beech death in the Maruia Valley, South Island, New Zealand. New Zealand Journal of Botany 23: 201-211.
    8. Wells, A., Stewart, G.H. & Duncan, R.P. 1998. Evidence of widespread, synchronous. disturbance-initiated forest establishment in Westland, New Zealand. Journal of the Royal Society of New Zealand 28: 333-345.
    9. Allen, R.B., Bellingham, P.J., & Wiser, S.K. in press. An earthquake=s impact on the structure and dynamics of a New Zealand Nothofagus forest. Journal of Vegetation Science.
    10. Allen, R.B., Bellingham, P.J., & Wiser S.K. 1999. Immediate damage by an earthquake to a temperate montane forest. Ecology 80: 708-714.
    11. Coomes, D.A., & Allen, R.B. Growth and competition along natural gradients in New Zealand mountain beech forest. Submitted to Ecology.
    12. Allen, R.B. 1993. A permanent plot method for monitoring changes in indigenous forests. Manaaki Whenua - Landcare Research New Zealand Ltd, Christchurch, New Zealand. 35 p.
    13. Bellingham, P.J., Stewart, G.H. & Allen, R.B. 1999. Tree species richness and turnover throughout New Zealand forests. Journal of Vegetation Science 10: 825-832.
    14. Hollinger, D.Y., Kelliher, F.M., Byers, J.N., Hunt, J.E., McSeveney, T.M. & Weir, P.L. 1995. Carbon dioxide exchange between an undisturbed old-growth temperate forest and the atmosphere. Ecology 75: 134-150.
    15. Callaway, R.M. 1998. Competition and facilitation on an elevation gradients in subalpine forests of the northern Rocky Mountains, USA. Oikos 82: 561-573.
    16. Crites, S., & Dale, M.R.T. 1998. Diversity and abundance of bryophytes, lichens, and fungi in relation to woody substrate and successional stage in aspen mixedwood boreal forests. Canadian Journal of Botany 76: 641-651.
    17. Allen, R.B. 1994. Plant Communities of Granville and Blackwater Forests and their Management. Landcare Research Contract Report prepared for Pine Plan New Zealand Limited. 18 p.
    18. Allen, R.B. 1995. Plant Communities of Paparoa Forests and their Management. Landcare Research Contract Report prepared for Pine Plan New Zealand Limited. 21 p.
    19. Allen, R.B. 1995. Plant Communities of Maruia Forests (Working Circle 4) and their Management. Landcare Research Contract Report prepared for Pine Plan New Zealand Limited. 21 p.
    20. Allen, R.B. 1992. RECCE An inventory method for describing New Zealand vegetation. Forest Research Institute Bulletin No. 181, Ministry of Forestry. 25 p.
    21. Mueller-Dombois, D. & Ellenberg, H. 1974. Aims and Methods of Vegetation Ecology. John Wiley and Sons, New York.
    Full name: DR ROBERT ALLEN Present position: Scientist and Programme leader, Landcare Research Part-time Lecturer, Ecology and Entomology Group, Lincoln University Present employer: Landcare Research Present work address: P.O. Box 69, Lincoln Academic qualifications: B.For.Sc.(Hons) (1977), University of Canterbury (forestry) Ph.D. (1988), University of North Carolina (botany) Years as a practising researcher: 20 years Honours/distinctions/membership of societies, institutions, committees: NRAC Postgraduate Fellowship (1985-1988) Member, N.Z. Institute of Forestry (1975-) International Association for Vegetation Science (1989-) Invited speaker at 3 international conferences over the last 5 years Visiting scientist (6 months) partly funded by University of Bayreuth, Germany Member, Department of Conservation Forest Research Advisory Group Professional positions held: 1992- Scientist/Programme leader, Landcare Research, Lincoln. Forest Dynamics. 1988-92 Scientist, Forest Research Institute, Ilam. Forest Community Structure. 1985-88 Post-graduate Fellow, University of North Carolina, U.S.A. Ph.D. thesis on quantitative analysis of large-scale vegetation patterns. 1981-84 Scientist, Forest Research Institute, Ilam. Impacts of introduced browsing animals on natural forest structure and composition. 1977-80 Forester, N.Z. Forest Service, Christchurch. Vegetation inventory methods. Present research/professional speciality: 1. Natural forest dynamics and its relationships to nutrient cycling 2. Species composition patterns in natural and managed forests 3. Impacts of introduced browsing animals on forests 4. Consultancy on natural forest management Number of refereed publications: 44 Number of patents: nil Number of significant publications not included in the above: 36 List of major achievements PERTINENT to this application: 1. Major publications (total of 19 in the last 5 years) Tested hypotheses about mechanisms controlling vegetation development: Osawa, A. & Allen, R.B. 1993. Allometric theory explains self-thinning relationships of mountain beech and red pine. Ecology 74: 1020-1032. Wiser, S.K., Allen, R.B., Clinton, P.W., & Platt, K.H. 1998. Community structure and forest invasion by an exotic herb over 23 years. Ecology 79: 2071-2081. Established the influence of disturbance on natural tree populations: Wiser, S.K., Allen, R.B., & Platt, K.H. 1997. Mountain beech forest succession after a fire at Mount Thomas Forest, Canterbury, New Zealand. New Zealand Journal of Botany 35: 505-515 Allen, R.B., Bellingham, P.J., & Wiser S.K. 1999. Immediate damage by an earthquake to a temperate montane forest. Ecology 80: 708-714. Bellingham, P.J., Stewart, G.H. & Allen, R.B. 1999. Tree species richness and turnover throughout New Zealand forests. Journal of Vegetation Science 10.. Determined properties of detrital inputs controlling nutrient availability: Clinton, P.W., Newman, R.H., & Allen, R.B. 1995. 15N immobilisation in forest litter studied using 15N-CPMAS NMR. European Journal of Soil Science 46(4): 551-556 Allen, R.B., Clinton, P.W. & Davis, M.R. 1997. Cation storage and availability along a Nothofagus forest development sequence in New Zealand. Canadian Journal of Forest Research 27: 323-330.

    Co-authored major review of New Zealand beech forest ecology

    Ogden, J., Stewart, G.H. & Allen, R.B. 1996. Ecology of New Zealand Nothofagus forests. Pp. 25-82, In: Veblen, T.T., Hill, R.S., & Reid, J. (eds), The Ecology and Biogeography of Nothofagus forests. Yale University Press, New Haven, Connecticut.

    2. Major achievements in commercial, social and environmental areas

    Completed 15 major commercial contract reports over the last 5 years for a range of agencies including Department of Conservation (5), Ministry for the Environment (6), Ministry of Foreign Affairs and Trade (2), Timberlands West Coast (1), Ministry of Agriculture and Forestry (1). Subjects included:

    Ecological studies as a basis for silvicultural systems:

    Svavarsdottir, K., Allen, R.B., Burrows, L.E., Coomes, D.A., Wiser, S.K., Smale, M., Benecke, U. 1999. Silvicultural research in selected forest types. Landcare Research contract report LC9899/119 for the Ministry of Agriculture and Forestry. 55 pp.

    Carbon storage in indigenous forests:

    Allen, R.B., Beets, P., Bellingham, P.J., Hall, G.M.J., Kimberley, M., & Wiser, S.K. 1997. Catalogue and evaluation of existing data sets for forest classes and scrub in New Zealand. Landcare Research/ N.Z. Forest Research Institute contract report for the Ministry for the Environment

    Monitoring changes in forest biodiversity:

    Allen, R.B. 1996. An Environmental Monitoring Approach for Timberland's Beech Management Working Circles. Landcare Research contract report for Timberlands West Coast Ltd

    3. Demonstration of involvement with end-users

    Input to forest inventory and management plans of the Department of Conservation and Timberlands West Coast; presented research results to scientists, land managers and policy makers at conferences and workshops; teaching and post-graduate student supervision in forest ecology at Lincoln University; input was made to Parliamentary Commissioner for the Environments review of Timberlands West Coast beech management plan; Published 4 popular articles in the New Zealand Tree Grower and New Zealand Forestry; Organising committee member for IUFRO conference on Interactions in Forest Stands (1995) and N.Z. Ecological Society conference on the Ecology of Biological Invasions (1996).