Hanalei Watershed
Riparian Restoration Project (#00-192-032)
Final Report, January 31, 2003
The Hanalei Heritage Program would like to submit the following final report for the Hanalei Watershed Riparian Restoration Project #00-192-032. The previous quarterly reports describe the clearing and planting processes. In this report we will present the final results of the project.
The project site, in the ahupua’a (traditional Hawaiian land division) of Waipa, is located in the greater Hanalei Bay watershed in the north shore of the island of Kauai (Figure 1). The three sites were selected for their prolific growth of hau bush (Hibiscus tiliaceus).
Figure 1. Location Map, Hanalei Riparian Restoration
Project, Kauai, Hawaii.
RESULTS
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Hau bush showed significant regrowth in plots that were stump cut with chain saws. In fact, at Site #1, regrowth averaged approximately 3m height and reestablished a 60% canopy cover (Figure 2). Some stumps had regrown to over 5m height within one year of cutting.
Figure 2. Hau bush regrowth at Site 1, averaging 3m in
1-year.
Total
plant species within each plot were identified before treatment and one year
after treatment (Appendix A). In general there was very little change in
species diversity and no consistent pattern among treatments (Figure 3, Figure
4 and Figure 5). Surprisingly, even shade loving species such as Basket grass
did not completely disappear even in the mechanical plots exposed to full
sunlight (Appendix A).
Figure 3. Species Diversity Pre-treatment and
Post-treatment, Site 1.
Figure 4. Species Diversity Pre-treatment and
Post-treatment, Site 2.
Figure 5. Species Diversity Pre-treatment and Post-treatment,
Site 3.
It was the relative abundance of species that changed most significantly. For example, the weedy Coster’s Curse was present, but in low abundance, in all but one plot prior to treatments (Appendix A). This species greatly increased in abundance with treatments, particularly in the mechanical plots.
These
changes were not well detected by the random plot sampling because much of the
vegetation grew as a shrub layer, and was not recorded as ground cover or
canopy (Figure 6, Figure 7 and Figure 8). This was also true of the hau bush in
the hand clear plots at Site # 2 and 3, where much of the regrowth 1-2m high
and not recorded as canopy. Ground cover showed the most changes with
treatments (Appendix A). Detritus generally decreased except in hand cleared
plots where decomposing bucked hau logs covered most of the ground. The percent
vegetation cover generally increased as was expected with exposure to more
sunlight. Furthermore, the quantitative assessment of the ground cover changes
was severely impacted by pig foraging.
Figure 6. Percent Canopy Pre-treatment and
Post-treatment, Site 1.
Figure 7. Percent Canopy Pre-treatment and
Post-treatment, Site 2.
Figure 8. Percent Canopy Pre-treatment and
Post-treatment, Site 3.
DISCUSSION
As
in most endeavors, our project was a mix of success and failure. Importantly
though, it provided answers to questions that we did not think to ask at the
outset.
We
learned that hand cutting of hau bush is not realistic because 1) It is
extremely dangerous, 2) accumulated debris is voluminous and poses a
green-waste disposal issue unless utilized on a large scale, and 3) regrowth is
so fast (1-5 meters in a year) that it would require constant maintenance.
Herbicide treatment is very effective but takes diligence to treat every root
bearing section. This method may be appropriate for small landowners with short
riparian sections, but the standing dead stems are unattractive and would
probably be cut down anyway. In large,
thick growths of hau bush that are almost impenetrable, the most reasonable
method is removal with equipment. Small excavators, such as the one used in
this project have very light ground pressure and can access low, wet banks.
They can pull hau bush away from the bank and stream into piles, or actually
mash it down in situ as a type of rough mulch. This work may leave exposed soil
immediately afterwards, but in our tropical climate these areas are naturally
revegetated very quickly.
The
native plants chosen for revegetation appear adequate, if not spectacular
candidates for riparian restoration. Again it is difficult to assess due to the
impacts of ungulates, but those plants that survived were healthy and vigorous
without any maintenance. Some of the Koa trees were over 2 m tall and the
Mariscus sedges had full foliage with new flowering heads.
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As an experiment, particularly in restoration, the project was largely a failure. Very few of the 1,800 native Hawaiian plants outplanted (900 Kou and 900 Mariscus) at the three sites survived (Figure 9, Figure 10, and Figure 11). This was due almost entirely to the impact of cattle and pigs. We perhaps should have anticipated this problem, since the detrimental impact of ungulates on Hawaii’s plants is well documented. However, the plants chosen were those that occasionally still occur in lowland areas thus should have been able to survive. In addition, it was assumed that most ungulate damage to native plants is density dependent, resulting from over grazing of cattle, and large, unhunted wild pigs populations. What we discovered is that even an occasional cow will find and selectively feed on native Hawaiian plants. In addition, these plants cannot recover from browsing or grazing. Even though the project area is regularly hunted and controlled for pigs, in some of the plots 80-90% of the ground had been turned by pigs (Figure 12). In some of the hand-cleared plots that were inaccessible to the cows, the native plants had survived to 9 months. At the 1-year monitoring interval however, pigs had destroyed almost all of the native plants. It appears that riparian restoration with native Hawaiian plants is simple not compatible with any numbers or frequency of ungulates. This is probably not an issue for small landowners removing hau and landscaping along a stream bank, but for large riparian sections, which are still typically grazed in Hawaii, native plant restoration would require a completely different land use concept.
Figure 9. Survival of Native Hawaiian Plants Outplanted
at Site #1
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Figure
10. Survival of Native Hawaiian Plants
Outplanted at Site #2
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Figure 11. Survival of Native Hawaiian Plants Outplanted at Site #3
Figure
12. Damage by feral pigs Site 3
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Although our project failed as an experiment, we are extremely satisfied with its outcome as a demonstration project, in that the results have profoundly effected the community. The project was conducted in Waipa Valley, which is owned by Kamehameha Schools, but leased to the Waipa Foundation for cultural and natural resource management. The implementation of the project showed the landowner and the Waipa Foundation the impact that hau bush was having on the stream and riparian areas. The landowner was so impressed with the work accomplished by the volunteers with the rented excavator, that the machine was actually purchased (over $60,000) and remains on site for riparian restoration and maintenance. The Waipa Foundation realized that its goal of native plant restoration was incompatible with existing cattle operations. It has now set aside a 10-acre reserve for native plant restoration (which includes 2 of the hau bush sites) and has leveraged an additional $50,000 for this project. Finally, they have set aside all riparian areas in the USDA-NRCS Conservation Reserve Program and these corridors will be fenced from cattle and managed more appropriately (Figure 13).
Figure
13. Waipa Stream Riparian Habitat
Restoration with Native Hawaiian Plants
(electric
fence to keep cattle out of project)
The
Hanalei Heritage River Program made all attempts to comply with the MBE/WBE
Utilization under Executive Orders 11625, 12138, 12432. P.L. 102-389 and EPA
Regulations Part 30 and 31. We purchase
supplies and contracted out excavator hauling with a minority owned business
for a total of $1,859 (19.8% of total spent on equipment, supplies and
contractual services). Our contributing
partner in this project, Waipa Foundation, is a non-profit foundation, directed
by Ms. Stacy Sproat, a Native Hawaiian woman. Persons of Native Hawaiian
descent contributed the majority of in-kind hours contributed by the Waipa
Foundation.
Malama
‘Aina a me ka wai, take care of the land
and water,
Jan
Surface
Watershed Coordinator