Appendix 1 - Soil biodiversity

Many people are familiar with the food chain concept of the forest, in which plants supply food for herbivores, such as leaf-eating insects, which then cycles through predators, such as birds. These same kinds of food chains exist on a microscopic scale in the soil, but with many times the diversity of species found above ground. Research into soil fauna diversity in the interior of British Columbia was initiated in 1992 (Battegelli and Berch, MoF); one year's sampling in mature forests found 18 types (families and orders) of arthropods and three types of worms. Moldenke has reported 75 species of mites per square metre of soil. The population estimates of these fauna are staggering. In the North and Central Interior, for example, the number of arthropods ranges on average from 350,000 to almost 700,000 individuals per square metre.

As shown in Table 1 (below), these fauna exist as many types: mites (Acari), springtails (Collembola), fly larvae (Diptera), worms (Lumbricidae), and snails (Gastropoda), to name a few. Our understanding of the function of the soil ecosystems to which these animals belong is virtually non-existent. There are estimated to be 48,000 to 60,000 species of soil arthropods in North America (estimates of around 35,000 have been made of BC), of which only 53% have been identified. Approximately 80% of the springtails have been identified, but the number and kinds of species are essentially unknown. Only approximately 17% of the mites have been identified to the species level. For example, out of a small sampling of thirty-four mites from two sites in BC, only eight could be identified to species.

In comparison to other species in BC, approximately 2500 species of vascular plants, 450 species of birds, 100 species of mammals, 20 species of reptiles and 20 species of amphibians have been classified. In these groups, there is very little that has not yet been identified. The life histories and ecology of the small proportion of identified arthropod types have not been well studied. Many functional groups are represented: detritivores, wood channelers, bacteriavores, fungivores, parasites, and predators. Many soil species can act in more than one capacity. We can only speculate on some of the interactions between arthropod groups that regulate important processes of the soil, and ultimately, the forest.

Table 1. Average number of soil arthropods and worms per square metre at the long-term

Faunal type	Williams Lake	Smithers	Prince George
Acari	302673	539838	329758
Collembola	65245	136470	53604
Araneae	161	494	31
Opiliones	2	1	1
Pseudoscopionida	75	3	262
Chilopoda	8	270	303
Diplopoda	12	5	138
Coleoptera (adult)	84	179	17
Coleoptera (larvae)	389	235	251
Diptera (adult)	0	142	44
Diptera (larvae)	7	2009	931
Lepidoptera (larvae)	3	2	5
Hemiptera	1002	2758	1151
Homoptera	1	0	0
Homoptera (aphid)	2	10	6
Homoptera (Cicadid)	3	0	0
Hymenoptera	53	9	45
Thysanoptera	24	44	1
Gastropoda	27	12	20
Lumbricidae	538	1363	1151
Megascolecidae	0	0	0
Enchytraeidae	9	0	0
Totals	37391	698663	400628

Ecosystem role of anthropods

One of the key soil processes in which arthropods participate is nutrient cycling. The fieldwork conducted to date in the northern interior shows that the most abundant fauna are fungivores, such as mites and Collembola. These indirectly affect nutrient cycling by grazing on the fungal biomass. In doing so, nutrients are released from the microbial biomass and made more available for plant uptake.

Grazing can also reduce the rate of organic matter decomposition by keeping microbial biomass levels low. This may be important in conserving nutrients. The types of fungal and bacterial species can also be affected by the feeding of arthropods.The production of faecal matter is also an important component to nutrient cycling. Converting litter into faecal matter changes their chemistry and shape, which seems to change their availability to microbial decomposition. This relationship is complicated by the apparently different properties of faecal pellets, depending on whether they originated from micro- or macrofauna, or from different species.

The movement of soil fauna leads to the transport of organic matter and microbes through the soil. This may prove to be one of the most critical roles of soil arthropods. On a large scale, some of the macroarthropods can move between soil horizons, the rhizosphere, and coarse woody debris. On a small scale, arthropods move between pores and aggregates that can redistribute organic matter to and from the rhizosphere. The effect of this movement on nutrient cycling may be especially important for otherwise immobile nutrients, such as phosphorus.

Habitat types

The forest soil ecosystem is comprised of several habitat types, each of which would likely have unique arthropod communities. The mineral soil and forest floor provide the most widespread habitat. The forest floors of the temperate and boreal forests are unique substrates in that they are massive accumulations of essentially biodegradable substrates or, in other words, food.

This enormous accumulation of food has decomposition tempered by environmental and biological factors, which leads to one of the largest and most complex habitats in the world. Within the forest floor are variations in site factors that lead to the formation of mor, moder and mull type forest floors. The faunal species, populations, and activity seem to increase along this gradient. The presence of coarse woody debris in forest ecosystems provides a unique and ecologically important habitat for soil fauna.

Another microsite is the rhizosphere, which is the soil surrounding feeder roots. This is a very microbially active zone, with large amounts of exudates from the roots that create a unique environment. In addition, most plants within the forest develop a zone of influence that can alter populations. For example, a Shepherdia plant with nitrogen-rich leaf litter can be expected to have different organism populations within its zone of influence than would, for example, an understorey spruce. Fungal mats (see below-Fungi) are uniquely hostile environments to organism growth. Soil factors, such as pH and nutrient availability, vary with depth, substrate type, precipitation, and age. These factors create an almost limitless variety of microsite, and complements of organisms, including arthropods, have evolved to occupy them all.

 

Approximately 69,000 species of fungi have been identified worldwide so far and it is estimated that there are about 1.6 million species in total.

A typical ratio of fungi to vascular plants for a given ecosystem is about six to one. Many of the fungi live in the soil where they function as pathogens, parasites, saprophytes, and mycorrhizal fungi. In temperate and boreal forests, fungi often constitute the largest biomass component of the forest floor. They play very important roles in decomposing organic matter that contributes to nutrient cycling. As disease organisms, they have important functions, such as thinning of weak and suppressed trees in overstocked forests.

The health of the forest ecosystem is even more directly linked to ectomycorrhizal fungi, which form a symbiosis with most of the trees and shrubs that grow in temperate and boreal forests.

The few species without ectomycorrhizal fungi usually have other types of mycorrhizae. All trees in the ectomycorrhizal forest are dependent on mycorrhizae for survival and growth, and will either die or will not grow without their ectomycorrhizal symbiont. The feeder roots of ectomycorrhizal trees are the organs of the tree that is responsible for nutrient and moisture uptake. Essentially every feeder root of an ectomycorrhizal tree is completely covered by a dense covering of fungus called the mantle or sheath, and every cortical cell of the tree's feeder roots are also individually surrounded by a layer of fungus called the Hartig net. This combination of fungus and tree root is what constitutes a mycorrhiza (literally fungus root). It is estimated that up to about 50% of the energy that trees store goes directly to its mycorrhizal fungi, which indicates the significance of the mycorrhizal fungus in this symbiotic relationship. 

There are currently estimated to be 5000-6000 species of ectomycorrhizal fungi. The fungi and mycorrhizae formed by them are highly variable in appearance and other characteristics.

They have different preferences for pH, temperature, moisture levels, season, and substrate type. The different types exude different kinds of antibiotics and take up nutrients in different forms, such as nitrate, ammonium, or organic nitrogen.

• Some kinds exude siderophores, which are organic molecules can aid in the uptake of iron; others exude enzymes to mobilize phosphorous or micronutrients.
• Some kinds show specific antagonism towards various disease-causing organisms, while others are capable of directly breaking down organic matter without an intervening saprophyte.
• Some kinds of mycorrhizal fungi form fungal mats, which are dense layers of fungus that physically, if not biologically or chemically, dominate some types of forest floors.
• Some kinds of mycorrhizal fungi connect overstorey plants to understorey plants and can transfer carbohydrates between trees of the same species or different species of plants.

These associations of interconnected plants are called plant guilds.

Some types of mycorrhizae prefer trees of different ages while others persist over the life of a forest. It is clear that the ectomycorrhizal fungi do many different things and are not equal.

Even within a given species of fungus, there is considerable adaptation, just as with provenances of trees. A typical tree has many different types of ectomycorrhizae to allow it to exploit the various conditions that may be found even within the rooting zone of a single tree. There have been reports of up to 150 types of mycorrhizae on a single Douglas-fir tree. It is common to find 30 to 40 species of ectomycorrhizal fungi in a stand, but that may be an underestimate because of the difficulties in sampling for them. 

Mycorrhizal fungi are dispersed by aerial spores, by spores transported in the guts of animals and by root contact. Some species have no known spore dispersal mechanism and are dependent on mycelia contact for dispersal.

Many small plants, such as Arctostaphylos, are ectomycorrhizal and can act as refugia for mycorrhizae after logging or other disturbances, though not all ectomycorrhizal fungi can colonize these species. Approximately 1000 species of ectomycorrhizal fungi form subterranean fruiting bodies (truffles or truffle-like mushrooms) are meant to be eaten so that spores can be dispersed in dung. Squirrels, voles, deer, bears, and other animals eat these types of mushrooms. The flying squirrel, which lives throughout the forested areas of Canada, is very dependent on the underground fungi. Mushrooms, above and below ground, are good sources of nutrients, often containing 25 to 30% protein. They vary in vitamin and nutrient content and a diverse population of fungi helps create a balanced diet for the animals that utilize them.

Many fungi are very important food sources for humans as well. Several species of mushrooms are harvested in BC, including chanterelles, pine mushrooms, morels, brain mushrooms, king boletus and giant puffballs.

Chaterelles, pine mushrooms and king boletus are ectomycorrhizal and require specific types of forests to produce mushrooms. Some types of mushrooms, such as morels, fruit abundantly under specific conditions, such as after a wildfire or broadcast burning.

In Europe, dramatic declines (in the order of 50%) in the number of species of ectomycorrhizal fungi in forests have been reported. The reasons for this are unclear but factors that have been suggested include pollution, over harvesting of mushrooms, and fertilization of forests.

Many of the forests of Europe are currently in a state of decline. It is not known if the decline in ectomycorrhizal species is contributing to the decline in the forest or if stress to the forest is causing decline in types of mycorrhizae.

However, there is ample evidence now to suggest that complex populations of ectomycorrhizae are synonymous with a healthy and stable forest.

There are many other types of organisms in the forest soil about which little are known. These include groups such as earthworms, potworms, nematodes, rotifers, snails and slugs, algae, bacteria, actinomycetes and cyanobacteria.

Nematodes are perhaps the largest single group by numbers of animals in the soil and act as predators, pathogens, and fungivores. All nematodes appear to feed on living tissue and there are at least 1000 species of soil nematodes.

In many situations, earthworms may be the largest faunal biomass in the soil. Estimates of earthworm mass have been as high as 12,000 kg/ha for sites in the Cariboo Forest Region, but estimates of 3000 kg/ha are not uncommon.

It was believed that earthworms were rare in conifer forests, but in many cases, that now appears to have been incorrect. Earthworms are important for speeding up decomposition of organic matter and improving the structure of mineral soil.

Bacteria have many roles as well, including disease causation, decomposition, and nitrogen fixation. Bacteria may fix nitrogen in association with plants, but there is considerable evidence about the importance of nitrogen fixation by free-living bacteria in forests.

• Actinomycetes are filamentous bacteria that are common in soils and are responsible for giving soil its characteristic earthy smell. Actinomycetes are a major source of antibiotics for human use and they are involved in nitrogen fixation in symbiosis with woody plants.
• Cyanobacteria are a special group of bacteria that can photosynthesize, and in many cases fix nitrogen. In some forest environments, it has been determined that cyanobacteria make a significant contribution to the nitrogen budget of the forest.

In short, there are many kinds of organisms living in the soil and contributing to the cycling of nutrients through the forest as well as other functions. To really see the complexity of a forest ecosystem, one has to look small.

Managing forest soils for biodiversity

The concerns about biodiversity from a soil's point of view reflect many of the same issues surrounding above-ground diversity. The relationships and workings of the soil ecosystem, as with other ecosystems, are too complex to fully understand the possible impacts of forest management.

The creation of large-scale, uniform disturbances of only pioneer species will reduce the rich diversity of habitats and hosts that characterize the many communities of soil organisms. Alternatively, under natural disturbances such as fire, the forest will retain island remnants of living trees, undisturbed forest floor and coarse woody debris, all of which act as biological legacies for the succeeding forest. At this time all we can do, to reduce the risk of damaging the soil ecosystem is practice management that results in patterns of disturbance more similar to those caused by natural processes.

Island remnants left by mimicking natural disturbance patterns will hopefully act as refuges from which species of mycorrhizae, fauna, and other organisms can spread back into the disturbed forest. In the case of some organisms, dispersion may be slow, and thus the retention of habitat on the small scale is important. This requires the retention of some coarse woody debris and undisturbed forest floor and mineral soil (e.g., by avoiding intense burning or excessive mechanical site preparation). Some types of organisms, such as the underground mushrooms, need an intact community of mammals, particularly small mammals, to disperse spores from areas where colonies of the fungi remain to areas where they have been lost. This requires the conservation of larger islands.

Some species of fungi show fairly large differences in strain characteristics with adaptations to specific environmental conditions. These types of strains are sometimes referred to as ecotypes. The ecological function of ecotype variation is currently not well understood but it may be important for providing very site-specific adoption. As a measure to retain this genetic variability, as well as the specific complement of fungi and other organisms present in a stand, one approach may be to preserve island remnants of each stand that is harvested. In other words, island remnants should not consist only of immature or riparian areas within a block but also representatives of the types being harvested. In some cases, it may be desirable to leave at least one or more widely spaced windfirm dominant trees. Even this will contribute to preserving the soil biological legacy. 

A second issue for management of soil biodiversity is the maintenance of soil integrity. Soil degradation, such as through the compaction of mineral soil, for example, will reduce porosity and alter moisture conditions, often to such an extent that this habitat becomes lost to many species. Soil displacement exposes new and possibly poorer substrates from deeper in the soil profile, which take some time to be colonized and become stable productive environments. In addition, soils that are greatly disrupted become biologically pioneering environments that may be susceptible to invasion by a variety of organisms that are alien to the intact ecosystem. These may be thought of as weed species, and in fact, weedy plant invasion may be one consequence of such disturbance. Other organisms, such as disease organisms, may also use this opportunity to establish. Losses of soil from erosion and mass wasting will also remove soil volume and reduce the biological legacy of the soil. Managing soils from a conservation point of view will, at the same time, help maintain biological diversity as well as biological integrity.