Master Thesis Woodland Grazing
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UNIVERSITY OF COPENHAGEN FACULTY OF SCIENCE Master Thesis Lasse Gottlieb Woodland grazing Effects of horse grazing on ground vegetation and forest structures Supervisor: Rita Merete Buttenschøn Co-supervisor: Niels Worm, Danish Nature Agency Submission: 29/07/2015 2 Name of department: Department of Geosciences and Natural Resource Management Forfatter: Lasse Gottlieb Title / Subtitle: Woodland grazing – effects of horse grazing on ground vegetation and forest structures Vejleder: Rita Merete Buttenschøn, Institut for Geovidenskab og Naturforvaltning, Københavns Universitet Medvejleder: Niels Worm, Naturstyrelsen Afleveret den: 29. juli 2015 Antal studieenheder: 60 ECTS 3 Content 1. Abstract ......................................................................................................................................... 6 2. Introduction ................................................................................................................................... 6 2.1. Effects of horses in relation to primary production .......................................................................... 8 3. Study area .................................................................................................................................... 11 3.1. Gribskov in a historical context ....................................................................................................... 12 3.2. Study sites ........................................................................................................................................ 13 3.2.1. Kollerup Enghave ..................................................................................................................... 13 3.2.2. Store and Lille Hessemose ....................................................................................................... 14 3.2.3. Sandskredssøen ....................................................................................................................... 14 4. Methods ....................................................................................................................................... 16 4.1. Ground vegetation........................................................................................................................... 16 4.2. Forest structures.............................................................................................................................. 16 4.3. Data analysis .................................................................................................................................... 18 5. Results ......................................................................................................................................... 20 5.1. Ground vegetation........................................................................................................................... 21 5.1.1. Species richness and density ................................................................................................... 21 5.1.2. Implications of abiotic factors ................................................................................................. 24 5.1.3. Spatial heterogeneity .............................................................................................................. 28 5.1.4. Diversity ................................................................................................................................... 29 5.1.5. Species composition and abundance ...................................................................................... 30 5.2. Forest structures.............................................................................................................................. 35 5.2.1. Species richness and regeneration of woody species ............................................................. 36 5.2.2. Browsing impact ...................................................................................................................... 40 5.2.3. Insect pollinated woody species .............................................................................................. 42 5.2.4. Deadwood................................................................................................................................ 43 5.2.5. Other forest structures; epiphytic bryophytes and lichens, hollowness, decay and woodpecker holes ................................................................................................................................... 44 5.3. Forest condition ............................................................................................................................... 45 6. Discussion .................................................................................................................................... 46 6.1. Ground vegetation........................................................................................................................... 47 6.1.1. Species richness and density ................................................................................................... 48 6.1.2. Species specific abundance alterations ................................................................................... 57 4 6.2. Forest structures.............................................................................................................................. 61 6.2.1. Tree regeneration and browsing impact ................................................................................. 62 6.2.2. Bark stripping ........................................................................................................................... 68 6.2.3. Browsing and grazing induced succession alterations ............................................................ 69 6.2.4. Other forest structures and the biodiversity ........................................................................... 72 6.3. Management ................................................................................................................................... 76 7. Conclusion .................................................................................................................................... 78 References ........................................................................................................................................... 80 Appendix 1 – Ground veGetation .......................................................................................................... 86 Appendix 2 – SeedlinGs and saplinGs of woody species .......................................................................... 97 Appendix 3 – Trees >2 m .................................................................................................................... 108 Appendix 4 – Deadwood .................................................................................................................... 112 5 1. Abstract The lack of natural dynamics and the intensive forestry management over the past centuries have had devastating consequences for the biodiversity found in woodlands in Denmark and the rest of northwest Europe. Woodlands are the ecosystem in Denmark that contains most species, but a high proportion of all the red-listed species are also associated with woodlands, particular either in the form of veteran trees and deadwood or with woodland glades and woodlands with enough light to develop species rich ground vegetation. Grazing management with livestock may affect these structures beneficial for the woodland biodiversity. However, examples of grazing management with domesticated herbivores in woodlands are few and hence the knowledge is mostly theoretical. Thus, there is a lack of the understanding of how large herbivores influence the woodland dynamics. In this study the short-term effects of woodland grazing with Icelandic horses on the ground vegetation and forest structures were investigated in three different woodland habitats (alder swamps, oak forest and beech forest) in Gribskov, Denmark. After just a few year of management the richness of vascular plants species were found increased in the alder swamps and the oak stands while the effects appeared negative in the beech stands. The species colonizing the grazed areas were along with those species which increased abundance found to be more tolerant toward disturbances. No effects were found on the richness of woody species. However, the horses had high browsing impacts on Fagus sylvatica, Alnus incana, Euonymus europaeus and Carpinus betulus but apparently without a higher impact in areas grazed throughout the year. Though the browsing by the horses are impeding the saplings of the browsed species, and in a single case reversing the succession in a dense beech stand, it is yet not possible to conclude whether and to which degree the horses are able the delay the succession. 2. Introduction With the change of The Danish Forest Act in 2004 up to 10 per cent of an individual area designated as forest-preserved land may be used for grazing with domesticated large herbivores (Danish Forest Act, 2004). Prior to this, woodland grazing was forbidden in Denmark for about 200 years, resulting in a division of the landscape into agricultural and forestry land with distinct boundaries between land uses. The consequence of the 200-years absence of domesticated herbivores was an increased tree density. This happened through enhanced growing conditions, if necessary by drainage, but also by plantation of all open